So my car drove a little weird yesterday and the temps went really high and got a warning light. Had it towed to a mechanic. Mechanic says the cooling fans are not turning on for some reason. Any ideas or suggestions I can point him towards? He's not an expert... just a one guy shop that doesn't work on Jags.

 

Start at fuses and relays. If they are good, check the coolant temp switch. If this is okay, there may be a harness problem. Finally, the ECM turns on the fans so it is the last in the chain.

 

Exkay8, please put your model year in your signature (see your forum control panel) , or at least in every post you ask question about it. There are different sources for different years, trust me.

Did your coolant just recently 'disappear' and hit the high temp warning gage limit, and initially overheat your car?

I remember reading in the xJ8 & XJR section where a member's car only overheated when the A/C was on...turns out he had a blown fuse for the radiator fans in the engine bay. I'm not saying this is your solution, but it could be related. Was your A/C on both times when you noticed the high temp and the car 'felt weird'?

I am going out on a limb and say you've got a leak somewhere...separate from the fan issue.

 

Thanks for the help. Sorry, when registering on this site, it asks for your car model and year. and I figured it was visible to others users somewhere. I fixed the signature.

There was virtually no coolant loss, it just overheated.

I did have the defogger on when it happened. Also, the a/c doesn't blow cold.

My mechanic threw his hands up, I'm about to drive this car about 6 miles, to another mechanic, I hope I don't do any major harm to it.

 

I would check the fuse first then the a/c relay and then the operation pressure on the a/c system. You will need a set of gauges to do this. You might say why the pressure? You’re a/c system has a pressure switch that is mounted below and between the fans. If the pressure in not correct in the system it will not let the a/c compressor engage. This switch also controls the cooling fans. If I recall the sequence, start the car with the a/c off, turn the a/c on and the compressor should engage and the cooling fans should turn on. I had the same problem and it was the pressure switch. I hope this helps!

A/C information http://www.gusglikas.com/AutoRepairTroubleShooting.htm
Wiring diagram for the car http://www.gusglikas.com/AutoRepairElectrical.htm

 

The fuses to check are:
Fuse #12 (10A) Engine Management Fuse Box..... 12v to low speed relay
Fuse #12 (30A) Engine Compartment Fuse Box..... 12v to High speed fan
Fuse #14 (30A) Engine Compartment Fuse box..... 12v to Relays

The thing to remember when checking the fans is:

They run in series, on low speed and in parallel on high speed.

 

Update:
It was a cooling fan relay. All seems well, thanks for the assistance.

 

Kudos to you!

 

2nd Update / Follow Up Question:

Past few times, I've noticed the cooling fans stay on after I shut the car off and take the key out. It sometimes stays on for 10 to 15 seconds. This is unusual behavior for my car, especially since the weather has been cooler in NY than the temps I've been driving around in all summer. The temp gauge reads about a tick above halfway before I take the key out, which is what it normally stays at. One thing I want to point out is that when my car overheated the 1st time, the same noise was made when I pulled over and shut the car off. Any thoughts? Is this normal? Thanks.

 

It will vary from car to car, the fans will tend to run for a brief period after shutdown, mine also stays on for a few seconds. Longer runs mean the water temp is showing above normal and the fans need to cool it down.

Is your water pump still the original plastic impeller kind? Flow may be causing the poor circulation, higher temps, and slower heat exchange rates thru the radiator.