Temp Gauge Confusion

[Tech_n]

I have a 98" Pontiac Grand Prix GT

I changed my thermo like 3x
I changed my water pump 1x
I flushed my radiator 1x
and I changed the top radiator hose because it had a leak.

but still
When I drive my car the needle stay a little above the middle temp line
but when the car is sitting, it floats up close by the needle before hot line.
How could I make the needle stay under the middle temp line and what could the problem be why this is happening?

[BNaylor]

Unless you still have a cooling system problem, your engine coolant temperature sensor (ECT) may be out of calibration. You can check the resistance with a digital multi/ohmmeter. It's located by the thermostat housing. Undo the electrical connector and measure across the pins or you can remove it completely for testing. It feeds the temperature gauge and PCM.

212 degrees - 177 ohms
176 degrees - 332 ohms
86 degrees - 2235 ohms
5 degrees - 21,450 ohms or 21.4K ohms
0 degrees - 25,000 ohms or 25K ohms








Thrasher CAI, DHP v1.0 PCM, SLP Headers,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 72mm TB,
TB spacer, MSD 8.5mm wires, Autolite 103,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials
1/4 ET: 13.210 sec. @ 104.490 mph
0 - 60 ft: 1.945 sec.

[Ripn12s]

Are the fans coming on? Sounds like the fans arent coming on and thats why the temp rises when sitting still. Have u flushed the system, maybe its all gummed up.

And did u bleed the air out of the system after replacing the parts?

[richtazz]

Are you using coolant at all, or is the temp guage just jumping? There is a known issue with the upper intake plenums cracking and sucking coolant into the engine, but you would be losing coolant. I would bet you have air trapped in the system still, and the air bubble is causing your temp fluctuations, if the sensor checks out.

[Tech_n]

Ok, explain step by step how you are suppose to bleed the air out of the system.

Also, if the coolant was leeking into the engine, wouldn't I see it in my oil. If so, I do not see it in my oil.

Also, both of the fans are coming on, is their a way you can adjust the speed of the fans.

[Ripn12s]

On top of the tstat housing there is a brass nut. Thats the bleeder valve. Turn it but do not remove all the way, then start car and wait for it to get up to temp. When only coolant is coming out of the bleeder valve then tighten nut back up.

[BNaylor]

Checkout this old link. Sounds like you have a similar problem. He had a problem where the gauge was not accurately reflecting what the PCM sensed on temperture. However, the root of his problem was actually a clogged radiator ( 5 internal lines) and it needed professional cleaning. He went through flushing, bleeding, thermostat replacement, fans working OK, etc.


http://www.automotiveforums.com/vbul...rheating+bleed






Thrasher CAI, DHP v1.0 PCM, SLP Headers,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 72mm TB,
TB spacer, MSD 8.5mm wires, Autolite 103,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials
1/4 ET: 13.210 sec. @ 104.490 mph
0 - 60 ft: 1.945 sec.

[Tech_n]

Ok I bleed the therm correctly, but it is still rising above 210 when I am sitting and sticking on or below 210 when I am driving.

When you take you car to be flushed at pep boys or BP Gas Station, do they use special tools or do they do it the way I do it.
By taking off the heater core hose, 1 at a time and pouring water down it the radiator with the car running.

[StevePT]

When you're driving you have forced convection cooling. The air passing through the lower air dam and up across the radiator and through the engine compartment keeps the temp needle down. The needle should be at the unmarked bold white line above 100 and below 210 while you're driving.

When you come to a stop, you no longer have that forced air cooling and since the thermostat is set at 195*, it will stay shut off until the engine raises the coolant temp back up and then it will open again and the temp sensor will start rising. The temp will get up close to 210 before the fans start to kick in.

One of the fixes people have for this is to switch to a 180* thermostat. If you live where it's cold, it's going to take longer for your heater to blow hot air if you do this.

There's another bleed screw on the coolant by-pass housing on the left side of the engine. It's the black tower just above the water pump. Loosen that nut with the engine running and wait until fluid starts to come out. Coolant won't start coming out of the brass screw at the thermostat neck until the engine temp is up enough to open the thermostat.

[Ripn12s]

"but it is still rising above 210 when I am sitting and sticking on or below 210 when I am driving."

how far above 210, because like steve just said sounds like its operating normally. try a 160 tstat if your in the hotter climates.

[Tech_n]

So that nut that is above the water pump will not bust if I loosen it, would it. Also, isn't that the bolt that is bolting the water pump together. So this pontiac have to valves where you can release the air pressure in the coolant

[ericn1300]

back to basics. a vehicle in motion will have the engine cooled by air being pushed thru the radiator. a vehicle stopped and ideling will have it's engine cooled by air being pulled thru the radiator by the fan.

if you have overheating while driving at speed you probably have a coolant problem. if you have overheating when ideling you probably have an air flow problem.

check the fan and shroud and front of radiator for debris and clean the radiator fins with a cleaning spray and high pressure water, with a cold engine of course. then check the fan for proper operation. when the problem occurs, try turning on the AC. this will overide the fan termostat and turn it on.

[Tech_n]

Should I still flush the radiator too
But cleaning the radiator, front and back should this solve the problem that I am having.

[BNaylor]

Originally Posted by Tech_n

Should I still flush the radiator too
But cleaning the radiator, front and back should this solve the problem that I am having.

The radiator is the primary component used for cooling not only the engine but the transmission too. It is a heat exchanger. If there is any coolant blockage within the internal coils then cooling will be degraded.

You can front and back flush the radiator by itself. However, before any flushing you need to use a chemical flushing solution like "Prestone Super Flush" to help loosen up old scale and any possible Dexcool sludge. Good luck and let us know how it turns out.

BTW - What temperature thermostat are you running and what coolant are you using?







Thrasher CAI, DHP v1.0 PCM, SLP Headers,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 72mm TB,
TB spacer, MSD 8.5mm wires, Autolite 103,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials
1/4 ET: 13.210 sec. @ 104.490 mph
0 - 60 ft: 1.945 sec.

[Tech_n]

I am using the 195 therm and dexcool, would it be better if I just replace the dexcool with the green coolant. Would that make the car stay cool better than the dexcool.