Car overheating... Fan will not kick on to cool it down!

[IslandGirl33]

My car overheated the other day. A mechanic found that the fan was not turning on. He checked the relays and changed the censor but still not working. The fan does run when the AC is on but will not turn on when the engines gets too hot.

Any ideas?​

 

[boomdriver]

I wonder if the shop looked at the correct relay and sensor..?

The control for the cooling fans comes from a signal from a temp sensor that the ecm uses to power a relay that basically just completes the ground. You could look at the plugs and grounds, but the a/c being able to power the fans (alternate route to the relay) tells me that its the temp sensor or the wires inbetween.
There are 4 temp sensors or switches in my engine....yours is slightly different but you still have more than one.

 

[Hib Halverson]

There are a couple of different fan systems depending on model year.

What year is the car in question?

Also, did your mechanic use the cooling fan diagnostic information in the Factory Service Manual to trouble shoot the system?

 

[Jeb]

There are a couple of different fan systems depending on model year.

What year is the car in question?

Also, did your mechanic use the cooling fan diagnostic information in the Factory Service Manual to trouble shoot the system?

I believe it's a 96 Coupe, Hib.

 

[Nick90vetteguy]

ya know this becoming very popular u may want to consider these steps, CHECK THE FUSES! I spent 550 bucks just to have a mechanic to say its the thermostat and replace it and turns out it wasnt, CHECK THE BATTERY! My dashboard console isnt accurate and I found out the worst way when I ran out of gas and my battery died . Along with the inaccuracy of the battery GET A LEGIT READING! sometimes these readings are incorrect and can trigger a panic attack on yourself. BURP THE SYSTEM!

Of course if its not these it maybe the relay fans, but check the fuses, replace them if you feel more safe. :eyerole

 

[Hib Halverson]

I believe it's a 96 Coupe, Hib.

It it's a 96, the both fans are controlled by the ECM. Could be a relay has gone bad or the ECT sensor has a problem, but the best thing to do with the 90-96 fan system is to run the diagnostic checks in the Service Manual. Do that and you cover all troubleshooting bases before you start buying parts.

 

[Nick90vetteguy]

It it's a 96, the both fans are controlled by the ECM. Could be a relay has gone bad or the ECT sensor has a problem, but the best thing to do with the 90-96 fan system is to run the diagnostic checks in the Service Manual. Do that and you cover all troubleshooting bases before you start buying parts.

GREAT ADVICE

 

[vetteoz]

My car overheated the other day. .... will not turn on when the engines gets too hot.

​

Question nobody has asked ;What temp is TOO hot?

 

[IslandGirl33]

Yes, it is a '96 coupe. The themostat was replaced along with the sensor and the battery is new.

Would it be a fuse if the fan runs when the AC is on? Different fuses?

The temp was off the chart (over 260). The needle was at it's peak and the coolant was literally boiling for several minutes or longer after the car was shut off.

 

[Hib Halverson]

A 96 has two fans. Both run at the same time. The fans have two speeds low and high. When low fans are commanded the fans are wired in series. When high fans are commanded they are wired in parallel. There are three fan relays which operate the fans and which are controlled by the ECM.

"Low fans" is commanded by the ECM when either: certain DTCs are set, ECT is above 219°F, engine oil temp is above 270°F or A/C head pressure is above 189 psi. Also, when engine speed is over 3500 rpm and oil temperature is over 261°F low fans will come on. The fans will go off once CT drops about 11°F. If A/C head pressure kicks the fans on, it must drop to 150psi before the ECM will shut them off. Min. on time is about 50 seconds

"High fans" is commanded by the ECM when either: certain DTCs are set, ECT is above 228°F, engine oil temp is above 277°F or A/C head pressure is above 225-psi. Also, when engine speed is over 3500 rpm and oil temp is over 266°F, the ECM will request high fans. The ECM will turn off high fans once coolant temp drops about 11° or A/C head pressure drops below 189 psi.

If you saw 260 on the digital display and the coolant boiled over, obviously the car was way overheating. If you ran the car like that for any length of time, engine damage is possible. Hopefully that's not the case.

I'd be looking for cooling system problems other than just the fans such as restricted air flow through the cooling stack. Also, overheating really stresses cooling system parts such as radiator hoses, heater hoses, belts, radiator caps and so forth. Considering the car is 15 years old, if those parts are original, I'd carefully inspect them for damage.

But, again, the best way to troubleshoot the cooling fans on a 90-96 is using the diagnostic table in the Service Manual.

 

[John Robinson]

One other possibility that has not been considered is the water pump. If lets say the impeller came lose from the shaft and did not turn you would not have any water flow. Just trying to think past fans and radiators to what else has to happen to keep the engine cool. How about a bad pressure cap or loose cap. Stuck thermostat. A leak somewhere that allowed the fluid level to get low and therefor not have a enough cooling capacity. This is a general question for everybody who will read this post when did you check the radiator fluid level last. With this heat we are in it would be a good idea to do so.


I wonder if the poster has checked the fuses yet. Between reading the thread and doing this post I forgot that the fans in this case were not coming on so some of what I said may not be applicable to this thread but in any case it may remind us that all overheating problems may not be fan related.

 

[Hib Halverson]

I'm going to guess it's not a fuse because the OP said the fans do run when the HVAC is on. My guess is one of the three fan relays has a problem or there is a wiring/connections issue to solve.

As for the "spun impeller"...that's one I had not considered but, once the fan issue is solved and a debris check is made, if the car still runs hot that's sure one problem I'd look into.

 

[Nick90vetteguy]

There are a couple of different fan systems depending on model year.

What year is the car in question?

Also, did your mechanic use the cooling fan diagnostic information in the Factory Service Manual to trouble shoot the system?

how about if it was a 90?

 

[boomdriver]

how about if it was a 90?

84....90 or 96....same solution to the problem regardless of how they operate,

there is an issue with either the fan signal switch OR the fan relay(s). The FSM flow chart is absolutely foolproof in diagnostics. Thats why the books are 3" thick between the 2 of them. Every base is covered.

 

[Bronze85]

I agree, the FSM is your best source for diagnostic flow charts.

 

[IslandGirl33]

Awesome suggestions everyone. When I get this resolved I will certainly post it.

Thanks so much all!!!

 

[Dr_Shakalu]

Did you check your temperature by the analog temperature gauge or by the digital gauge temperature gauge? Corvettes are made to run a little hot and most of the time, the analog gauge is faulty so it's better to use the digital gauge. Also, have you recently done any work involving you coolant. Boiling fluid can also be from not getting rid of (burping) the air in the coolant system. Hope this helps, Ed.

 

[1989landjet]

On my 89 vette I hit 260 degrees once.I shut the car off right away as this is too hot.I ended up cleaning a bunch of junk out from between the radiator and AC condenser.And I went 1 further and installed a 160 thermastat.Now my average run temp is 170 to 185,and around 200 if Im having some fun carving corners or thinning out the back tires.If you drive the car in the winter I'd go with a 180 thermastat.Also- Mid america sells a fan control kit that runs independant of the cars ecm and plugs directly into the cars wiring system,so theres no cutting of wires.I think you'd know if you had an impeller issue just by taking off the radiator cap(cold engine);start it up and look into the radiator with a flashlight as you hit the throttle a few times;You should see the coolant level drop quickly on throttling and returning back to normal level at idle.If that happens I wouldnt worry about the impeller. Good luck to ya!