Chevy Impala overheating?


This Impala would be idlyng for 30/40 min.Temp normal. If you drive the car temp will go up after 10/15 min of driving. The fans come on,temp goes to where it shoud be 195, and after another 10/15 the same scenario happens. Temp goes to 210.

I have replaced, new from GM, thermostat, water pump, the 3 fan relays, the two fans, all water houses,temp sending, and flushed the radiator. Still the same problem.

The gage is working good, the on board computer is good. What is the problem??? Will the trans temp sensor would be the problem?. This is the only part not replaced.HELP SOMEONE!!!

Tow dealers think that Im delutional…

Tanks in advance for the help Jose


Just curious, did you replace the radiator cap? If the cap is not maintaining pressure, the boiling point of the coolant is lower.

Ed B.


Yes I did and, also and had radietor floshed profetionally. I asked the shop. They sujested to get a radiator with bigger capasity???


Are you missing the radiator deflector/air dam? Its a $20 dollar dealer part. When mine was missing temp gauge would run one to two notches above halfway, with it installed gauge reads a notch below halfway even on a 99 degree day on the highway


How old is this car? If the coolant has been ignored, the rad could be bad. Is the lower radiator hose OK? I wonder if it is collapsing.


Is the lower radiator hose OK? I wonder if it is collapsing

I was thinking the same thing. They can look OK on the outside and have an internal problem. Also on some cars it may not be the “lower” hose but any hose.


Well this is what is very annoying, and puzzling. I have ALL new hoses, new thermostat fan relay switches (3 total), new radiator cap, new water pump, new temp sensor, new thermostat, radiator flushed, coolant mixed with distilled water, at a ratio 60/40 (60 coolant and 40 water), new fan tray, all GM. Taken to 2 different dealers they can’t find any problem. they have ck gage, and on board comp it cks OK.
This is a 2000 impala with 3.4 engine and 125,000 miles, All interstate. 2 month ago started acting up, and I stated replacing parts even if they ck ok.


2000 3.4L

Have your best tech do a coolant pressure test.

Because of the overheating situation, I’m wondering if you have the start of an intake manifold gasket leak.

Rebuilding the engine piece by piece is very expensive and obviously isn’t fixing the problem.

If the manifold is starting to leak coolant [slowly] out from the right side of the engine manifold (likely due to the bolts working loose), the heat of the engine block may be enough to evaporate it before it hits the ground and become obvious.

The firewall side of the manifold is difficult to see due to all the emissions components and such in the way.

Have you noticed a miniscule amount of coolant disappearing from the coolant reservoir?

Use a felt pen and mark the FULL COLD level on the reservoir
Ensure the coolant is up to that mark when the engine is COLD. (ie, in the am before starting)

Check the level each day or every second day for a loss of coolant.

I had the misfortune of having the infamous GM leaking intake manifold gasket in my 2000 Olds Silhouette and it also started leaking VERY slowly from a corner manifold bolt.

Thankfully, to the outside and not into the engine where the coolant mixes with the oil and if not detected immediately, can cause major engine damage.


I think you are just running out of cooling capacity. Clean the bugs off the radiator and condenser and if the problem persists, just replace the radiator. It’ll make a world of difference. They just get gunked up and lose capacity over time.



Well, the radiator was cleaned by a good reputable shop. I been working on this car since 06:00 this morning> tightening intake manifold up to factory specs, disconnected/ reconnected all connectors, and I can see some improvements.??? Like you said maybe beginning to leak at the intake manifold, just enough to cause problems but not enough to be noticed. Now if I drive with the air cond On it stays at the temp that it use to run when new, it may go up just a hair up and when you move the car it goes back to where it was.
I believe that if I replace the intake man gasked it will cure this problem.
Do the cooling fans start working when it reaches the normal temp,like slow on one fan and then as needed the second fan, or they come, both at the same time, when hot. With the air cond on one fan starts and when normal temp is reach the other starts, keeping the correct temp. Is this normal???
Where could I find info as to the way these fan should operate, I installed new fan relays (3), I am assuming they are good. or Could it be that I am overlooking another sensor???


By the looks of the wiring digram it looks like relay #1 energizes both fans in a series circuit causing them two run slow. When relay #2 and #3 energizes it changes the fan wiring circuit to a parallel circuit causing the fans to run fast. BTW you never mentioned if you did or did not have the plastic air dam on the radiator support under the car. This makes a big difference.


Before you change the intake manifold gasket, have a shop do a coolant pressure test.
You may save a lot of $ and work.

Tightening the manifold bolts won’t stop a gasket leak once it starts.

The fans work in conjunction with the PCM and the coolant temperature sensor (I believe that is screwed into the intake manifold).

The Haynes repair manual covers these problems pretty thoroughly, but there is too much to type. You may want to get one for your vehicle. (about $18-$20 at almost any automotive store)


Yes, I do have the HAYNES MOTOR repair manual for this car and for all other cars that I own. However it does not say how this fans should work. I guess I should be able to figure it out from the diagram…
But as you said. Fans come on with the air cond on.
If the air is of they do not come on until past the normal temp around 210. Fans come on, cool radiator and shut off. After 10/15 min starts heating up again, If you turn air on, it will cool off and stay running cool. Why???
With air on, car runs at normal temp, turn of the air and temp fluctuates between high and normal, it takes about 10 to 15 min for temp to start going past the normal operating temp.
What is the cycle of these fans???.
I marked with a felp tip the water reservoir and, this morning it was right where I place the line(I’ll keep an eye on it).I let the car run for almost 2 hrs with the air on. NO PROBLEM turn of air and TEMP goes HIGH, and , it looks that It does not have a leak.


fans coming on 15 degrees above theromastat rating sounds perfectly normal to me. IMHO, 210 is not overheating.


Does your Impala have two (2) cooling fans?

I just warmed mine up from cold. (I drove around until the engine reached operating temp)
It warms up quicker and uses less fuel and causes less pollution.

When I think about the things I do to try and answer these posts…

When the engine reaches op temp the thermostat opens and the coolant circulates through the rad cooling the fluid down before it goes back into the engine. (You likely know this already)

If your t-stat does not open at the t-stats’ temp rating (ie. 180 or 195 degrees) the cooling fans start cycling to cool the engine down.

I have noticed with mine (I was checking for noisy pulley bearings) that once the temp is up to normal the gauge shows a steady temp reading and the fans do not cycle.

My cooling fans run at the same time when I turn the A/C on and run for a minute after I turn the A/C off.

Now, I’m assuming (hate that word) BOTH fans come on when driving under load AND when the A/C is on.

I don’t have first hand knowledge of any difference.

When I am stuck in slow moving traffic (rush hour) the engine temp tends to creep up a bit higher than normal.

My tech of 16 years has told me GM set the computer for the engine to run a little hotter than normal when idling in order to burn the exccess emissions.

Once speeding up, the fans kick in and the temp immediately drops back to normal.

Have you checked the engine temp sensor? NOT the one you replaced.

Closely check all the wiring connections to everything.

I hope that helps a little.

If you want to learn more about the cooling system go to and click on ‘auto’ in the upper left corner.


WTF is this? how…fworks?

I typed in the complete url and that is what shows up here.

Man! It’s supposed to show…


Well, I am a retired aircraft mechanic from Easter Air Lines. I felt ashamed to admit that this car could do this to me and , can’t figure this out.
We at EAL could not allow ANY part on ANY equip not to work properly.
The cooling of a car is designed to work at a set temp, THAT is if all is OK.
This car was working fine… I had never seen temp go past 195. It could be 100 degrees outside still it ran at 195, With the air on or off.
About two moth ago the temp gage went past the mid point 200, I did not liked this, ck and found water pump a little wet on the weep hole. Replaced water pump and at the same time the hoses they were old so I replaced them. Filled up the radiator and again temp went pass the mid point, I replaced the temp sensor and thermostat even when both ck OK.
Tested the car and again the temp went up past mid point.
The elect diagram shows 3 fan relays,even tho they worked when ckd. (they were 6 yrs old), I replaced them just to rule out the possibility that they could be the problem, or cause problems later.
Last thing were the fans, they needed to be changed anyway since one was making some noise. I also had the radiator cleaned by a shop.
What bothers me is that the car can be stationary in my driveway idling for hrs and temp would stay where it should be 195 (with hood open or close).
Drive the vehicle and takes almost 15 min for the gauge to start going up. this is done rather fast.
Both fans kick in and temp drops immediately.
What I was asking was if Anyone knows when this fans should kick in and in what sequence.
When temp goes high I ck the sensor leads and get a reading of 178 ohms. when cold the reading is about 3400 ohms.I am reading the temp at the base of the sensor with a laser temp reader.
When the air cond is running the temp never changes (195-196) the fans start running almost as soon as normal temp is reached, they cycle on and off at a slow speed. I am assuming this is the way and that the signal from the sensor tells the PCM to activate the fans as soon as temp is normal there is no need for the PCM to activate the fans,therefore the on and off of the fans.
Why this is not happening when the air is not on???


The Fans kick on it these cars late, and at a higher temp than I personally would like. I belive it is 210 for the 1st fan and 220-225 for the second?? I also have a 2000 Impala and when sitting in traffic my temp gauge can go up to almost 3/4 before it comes back down on a hot day with the AC on. While moving it will usually stay just under 1/2 way up the gauge. I belive you can get a re-programer to program the fans to come on earlyer. This may help, but I think all and all you are OK and should not be looseing any sleep over it.


OK, I dug this up at the North America Impala club. Read down the thread and the parameters are listed


Like I said, I think you are just running out of cooling capacity. Replace the radiator and be done with it. If they already cleaned it, it has lost some of its ability to cool the water so just replace it. Fans aren’t designed to come on until 220 or so. When you use the air or the heat, you are adding extra cooling capacity in the heater core and that is enough to make the difference. You are just right on the edge of having enough cooling. When you add more heat as in driving the car, or more cooling as in the air on, that’s enough to make a difference. Just replace it. Been there done that. It’s hard to swallow but you’ll be happy you did.