Temp Gauge Confusion

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?

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







http://i5.photobucket.com/albums/y186/lizzywiz/gtp.jpg
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.

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?

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.

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.

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.

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/vbulletin/showthread.php?t=412507&highlight=overheating+bleed





http://i5.photobucket.com/albums/y186/lizzywiz/gtp.jpg
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.

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.

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.

"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.

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

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.

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

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?






http://i5.photobucket.com/albums/y186/lizzywiz/gtp.jpg
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.

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.

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?

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?

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?


You could use the 180 degree thermostat but the 195 degree works fine once you get the cooling system bugs worked out. The 195 will help on emissions and the heater will work better during the winter. I use a 160 in my GTP but I'm down South and I have a DHP PCM with fan turn on point of 186 degrees but thats not applicable to your situation.

A lot of us on the forum have switched over to the Prestone Extended Life coolant. It's in the yellow bottle and is green. However, it is based on the same technology as Dexcool. OAT (Organic Acid). It doesn't hurt aluminum and can actually be mixed with Dexcool in the event there is any residual even after a good flush. I've had no problems with the Prestone EL and the engine operates cooler. My gauge has never read over 190 degrees. I would highly recommend that you can the Dexcool.








http://i5.photobucket.com/albums/y186/lizzywiz/gtp.jpg
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.

I agree with Bob 100%. The Prestone EL in the yellow bottle isn't as corrosive as Dex-cool, and protects aluminum just as well. The Prestone in the silver bottle is the same crap as Dex-cool, so don't bother. Don't believe the 100k+ claims for the change interval either. Change it out at least every 75k or 3 years, that way any sludge trying to form will be flushed out.

Let me inform you on something that is occuring, When I am at a stand still and I rev the car RPM up to 2 the coolant level drop down at 210, but when it is just idling, it rises back up at the needle beside the red.

So this would be a problem that is occuring with the flow of the fluids in the radiator. I know I do not have a blown head gasket because there is no white smoke.

Another thing that might can help you all out is

When I rev my car's RPM around 2,000, the temp needle basically dropped around 210 or below. When the car is just sitting around 1,000-1,500 the needle starts to rise.

Another thing that might can help you all out is

When I rev my car's RPM around 2,000, the temp needle basically dropped around 210 or below. When the car is just sitting around 1,000-1,500 the needle starts to rise.

When you increase the idle naturally you're increasing coolant flow via the rotation of the water pump. When you are at cruising speeds how's the temperature reading. If the cooling system is up to snuff it should read way below 190 degrees when the car is moving.

Can you re-cap what you have done to date to resolve the problem.







http://i5.photobucket.com/albums/y186/lizzywiz/gtp.jpg
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.

I changed the water pump,
change the Thermo and put a 195 in
I flushed the radiator
changed the upper radiator hose because it burst
out of all that I bled the system.

I changed the water pump,
change the Thermo and put a 195 in
I flushed the radiator
changed the upper radiator hose because it burst
out of all that I bled the system.

Are you getting any funny sounds when you first start the engine or at turn off? Sounds such as coolant/water flowing behind the dashboard like from the area of the heater core, etc. Do you have the original intake manifold gaskets - have they ever been replaced?





http://i5.photobucket.com/albums/y186/lizzywiz/gtp.jpg
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.

It has the original intake manifold on it, I have never replaced it. When I start the car in the morning, I hear a sound like a suction noise, but it is not leaking coolant inside, so could this be a problem.

Now the problem is solved. I had to flush the coolant out of the system and put the green coolant in and bleed the system. Now my car stays below 210 and when in traffic, the car might go 1 needle above 210 and then it dropes when the fan kicks on.