Low Oil Pressure Revisited - Rebuilt enigne

[dpson]

I know this issue has been brought up before, but I need some advice on the best place to start given the following conditions:

1962 Lark
rebuilt 259 V-8
non-full flow block
no external oil filter

An oil pressure gauge has been attached to the right head below the oil sender unit. Engine shows 25 psi on cold start (75 degree air temp.)at idle and will jump up to 50 to 75 psi with increased throttle. As the engine warms at idle the oil pressure steadily decreases and after about 10 minutes is under 5 psi. There are no external oil leaks. The fellow who rebuilt the engine said the crank was turned and all new bearings of proper size were installed, plastigauged and were within spec. Engine runs well and doesn't appear to burn any oil.

I'd like to start with the least invasive items first and then work to those that might require pulling the engine, etc. Where should I start first to try to figure out what is causing the low oil pressure?

Dan Peterson
Montpelier, VT
1960 Lark V-8 Convertible
1960 Lark V-8 Convertible (parts car)
1962 Lark V-8 Regal Convertible

[Roscomacaw]

I wonder if it's got the regulator valve in place! Have you checked?

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

[55studeman]

Think of it this way, if the oil pump is good, then that loss in pressure is happening somewhere in that engine and you just have to check the common points and check off each point as you go through them. So you'll find it, it's not a black box, the oil goes here and there, follow the diagrams and last but now least get some advice from Jim Pepper and Ted Harbit who really know the oil system well.

Overall your 25 psi at cold startup might be considered low, even for a Studebaker, a brand that is known for lower oil pressure. So you might have two problems, an overall lack of pressure that could be due to several unaddressed "rebuild" issues that is maybe out of spec, and second a problem where at warm temps you have a slowly decreasing pressure such as a small microscopic pin hole leak that enlarges with heat and eats away at your pressure.

Some more info would also help, such as how long has this been going on? Since rebuild or just recent? Any unusual or aggressive driving or long stretch drives?

For starters the common mishaps are:
1) Check your relief valve (also called the regulator valve) located to the front rightside, by the timing cover, and make sure it is EXACTLY to specs according to the shop manual, and that it is clean and the hole inside is clear. Any problem here could easily cause oil pressure fluctuations you are having. And don't block it or stretch the spring to get high pressure, it doesn't work that way...you'll simply cause long term destruction of the timing gear and other problems.

2) Double check your oil pump specs, the gear clearance (top and sides) and the plate, and movement of the pickup arm. Your pump is probably okay because of the high reading you got, but who knows, it could have something out of spec that shows up when it gets warm.

3) Missing oil gallery plug located in the distributor hole, right in the bore wall located at 12:00 position (12:00 being the front of the engine, 6:00 being the rear. This plug should be removed for cleaning the block BUT it is often forgotten to be put back because it is not a common location like other brand-x engines. This is probably not your problem because of the up and down nature of your oil pressure but might be part of the overall low pressure.

Speaking of oil gallery plugs, it occurred to me that maybe you have a loose one or one installed incorrect or dirt such that it has a microscopic leak that lets loose or opens up when the oil gets warm and thinner. Maybe?

4) Camshaft bearings, they only wear down over time and shops often overlook this especially if you do part of the engine assembly and they don't have a cam to check the wear and fit. There could be loose bearings or problems that could occur as the engine warms up.

5) Valve lifter, lots of wear and very little usually done during the rebuild for them. For higher mileage blocks, the bores get very tapered and let out lots of oil that should be going elsewhere.

6) Rocker arms, if too much wear or some other unknown issue there, it could be a dumping spot where the oil flows out too quickly when warm and produces your loss of oil pressure. The rocker arms are often ignored.

7) Is the oil returning from the top of the engine back down okay? Delays by blocked drain holes by a incorrectly installed head gasket or blocked lifter valley drain (near the distributor) slows the oil such that the oil pump is starving for oil.

8) Oil, are you using a brand name with the correct viscosity? I won't go into correct viscosity because there's so much opinion on this but TW co-op has done many articles on this and it should be referenced to get the right kind.

9) Did the shop actually do the main and rod bearings correct? You never know and it is a Studebaker, even if they are good sometimes it's that off-brand that brand-x guys aren't familiar with that can cause a problem...something a studebaker guy would know and do right.

I'm sure you'll get some more tips from others, but this covers the usual found in the TW and in the forums. It's a hassle for sure, to t

[jjones]

The pressure reading sound just like my rebuilt 259 on its first startup. I would bet it is that d**m oil gallery plug. Been there, done that, and felt really dumb, but it seems to be a common mistake. Some people have apparently managed to install it through the distributor hole but after several trys, I had to pull the engine. Good luck.

jj

[DEEPNHOCK]

In addition to what was said here...
One thing I see a lot is excessive rod side clearance.
That will also allow some loss in pressure.
Jeff[8D]


DEEPNHOCK at Cox.net
Ocala, FL.[u](For 4 more days!)</u>
'37 Coupe Express (never ending project)
'37 Coupe Express Trailer (project)
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http://community.webshots.com/user/deepnhock

[dpson]

Thank you all for the suggestions. As it turns out I've decided to hold off in doing anything for the time being due to back problems (siatica, doc says no bending or reaching for long periods, etc. this getting older sure is fun). I put the car in storage yesterday (rented space, cause I'm out of room at home) and will take a crack at it in the spring. Based on email correspondence with Bob Johnstone I'm leaning toward the rear oil galley plug. I'll let you know what I find. Thanks again!

Dan Peterson
Montpelier, VT
1960 Lark V-8 Convertible
1960 Lark V-8 Convertible (parts car)
1962 Lark V-8 Regal Convertible