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bradnree
07-20-2006, 06:42 PM
What are the cures and causes of vapor lock ??? Thanks for responding from your experiences....Brad

PackardV8
07-20-2006, 06:59 PM
The cause is gasoline flashing into vapor and the resultant pressure rise preventing liquid gasoline from being able to get into the carburetor.

The cures are:

1. A bypass-return filter line to the fuel tank which keeps fresh fuel moving through the line and thus reduces the heat absorbsion which occurs when fuel sits in the line next to an exhaust manifold.

2. Electric fuel pump

3. Insulate the fuel line.

4. Insulated carburetor-to-manifold base gasket or block.

thnx, jv.

PackardV8

Tom B
07-20-2006, 08:29 PM
Electric Fuel pump is the first choice, but it has problems, it must be connected to a oil pressure switch to kill it in case the engine stops.

I tried the gallon of Diesel fuel last summer, put one gallon oil in the tank, filled it up and vapor locked on the way home. Not a sure cure.

An electric pump can be installed above the rear axle on the driver's side, near the tank to push the fuel through the line, and is hidden, a la original.

Tom Bredehoft
'53 Commander Coupe
'60 Lark VI
'05 Legacy Ltd Wagon
All three Indiana built
cars

Roscomacaw
07-20-2006, 08:41 PM
Man, it must be just good fortune - but I've had VERY few incidents of vapor lock in the 17 years we've lived in this torridly hot valley (107 today - 110 for the coming weekend!)
I drove around in the Transtar yesterday and today and never had a stumble. The 60 ragtop - if I drive it in over 100 degree temps, park it for 5 or 10 minutes and come back and take off - about 30 seconds after I drive off, it'll stumble (even stall if at idle) for a bit before it smooths out and goes down the road just fine.

Not bragging mind you, just noting that as hot as it gets here during 5 or 6 months, I've never been sitting on the side of the road with the hood up because of vapor lock.
Days like today, I keep waiting for it to strike - never happens.

I've recommended the fix that Tom talks about and have gotten rave reviews back from most who've tried it. You can use a gallon of diesel, kerosene, or even Marvel Mystery Oil if you wanna spend that much! It lowers the volatility of the gasoline and quells it's yearning to go to vapor when heated. For most cars that run on "pump gas" it shouldn't make any difference in performance. For those with higher compression ratios, I don't know.

Miscreant at large.

1957 Transtar 1/2ton
1960 Larkvertible V8
1958 Provincial wagon
1953 Commander coupe
1957 President 2-dr
1955 President State
1951 Champion Biz cpe
1963 Daytona project FS

GTtim
07-20-2006, 09:03 PM
I believe that a lot of the time vapor lock gets blamed when it isn't really the cause. Other contributors can be, incorrect timing or a poorly functioning radiator both of which can cause higher engine temperatures. A weak fuel pump can also be a contributor to the problem. One of the remedies that wasn't mentioned is to move the fuel line out from in between the head and the power steering pump. Check the fuel pump performance, move the fuel away from the engine, install a filter with a return line and use the diesel fuel if you want.

Tim K.
'64 R2 GT Hawk

Tom B
07-20-2006, 10:14 PM
My bone stock '53 Commander Coupe has experienced vapor lock at 55 mph at 70 degrees, cloudy day. When the Electric pump was turned on, the engine caught and took off in about three seconds.

The (stock) fuel pump is on top of the engine, right behind the fan. The switch is mascarading as the Fog light switch at the left end of the dash.

http://www.alink.com/personal/tbredehoft/cars.gif

Tom Bredehoft
'53 Commander Coupe
'60 Lark VI
'05 Legacy Ltd Wagon
All three Indiana built cars

whacker
07-20-2006, 10:57 PM
On the sixes, there is supposed to be a heat shield between the fuel pump and the engine. Many times this heat shield is removed for one reason or another, and causes the vapor lock. On the 51 to 54 V8 (232) the fuel pump is right on top of the engine - heat rises! The factory solution was to relocate the fuel pump to the front timing cover and let the fan blow on it. Big help, but not a cure. The best solution I have found is the electric fuel pump, but others swear to other solutions. The real cause is the new fuel mixture we are forced to burn, it boils at a lower temperature (is more volatile) than the old stuff these cars were designed for.

DilloCrafter
07-20-2006, 11:55 PM
Biggsy,

When I was in California last year, buying my truck, I noticed the strong smell of alcohol in the gasoline while pumping it at a gas station. Does the ethanol in your fuel make the gas more or less likely to cause vapor lock?

All of us who live in states that don't yet require ethanol in the fuel could benefit from the answer to this question.

This could give us an idea of what we'll need to do to run on the 85% Ethanol that will soon be offered as an option here in Texas.

http://rocketdillo.com/studebaker/misc/images/Current_Avacar.gif[/img=left] - DilloCrafter

1955 1/2 Ton Pickup
[i]The Red-Headed Amazon
Deep in the heart of Texas

curt
07-21-2006, 07:13 AM
Vapor lock can in reality be a fuel feed restriction such as a semi/pluged pick up tube, or some type of restriction in the fuel line, been there and cured it with a cleaned pick up tube and a cleaned fuel tank.

bradnree
07-21-2006, 07:34 AM
I live in Kansas and I have had nothing but trouble since the new fuels are on us with my car. We've corrected many things but still are having the problem. Thursday at 60 m.p.h., 101 degrees, it dropped, then caught its breath and then totally died 6 miles later.
I have a friend with a Thunderbird 292 and it continues to drop on the highway and it too dropped on Thursday---tried larger fuel line from the tank, electric pump, diesel, new electrical, rebuilt carb and nothing works on the "bird".........brad

1949commander
07-21-2006, 09:38 AM
From vast experience of trying to fix my 49 Commander from what seemed like vapor lock I finally found that most of my problem was due to a NOS fuel cap I bought. The cap looked great but the little valve inside the cap was rusted and didn't work like it should have. Anytime the temperature is higher you should have pressure in your fuel tank. You can tell this by slowly opening your gas cap. There should be sound of escaping air pressure. What the cap was doing was letting the pressure not build and also creating a slight vacuum in the tank. This makes a larger vacuum the longer you drive the car since the cap would not let air in as the fuel pump pulled gas out, this would go on until you get fuel pump air locked. Try buying a brand new gas cap from your local part store Stant still makes caps that fit all post war Studes. Then after your car has set in the heat of the day try opening the cap. If you don't hear air pressure escape you may have a leak in your fuel system somewhere. The pressure is necessary to ensure the fuel isn't in a vacuum state as the pump is drawing the fuel to the pump. This pressure during hot weather raises the boiling point of the fuel just like a pressure cap on the cooling system raises the boiling point of water. How ingenious those engineers were before we had computers! I still have an electric pump wired to an oil pressure switch just incase. But until I found the gas cap problem, I couldn't drive the car at high speed for long until it leaned out due to insufficient gas delivery. An incorrectly working fuel cap can cause premature fuel pump diaphragm wear etc. I have driven my 49 in the Hot Humid days here in Indiana the last week or so and not a hint of vapor lock. I idled in traffic and I know the air temperature on the road had to be 100+ degrees and no problem. They sure designed a great car in the 49 Commander if you just make sure it operates the way those ingenious Studebaker Engineers designed it. I have put lots of miles on it since I found the root cause of the problem and no matter the weather it runs perfect!! It never runs more than 170 deg even in 90+ degree heat and a non-pressure cooling system. Hats off to ‘Chruch’, Gene and Roy, those guys were genius in their day! I hope this helps![8D]

Restore it, don't replace it.Keep the Studebaker reproduction industry going

Roscomacaw
07-21-2006, 10:02 AM
Thanks for the rundown on your problem, 49. I do think that vapor lock, having taken on a mystic legend about itself - especially with the industry switch from carbs to FI - gets blamed for other, un-understood maladies.
You know.... "I've tried this and I've tried that and I can't think of anything else to replace so it must be that ethereal bug, Vapor-Lock! I remember my buddy's dad tellin' us about how HIS dad got vapor lock once on their vacation in 1958"

I'm NOT saying it can't happen, but I am saying there's lots of folks that wouldn't think of a bad GAS CAP - of all things! Or other possible factors, for that matter.[}:)]

Miscreant at large.

1957 Transtar 1/2ton
1960 Larkvertible V8
1958 Provincial wagon
1953 Commander coupe
1957 President 2-dr
1955 President State
1951 Champion Biz cpe
1963 Daytona project FS

whacker
07-21-2006, 12:51 PM
When they do finally start selling E-85 in your state, go out and buy a cross, or better yet a crucifix, and every time you go to a gas station hold that cross between you and the pump that sells E-85! Never put E-85 into a vehicle that wasn't designed for E-85. It requires a stainless steel fuel system, a different fuel guage float, different seals in the fuel pump and fuel injectors. If you put that stuff into a Stude, you will blow yourself to your just reward. You will also ruin your Studebaker. I live in a state where E-85 is sold. The Gasahol (15% alcohol) is bad enough. I use ethanol blend in my S-10 pickup, but I pay extra, and drive farther, to get real gas for my Stude.

Sonny
07-23-2006, 02:03 PM
quote:Originally posted by whacker

When they do finally start selling E-85 in your state, go out and buy a cross, or better yet a crucifix, and every time you go to a gas station hold that cross between you and the pump that sells E-85! Never put E-85 into a vehicle that wasn't designed for E-85. It requires a stainless steel fuel system, a different fuel guage float, different seals in the fuel pump and fuel injectors. If you put that stuff into a Stude, you will blow yourself to your just reward. You will also ruin your Studebaker. I live in a state where E-85 is sold. The Gasahol (15% alcohol) is bad enough. I use ethanol blend in my S-10 pickup, but I pay extra, and drive farther, to get real gas for my Stude.


EXCELLENT points whacker! NEVER, EVER put E-85 in a Studebaker, (or ANY vehicle), that hasn't been specifically set up to use it! It cannot be used in brand new vehicles that haven't been set up to use it! As whacker said, you will need a complete re-do of the fuel system, including a new tank, stainless fuel lines, electric pump, etc.. Bad news is, there's no fix, (seals, etc.), available for carbs, (especially OLD carbs.), at this time. I doubt that there ever will be any consideration for carbureted cars, "they" would LOVE to get rid of "us" anyway.

Vehicle makers are already putting out, what they call, "Flexfuel" vehicles. In other words, they have had to modify their own, newest offerings to use the stuff. I sell used auto parts, and I can tell you that it's already a nightmare for everyone. The requirement that E-85 be the "standard" fuel hasn't even started yet, and we're ALL running into problems NOW. But trust me, it's gonna be a requirement that every new vehicle use E-85. Even the chitt fuel we have to put up with now will become hard to find eventually.

The point is, I guess it's already time to start planning for the future. I dunno what all of the other old car people are gonna do, but I'm hoping that everyone sticks together and insists to our government that old cars aren't left out in the cold. For the government, it's a win-win situation, they get pollutants down, reduce dependency on foreign oil AND cure the "old car problem", all in one drop of the hammer. Watch for states like CA and NY to jump on the "everybody has to use E-85 bandwagon" as fast as they can. Those states are constantly trying to legislate us into "modern" compliance, so this new federal fuel requirement will be a boon for those so set against us.....

Oh! Almost forgot one point that I wanted to make. Using diesel, along with the fuel we have now, makes very good sense. The new fuels have reduced "lubricity" and diesel replaces some of the lubricity AND HP that's been taken out. I strongly recommend that, no matter what, you use diesel in your Studebaker now.

Sonny
http://RacingStudebakers.com

PackardV8
07-23-2006, 03:27 PM
Sonny and I rarely disagree, but I have never seen any hard data running diesel fuel mixed with gasoline increases horsepower. Most of my experience indicates it lowers octane and will cause more pinging on engines near the threshold.

thnx, jv.

PackardV8

Roscomacaw
07-23-2006, 03:31 PM
OK, so on a related question - what sorta rear-view mirror, dangly, cutesy air freshener should I use in my Studes??? Is there any difference between, say, the one's shaped like a pine tree and the one's that are cut in the siloutte of a curvaceous lass?
Would my Stude be more appreciable if it SMELLED like a pine forest or a, ah, yeah - anyway.... I'd like some opinions.[:I]

Hmmmmm.... anyone know of a source of these that bear a likeness to the Studebaker crest emblem?[:0]

Miscreant at large.

1957 Transtar 1/2ton
1960 Larkvertible V8
1958 Provincial wagon
1953 Commander coupe
1957 President 2-dr
1955 President State
1951 Champion Biz cpe
1963 Daytona project FS

StudeDave57
07-24-2006, 12:56 AM
I think I 'smell' a business opportunity or two in this post somewhere... [:0] :) :D [^] [:o)]

StudeDave [8D]
V/P San Diego County SDC
San Diego, Ca

'54 Commander 4dr
'57 Parkview (it's a 2dr wagon...)
'57 Commander 2dr
'57 Champion 2dr
'58 Packard sedan
'65 Cruiser

len
07-24-2006, 06:01 PM
After reading the replys it sounds like my 1955 stude needs a pressurised cap. Mine appears to be not pressurised. I have driven in some pretty hot weather, Ca. with no problems so far. What would be the correct cap. Thanks

Milaca
07-26-2006, 12:31 AM
Diesel fuel has less BTU's than gasoline, therefor creates less power. Also, diesel may alter ignition timing in high compression engines as it combusts under compression whereas gasoline has octane added to prevent compression ignition. I have not tried diesel in my Stude, but i imagine its about the same as adding carburetor cleaner to the gas tank. The carburetor cleaner that ive used smells like #1 diesel or kerosene anyway. The one issue that i have with adding a quart of diesel fuel is the smell. Wouldnt this make the exhaust smell strong? I wonder if 2-stroke oil would work....you could jokingly tell people that you have a snowmobile engine under the hood!

quote:Originally posted by PackardV8

Sonny and I rarely disagree, but I have never seen any hard data running diesel fuel mixed with gasoline increases horsepower. Most of my experience indicates it lowers octane and will cause more pinging on engines near the threshold.

thnx, jv.

PackardV8

curt
07-26-2006, 07:13 AM
I had a neighbor who was a Phd chemist. He said add one pint of diesel to a tank of gas to reduce preignition knock. The fellows adding more seem to do well and have no problems. I do know diesel , alcohol, etc can be hard on fuel pumps if the diaphram and parts are not made for such additives. The National will be interesting, Nebraska is a corn state, I suspect alcohol will be in every drop of gas.

41 Frank
07-26-2006, 07:41 AM
Yes Nebraska is a corn state but most all stations sell fuel with and without alcohol here,I never use super unleaded or gasohol as it used to be called in my Studes. In my opinion it increases the chance of vapor lock and helps dissolve most pourin fuel tank liners plus it gives poorer mileage since a gallon of alcohol contains less btu then a gallon of gas.

tomnoller
07-26-2006, 07:53 AM
As Bob Palma has addressed the oil issue in the Co-Operator, I'd like to see his, and maybe Jim Pepper's opinion of using diesel fuel in our Studes...how much and how often.
A fellow giving a seminar at the Spokane meet last year suggested a half-cup of Marvel Mystery Oil with each tankful of gas. I suppose like chicken soup for the dead man; it couldn't hurt. <G>

Western Washington, USA

Dick Steinkamp
07-26-2006, 09:44 AM
quote:Originally posted by tomnoller
I suppose like chicken soup for the dead man; it couldn't hurt. <G>


Nice to start the day off spewing coffee all over my screen and keyboard. Thanks a lot, Tom :(:D



http://thenobot.org/images/s2d/s2d_01.jpg

chrysleritis
07-26-2006, 01:53 PM
My vapor lock problem turned out to be restricted fuel flow: some clown (not me, the other clown) had probably put a jack under the fuel line where it runs along the frame through the front wheel well, and the line was squashed flat like a paper soda straw. I re-plumbed the fuel line from tank to pump. In the process of tracking that down, I also added the fuel pump-top heat shield and a real fuel filter before the pump. But I also second the suggestion that lots of things masquerade as vapor lock. Dirty carb. Dirty fuel pump. Dirty lines. Dirty pick-up tube. It's probably best to think of vapor lock as "insufficient fuel delivery under load" and run a checklist for that problem.

nels
07-30-2006, 03:04 PM
I noticed this discussion on vapor lock and thought I might add something. The early fuel pumps had the glass bowl filter on the intake/suction side of the fuel pump. If the cork seal between the glass bowl is cracked or not properly sealed, the fuel pump will suck air instead of fuel. More often than not, this is the root cause for the no fuel problem at the carb. The later cars put the filter after the pump.

GTtim
07-30-2006, 09:25 PM
Here is one more to throw into the mix: On the way home on a hot day on a long trip, the Hawk died at the stoplight and restarted with a lot of difficulty. Driving on the highway the car seemed fine, but when the accelerator was floored the engine would go flat and just fumble along. The cause? The next morning the symptoms persisted and I found that the coil was the problem. I've also been told that the points condenser will give similar symptoms when it is failing. My point is, that it isn't always fuel related issues causing this sort of problem.

Tim K.
'64 R2 GT Hawk

Sonny
07-31-2006, 12:27 AM
quote:Originally posted by Milaca

Diesel fuel has less BTU's than gasoline, therefor creates less power. Also, diesel may alter ignition timing in high compression engines as it combusts under compression whereas gasoline has octane added to prevent compression ignition. I have not tried diesel in my Stude, but i imagine its about the same as adding carburetor cleaner to the gas tank. The carburetor cleaner that ive used smells like #1 diesel or kerosene anyway. The one issue that i have with adding a quart of diesel fuel is the smell. Wouldnt this make the exhaust smell strong? I wonder if 2-stroke oil would work....you could jokingly tell people that you have a snowmobile engine under the hood!

quote:Originally posted by PackardV8

Sonny and I rarely disagree, but I have never seen any hard data running diesel fuel mixed with gasoline increases horsepower. Most of my experience indicates it lowers octane and will cause more pinging on engines near the threshold.

thnx, jv.

PackardV8


Milaca,

You might be correct if you were running nothing but diesel fuel in a gasoline engine. It's the MIX of a very small amount of diesel that's useful to enhance the qualities of modern fuels. No, there is no smell, what so ever, I use it in every tank of gasoline. I dunno what brand of carb. cleaner you're using, but carb. cleaner shouldn't consist of nothing but diesel fuel.

Also, I don't have the article in front of me, but the diesel fuel mix definitely enhances the octane and "burn-ability" of the "new" gasoline, ESPECIALLY the "gas-o-hol" that we're stuck with today. Diesel mix was NOT as useful in the gasoline of years past, they included ALL of the necessary ingredients that our “old school” engines need. Diesel fuel mixed with gas-o-hol of today also replaces some of the lubricity that's been removed. New cars do not need the extra lubricity, (they've been manufactured to survive on the new fuels), our old school engines do!

Sonny
http://RacingStudebakers.com

Milaca
07-31-2006, 12:21 PM
Sorry, i was incorrect in stating that gasoline has more BTU's than diesel. The info i found on a petroleum website states that #2 diesel has 138,500 BTU's per gallon whereas gasoline has 125,000 BTU's per gallon. However, diesel has much lower octane than gasoline. Sorry for any confussion.

quote:Originally posted by Sonny


quote:Originally posted by Milaca

Diesel fuel has less BTU's than gasoline, therefor creates less power. Also, diesel may alter ignition timing in high compression engines as it combusts under compression whereas gasoline has octane added to prevent compression ignition. I have not tried diesel in my Stude, but i imagine its about the same as adding carburetor cleaner to the gas tank. The carburetor cleaner that ive used smells like #1 diesel or kerosene anyway. The one issue that i have with adding a quart of diesel fuel is the smell. Wouldnt this make the exhaust smell strong? I wonder if 2-stroke oil would work....you could jokingly tell people that you have a snowmobile engine under the hood!

quote:Originally posted by PackardV8

Sonny and I rarely disagree, but I have never seen any hard data running diesel fuel mixed with gasoline increases horsepower. Most of my experience indicates it lowers octane and will cause more pinging on engines near the threshold.

thnx, jv.

PackardV8


Milaca,

You might be correct if you were running nothing but diesel fuel in a gasoline engine. It's the MIX of a very small amount of diesel that's useful to enhance the qualities of modern fuels. No, there is no smell, what so ever, I use it in every tank of gasoline. I dunno what brand of carb. cleaner you're using, but carb. cleaner shouldn't consist of nothing but diesel fuel.

Also, I don't have the article in front of me, but the diesel fuel mix definitely enhances the octane and "burn-ability" of the "new" gasoline, ESPECIALLY the "gas-o-hol" that we're stuck with today. Diesel mix was NOT as useful in the gasoline of years past, they included ALL of the necessary ingredients that our “old school” engines need. Diesel fuel mixed with gas-o-hol of today also replaces some of the lubricity that's been removed. New cars do not need the extra lubricity, (they've been manufactured to survive on the new fuels), our old school engines do!

Aw hell, why bother, same ol' sh-tuff.......

Never mind, forget about mixing diesel with gasoline, I dunno what I could have been thinking. I'd recommend that no person even THINKS about mixing diesel fuel in their gasoline. Please completely disregard anything that I've said about mixing diesel and gasoline.....

Sonny
http://RacingStudebakers.com

Sonny
07-31-2006, 07:57 PM
Originally posted by Milaca

quote:
Sorry, i was incorrect in stating that gasoline has more BTU's than diesel. The info i found on a petroleum website states that #2 diesel has 138,500 BTU's per gallon whereas gasoline has 125,000 BTU's per gallon. However, diesel has much lower octane than gasoline. Sorry for any confussion.


No problem Milaca. But, (and TRUST me on this one, I didn't want to get into the scientific comparison of gasoline and diesel), comparing an octane rating (gasoline) to a cetane rating (diesel), couldn't be further removed, (VERY apples and oranges....). Not trying to be a know-it-all, or mean spirited about it, but it takes some knowledge of the unique properties of these, actually very different, fuels to understand their ability to work together.

For public information, and ONLY as a classification/qualification of these fuels, a cetane rating is considered the diesel equivalent to gasoline's octane rating. However, unlike an octane rating, which rates gasoline's resistance to spontaneous ignition, the cetane rating number (usually 40 to 55 for medium to high speed engines) notes the ease with which diesel fuel ignites. Bottom line, the higher the cetane number, the fuel ignites easier; the higher the octane number, the fuel ignites harder.

Highway vehicles use the diesel classifications, 1D and 2D, the main difference is viscosity and pour point, (1D during cold weather is thinner and 2D during warmer weather, thicker). A 2D fuel is prefered always because it has a higher viscosity and pour point. The higher viscosity provides better lubrication qualities for the moving parts of the diesel engine's expensive and complicated fuel injection system. Because 2D fuels contain more Btu's per gallon, they are able to deliver more power per gallon. This is critical to diesel engine power and economy. The higher the Btu rating a diesel fuel has, the greater power yield per gallon; thus, higher power begets better economy.

Now, concerning higher octane rating, the slower the burn when ignited during the compression burn cycle of the piston allows for better control of burning for high compression engines. So, the idea of "octane rating" is to be able to match the correct gasoline to a particular engine design to ensure complete burning of the gasoline by the engine for maximum power. High compression engines MUST have slower, more controlled burning to develop their maximum power.

Contrary to popular belief, using a higher octane in modern engines does NOT control/reduce engine "spark knock". It DOES in our older engines using carburetors, and here's why.....

Carbs. cannot regulate the air/fuel mix going into the engine as accurately as computerized fuel injection systems. Also, carburetors need regular adjustment and usually these adjustments are not made regularly, causing too much fuel to be mixed with the air. When this happens gasoline does not burn completely, it "soaks" or remains wet and un-fired in the combustion chambers, causing carbon deposit buildups. This causes premature ignition of the gasoline due to the intense heat in the engine cylinder, which keeps the carbon buildup "glowing" before any fuel enters the cylinder, prematurely firing the fuel when fuel DOES enter the cylinder, creating "spark knock".

When this happens, people change to higher octane gasoline, thinking that they're getting more power or "better" burning or more "powerful" fuel, when in fact, all they're REALLY doing is simply taking advantage of the "slow burn" feature of higher octane, resisting premature burn, thus minimizing the knocking problem, period.

So, the point of all this? IF you do not have carbon buildup in the cylinders of your "old s

Milaca
08-01-2006, 03:20 PM
I have no dispute with anything you stated except for one thing. During hard acceleration, my 1995 Mustang GT knocks when using regular gasoline (87 or 89 octane). When using higher octane gasoline, there is no knock. The car is all original and thus has fuel injection. However, unlike a fuel injected diesel engine, it is not direct injected. If it was direct injected, I dont believe that it would knock.

quote:Originally posted by Sonny

Originally posted by Milaca
[quote]quote:
Sorry, i was incorrect in stating that gasoline has more BTU's than diesel. The info i found on a petroleum website states that #2 diesel has 138,500 BTU's per gallon whereas gasoline has 125,000 BTU's per gallon. However, diesel has much lower octane than gasoline. Sorry for any confussion.


No problem Milaca. But, (and TRUST me on this one, I didn't want to get into the scientific comparison of gasoline and diesel), comparing an octane rating (gasoline) to a cetane rating (diesel), couldn't be further removed, (VERY apples and oranges....). Not trying to be a know-it-all, or mean spirited about it, but it takes some knowledge of the unique properties of these, actually very different, fuels to understand their ability to work together.

For public information, and ONLY as a classification/qualification of these fuels, a cetane rating is considered the diesel equivalent to gasoline's octane rating. However, unlike an octane rating, which rates gasoline's resistance to spontaneous ignition, the cetane rating number (usually 40 to 55 for medium to high speed engines) notes the ease with which diesel fuel ignites. Bottom line, the higher the cetane number, the fuel ignites easier; the higher the octane number, the fuel ignites harder.

Highway vehicles use the diesel classifications, 1D and 2D, the main difference is viscosity and pour point, (1D during cold weather is thinner and 2D during warmer weather, thicker). A 2D fuel is prefered always because it has a higher viscosity and pour point. The higher viscosity provides better lubrication qualities for the moving parts of the diesel engine's expensive and complicated fuel injection system. Because 2D fuels contain more Btu's per gallon, they are able to deliver more power per gallon. This is critical to diesel engine power and economy. The higher the Btu rating a diesel fuel has, the greater power yield per gallon; thus, higher power begets better economy.

Now, concerning higher octane rating, the slower the burn when ignited during the compression burn cycle of the piston allows for better control of burning for high compression engines. So, the idea of "octane rating" is to be able to match the correct gasoline to a particular engine design to ensure complete burning of the gasoline by the engine for maximum power. High compression engines MUST have slower, more controlled burning to develop their maximum power.

Contrary to popular belief, using a higher octane in modern engines does NOT control/reduce engine "spark knock". It DOES in our older engines using carburetors, and here's why.....

Carbs. cannot regulate the air/fuel mix going into the engine as accurately as computerized fuel injection systems. Also, carburetors need regular adjustment and usually these adjustments are not made regularly, causing too much fuel to be mixed with the air. When this happens gasoline does not burn completely, it "soaks" or remains wet and un-fired in the combustion chambers, causing carbon deposit buildups. This causes premature ignition of the gasoline due to the intense heat in the engine cylinder, which keeps the carbon buildup "glowing" before any fue

Sonny
08-02-2006, 12:51 AM
quote:Originally posted by Milaca

I have no dispute with anything you stated except for one thing. During hard acceleration, my 1995 Mustang GT knocks when using regular gasoline (87 or 89 octane). When using higher octane gasoline, there is no knock. The car is all original and thus has fuel injection. However, unlike a fuel injected diesel engine, it is not direct injected. If it was direct injected, I dont believe that it would knock.

My 86, 6.9 Ford diesel is indirect injected, (IDI motor in Ford jargon). Direct injection for Ford diesels didn't come about until the middle of '94, with the advent of the "Power Stroke" - 7.3.

Your knocking problem could be a couple of things, possibly ignition timing, intake vacuum leak, (lean cylinder "knock"), but a bad/worn injector spray pattern is the most likely culprit. Most injectors are two-stage type, (inner and outer sets of nozzles that open at different pressures), and mebbe it's only one stage of the nozzle that's bad. Also, a weak cracking pressure can make the injector "dribble" unregulated fuel into a cylinder. A bad injector can cause carbon to build in a chamber, (if it's been bad for a while), but it's rare, and usually isolated to a single cylinder.

The reason I suggest the injector is because I've experienced it. I'd put rebuilt injectors in the 6.9 and it developed a slight knock under acceleration, constant under a load. Took it to the diesel shop and they isolated the injector in #7 cylinder. Bottom line, new injector, they filled a new fuel filter up, (quart size on the diesel), with some kind of cylinder cleaner, started the engine and no more knock.

Since there's so many variables to an injector working properly, I'd get 'em all bench tested to be sure that they're all up to par. I KNOW it's a real pain, like not wanting to get your modern car professionally "scanned" to find a tough problem. But I've found that ya might as well just do it, pay and get it over with. My diesel guys knew right away what to look for and had actually isolated that #7 injector before they pulled it! They simply cracked the fuel line nut on top of each injector while it was running, (called it "feathering the cylinder"), and could tell which one was bad by the sound the cylinder was making, (whew, talk about KNOCK when you do that!).

For an injected gasoline engine, I dunno for sure, but I imagine that you would use the same technique, plus you can administer the cylinder cleaners available from the Ford dealer. I have used the "spray water in the intake" trick a time or two to get rid of built up carbon, but that's a VERY tricky operation. You can also "clean" off/out the carbon "seal" that naturally forms, (sealing the head to the cylinder); OR, get some of the carbon bits that break loose under a valve.

I baby my diesels, only use the expensive cleaner/conditioner in every tank, never have had another problem. Good luck with you car. Hope you figure out what that knock is, I know how frustrating it can be....


Sonny
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