99 Grand Cherokee cooling fan question

[DaveB]

A friend of mine overheated their 99 Grand Cherokee and wanted me to figure out whats wrong. What I found was that there wasn't a normal fan and fan clutch but just an aftermarket electric fan and relay setup on it that the previous owner had put on it. When they first got it the fan would never turn off so they pulled the fuse on it. Now the fan never turns on and they got it so hot they exploded the side of the radiator housing off . In the main fuse and relay box there is a 40 amp fuse for the cooling fan but I can't find the relay that would turn the fan on. The aftermarket relay was wired directly to the battery with the relay enable power coming from the old fan plug. I am assuming that the fan relay is bad but I can't find it, does anyone know where it might be ?

 

[92XJeeper]

Maybe I misunderstood, but if the aftermarket relay is wired directly to the battery, can't you just trace the wire?

 

[DaveB]

Maybe I misunderstood, but if the aftermarket relay is wired directly to the battery, can't you just trace the wire?

The aftermarket relay is wired up so that the enable to the relay comes from the factory fan relay and the power comes directly from the battery so without the signal from the factory relay the aftermarket relay doesn't come on. I thought I had found the factory relay under the right side headlight assembly and after doing a bit of homework on the web I discovered that what I thought might be the relay is in fact the relay. Unfortunately some designer at Jeep needs a lesson in making things repairable, it looks like I'll have to take out the headlight assembly and possibly the front bumper plastic piece to get to it. After reading up a bit on it the factory relay is a pulse width modulated controller that controls the fans speed based on temperature. I don't think the aftermarket relay is going to work correctly with the factory relay so I'll have to rewire it up correctly.

 

[Jay5.9L]

How hard would it be to ditch all the aftermarket stuff and thow in a stock clutch fan?

 

[DaveB]

How hard would it be to ditch all the aftermarket stuff and thow in a stock clutch fan?

I had that idea too but there is a threaded stub that sticks out of the water pump so I would either have to find a fan clutch that threads on or change the water pump. I also know that the computer stores codes for fan relay issues so I would need to figure out how to keep it from logging error codes.

 

[DaveB]

Well I got a new radiator in it and the fan control module working but it is still overheating. The top radiator hose is under way too much pressure and the overflow bottle is bubbling even before it gets very hot. I'm going to see if the thermostat is stuck shut but I'm afraid it may have a head gasket leak.