heating info on 4.0

[skippy62]

Hi Everybody. I have a question that maybe somebody can give me some input on.
Last year I replace my Rad. I went from closed to open system.
This year about April I notices my temp gauge going up and it went to about 225. I have a 195 thermostat. It will go a little higher with the air on. But it has yet to over heat or blow out any water.
can the gauge be bad or the thermostat or bad sending unit.can the rad. cap be bad?
has anybody exp.this?
1990 4.0 auto no trans. cooler
is the sending unit on the back right part of the engine?
also the gauge does not go back to the bottom but stays right where you shut off the engine. The XJ has been setting for a day now and the gauge still shows about 225.I turned the key on and the gauge dropped back to 100 but when I shut the key off it looked like it started to go back up. Thanks for any input on this matter. :All Good:

[JohnXJ]

All of the things you mentioned could cause the problem. The gauge staying in the middle when you shut the key off is normal.

[BFA]

Do you have a 2- or 3-row radiator? Jeeps run hot and mine ran hot sitting in traffic, pulling boat, driving long distances, etc. I just installed a 3-row radiator (thread on next page) and now it only goes over 210 to open the thermostat.

Al [img]/ubbthreads/images/graemlins/cool.gif[/img]

[skippy62]

Thanks Guys:; It is a 3 core. like I said it has not caused a problem but would like to fix it before it did. It alwasy ran about 210 or a little lower.
But I would appreciate any more info..

The guages in your instrument cluster (or most OEM gauges for that matter) are not really accurate. The best way to check your temp is with an Infrared instant read thermometer. FWIW, lots of folks dislike engine temps above 200 but truth of the matter is that is right about where these are designed to run. Getting them to run cooler than 195 F WILL result in significantly LOWER fuel economy and increased emissions.

[BFA]

I haven't noticed a change in fuel economy yet. I'd rather have a nominal change in mpg than having run almost in the red (engine damage) while sitting in traffic or towing or long distances in the heat. It hangs next to the left of the 210 mark. In fact, it hangs in the same place when the old radiator was in except it doesn't go over 210 now. [img]/ubbthreads/images/graemlins/cool.gif[/img]

Al [img]/ubbthreads/images/graemlins/40BEER.gif[/img]

[mrbill]

Hey Skippy, Don't forget that a 195 degree t-stat will not make your engine run any cooler it just opens up sooner. As for the overheating, I would also check to be sure your serpentine belt isn't slipping.

[NIX]

If you fear a blown headgasket, have a CO sniffer at the radiator cap...

[skippy62]

Well guys you have all giving me some good info.
I just replaced the head gasket so I am ruling that out.
I am really thinking the most obvious the thermostat but it has really not overheated.
I will check the belt today but it sounds like it is tight.
I do have to say that the old girl is running pretty good for 190,00 miles. She does nor leak or burn a drop of oil and that is why I like to get to things before they happen if I can.
She will prolly become my trail rig as soon as I can get a locker for the rear. But nothing real aggressive like my CJ was. and find that rumbling noise at 45 mph. one more u-joint to change and then I will look somewhere else.

Thanks again...

[NIX]

I replaced my engine and the newone had a T-stat that opened only after lying in boiling water for some time. So that was a bad one...