2000 Grand Cherokee - 4.7

Background - Vehicle has been very well maintained it's entire life

Coolant has been flushed and has always been clean, etc.

Starting to run warm a few months ago, almost got into the red one day.

Have replaced the thermostat twice, changed the fan clutch. Installed new radiator, some scale build up inside the old one but not bad.

Installed new temp sensor.

Installed new water pump - old one looked fine.

Still was running hot under load.

Did a pressure test - Tiny bit of loss, but stabilized.

Figured what the heck and tore it down yesterday. Both head gaskets actually looked pretty good and the pistons/valves looked normal.

I'll have the heads pressure tested and trued, but if it's not the head gasket I'm at a loss? Any ideas?

Thank you

 

What's up with the E Fan? not sure what you mean by "under load" But the E Fan should kick on after the temp reaches 210. Check the relay on that and make sure the fan itself does work.

 

Names throwing a blank, but I replaced the deal that controls the electric fan a while back and checked it again. Regardless, the fan is working as it should.

MAY have found the issue?? As I was just washing up parts, right behind the thermostat is corroded and broken out. Found some pictures on line and mine looks different and a sizeable piece is gone/corroded away. Behind my water pump is good, as I've seen other pics online where that was all corroded out.

Wondering if what's missing is causing some circulation issues?



Under load = Driving

 

There is one other possibility that was discussed at great length here about a year and a half ago or so. It was a problem that was easy to never factor in. After several days of Q&A exchanges it turned out that the vehicle in question was put out from the factory with the wires actually reversed in the electric fan connector plug.

It was making the E fan run backwards and rather than draw air it was trying to push back out the front causing the electric fan half of the radiator to be canceled out and not helping to cool at highway speeds. I honestly don't remember what year or model it was but it was eye opening for sure. The discussion is here somewhere if you have the time to search it out.

You could have that same year and model, I would check to make sure that when the electric fan comes on it is actually drawing as much air as it should be through the radiator and not running in reverse.

But also keep in mind that about 80% of every make and model get hot under very heavy load conditions This is when gearing down to spin the fan faster, reducing the engine load factor, and patience comes into play. I found I have to drop out of overdrive or even grab another gear before it gets too warm, not after, after is too late and it's not going to go back down until the load conditions change no matter how many lower gears you grab...

I found that when I try to push overdrive as far as I can get it, it is too late and I done went too far already.

 

Bugout, thanks for the reply... 99.9% sure the fan isn't or wasn't the issue. I've had this jeep 3 years and a friend of mine before that about 3 years.

I'm not talking about under heavy load, as it's towed my boat more than a few times. I'm talking literally just driving through town and the temps would spike.

Happened once last summer, thought at that time it was due to pulling my boat and it was a hot day. Never happened again until a few months ago coming back from a couple hour drive.

 

Curious? do you remember if or think a good wind may have been coming at your stern during these episodes? A strong wind from the rear has heated up many vehicles that normally would not get hot. Wouldn't think so, but it really can.