Rakkasan_Jeep

Well after a few years ago replacing all the cooling parts, I'm having issues of my truck still spiking past 210. I researched it and was suggested it might be the relay for the cooling fan. I talked with my dad who is a master mechanic and he told me to check the temp. sending unit. I checked Autozones website and that particular part doesn't exist on my Jeep. Any clue what it's called?

Bustedback

Coolant temp sensor.

Rakkasan_Jeep

Thanks Bustedback.. that helped a lot, having my blonde moment.

Rakkasan_Jeep

Come to think of it, would a faulty temp sensor cause the cooling fan relay to not send a signal to the cooling fan to not kick on?

Bustedback

It could. Is the check engine light on?

Rakkasan_Jeep

Nope, it's never kicked on at all.

bigbadon

What does your coolant look like? Do you see any brown mud in coolant? Do you ever have to add coolant to the reservoir?

JJCIII

If there is any buildup on the sensor itself, then it can send false readings.

dave1123

You might want to flush the block out by running some CLR or Limeaway for about 30 minutes. When you drain it, pull the block drain plugs out and clean out the drain holes with a screwdriver. You'd be surprised what kind of trash is in the bottom of the water jacket.

I've lived with hard well water for 20 years, and mine cruds up pretty quickly. You can eliminate this by buying readymix, But I generally don't. Maybe I should.

Rakkasan_Jeep

Nah, the coolant is clean. I work in a mechanic shop so I did a flush to it not long ago. Just trying to figure out why the cooling fan wont kick on. It's supposed to kick on when the AC clutch is engaged.

dave1123

It could be the fan relay.

Rakkasan_Jeep

Ya, but even after talking with my dad last night, for the fan relay to crap out, wouldn't the coolant temp sensor have to fail as well or be faulty?

dave1123

Nope. The relay may be getting a signal and not working.

Rakkasan_Jeep

Ahh ok. Well now the problem is locating the damn thing. I've tried my book, Alldata and Autozone and they seem to have the location for the 4.0 but not the 4.7 with "N" in the VIN. I called the dealership here and they pulled up a schematic using the last 8 on my VIN and from what I'm being told it's a hydraulic cooling fan with the relay attached to the hydraulic part where the power steering lines connect on the fan shroud.

dave1123

JMHO, but I think the hydraulic fan was a bad idea in the first place. It was a attempt to reduce the electrical load on the system, but creates it's own problems.