Since I got the car back from the garage, the engine has been running hot—or at least that's what the temperature gauge is showing. For context, the temperature sender was recently replaced with a new NTK EF0047.
Here are the symptoms:
The engine warms up gradually as usual, but the temperature keeps rising until it’s just below the red zone on the gauge—around 245°F.
Once it reaches this point, the temperature stays relatively stable, occasionally dropping slightly but never going below 230°F.
The cooling fan rarely turns on, even though it should activate when the temperature exceeds 235°F. The fan only kicks in occasionally when the car is idling and stationary.
Today, I drove the car for about 20 minutes in cold weather (40°F). The temperature hovered between 240°F and 245°F by the time I arrived. After parking, I checked the coolant pipes near the mirrors on both sides of the car:
The driver's side pipe was hot.
The passenger's side pipe felt cold—not outside temperature cold, but nowhere near as warm as the driver's side pipe. This suggests the radiator is doing its job effectively.
On the return trip, the temperature gauge read slightly lower, around 230°F. When I got home, I checked the pipes again at the same locations, and this time both were almost equally hot.
I also inspected the pipes for visible damage. They seemed fine, with no signs of crushing. On the passenger side near the front, I noticed a few small dents, likely from hitting the underside of the car on speed bumps, but these don’t appear severe enough to impact coolant flow.
So, what could be causing this, and how can I troubleshoot the issue further?
I dont trust a GM gauge for nothing. Please screw in a manual gauge and see what the actual temp is. That will atleast point you in another direction. (Waterpump Impeller / Bad Rad)
Waterpump is two years old and has metal impellers. The radiator is one year old. Both were working perfectly before the repairs so I don't see why they would fail now. I'll try to measure resistance of the sender.
You could buy a cheap laser pyrometer and do a test at the radiator with it. The ones that I have seem accurate. If you are concerned about head gasket leakage you can buy a test kit that will tell if exhaust gas is leaking into the water jacket. Have you verified that the cooling system is full and bled to remove all air pockets? BTW have your checked if the cooling fan is coming on?
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
[This message has been edited by Dennis LaGrua (edited 11-19-2024).]
You could buy a cheap laser pyrometer and do a test at the radiator with it. The ones that I have seem accurate. If you are concerned about head gasket leakage you can buy a test kit that will tell if exhaust gas is leaking into the water jacket. Have you verified that the cooling system is full and bled to remove all air pockets? BTW have your checked if the cooling fan is coming on?
We did the laser pyrometer test already and got weird results. While the gauge displayed about 245°F, the temperature on the temp gauge sender was about 265°, but that was probably because it was near the exhaust header. The temperature on the radiator was about 140°F - but come to think of it, I measured on the part that cools/heats the transmission oil... I'm pretty sure there's no gasket leakage because they specifically looked for that when they were working on my engine. I haven't verified yet if the cooling system is full and properly burped although the guy who did it, has done it on hundreds of Fiero's before so he knows what he's doing. Also, I don't hear any bubbling.
And yes, the fan comes on but only after a while when idling and stationary.
Yeah, problem is, I don't have a laptop with a serial port anymore...
Well, acquire the appropriate USB cable then! Seriously though, I think anyone with a Fiero should be equipped to be able to scan their engine with WinALDL. It just saves so much guesswork.
You know that dash coolant gauges aren't 'accurate'
When I replaced the coolant gauge sensor / warning switch, I tested the reading by:
*On a cold start, I hold a hand around the radiator hose on the driver's side {input} so I can feel the coolant temperature *The Thermostat is 'Closed' as the engine is warming up, and the radiator hose will feel 'cold' too *When the Thermostat OPENS, I felt the rush of ~190-degree coolant *At this moment, I read the coolant gauge
My dash coolant gauge showed ~170-degrees so I know that my gauge reads low......
Again, merely a thought, VN
------------------ Original Owner of a Silver '88 GT Under 'Production Refurbishment' @ 136k Miles
I backed up and read the entire post again. You said the cooling fan rarely turns on. Without the fan on, cooling will be minimal. Apply power to the fan direct and see what results. Are you losing any coolant?
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
No, I'm not loosing coolant. The fan does come on, but rarely. And when it does, temperature drops, but not drastically. I have a new radiator which cools much, much better than the stock radiator so I know it cools quite a bit - even without the fan on.
I need to make/buy an ALDL cable and see what the ECM says...
You have two temperature sensors operational; A) The gauge sensor and B) the fan sensor.....you changed the temp sensor and your gauge is reading high...but your fan rarely comes on- which is (basically) normal.
l think the gauge sensor is off....your fan would be on all the time if the temperature was really way up...change the fan sensor out for another (different manufacturer) sensor.
Should have stated "Change your GAUGE sensor for another one...(sorry)
[This message has been edited by cvxjet (edited 11-26-2024).]
l think the gauge sensor is off....your fan would be on all the time if the temperature was really way up... change the fan sensor out for another (different manufacturer) sensor.
???
I don't really understand the reasoning for this. The cooling system isn't demonstrating any overt signs of overheating (ie puking coolant out the reservoir). The Fiero's temp gauge reading incorrectly is a common issue. I don't see the point then of changing out the fan switch... unless it's to perhaps install a 210° on and 200° off fan switch, which is a common mod.
[This message has been edited by Patrick (edited 11-26-2024).]
It very well could be the gauge sender - the one on the corner of the head, below the coil. I saw one on a friend's car go bad a few weeks ago. First one ever. Figured it out it was that, after he did everything else.
The temperature sender (or the "gauge sensor") was replaced for a new one when the engine was fixed. So yes, it could be defective but it is already a new one.
Cliff I think I would go back to your mechanic and ask him to check the actual temp compared to gauge reading. At least then you will know if it is truly running hotter than it should. He will have the tools to make a proper assessment. sleek
No, I'm not loosing coolant. The fan does come on, but rarely. And when it does, temperature drops, but not drastically. I have a new radiator which cools much, much better than the stock radiator so I know it cools quite a bit - even without the fan on.
I need to make/buy an ALDL cable and see what the ECM says...
Sounds like the fan motor might be tired. Change the fan motor, it's a cheap easy repair. If all else fails, use the search feature (sorry couldn't resist)
The fan is fine. When it comes on, it spins as it should.
We already took temperature readings (with a temperature gun). The (new) temperature gauge sender read 130°C/265°F, measured at the metal part of the sensor. But since that sensor is only inches away from the exhaust header, we weren't sure if that was the actual temperature of the coolant.
I have a thermal camera. As soon as the weather clears up, I'll take some more readings on different spots.
A shop should have a thermal transducer that hey screw in in place of your sensor and will give you an exact temp reading so you know for sure the internal liquid temp. Believe me I have been doing this for almost 60 years. sleek
*On a cold start, I hold a hand around the radiator hose on the driver's side {input} so I can feel the coolant temperature *The Thermostat is 'Closed' as the engine is warming up, and the radiator hose will feel 'cold' too *When the Thermostat OPENS, I felt the rush of ~190-degree coolant *At this moment, I read the coolant gauge
My dash coolant gauge showed ~170-degrees so I know that my gauge reads low......
Curious: Did you read the coolant gauge the moment the thermostat opened?
... what does WinALDL tell you the actual coolant temperature is?
Seriously though, I think anyone with a Fiero should be equipped to be able to scan their engine with WinALDL. It just saves so much guesswork.
(sorry couldn't resist)
