I have a 1999 XJ, the guy i bought it from said he put the old 4.2 L in it, but i can tell any difference from a normal 4.0. It’s started overheating recently & i have no idea why. It has a 3 shroud E-Fan aluminum Radiator that worked great for a while but it recently started again. New 160° therm, been flushed countless times, Water pump is good, no leaks, hood gap to help with heat soak, New A/C system, the only other thing i’ve done to it, is that it’s on 33’s now, which shouldn’t overwork the engine at all. I’m just lost & want to drive it again without blowing it up.
Note- the only thing the dash has is idiot lights so i have no idea what the actual temp is when it comes on & i usually only run water through the cooling system instead of coolant, unless it’s winter.

 

I know you said it was fine for a while but have you burped any air out of the system?

 

Yes i did it saturday when i put in the thermostat.

 

Have you checked the ignition timing? I’m assuming you have a 4.2 block/bottom end with a 4.0 head

 

Also, is the water pump for an XJ or for a 4.2? Some or all 4.2s use a w.p that flows in the opposite direction than an xjs

 

No i have not but im not lacking any power

 

No idea, i can try & look into that tommorow

 

What are you doing to prevent the block and head from corroding on the inside of the water jacket?

 

Nothing besides using distilled water

 

You probably should be running a 195* thermostat and a 50/50 blend of coolant and water. Water alone has a much lower boiling point than the coolant mix. With a 160* thermostat, the radiator has no time to cool what is circulating as the 160 probably is not closing and the water is continually running through the block, heating up.

Todd

 

You can also add water wetter to resist corrosion, also would help keep temps cool if you run straight water

 

Get rid of the radiator and e fan setup and go with a factory style replacement radiator, clutch fan, fan clutch for a 4cyl XJ, factory e fan, fan shroud, and 180 or 195* thermostat.

 

I'd be willing to bet you've got a nice layer of rust on the water jacket that's providing insulation between the engine and the coolant/water.

 

This is true, when I did my zj head they tanked it with new freeze plugs and since then it never even gets close to hot, no matter if it’s 100 out I can drive it forever and it wouldn’t overhear no matter what .Of course that is a ZJ and the XJ is harder to cool.
You could do some flush treatments.
I would agree you need the 195 T stat with a 50/50 mix. Those are the basics.