87 coupe, overheated, gauge read 270 with the red bar, so I pulled over as soon as I could, by the time I got the hood up to look at the engine, the gauge was 299( I do not think the star wars dash will let it display above 299).I shut the engine down, but noticed that the electric fan was not running when the engine was on. I had been running the AC while going down the Florida turnpike at night.
I have had fan problems before, so I assumed that was the culprit again.
Towed the vette to the dealer at 1 a.m.
Talked to them the next day, at first they call back to say it is running fine, 30 minutes later they say the fan cuts off when it heats up.
I tell them to change the fan and relay.
Vette runs fine for 4 days./
Then it over heats again, I pop the hood, fan is running, I did not wait till it got to 299 to see if it would cut out.
I figure the thermostat is the problem now, which I removed today.
My question: Will the fan turn off it the car gets too hot?
My thinking is the thermostat was the problem all along and the dealership just changed the fan because I told them my observations.
Of course, it could be both. No the water pump is not making any strange noise, and I would not think it is the pump, because the problem is intermittent.
I am now testing the car with no thermostat. When the car runs, cap off, I can see the fluid flowing.


[Modified by beachcat, 1:18 PM 3/17/2003]

 

Put in a 160 thermostat, flush the coolant system totally. I would run a 60-40 water/coolant mix during summer.

Clean the front of your radiator, and add a manual fan switch wired to the main fan.

 

I have never heard of a fan turning off because of hight temp. Except if you boiled alot of your coolant off, then the coolant sensor read and the ecm wouldnt turn the fan on.If your car overheats again, turn your heat on and make sure it is hot as well, if its not you may have a pump problem.
If you decide to do a manual switch, there should be a green w/ white striped wire coming out of the fan relay. You can cut that wire and run the end that goes to the relay through a switch to GROUND.

 

During my testing with no thermostat, I have turned on the heater, and it does get hot. The fan comes on at the right temp or when I put the AC on, so I am confident in the electrical side of things right now.
The last time it overheated the fan ran constently but it never lowered the temp. The area in front of the radiator is clear. I will keep testing it.

 

I have an '87 coupe also, I live in CA and I run no thermo. Temp is around 145F on the freeway at night and 180 around town in the day. I have a 200F fan temp swicth that comes on only if I'm sitting at a fast food drive-thru too long. It turns on both fans. I run about 3/4 of a gal anitfreeze to lube the water pump. Water cools better than antifreeze but has no lubrication.

If you've taken off the top shroud to look down in-between the radiator and the A/C condensor (that's the ONLY way to check for debris) then that's one prob you won't have. I did. Blew both head gaskets.

My rad is new also. The crud that accumulates inside an aluminum radiator can't be cleaned out or so I've heard. You can get a new one on the Internet for about $125. Cheap insurance for not having to worry about your car overheating after you've checked everything else out.

Yes, the coolant gauge digits only go to 299F but the the oil temp gauge goes to 350F. I know. That's why I'm a stickler now for a cool running car.

BIG JIM

 

Yup, pulled the shroud and I am clear. The radiator is about 3 years old, same for the water pump.
It just seems to coincidental that both the fan and thermostat go at the same time. If it is a thermostat and or fan problem.

 

With temps that high, you could have blown a head gasket. Does the coolant stay in the system? Besure the expansion tank is full and the overflow is at least to the cool mark. Run it up to temp (215+) then let it cool. See if the expansion tank is still full. If not, you may be blowing combustion gases into the cooling system and displacing the coolant.

Watch the oil closely as well. If it starts to look like a milkshake, stop driving.

 

Unfortunately I have had experience with a blown gasket and milkshake oil, so I am looking for all those signs.
Thanks.
Just gonna test it sans thermostat for a few days.

 

Personally, I cant run my car without a t-stat. The temp takes a while to overheat but it always does it. If I run a 160 t-stat, I usually run around 170-175 without worry.
As far as over heating, you could have a blown head gasket and not be leaking coolant. It can blow between cylinders(which could cause overheating) and also to oil passeges. You may need to do a compression test to be sure. Also if you have a timing light, you might want to check the timing just to be sure.
Make sure that your fan is spinning the correct direction. I believe it is clockwise(from the engine side).It is suposed to be pulling the air throught he radiator, blowing the air towards your motor. You never know if the tech at the dealership is smart,sober and coherent all at the same time.

 

Hey Beachcat,

I just thought of something. ALL C4's (at least the 3 that I've had) will overheat if there's air trapped in the cooling system. In spite of the "3 cycles up to N.O.T." stuff you read in the manuals, there's only one way of getting rid of that trapped air that works for me.

Loosen the rad cap to the first notch. Let it idle until the temp is passed the point that your thermo opens. Turn it off and jack up the front end until the radiator is higher than the top of the engine. You only have to jack one side to do this. Take the cap off and leave it that way overnight. The next morning the trapped air has worked it's way out, now fill it up with water before you let the car down and the trapped air prob is solved. If you have that prob.

The old mustangs had a problem with that and that's where I learned the trick. To solve the prob permantently, drill a small hole in the thermostat so air can escape even when the thermo is closed or run without the thermo.

FWIW,

BIG JIM

 

Update: I ran it with no thermo today. Drove around town, average speed 40, made two stops, one was lunch. I had the targa top off but ran the bilevel setting for the AC. Temp never got above 192. Went out on the Turnpike for about 8 miles at 70 mph, then got off and drove at about 40-50 for a couple of miles when I noticed the temp start to climb again. It got to 265 before I pulled over. It was boiling over to the overflow tank. I let it sit for 30 minutes, temp droped to 200 , I looked at the overflow tank, and the coolant had been sucked back in. I opened the cap, started the engine and could see the fluid being pushed, indication that the pump was working, closed her up and drove 3 miles home with no problem.

Can a water pump be intermittent?
Is it possible that the radiator cap opens too soon and lets out the coolent thereby causing it to overheat?


Thanks for all inputs and ideas so far. :cheers:

 

It is possible to have a cap openning to soon. That would also cause your car to boil at a much lower temp. Does you car overheat when your just idolling? Make sure your air dam is still bolted beneith the radiator.Without the air dam,there is nothing to channel the air up to the radiator while your driving

 

Air dam is good, just replaced it a couple of months ago when I got the new paint. I think I will try the cap.
Anyone know what pressure it should be? I dont always trust the book.

 

The fan is pulling air thru the radiator. The strange thing about this whole problem, is that it will heat up to 225, then the fan kicks on then it will cool down to about 190 something and the fan kicks off. When this happens it tells me that the fan is working at the right time and that the fluid is flowing thru the radiator with the push of the pump. This will run fine for awhile, then all of a sudden it wont. :banghead:

 

:iagree:

 

 

With the rad cap off and racing the engine slightly above the opening temp of your thermostat, you not only should be seeing moving coolant, the coolant level should be close to the neck of the filler (if not fill it cap it and then let engine back to idle). One easy thing to try is to take your garden hose and blast water backwards through your radiator (hold onto the fan blade) over its whole area, then blast water in between the gap around the radiator cap (this washes the debris out of the bottom). This is an easy way to clean out fine debris stuck in the fins. It helps my 87. Take a look at the a/c condenser fins through air scoop and straighten any bent fins as bent fins reduces air flow. Check for a collapsed radiator hose when it gets hot (jump out and look while racing the engine), yours might be collapsing only after it gets real hot but is ok before that. Lastly, replace your GM water pump with a Stewart, it pumps 41% more coolant and keeps my engine cooler than the GM. A 160 stat will not allow your coolant temps in the summer to run any lower than with the stock 195 stat. I have always run my 195 stat and at stoplights in 95 temps with the original water pump and the fan forced on by my toggle sw, the coolant would rise to 210-215 and slowly drop to 195-200 when underway. With the Stewart, same condx, it goes to 200 and quickly drops to 195 when I get under way.
With the a/c on, the radiator gets warm air from the a/c condenser and you will experience higher coolant temps. When the temp soars, turn off your a/c when you are under 35 mph.


[Modified by jfb, 6:56 PM 3/18/2003]