Been having quite the issue with my 2000 4.0L XJ, replaced everything in the cooling system yet it still overheats, it can sit and idle forever while the temp hovers around 210, yet when I go to drive it it starts to climb to the next tick then it eventually spikes. The coolant reservoir also starts to boil over when it gets to this point.

I've replaced/checked...

• Head Gasket
• Radiator
• Upper and Lower hoses
• Water pump
• Thermostat (two times)
• Fan Clutch
• Radiator Cap
• Reservoir tank with new line
• Head was tested and came back OK

Looked at the harmonic balancer and the rubber on it does have a few cracks but I marked it with a marker and drove it around for a bit, came back and the line wasn't broken up. Checked the dipstick and the oil cap and it looks as a normal dipstick/cap should, no milkyness. System was flushed as well, I also have the heater core disconnected until I can get it rebuilt and have the in/outlet hoses connected to each other so it just loops.

Completely at a loss here, any ideas?.

 

Is the fan shroud intact?

Any chance there are air pockets in the system that haven't been let out?

 

Is the radiator sealed around all four sides ? Does it have any other rads (power steering or A/C) in front of it that might be dirty or blocked ?

 

Fan shrouds are intact, felt around the rad and dont feel/see any obvious cracks, and I have not had any leaking problems other than the reservoir dumping coolant when it got to overheating. Power steering, ac etc are all clean.

Also forgot to mention that the electric fan was blowing the wrong way so it's been switched to blow onto the engine, it kicks on once it gets to operating temperature.

We bled the air out after the head gasket and the coolant were replaced, unless we missed some somewhere wouldn't that of worked it's way out by now? It's been almost a month since the heat gasket was replaced.

 

I have no idea why below is showing up in red!

"...….the mechanical fan was blowing the wrong way...……………., it kicks on once it gets to operating temperature."

Do you mean the auxiliary fan (electrical one)? If so it should only come on when the temp gets to a certain point above operating temp or at certain times when the a/c is on.

 

Oops yeah I meant the electric one.

 

No problem. I figured you did.
Did you properly burp the system by putting the front of the Jeep on an incline...then with the cap off, let it get up to op temp and make sure there aren't any pockets of air in the system. As air will rise to the highest point in the system.?

 

Have you ever had to do anything with the freeze plugs (leaking, replacement, etc).Sometimes freeze plugs are just driven into the block and new ones put in place, and they can restrict cooling flow.

Just curious, what brand thermostat are you using?

 

It was burped on an incline by squeezing the hoses, all done at operating temp.

Never touched the freeze plugs unless the previous owner had work on them, but I got the jeep over a year ago and it only started giving me these issues over the past couple of months. Also got the thermostat through advanced, a 195 deg one, and I believe its a motocraft one which was replaced twice earlier in the troubleshooting thinking I just got a bad one initially.

Another thing I forgot to mention was the previous owner put in head gasket leak sealer in it, once the head was taken apart loads of gunk that apparently exists as a byproduct was found, that was all flushed along with the system, unless it built up somewhere?

 

It might have built up somewhere, and be restricting the flow. Try this: Drain the coolant out. Replace with water, and add 1/4 cup of Dawn dishwashing liquid. Drive it around for a week or so. Drain, rinse, refill. See what happens.

 

Ok what is new and what is old

I've replaced/checked...

• Head Gasket
• Radiator
• Upper and Lower hoses
• Water pump
• Thermostat (two times)
• Fan Clutch
• Radiator Cap
• Reservoir tank with new line
• Head was tested and came back OK

 

I would say look to the one thing you haven't swapped yet: The heater core. Sometimes they get rusty and plugged up and can impact the whole system. Also make sure you use a good thermostat. Cheap ones have burnt me before and left me stranded.

 

Are you able, or have you,used an infra red temp gun to measure the inlet and outlet hoses to see what the temperature difference across the rad is? The typical temp drop should be about 10*
Is it a single row radiator, and was it replaced or just checked? I ask because you say some byproducts were found earlier in the engine and they would certainly cause issues in a radiator.

 

He mentioned the heater core is currently bypassed.

I'm going with the radiator is plugged up with that god-awful leak "fixer" crap and would try BlueRidgeMark's advice.

 

Yeah I'm gonna flush it again with water and soap and hope for good results, I'll update when I find out