Temp Gauge Not Reading RIght

[2000 Grand Prix GT Blue]

My 2000 Grand Prix GT (non-supercharged) had had issues running hot. Finally i got sick of waiting money trying to fix it myself and took it to a shop to get looked at. What happens is it has a 180 thermostat so it should run around that temp... but mine will ride around 195. Thats not bad at all. but the problem is when im idling or stopped in traffic it will get all the way up to 235 and drop back down. I've already replaced all the obvious; new thermostat, water pump, radiator, flushed and filled system, new temp sensor, fan relays and theres no blown gaskets. So i basically have a brand new cooling system. So anyways i take it to the shop and they hook it up to some computer thing and turns out my car is absolutely fine. Its not actually overheating. My gauge is wrong.. but it has a brand new temp sensor. SO I'M STUMPED! Anyone got advice?? All i can think is my new temp sensor never worked or i have either a bad gauge or wiring to the gauge.. PLEASE HELPPPPPPPPPPP

[BillBoost37]

Sounds like it's fine to me as well. Your stock fan settings are approximately low speed on at ~212F and high speed on at ~228F. To see 235Fish is about right.

Have someone with a tuner bring your fan settings down to better work with your thermostat and you'll be much happier. I set all my cars down a bit and that alleviates the traffic/off ramp increase in temps that you see.

[2000 Grand Prix GT Blue]

But my issue is that when they had it on the computer the temp only read around 203 from the PCM when the dash was giving a reading of 225-235..

[SnowDrift]

There are two different probes for temp. One for the computer and another for the gauge. They're likely to be in different locations and reading different temps. is likely.

[2000 Grand Prix GT Blue]

are u talking about a sending unit to the gauge..? cause when i looked it up theres not supose to be one on Grand Prix's.... just the temp sensor

[BillBoost37]

Ok, you didn't say that. You said they told you it was fine and everything was fine.

If the dash is showing a different number than the pcm, it's either the sender, wiring between sender and dash or the cluster itself. Depending on year and how GM set it up, you can test the various items with a multimeter.

Honestly though, what you describe is a perfectly working gauge and cooling system. Right up until you mention the cluster has a different reading than the pcm. I'd double check with the shop to ensure you understood them correctly and that the pcm temp was different than the cluster.

[Bio248]

are you serious about where you posted this? did you just pick the first forum you saw and went at it? jesus christ, at least try to not be a dick.

moving.

[SnowDrift]

curious - where was it? I came across it in "new posts" so I didn't see.

[2000 Grand Prix GT Blue]

Do you think I should just take it to the dealership? Cause I know it's gonna be a pain to find out if itsthe wiring or the dash or what not...

[2000 Grand Prix GT Blue]

And yes the gauge is off. He shower me te computer and when the dash showed 235ishh the computer said the PCM was reading around 203..

[SnowDrift]

<<There are two different probes for temp. One for the computer and another for the gauge. They're likely to be in different locations and reading different temps. is likely. >>

[BillBoost37]

On a series 2 motor there is one temp sender that is located in the LIM. Easy to find if you look at the LIM under the thermostat housing, or follow it's wiring.

The sensor has two elements built into it. This is why it is a three wire sensor. One ground and two outputs. One for the pcm and one for the gauge.

[2000 Grand Prix GT Blue]

Do you by chance know which wire goes to the gauge?? I think ill just get a better quality sensor and if that doesn't work ill just follow the gauge wire as far as i can and look for problems. maybe just replace the whole wire. Also what do you mean by LIM?

[BillBoost37]

LIM is short for Lower Intake Manifold. The LIM is the part of the engine that the coolant sensor is screwed into.

There are other tests we could give you if someone has the manuals for the car. Those would tell us what resistance etc the wires should be reading and you may be able to test as to why your readings are wrong.

[SnowDrift]

On a series 2 motor there is one temp sender that is located in the LIM. Easy to find if you look at the LIM under the thermostat housing, or follow it's wiring.

The sensor has two elements built into it. This is why it is a three wire sensor. One ground and two outputs. One for the pcm and one for the gauge.

I apologize, then. I did not know that.

[BillBoost37]

Never a worry ... we all learn cool stuff everyday. There's hardly a day that I'm surfing the forums that I don't pick up some knowledge from another.

The versions of the 3800 before the Series II all used two sensors and that's commonplace in many other vehicles as well.