Cool/Heat: Almost over-heating

[Dick LeRoux]

Drove up to La Conner and the entire way up (70+ miles) the temp. gauge is rock steady at 180. Coming back, it starts to climb. 195, 200, finally up past 240, turn on the heat & it starts to fall and limped home but still at 195 - 200. Never lost any coolant. Changed the thermostat and yesterday during the day everything is steady at 180 - 185. Go for a cruise last night and the same thing happened. Up to 195, all the way up to 220 +. Again with the heat on we make it back but still reading 195 - 200. Coolant level still the same. Starting out everything is fine. Let the car sit for a couple of hours & then it almost overheats. Any ideas as to where I should start? Thermostat #1 replaced about 3 months ago. Thermostat #2 replaced last Thursday. Go for thermostat #3? '63 Avanti, R2 automatic, 69,000 miles

[Studerick64]

Maybe your gauge is the problem and not an actual overheating problem?

[63 R2 Hawk]

My Hawk reads high temps but I've checked it with a bulb thermometer in the radiator tank and an IR gun on the sender area several times and both read 180* when gauge says 200+. I remember reading somewhere on this forum about putting a resistor in the sending unit circuit to correct a high reading gauge, a common problem, but I can't seem to find the post.

[jackb]

Having experienced all of post #3 in my GT Hawks, I would still be mindful of what condition my radiator is in AND when the block drain cocks were last removed for complete flushing of the block.....

[karterfred88]

I'd suspect the temp sender, once it gets hot the resistance may be off, sending a false signal to the gage, besides they are cheap, if not the easiest thing to get to, on the back of the head (especially on the Avanti). Since you didn't have coolant loss, the gage is probably just reading high. The thermostat change won't affect the actual running temp once open, it just opens at the preset temp to allow coolant flow, closes back up when it drops below the setting, and cycles as necessary. If it opens and the coolant temp is higher than its setting it will stay open. I'd put the old one back in as it seems to be set closer to 180, better than the new one. The quality on these thermostats seems to have gone south, since they are all old school designs.

[Green 53]

Check the radiator with a thermo gun. I had a gauge go wacky on one of my cars. The gauge would be fine and suddenly jump to 240. New sender didn't fix it but a new gauge did.

Denny L
1940 President Club Sedan street rod
1964 Avanti R1
1964 Daytona convertible R1

[Dick LeRoux]

The gauge has always been rock-steady @ 180. It just started acting up a few weeks ago. At first I was wondering if the gauge worked because it always read 180 but then it started to rise for no noticeable reason. Up to over 240 but then it comes back down when I turn on the heat so the gauge does respond but it only went down to 195 at its lowest. New thermostat & Fluke laser thermometer says 182 when running about 1/2 hour but then same thing happened yesterday. I'm leaning towards the temp sending unit as the offending member.

[PackardV8]

Good advice, all. Verify the actual temperature via several different sensors. Don't just trust aming a Harbor Freight IR gun at the radiator. Stick a direct-reading thermometer in the radiator filler neck.

And yes, even at 60K miles the block can be sludged up. Stude was terrible about leaving core sand in the blocks. At the very least, remove the threaded plugs on the sides of the block. I actually made a tool with a short pipe nipple and a garden hose adapter. Have the engine idling, remove the radiator cap, open the drain petcock and then turn on the hose and shoot water into the side of the block. Let it run until the water coming out the front is clear, then switch to the other side. Not as effective as removing the core plugs, but much easier.

jack vines

[Commander Eddie]

The theme here seems to be the gauge may be the problem. The gauge in my '55 kept reading hot. I had the radiator re-cored, new water pump, new thermostat and new hoses. It still read as running hot. I, and a couple of other mechanics took reading on the block, heads, hoses, and top and bottom of the radiator with laser thermometers and all the the same results. Running temperatures were right on. So, it was the gauge. I feel better about driving it now but do want to get the gauge adjusted (resistor) or replaced along with the temperature sending unit so that I will actually know if it ever really does overheat. Right now I would not know until I saw the steam.

[karterfred88]

The gauge has always been rock-steady @ 180. It just started acting up a few weeks ago. At first I was wondering if the gauge worked because it always read 180 but then it started to rise for no noticeable reason. Up to over 240 but then it comes back down when I turn on the heat so the gauge does respond but it only went down to 195 at its lowest. New thermostat & Fluke laser thermometer says 182 when running about 1/2 hour but then same thing happened yesterday. I'm leaning towards the temp sending unit as the offending member.

For less than $30.00 I'm with you, but be sure to check the sender wire carefully first. If it has worn covering anywhere and briefly touches the back of the block or the connector is loose it can do the same thing, been there, fixed that, and the gage works fine now. That thing vibrates back and forth between the block and the body, 50 years of it and the concentrated heat right there can take its toll.

[mch]

Very interesting read, thanks for the input. What is a reasonably priced and reliable IR gun?
Mark

[Lynn]

I actually made a tool with a short pipe nipple and a garden hose adapter. Have the engine idling, remove the radiator cap, open the drain petcock and then turn on the hose and shoot water into the side of the block. jack vines

I made something similar for BMW big six engines. They are notorious for running hot. Amazing what a back flush can do.

[JoeHall]

Is it a Hawk? Is it only running hot at night, when the headlights are on? If so, does the gas gauge also read high at night? I have had that happen in Haws, due to a grounding problem. They share a common ground, through the oil pressure gauge oil line, via a strap or clamp that is connected to the firewall with a screw. Might wanna check that strap/clamp, and remove the screw in the firewall and hit it on a wire wheel.

[dynolou2]

Jack , can you post a picture of your backflush device? thanks Lou Cote

[TWChamp]

My Model A had a lot of rust build up around the two rear cylinders. I made an adaptor to connect a sump pump in a large tub of water to backflush the block. It take a large forceful flow of water to wash that junk out, and the sump pump did a good job. I then turned the radiator upside down in the same tub of water, and used the sump pump to back flush that. Between the block and radiator I got about 3 cups of rust flakes out. Studebaker engines, when out of the car, should have the welch plugs removed to clean the inside of the cooling chambers.