Okay, so I have my good ol' reliable '88 XJ Pioneer 4.0, it kicks butt, has only 144K, runs great. A few years ago I did a coolant bottle swap with one from a Dodge Intrepid, changed the thermo and drilled the two little holes at 12:00 & 6:00 respectively following instructions from another Jeepster who did this. It worked like a charm, the bottle no longer leaked because it has as genuine steel jacketed radiator pressure cap, and I did not have to go through all the acrobatics of getting the air out of the system because the two little holes did this for me. They were small enough so that coolant flow was not affected.
It made my 88 run so cool I could not believe it, and it still does, except when it idles . It creeps up towards the red zone if I let it idle for 5min. or so. It goes right back down if I start driving it again but I am puzzled why it does this. If you have any ideas how I can start checking I would appreciate it.

 

Get a new fan clutch if you haven't already.

 

clutch fan or shroud missing.

 

Good advice above.

The #1 cause of temp creep at idle ONLY is a bad fan clutch.

Often overlooked, inexpensive and easy to replace.

 

About three years ago I replaced the clutch assembly along with the bottle and the rest of the stuff I did based on what I read here. It was the cheapo large chain auto store part. It's cheap enough so I can replace it again and see how it behaves. Is there a better brand or type of fan that is a direct bolt-on alternative to the factory one?

Is the secondary electric fan suppose to kick in if the engine gets to a certain temp? Or is that only for when the A/C is on? On my 2001 XJ that fan comes on only when the A/C is running.

 

should kick on at certain temp

 

225 i believe.

 

FSM says 218.

 

Renixs different...

 

Maybe it is possible to glue clutch to its axle w/o removing it.

I never did that.

 

car5car, you don't want to glue the clutch to the axle because then if you are at around 4k rpm, you can actually damage your fan and break more stuff than you intended to.

 

'

not to mention sounding like a plane taking off everywhere you go and the hp.and mileage loss

 

That's the way they all used to be years ago, no fan clutch, just a direct connection. It WAS one less thing to break, lol. But the fans back then were designed for continuous high-rev operation too. No overdrive back then either, running 3500-4000 RPM on the highway wasn't unusual. Man I miss cheap gas.

Once you get moving the air flow from forward movement exceeds that generated by the fan, so the fan isn't doing anything useful. In fact it's really just in the way. Letting it freewheel actually allows more air to flow that if it were under power. Directly connecting it wouldn't do anything other than save the couple bucks a new clutch costs, and since you'd have to remove it to lock it up anyway...may as well just swap in a good one.

 

not true on our little radiators the fan still comes into play went thru this with mine fan clutch replaced highway temps came back down