Engine running hot but never overheats

Tiny
CLOROX.BLEACH
  • MEMBER
  • 2004 CHEVROLET IMPALA
  • 207,500 MILES
I am having a problem with my engine running hot. It runs fine when I have on the heat, but when I turn on the AC or ride without the AC, the temperature hand moves from normal operating temperature (half way mark) all the way over to the three quarters mark on the temperature gauge. It has never passed that point. It will get there, then it will slowly fall back to normal operating temperature, and then rises again. I am not losing any coolant and I am unsure of what could be causing this. I asked two repair shops and one person told me that it was normal for my car and engine to do that and the other repair shop told me that it was nothing to worry about altogether. I am unsure of what to think because I never had a car that runs hot like this.
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Thursday, September 15th, 2011 AT 1:11 AM

10 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
If you feel it is raising to a point of concern and it has not done it before, there is a problem.

The fact that it lowers with the heater on is not uncommon. The heater core acts as an additional (small) radiator where coolant has extra time to cool.

On the other hand, the AC places an extra load on the engine that can cause it to run hotter.

Now, if the car only heats up when you are at a stop, make sure the cooling fans are running (when the gauge shows hot). If they are not, they need to. When the car is sitting, there is no air flow through the radiator to cool the coolant. As a result, the fans draw the air through it to keep it cool. When you drive, air flows. Therefore, if it is heating up while you are moving, I would suggest replacing the thermostat. It is a cheap part to start with and if it is sticking, it could be causing the problem as well.

If you want, we have a "how to" for checking the thermostat on our homepage under the DIY section. The hardest part is removing it. However, I would just replace it if I remove it. They are like $5.00.

Let me know if this answers your question and helps. If you have other questions, let me know.

Joe
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Thursday, September 15th, 2011 AT 1:36 AM
Tiny
CLOROX.BLEACH
  • MEMBER
My coolant fans are running and I have had them checked before. The radiator is also full to the top with coolant as well. I will try to replace the thermostat and see if that resolves anything. I have one more question though, would driving the car while it is hot affect anything? Like I stated before, the temperature hand rises and falls but never overheats.
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Thursday, September 15th, 2011 AT 1:42 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
You do not want the engine to overheat. If it does, it can cause other problems such as a blown head gasket, warped head. Because I am not there, I truly do not know how hot it is getting which makes it hard for me. Regardless, chances are it will continue to get worse over time. I would first start with the thermostat. Also, since you have to drain the radiator regardless, go to the parts store and get yourself a good radiator flush and flush it. That way you can get two jobs done in one and not have to re-drain the radiator if the thermostat does not fix the issue.

Hope this helps.
Joe
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Thursday, September 15th, 2011 AT 2:16 AM
Tiny
CLOROX.BLEACH
  • MEMBER
I have had my thermostat changed and the radiator flushed out and added new coolant to the system. It still is doing the same thing. I took it to multiple shops and I continue to get mixed answers. I am unsure of what to do next. I do not have any leaks and everything seems to be working fine, but the temperature hand still rises above normal operating temperature and occasionally falls down back to normal operating temperature.
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Friday, September 16th, 2011 AT 3:30 AM
Tiny
CLOROX.BLEACH
  • MEMBER
I have also noticed a sharp drop in fuel economy, and the transmission starts shifting harder when it is hotter than it is supposed to be.
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Friday, September 16th, 2011 AT 3:32 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Can you tell me what they have checked so far?
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Friday, September 16th, 2011 AT 3:47 AM
Tiny
CLOROX.BLEACH
  • MEMBER
So far I have gotten my spark plugs changed, my coolant system flushed, and a new thermostat. Everything else seems to be in working order says the people I took it to.
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Friday, September 16th, 2011 AT 11:19 AM
Tiny
CLOROX.BLEACH
  • MEMBER
My temperature stays within this range. It does not go over that line, but it gets there and falls back and rises up again.
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Friday, September 16th, 2011 AT 5:29 PM
Tiny
CADIEMAN
  • MEMBER
When it goes to 3/4 the fans come on and it drops to 1/2. If you were overheating you would know. A restricted radiator can cause this or a faulty coolant temperature sensor. Thank you for using 2CarPros.
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Friday, September 16th, 2011 AT 5:45 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
If everything is good with the cooling system, the only thing I can think of is a bad temperature sending unit. That is what sends the signal to the gauge. However, I cannot understand why it would do what you described unless there is a resistance problem within the switch itself.
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Saturday, September 17th, 2011 AT 3:40 AM

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