smacota1

1965 with NOM 350 4Spd.

I have noticed something strange happening with my temp gauge. Been driving the car quite a bit since putting new tires and can safely drive the car. Temp gauge always stayed around 180 -190, just to the left of the 210 mark.

Yesterday noticed as I drove the car around 45-60MPH the gauge would move up to around 250 temp. As soon as I started slowing down the temp would move back down to normal and do it very quickly. Stopping at a light and it would stay normal, as soon as I accelerated it would go back up. Engine ran fine and did not seem to be overheated.

Hard to shoot a temp because as soon as I stop car the gauge is reading normal.

This is also in 30 degree temps.

7 blade fan with fan clutch, has OEM a/c but belt removed, new 165 thermostat and new aluminum radiator.

Alternator belt tight with no slipping, coolant level normal and clean.

Totally the opposite that normally happens where overheating during stop and go city driving.

Can't mess with things until this weekend, but would appreciate tips of things to check and explore.

65GGvert

Minor point, but 65 center mark was 180, it didn't change to 210 until 66. Only a couple of things come to mind, but just guesses. The water must not be circulating at high rpms. The problem with that theory is it probably wouldn't cool back down that fast, but possible I guess. The second is an air pocket in the coolant that maybe collected below the sensor and when coolant flows slowly it pushes the air out. Neither one of those theories make me feel fuzzy and warm. If it really shows 250 and quickly drops back at idle, it should be a sensor problem and not a temperature problem. These sensor can do weird things, but I would try to verify that the temp actually went up before working on things like water pump, fan, belts, etc. If it drops back to normal in the time it takes to raise the hood and check it, it's not really going to that temp. My first try would be to swap the sensor and make sure the air was out of the system. Good luck and post back what you find.

EDIT: Did it do that before you changed the thermostat?

dplotkin

I'd be curious to see a DVM volt readout across the battery while revving it.

Dan

65GGvert

Good thought, check the battery voltage at the rpm's at which you are seeing the problem.

smacota1

I will try to do this this weekend.

Since you mention this it also seemed my dash and interior lights seemed to be much brighter than they have been before. Don't drive much at night but I did the other evening. Also my amp gauge seemed to be more on the positive than it has been before. Could possibly be related.
Thanks

smacota1

No did not do this before the change.

65GGvert

I recently had similar voltage issues at rpm and the cheap Chinese voltage regulator that came on the car when I bought it was shorted. It was also drawing the battery down over night. I replaced it with a used Delco-Remy and all is perfect.

Vettegeezer

Regarding measuring temps. while driving, if you have one of those remote meat thermometers that transmit to a portable unit, these can be used. I did this by taping the probe to the rad. hose close to the thermostat housing and routed and taped the probe wire away from any moving engine parts to the transmitter unit which itself was taped securely to the fender away from any moving parts. You can now monitor the temps. on the receiver unit located in the car cabin.
Phil M.

dplotkin

I think you found your problem, and I would keep the lights & radio off until you resolve it. To my knowledge GM did not use little voltage regulators on the instrument cluster as did Ford & Chrysler to dampen needle movements in response to voltage swings in the system.


My guess is a new voltage regulator under your hood will fix this one. I would do it soon as your alternator is likely being pushed to full output and they don't stay happy for long that way.


Dan

smacota1

Got one ordered last night....problem is the temp goes way up and way down quickly depending on the RPM. But it will be nice to at least have a measuring tool to verify the gauge accuracy.

dplotkin

I suspect your regulator is shorted and has the alternator field coil grounded driving alternator to 18+ volts and creating havoc with the instruments. Always good to have a baseline operating temperature by using an IR gun so you know reality vs what the gauge says, but in this case its your alternator getting the heat, not the engine!

GCD1962

Not necessarily. I had this happen to a car that had a borum tube type of gauge. I always thought it was a air pocket or some time of restriction tht would come and go. Never figured it out

dplotkin

Why do you say "not necessarily" and then disclose that you never found your problem? The temp gauge on a C2 is electric. Try re-reading all the posts above.


Dan

GCD1962

I know its' electric but I had the same problem with a non-electric. It had the same flucation. I'm saying it might be something else that is not related to it being an electric gauge. Didn't find the problem, so what ? I learned to live with it because it was consistent in its flucation and didn't affect the performance. It could have been an air pocket (i doubt), or something that would block the flow, release do to flow change, the repeat again. It was most likely in the block passages and old chunk of the casting core, or a piece of slag that broke off.

65tripleblack

dplotkin

Really? You would go in that direction knowing the gauge is electric, the poster says the temp needle follows engine revolutions, his ammeter is reading high and his lights look too bright?


Dan

Vitaminmopar

If the problem resolves not to be electrical related check your lower radiator hose. You wrote you had installed a new radiator. Check the lower hose has a spring inside to prevent it from collapsing and is not installed backwards. I have read here on the forum that if the fan belt touches the hose it is on backwards.

ejboyd5

Changes in needle position occur too rapidly to be accounted for by water flow variation. Go to electrics for solution to problem which appears to have linear relationship with engine RPM and output voltage.

smacota1

Hopefully will be able to dive into the diagnosis tomorrow. The radiator was replaced by the PO and I do feel a spring in the hose, that is not to say it is installed correctly. But the temp gauge issue just started as well as the bright dash lights.

I live in a townhome complex so working on the car at night and having to crank and run it is a problem with noise disturbance and frowned upon....(the NOISE though is music to me)
The car has sat since Sunday and last night I did check the static voltage on the battery and it read 12.6 volts so hopefully the battery seems to be fine.
I think with the new issue of really bright dash lights and the amp meter showing more positive than it normally does I am hoping it is a simple VR issue. Ordered a replacement just in case and if not at least a spare to keep around.

Should have more updates this weekend.

Thanks to all for the great tips and suggestions.

Vitaminmopar

I don’t know how many accessory drive belts you have but if you have more than one driving the water pump you can disconnect the alternator and take a short drive to see if the problem goes away. If you have a belt for the disconnected AC compressor installing a belt will drive the water pump. If you don’t have a second belt driving the water pump, wait for the voltage regulator to arrive. No sense in spending money when you don’t have too.

I would not do this test if your battery is weak or really old but with a reading of 12.6 VDC sitting your battery should be fine. The only thing you will change some by driving is the battery state of charge and a short 20 minute drive will not discharge the battery enough to hurt anything. If you have a battery tender or charger you can connect the battery to bring the charge back to full. Don’t worry about it if you do not have a charger. The battery won't be harmed anymore than having played the radio for hours or left the lights on for extended periods or cranked a car multiple times trying to start it.