Also, have a 1997 trans-am running hot


Asked by Mar 31, 2013 at 02:29 PM

Question type: Maintenance & Repair

Car runs great any speeds above 40 or 50mph. But once at freeway speeds for around 20 or 30

mintues, then incounters stop & go traffic, the temp will creep up, during the stop goes to over

240 and even into the red if I dont stop and let it cool down.
I"ve replaced and checked lots of

stuff as follows.
Raditor cap, new fludes, more than 50/50 mix. estimate about 80/20
New water

pump, radiator& thermostat. Engining block temp sensor.
air dam in place.
Checked both fans &

relays.working. however Fans dont seem to turn on soon enough?
maybe water temperture sensor gauge

to old and faulty reading?
any thoughts, ideas are appriciated!

15 Answers


I would check the actual temperature as you suggested. The gauge on the dash may be reading high. If you have a scanner, you can see what temperature is being seen by the ECU.

Best Answer Mark helpful

Check your ignition timing. If it's retarded (late) you've got a worn or jumped timing chain. Other symptoms of this are lack of power & late shifting of the transmission. HTH. -Jim

1 people found this helpful.

air fully bled outta the thermostat housing thru the allen bolt? also.. are u using distilled water to avoid deposits in the coolant?


80/20 mixture is not going to work which is most likely causing your current problem. Coolant is only there to increase the boiling point of the water and to prevent freezing in the winter. The water is what actually transfers most of the heat from the engine to keep it cool so if you have mostly coolant in the system you will most likely run too hot. Change to a 50/50 mixture before trying ANYTHING else.

1 people found this helpful.

Ok, getting hotter here in Houston, and the problem has come back. to respond to some of the answers, I did use only Distilled water and reduced the mixture of Antifreeze to a 50/50 mixture. The Car runs great with no sort of timing issues. the bottom air reflector is in place. Today when it was running Hot I jacked up the car, and looked at the fans, Both Fans were running, but at a reduce speed, not really pushing much hot air. I read the temperature with an infrared red temperature probe at the block temperature sensor and it was reading the same as the gauge inside the car, around 255F. I turned on the A/C full blast fan on high, and Both radiator Fans come on high speed, really pushing a lot of hot air, You could here them running outside the car. So the question is, what controls the Radiator fan speeds? Why are they not coming on, unless I turn the a/c high?


There are usually 2 fan relays on GMs. One for high & one for low speeds. They are controlled by the PCM (Powertrain Control Module). Have you changed the coolant temperature sensor? Some vehicles use 2. One for the PCM and one for the gauge on the dash. The PCM uses temperature information from the coolant temperature sensor to switch on the fans at about 220°F then as the temperature continues to climb switches the fans to high at about 240°F. Also, when you switch on the air conditioning this sends an "A/C request signal" to the PCM which increases idle speed about 50 RPMs and usually starts the radiator fans as well. If the coolant temperature sensor is bad the PCM can't "see" how hot the engine is really getting and might not be switching on the fans when they need to be running. HTH. - Jim

3 people found this helpful.

Ok, thanks for the answer. I have replaced both the sensors. 1 of them at the water pump, and the other on the engine block. Also, replaced the connector to the 1 at the engine block. I think the one at the engine block is for the dash board gauge, due to when it was disconnected, the gauges didn't work. I will try and replace both the fan relays. Perhaps one of them is reducing the current going to the fans some how?

1 people found this helpful.

You're welcome. Good idea about the relays. Did you replace the coolant temperature sensor with an AC Delco sensor? I've read that aftermarket sensors may not have the same (correct) resistance value as an original equipment type AC Delco sensor. this can be a real problem because the PCM reads this resistance value to determine engine coolant temperature. Also, if the new sensor has no sealant on the threads, do not add any. This may skew the resistance reading to the PCM as well. Only add sealant if any installation instructions, or your shop manual say so. has your sensor. Part #2134396 for $18.99. You should also be able to get it, using that part number, at the parts counter of your local Chevrolet Dealer. HTH. -Jim

1 people found this helpful.

Ok thanks for the answer. I replaced the ECT sensor on the water pump with an O'reilly aftermarket. It came with thread sealant already on the threads. I will try the AC Delco part you've recommended. The relay was expensive, like $27 each. So I've swapped the fog light, smoke pump, and their was a spare relay in the compartment. with the 3 Fan relays. I think the 3th fan relay is the internal fan, but no sure. I'll see what happens this next week in traffic. Do you think that the incorrect resistance value reading on to the PCM could cause the Fans to run at lower speeds? I would think it would either be ON, or OFF. I don't know why the engine temp, is above the 240F level and the fans are running so slow? like 50% of the high speed when the A/C is on. I'm going to buy the Harbor freight CAN OBDII could reader item #98568, does anyone know if this will read the engine temperature?


It's been my experience with GMs that two fan speeds are used. High and low. When the coolant temperature rises to about 220°F the PCM switches the fans on low speed. Then if the coolant temperature continues to rise the PCM commands high speed. The only way the PCM knows what the coolant temperature is, is by the resistance value from the coolant temperature sensor. So if your sensor isn't showing the correct resistance for the actual coolant temperature the PCM won't know to switch on the fans and/or to switch from low to high speed. I'm not familiar with the scan tool you're looking at. Usually ones that give specifics, like coolant temperature, freeze frame data, engine RPMs, fuel trim data, etc. are quite expensive. At NAPA, we sell ones that just read trouble codes for about $50.00. Then on the other end of the scale, for about $4,000.00, you can get a scan tool that does everything. PCM, BCM, ABS, transmissions, etc. Those are the ones shops have. My scan tool cost me about $225.00. It reads trouble codes from the PCM and gives explanations for the codes. It's enough to point me in the right direction when a problem pops up. Keep us posted. HTH. -Jim

1 people found this helpful.

Just looked at that scan tool on Harbor Freight's website. This is your basic OBD II scan tool. It will show trouble codes with explanations from the PCM on 1996 to current model year vehicles. Very handy if your "check engine" light comes on. But it won't give specific information like coolant temperature, fuel trim value, etc. -Jim

2 people found this helpful.

I have a 97 T/A that had the same exact issue, go to the SLP website and buy the radiator cooling fan override switch. I learned these cars have horrible air flow to the radiator due to poor ventilation. Not to mention the car wont turn the fans on until its too late. The override switch is the best $50 I ever spent. It has high, low, and auto/off. Easy installation, other than running one wire to the interior, it literally just plugs right into one of the harnesses over the passenger side front wheel well. Its a VERY common issue from what I have seen. Try this before you put your wallet in a coma! If this doesn't work your only out $50, instead of a few thousand. I live in SC so I understand your plight with high temp and a car that DOESN'T HAVE A GRILL, the car will quite literally try to bake itself when not moving. Try the switch out, granted it will need to be controlled personally, but that in itself can be a plus. Best of luck! PM me if you have any questions about the switch.

3 people found this helpful.

i have changed all and every parts. the cooling fan doesn't kick on unless the ac is turned on. unless the ac is turned on, the car will overheat because the fan will never turn on regardless of temperature

theres 3 relays that runs thoses fans. in summer months and we get stuck at thoses long traffic stops. this is what you mean, same as me. runs way to hot, fans dont turn on. jack the relays to turn all fans on as soon as you start the car. this works great in summer fall and if you drive in winter, in fall. then undo your fan jack back to normal. it helps very much. relay 3 runs both 1 and 2 relay. jack both to run all the time as soon as you start your car.

it works much better then waiting till the dam car is half dead from heat because GM didnt program them correctly. yull see.

Your Answer:


Looking for a Used Pontiac in your area?

CarGurus has 9,648 nationwide Pontiac listings starting at $750.


Pontiac Experts

  • #1
  • #2
    Tom Demyan
  • #3
View All

Content submitted by Users is not endorsed by CarGurus, does not express the opinions of CarGurus, and should not be considered reviewed, screened, or approved by CarGurus. Please refer to CarGurus Terms of Use.