View Full Version : xj running hot

March 30th, 2007, 02:19 PM
I thought I might pick some more experienced brains to figure this out. My 2000 XJ 4.0 is starting to run hotter than normal, above 210 degrees. Belt is in good shape & tension is OK. When driving it stays close to 210, but when I slow down or stop it starts to rise above 210. I put a 180 stat in ~ 2 months ago and it ran below 210 until the last week or so. I already checked the fuse for the eletric fan & it's OK & I know there is also a relay, but I don't remember how to check a relay and I'm not sure how to check the thermal fan clutch. The fan does keep spinning for about 5 seconds after shutting the engine off when hot. Any suggestions/advice would be greatly appreciated. Thanks.


Creative Fab
March 30th, 2007, 03:29 PM
check for debris along the bottom side of rad. it could have some external blockage via some mud?

And sometimes new thermostats will fail

Then check under the cap with a visual inspection for clogged tubes. Might need a good flushing!

March 30th, 2007, 08:59 PM
If the temps climb at idle, it might have something to do with the fan and fan clutch, if the temps rise at higher speeds, like 55+mph, then its not the fan clutch....

If the fan clutch has oil on it, its bad. If it spins free after you warm up the engine, say more than 2 revs by hand (drive it a while too, then shut it off and check) then its bad....

I had similar issues in my TJ back when it was new. I wasted 2 fan clutches in it by letting it run when in deep water (stuck). I also tried a 180 deg stat that didn't do anything. I replaced the fan clutch and it fixed my low speed heat problems and then I put the old 195 deg stat back in.

Since then I've come to the belief that the cold thermostats aren't good, you need to get the whole system working properly and you won't have any cooling issues. I run a 3 core radiator, a high flow thermostat housing and a 195 stat, never has it climbed over 210 even blasting up dunes and mud....

Keeping the radiator clean will help too! I used to have to pull the radiator out after every muddy trailrun to clean the caked mud out of it. I have since pulled out my AC unit including the condenser and haven't had any mud or debris problems since....

Good Luck!


April 2nd, 2007, 09:53 AM
Thanks for the input...it gives me a place to start. The temp does rise while driving for more than 20-30 min, and continues to rise when slowing or stopped. Also, system was flushed & new coolant added when I changed the thermostat and the radiator does not have any build-up on the fins. I'll keep looking.

I don't think I'll be able to get rid of the a/c since my wife & daughter go on trips, too!


April 2nd, 2007, 10:19 AM
Considered the water pump? Do this test while cold. Take the thermostat out. Remove your radiator cap. Start the engine. You should be able to see water flow.

If you don't see flow, it could be the water pump or something plugged as said before.

This test does not work in all cases. It depends on where the inlet/oulets are at and where the cap is at.

April 5th, 2007, 11:01 AM
Thanks for the info. Water pump seemed to be ciculating fine, so I replaced the stat with a 195 and also the replaced the rad cap. The housing started to leak about the same time it started to heat up, so maybe a pressure problem, too? All is well so far, even though winter seems to have returned for a week or so...I'll see what happens if the weather ever warms up. Again, thanks for the help.


April 5th, 2007, 11:12 AM
Hey Brad, maybe it's that HUGE 8274 on the front!! :lmao: JK

Slightly off topic...
I saw in your signature you have a Dynomax cat back system... how do you like it?

April 5th, 2007, 01:13 PM
<div class='quotetop'>QUOTE(Ultimate Air &#064; Apr 5 2007, 10&#58;12 AM) 23913</div>

Hey Brad, maybe it&#39;s that HUGE 8274 on the front&#33;&#33; :lmao: JK

I thought about that, too. I didn&#39;t get it on until last fall when the weather started to cool down, so it will be interesting to see what happens this summer.

Slightly off topic...
I saw in your signature you have a Dynomax cat back system... how do you like it?

I like it...not too loud. I still have the factory exh manifold (waiting for it to crack before going the header route) so performance-wise I did not gain as much as what you could by swapping in a header, but I do notice a difference in the mid-range, especially when passing on 2-lane roads. For the low cost of the cat-back vs. Magnaflow, Borla, etc. I will stick with Dynomax in the future.

P.S. Thanks for the awesome pics from SnoFari 2007&#33;