Getting hot - Engine Temperature Gauge
Thread Starter
Instructor
Joined: Jul 2020
Posts: 196
Likes: 14
From: Houston Texas
Getting hot - Engine Temperature Gauge
1990 C4 Automatic, Base Model
I replaced the head gaskets about 1.5 years ago. The engine was always getting up to the 'Red' line, and I eventually saw milky oil while checking the oil. I was unable to remove number 8 plug and presumed that the head gasket was blown and sealed that cylinder (plug). Took it apart, heads went to a machine shop, both were warped.
I installed a third auxiliary fan, constant on with 'key on' position. Seemed to make a difference.
That bring me to today: Engine runs at needle reading mid range on the gauge. If sitting in traffic on a hot day, I see the gauge go from midrange to deep 'red'. Once I get moving again, it flows back to that happy mid range on the gauge. I am told that the secondary auxiliary fan will activate at around 230 engine temperature. Since I have had the car, I never heard that fan come on. I tested it before, hotwired for testing, and it does work.
Question for the experts in this area. What can I do to get a stable engine temperature? I have tuned the engine (new cap and rotor, plugs, plug wires, adjust/set timing, affirmed vacuum is correct, radiator flushed one a year with new coolant.. Looking for a solution, please
I replaced the head gaskets about 1.5 years ago. The engine was always getting up to the 'Red' line, and I eventually saw milky oil while checking the oil. I was unable to remove number 8 plug and presumed that the head gasket was blown and sealed that cylinder (plug). Took it apart, heads went to a machine shop, both were warped.
I installed a third auxiliary fan, constant on with 'key on' position. Seemed to make a difference.
That bring me to today: Engine runs at needle reading mid range on the gauge. If sitting in traffic on a hot day, I see the gauge go from midrange to deep 'red'. Once I get moving again, it flows back to that happy mid range on the gauge. I am told that the secondary auxiliary fan will activate at around 230 engine temperature. Since I have had the car, I never heard that fan come on. I tested it before, hotwired for testing, and it does work.
Question for the experts in this area. What can I do to get a stable engine temperature? I have tuned the engine (new cap and rotor, plugs, plug wires, adjust/set timing, affirmed vacuum is correct, radiator flushed one a year with new coolant.. Looking for a solution, please
Le Mans Master
Joined: Dec 2005
Posts: 8,581
Likes: 966
From: Communist Colorado
Have you cleaned between the radiator and condenser? ALOT of dirt, bugs, leaves etc will gather up in that area. If you're confident all the other components in the cooling system are working as designed, then this is a good place to start.
Thread Starter
Instructor
Joined: Jul 2020
Posts: 196
Likes: 14
From: Houston Texas
Yes, I have cleaned that area. There was no debris there. I keep the engine compartment spotless. I have read a lot about engine temperature for this car, but I am still watching the temperature gauge rise, when sitting in traffic. It always cycles back to midrange on the gauge once I get moving after being stuck in traffic
Le Mans Master
Joined: Jul 2004
Posts: 6,228
Likes: 698
From: Clifton Park, NY ............Clearwater, FL ... 85 Original Owner
Yes, I have cleaned that area. There was no debris there. I keep the engine compartment spotless. I have read a lot about engine temperature for this car, but I am still watching the temperature gauge rise, when sitting in traffic. It always cycles back to midrange on the gauge once I get moving after being stuck in traffic
Instructor
Joined: Dec 2024
Posts: 216
Likes: 85
From: Phoenix, Arizona
What is your digital temp showing? Mechanical gauge ive read can be misleading. When the main fan triggers, does your temp come down when in traffic?
Last edited by ramahon; Mar 2, 2026 at 05:36 PM.
Instructor
Joined: Dec 2024
Posts: 216
Likes: 85
From: Phoenix, Arizona
Add a picture of your air dam, both from 1-2 feet out so we can see if anything stands out on your car taking getting the proper air flow in and one closer to see the AC condenser fins.
Last edited by ramahon; Mar 2, 2026 at 03:03 PM.
Thread Starter
Instructor
Joined: Jul 2020
Posts: 196
Likes: 14
From: Houston Texas
Engine getting hot
Part of my radiator review was running water through it from the engine side. I have done this about 4 times. And, of course the radiator was out to do some other front end work, and I ran water through it from the engine side to ensure quality air flow. The radiator has never had debris blocking air flow
Racer
Joined: Feb 2010
Posts: 371
Likes: 65
From: south wilmington il.
First is to check that the REAL TEMP is what the gauges show. Get a heat gun and check the radiator and heads for REAL temp. Is your radiator over 30 years old? It could be plugged from corrosion. Put in a new 185° thermostat, and check flow from waterpump if it's also original. Check between radiator and condenser for debri, not just running water or blowing air. You might be able to see between them from underneath the car but it's best to take the shroud off to get a good view. My 95 lt1 guage shows high but the digital guage shows normal, so i confirmed the REAL temp with a thermal reading gun. You have to figure out if the sender or fan control is working, but you need to confirm the REAL temp first. If the thermal gun shows 225 and the fan turns on at 230 you'll have to rule out the sender by putting it in water to verify its reading correctly for 230° by completing its circuit or in other words switching on at 230. I can't think of any other things that would cause it to overheat except a vacuum leak but it would also cause noticeable driveability problems. Just some ideas for you try or have a mechanic look at it.
Last edited by merc49; Mar 2, 2026 at 09:58 PM.
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Melting Slicks
Joined: Nov 2016
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From: So Cal
2023 C4 of the Year Finalist - Unmodified
His fans work correctly. He proofed them in this thread about a year ago. He was using the C68 to read the coolant temp data that the ECM uses to control the fans. His secondary fan came on at 234F. Both fans came on with the ALDL A&B jumpered. There's nothing wrong with his fan controls.
Other than "deep red", I see nothing abnormal in the above behavior.
His gauge may be out of calibration, but I think what his real problem is, is that he doesn't understand what "normal" operation is. The 1990 has a designed allowable normal operating temperature range of 190-ish (thermostat controlled minimum temperature) to 235-ish (second fan turn-on temperature). He proved that his engine is operating within that range a year ago. It is in the linked thread.
It is difficult to fix something that isn't broken.
It's even more difficult to convince someone that they don't have a problem when they don't understand how something is supposed to work.
Engine runs at needle reading mid range on the gauge. If sitting in traffic on a hot day, I see the gauge go from midrange to deep 'red'. Once I get moving again, it flows back to that happy mid range on the gauge.
His gauge may be out of calibration, but I think what his real problem is, is that he doesn't understand what "normal" operation is. The 1990 has a designed allowable normal operating temperature range of 190-ish (thermostat controlled minimum temperature) to 235-ish (second fan turn-on temperature). He proved that his engine is operating within that range a year ago. It is in the linked thread.
It is difficult to fix something that isn't broken.
It's even more difficult to convince someone that they don't have a problem when they don't understand how something is supposed to work.
Thread Starter
Instructor
Joined: Jul 2020
Posts: 196
Likes: 14
From: Houston Texas
Yes, one fan turns on when I turn on the a/c. The factory secondary fan has never been triggered to turn on. I have tested it by running 12 power to it. It works just fine. However, according to the dash mounted temperature gauge, when that needle burries hot, the fan does not turn on.
Again, when driving, the temperature gauge stays in or near the middle of the gauge. But, when stopped in heave traffic (traffic jams), the gauge clearly, and quickly bottoms out on the hot side.
Again, when driving, the temperature gauge stays in or near the middle of the gauge. But, when stopped in heave traffic (traffic jams), the gauge clearly, and quickly bottoms out on the hot side.
Racer
Joined: Mar 2025
Posts: 494
Likes: 242
Yes, one fan turns on when I turn on the a/c. The factory secondary fan has never been triggered to turn on. I have tested it by running 12 power to it. It works just fine. However, according to the dash mounted temperature gauge, when that needle burries hot, the fan does not turn on.
Again, when driving, the temperature gauge stays in or near the middle of the gauge. But, when stopped in heave traffic (traffic jams), the gauge clearly, and quickly bottoms out on the hot side.
Again, when driving, the temperature gauge stays in or near the middle of the gauge. But, when stopped in heave traffic (traffic jams), the gauge clearly, and quickly bottoms out on the hot side.
Thread Starter
Instructor
Joined: Jul 2020
Posts: 196
Likes: 14
From: Houston Texas
About a year and a half ago, I was driving the car every day. This condition was the norm. Well, I ended up with a blown head gasket. This is a reason why I am sensitive to this temperature situation.
When the traffic moves again, the temperature gauge shows the needle return to about the mid point on the gauge.
My primary, or original question related to learning if there is anything that I can do to better manage the engine temperature.
Racer
Joined: Mar 2025
Posts: 494
Likes: 242
My assessment is: When driving, the temperature gauge shows the needle about mid range on the gauge. In heavy stopped traffic, I see the needle on the gauge creep up to and onto the deep right side of the temperature gauge. The aux fan does not come on. The AC is on and the complementing fan is operating. Another poster stated that the gauge does not reflect the actual temperature, and that the system is designed to activate the aux fan when the temperature reaches 230 degrees. I presume, from this comment, that the actual temperature does not reach 230 degrees.
About a year and a half ago, I was driving the car every day. This condition was the norm. Well, I ended up with a blown head gasket. This is a reason why I am sensitive to this temperature situation.
When the traffic moves again, the temperature gauge shows the needle return to about the mid point on the gauge.
My primary, or original question related to learning if there is anything that I can do to better manage the engine temperature.
About a year and a half ago, I was driving the car every day. This condition was the norm. Well, I ended up with a blown head gasket. This is a reason why I am sensitive to this temperature situation.
When the traffic moves again, the temperature gauge shows the needle return to about the mid point on the gauge.
My primary, or original question related to learning if there is anything that I can do to better manage the engine temperature.
It was my experience with my car that when the cooling system was properly configured and working, it ran within specifications regardless of the operating condition (even on a warm day idling in LA traffic). The aux fan kicked on and the temp went down.
No modifications from original configuration (a third fan or anything) were needed to achieve this. Something is still wrong or overlooked..
- Your Aux fan works when voltage applied, work backwards to see if it gets voltage at the proper temperature. Check wiring, then work back to sensor to make sure it's grounding, fuse, etc. You probably know all this..
-There's another possibility, an uncomfortable one, but perhaps heads are still warped or there is a hairline crack in the block from your original head gasket break.
I flushed cooling system, replaced water pump, thermostat, and installed new air dam (was missing) and my heating at idle problems went away.
Thread Starter
Instructor
Joined: Jul 2020
Posts: 196
Likes: 14
From: Houston Texas
Hi Al,
It was my experience with my car that when the cooling system was properly configured and working, it ran within specifications regardless of the operating condition (even on a warm day idling in LA traffic). The aux fan kicked on and the temp went down.
No modifications from original configuration (a third fan or anything) were needed to achieve this. Something is still wrong or overlooked..
- Your Aux fan works when voltage applied, work backwards to see if it gets voltage at the proper temperature. Check wiring, then work back to sensor to make sure it's grounding, fuse, etc. You probably know all this..
-There's another possibility, an uncomfortable one, but perhaps heads are still warped or there is a hairline crack in the block from your original head gasket break.
I flushed cooling system, replaced water pump, thermostat, and installed new air dam (was missing) and my heating at idle problems went away.
It was my experience with my car that when the cooling system was properly configured and working, it ran within specifications regardless of the operating condition (even on a warm day idling in LA traffic). The aux fan kicked on and the temp went down.
No modifications from original configuration (a third fan or anything) were needed to achieve this. Something is still wrong or overlooked..
- Your Aux fan works when voltage applied, work backwards to see if it gets voltage at the proper temperature. Check wiring, then work back to sensor to make sure it's grounding, fuse, etc. You probably know all this..
-There's another possibility, an uncomfortable one, but perhaps heads are still warped or there is a hairline crack in the block from your original head gasket break.
I flushed cooling system, replaced water pump, thermostat, and installed new air dam (was missing) and my heating at idle problems went away.
I will check my situation based on your input. Let's see if I can get resolve
Racer
Joined: Mar 2025
Posts: 494
Likes: 242
Thanks for the input. I considered a cracked block when I learned about the head gasket. I did the repair, and I monitored the engine, and oil, to see if there was an apparent leak inside or outside. Before the head gasket repair, this was happening. Another poster stated that the system is operating normally. Yet, head gasket repair. I have changed out the thermostat twice. Perhaps, I need to replace it with a 160 degree thermostat. I currently have a 195 degree thermostat.
I will check my situation based on your input. Let's see if I can get resolve
I will check my situation based on your input. Let's see if I can get resolve
Safety Car
Joined: Mar 2017
Posts: 4,206
Likes: 1,325
From: LeClaire Iowa
Thanks for the input. I considered a cracked block when I learned about the head gasket. I did the repair, and I monitored the engine, and oil, to see if there was an apparent leak inside or outside. Before the head gasket repair, this was happening. Another poster stated that the system is operating normally. Yet, head gasket repair. I have changed out the thermostat twice. Perhaps, I need to replace it with a 160 degree thermostat. I currently have a 195 degree thermostat.
I will check my situation based on your input. Let's see if I can get resolve
I will check my situation based on your input. Let's see if I can get resolve
Safety Car
Joined: Dec 2009
Posts: 4,363
Likes: 429
From: Birmingham Al
Have your radiator flushed by a radiator shop, running water in and out will not do it, it's not flow but the amount of flow in and out .. The radiator is very old needs to be cleaned in a for real shop .. or replaced ..
Thread Starter
Instructor
Joined: Jul 2020
Posts: 196
Likes: 14
From: Houston Texas
I did a visual inspection after taking the heads off. Interestingly, I did not know that I had a blown head gasket. I happened to do a pre-drive check one day, and I checked the oil. I saw the milky substance and did a scope of each cylinder to see what I could see. Number 8 plug was too tight to come out. The engine was running fine, no smoke out of the exhaust, no misfire, however, engine temperature went up quicker during that time, and I was always topping off the reservoir.