temp spikes

[HeavyMetal]

when its hot, the XJ will idle for a couple minutes, itll hover around 220 after slowly creeping up, then instantly spike up to the red and be overheating...this is with the electric fan running and a brandy new waterpump

thoughts?

it wont overheat when driving around, only when stopped sitting

[CumminsJeep]

theromostat sticking or something?

[Bigbike]

Mine was doing this a few weeks ago, I swapped in a 180* thermostat, new radiator, flushed the whole system, now It stays around 210-220
i thnk I have rtv in a coolant port in the block too.

[Ruepart Hoaxley]

Check your radiator hoses, make sure they're not collapsing. How's the clutch on the mechanical fan?

[CumminsJeep]

Check your radiator hoses, make sure they're not collapsing. How's the clutch on the mechanical fan?

just to elaborate on this....the lower hoses should have a spring in them to prevent collapsing and the upper should be pressurized enough that it should not collapse but hey anything can happen. Also, if the fan is bad it will be hitting the shroud, but I dont remember you having a shroud in there, Will.

IMO I would start with a thermostat and see where that gets you. Oh and replace the rad cap as well

[HeavyMetal]

i put a shroud back in last week. the fan hits the shroud on hard left turns, but otherwise not normally at all...i imagine that is mount related though...although i just replaced the motormount

[CumminsJeep]

i put a shroud back in last week. the fan hits the shroud on hard left turns, but otherwise not normally at all...i imagine that is mount related though...although i just replaced the motormount

you would notice if it was bad and it would be wiggling. so i doubt its that.

[Magilla]

I told you to replace those god damn muffler bearings.

[SupermanIce-J]

ZJ 4.0 clutch fan w/o maximum cooling if your clutch fan is bad.

[OWEN]

I was having the same problem in my little flatfender with the flathead, I replaced the hoses and thermostat and the problem is gone. I like to troubleshoot stuff, but I figured try the preventitive maintenence items first.

[clean4drxj]

go with the T-stat, I had it happen to once or twice.

[HeavyMetal]

looks like im tryin the theromostat first, thanks gents

[Buffalo Phil]

looks like im tryin the theromostat first, thanks gents

Easy to replace, don't sweat it.

[Bigbike]

Just for the know, you can only get a Lower radiator hose with a spring in it from the dealership, they run about 30 bucks.

[customcreationsllc]

after you get the thermostat out throw it in some boiling water and see if it opens.
I would still put a new one in they are cheap enough but it will give you a piece of mind if it was the problem.

Do you have good heat out of the vents?

I've seen this before a drain and fill sometimes fixes it, not sure exactly why I've pulled out the thermostat checked it put the same one back in and it runs cool.

I think there are some small air bleed holes in the system like the thermostat maybe it's when they get clogged this happens. Maybe air pockets block off parts of the engine block.

Is your temp gauge off? If it is ready fine driving probably not.
Can you plug in a scanner and read the computer temp gauge?

Good luck
~Justin