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The 'ol overheating problem :(


NAXJA Forum User
1995 Auto 4.0, 3in lift, 31's, 4.56 gears (30, 8.25), Rocket Air Tube, Borla Header, High flow cat, Flowmaster, stock rear 2in pipe.

Ok, When I am in town, driving under 60mph my jeep is as cool as a polar bear with the AC running. Over 60 on the freeway, the temp slowly climbs over 210 and continues up to the white line before the red (235?) it takes about 20 minutes or so to do this. As a test, last night I ran at about 75mph with the AC on in approx. 68 degree weather and it was creaping up to just on top the 0 on 210 - the airflow of driving fast is not cooling or not helping much.
Since I am running 4.56 gears, the RPM's are higher - I think this is this the likely cause of my problem. So the engine is turning faster but shouldnt be working as hard because it is overgeared for 31's. I don't have a tranny cooler but I don't think that would be it. With the AC off, the jeep still gets a little over 210 in 80 degree weather. So, going to the desert is not an option. You might say, just drive 55 on the fwy but this really isn't an option in LA where everyone drives 85+.
I have changed the radiator to a new alum 2 core, changed T-stat, changed water pump, changed clutch fan, had a shop check the torq converter - no problem. I have not changed the lower hose on the rad. but it seems to not squish that much so I think the spring located just a little farther back is fine holding it out. I am about ready to change the temp sending unit but I dont think that is my problem. Please help as this is cutting into my wallet!

Thanks in advance,
Phil Hover
[email protected]
This is a really wild guess ... water pump cavitation?

Check the flow at high rpm. There could be air in the system, too, maybe.

My Xj does the same thing and i haven't got it fixed yet. my best guess for ya, is to find a pretty steep drive way and park it so that the front of the engine is alot higher than the back say 1-2". Xj's are kinda funny the head is almost level with the top of the rad. this can cause problems with air bubbles getting stuck inside the head. when you park it with the rad. higher up you force the coolant to fill up the head. so park it on a steep drive way and let it cool down. I now this could take some time. but let it get to the point where you can keep your hand on the upper rad. hose for atleast 30 seconds. and then pull the cap off the rad. and see ho full it is. add if needed. and makes ure that you overflow always stays full.
do you have a front skid plate and/or athe splash-mat still in place?

Your issue may be more erelated to the diff hangin' down and creating a little pressure wave right where the radiator's airflow want's to dump-out (leaving you with less than good airflow).

Also, what front bumper are you working with? There should be a 4x8" ovoid hole in the radiator support behind the center of the bumper - you can cover that (on the bumper side) with part of an old mud-flap and a few self-tapping screws (to increase the negative pressure behind the radiator) - some bumpers (including bent OEM ones) will "unmask" that hole enough to allow a little too much air flow.

When you replaced your radiator, did you re-install all of the fan shrouds?

Does sound perplexing. You've done about everything i would have looked into. When you do climb on up in speed you are putting more load on the engine. This is when you will notice a slightly leaking headgasket most likely to start to fill the cooling system with air. I'd ck to make absolutely sure there is no CO present in the radiator. Takes only a sec to test. Also, does it really seem like the engine is getting hot, or is the temp sensor screwing up? Is there an associated loss of power or increased detonation?
I will try to burp the radiator and check for air pockets. I dont have a skid plate but I do have the splash guard and I am running a ARB bullbar with no winch.
I believe last time I checked, I may not have the lower shroud on the clutch fan - would that make a difference? As far as the water pump cavitation it is possible since the engine is running fast. I will first check for air then perhaps check the flow rate.

-Phil Hover