I have a problem, and I can't really find anything concrete by doing a search. A couple days ago, my engine seemed to start running hot. The guage would read about 120*C all the time (near redline). I touched the rad and the engine, and they are just mildly warm to the touch, so I KNOW its not getting that hot. I'ev touched the engine at running temp and its much hotter than it was, yet the guage wanders around 120*C.

I replaced the coolant temp sender (in the drivers side head) today, and it didn't help, its still reading way high.

The guage does peg when I start to crank the engine with the starter, so that should mean the guage is working properly, right?

I can't figure this out!!

 

The gauge pegging when starting just means the circuit for the gauge is ok...not that the gauge is reading properly. We really shouldn't call it a gauge anyway, they aren't that accurate (Gm calls our gauges a trim group). My temp gauge reads too low, I have a 180*F thermostat and the gauge never gets above 120*F.
you need to verify the temperature of the engine at the sender to make sure the engine isn't getting that hot. An infrared thermometer is best, that is what I used.

 

Remember the gauge reads the temperature of the coolant in the block, not the rad, so feeling the rad won't tell you anything. If the engine feels hotter than normal, the gauge could be working correctly. Make sure your coolant is flowing properly. How are your water pump and thermostat?

 

That right there are the questions at issue. (In other words, )

 

Thermostat is about 2 months old, and I know it works fine. The waterpump is the original, but doesn't leak or make noise, and works just fine also.

Thats why I mentioned the heat in the rad... if either of these were not working, then coolant wouldn't be circulating through the rad. And because the rad is getting warm, that means coolant is circulating, no?

Apeiron - I think you might have my situation backwards... the guage reads way too hot, but the engine is still very cool to the touch. Its nowhere near as hot as the guage says it should be.

 

Maybe a nice airpocket then. This is the same symptoms with two different sensors correct? Did you do anything recently that ay have allowed air into the system (prior to the sensor change if this was occuring with both)?

 

This problem started before the sensor change. The only thing that might have let air into the system is when I changed the intake manifold, but that was over a month ago, and this is my daily driver, and I haven't had a problem untill only a few days ago, so I doubt the manifold change did anything.

 

After I got home from work today, I started up the car. After about 10 seconds, the guage climbed up to 120*C again, so the problem is still there.

Here is what I've done today:

- Unplugged the wire to the sensor, guage read dead cold, which I think is right.

- Touched the wire to engine (grounded) and the guage maxed out, which IIRC is also right.

These do these two tests rule out the guage as the problem?

I ran the engine for about 10 mins idling, to get a little heat in it. I felt the thermostat open, because the upper hose got warm quickly after the egine had been running awhile. The rad warmed up a little shortly after that. So I do know coolant is circulating, BUT, the temp on the guage did not drop at all for any amount of time, it just stayed at the 2nd bar of redline.

The engine never got hot enough to turn the rad fan on either, so the coolant temp can't have gone past about 110*C because thats where my fan always comes on, but rarely in the winter because its too cold.

ANYONE have ANY ideas? This is driving me absolutely NUCKING FUTS!!!

 

Leak? Did you retorque the intake bolts? I assume there are no leaks on the outside of the engine. Check your engine oil for antifreeze. If the coolant passage in the intake is leaking into the engine it could cause an air pocket.

Sounds like the gauge is ok, since it takes a few seconds to go up high. All the other checks on it are alright.

 

Theres no coolant leak... no visible ones on the outside, and no internal ones either. The oil is clean and looks just how it should for being 1500 miles old, and the coolant level never goes down.

The intake bolts I checked on every couple days after the swap untill they didn't need to be retorqued anymore. That ended about a week or so after the swap. I checked them again last night and they are still tight.

I'm 99% sure its something electrical, and the engine is not actually doing what the temp guage says its doing. I know its NOT getting as hot as the guage says, because When the guage says the engine is at 120*C (redline, overheating) there is still frost on the cylinder heads and the rest of the engine. It also only takes about 10 seconds for the needle to get that high after the engine is started from dead-cold. There is no way the engine will go from -20*C to 120*C in 10 seconds. Just not gonna happen. So its gotta be an electrical problem.

 

BTW - this is what my guage does when I ground it out. This is also what it does when I crank the engine over. I thought I'd post this, because someone I know said this isn't what it should be doing, but that it should just hit the top of the redline, but I thought it was supposed to stand straight up.

 

The temp gauge should peg out when you ground it and when you start the car. Sounds like your gauge is working normal in that sense.

 

Try comparing with an aftermarket gauge, or swapping in another gauge to see if they read differently.

 

The gauge in my car (factory gauge 90 Formula), reads 20 degrees hotter than what the car actually is. i had my car in at a local performance shop to help me trouble shoot some wiring issues and we found that out.

 

I bought a mechanical guage yesterday, but I haven't had a chance to do anything with it yet. After running the car today though, it seems like the guage is working again, although the engine does seem to be running a little warmer than usual(if it is infact correct) but not much, and definitely not like it read before. Maybe thats just the new sender?