if anyone can help my xjs keeps over heating iv changed thermostats water pump expansion tank and cap electric fan stopped working {that's another day} iv put a direct feed to fan until i resolve the overheating. iv bled the system

 

what kind of xjs do you have what year engine size etc because there are some changes in the cooling systems they are not all the same off hand though i wonder if the radiator is clogged also how hot does it get and when does it get hot

 

ye sorry Doug not to hot on the computer either. its a, 89 5.3 .it goes up to N after about 5 Min's, stays there 2-3 Min's then creeps up a little more i pull over before the H .The rad is the next job i think, as you said ill probably get it rebuilt.. is it possible to get the rad out without dismantling the ac rad iv tried the valves on top of ac it seems empty

 

Yes, the radiator is the next step. Besides the possibility of being internally clogged you'll almost certainly find exterior clogs in the form of leaves and debris....sometimes covering a full 30% of the core.

Removal is a bit of a pain....the lower hoses are a bit tricky. No need to undo anything with the a/c but you'll need a helper to help lift it upwards and rearwards out of the engine bay.

Once out, send it to a radiator shop for a good professional cleaning.

When everything is put pack together you'll need to bleed the system. Did you bleed it after the other work?

Also.....check your fan clutch. Warm up the engine (the hotter the better, but not to the point of overehating) and then turn it off. Now spin the fan by hand. It's should not spin more than one turn. If it does, replace it.

Cheers
DD

 

"Also.....check your fan clutch. Warm up the engine (the hotter the better, but not to the point of overheating) and then turn it off. Now spin the fan by hand. It's should spin more than one turn. If it does, replace it."

Are you saying that the fan should not spin more than one turn? If it does turn more than one turn, it is defective?
Thanks for any info as my '88 5.3 XJ-S is experiencing similar behavior now that we have summer time heat. 90's and 100' here in the NW. (SE Wa state)

 

"....should NOT spin more than one turn." I'll go back and correct that mistake.

Opinions vary a bit on how many turns. One turn is the standard I use. To be more liberal, turn turns...and it certainly shouldn't freewheel.

If in doubt, and your running to warm, replace it!

Cheers
DD

 

got the rad out Doug,yes it was clogged as you said with leaves and feathers, ill get it rebuilt as well, i did look at the fan clutch and went straight for the jugular and rigged up a temporary solution so that it didn't spin at all but it still overheated but slower i think ill try your method when i put the rad back. Cheers

 

Something not to rule out is the gauge...is it really overheating or does the gauge just think it is?These gauges are notorious for inaccuracy.Don't take me wrong, all Doug's suggestions should be done as a matter of course and good maintenance practices,and we all know overheating WILL KILL our V12s.I spent 2 summers fretting and fixing all the above and Kirby's extra ground and STILL she kept saying"too hot too hot".Finally put in a real gauge and she shows 190 all day long,in town,on the highway,up,down, all around.
Just something else to consider,Good luck
Les
88 1/2XJ-S

 

Good point about the gauges being innaccurate

A number of years ago on another forum (Les may remember) some of got out out infrared thermometers and compared notes. With the needle at the middle of the "N" there was (as much as) a 20º variance, car-to-car, in indicated vs. actual temperature.

If the needle keeps climbing, though, that's a sure sign of trouble.

The V12 XJS cooling system doesn't have much extra capacity. When everything is just right it'll do the job but if anything is sub-par, it won't cope.

Mine was fine in 95% of all driving conditions. The only time it wouldn't keep up was in gridlock traffic in 100º ambient temps.

Cheers
DD

 

Ya Doug,I remember those comparisons.Something I wonder about IR,it takes exterior temps...but how does it relate to the interior engine temp?
Sorry not trying to hi-jack thread.
Les

 

If you take a reading at, let's say, the radiator neck or the thermostat housing the coolant inside is at about the same temp as the surface you are aiming at, given how thin the surfaces are.

Cheers
DD

 

got it, thanks Doug
Les

 

good to know about the gauge just in case when i put it back together and it still runs hot, then i wont kick it. The rad man is on holiday at the mo so ill let you know how it goes with that when he gets back.The car seems to have a few electrical problems, well more than a few, kick down doesn't seem to work, as i said before the the electric fan only works with a direct feed ,iv changed the therm switch the relay am not to sure which one it is though is it the yellow one ,and the horn that's just stopped working ,and theirs a long storey about the alternator.

 

Hi Pete, the fan and horns are on the same fuse under dash,just in case you overlooked the "simple",I know I often do....
By the way my diode pack for that circuit was blue Pektron on left side fender.
Les

 

well it seems to av don the trick it runs just at the bottom of the N , put the re built rad in at the week end iv taken it for a run a couple of times even in slow traffic and it seems ok ., Why didn't the wise men at the design stage put all the fuses in the same place on all the xjs models , i think i found the horn fuse under the bonnet on the left side. well i changed a fuse their that had gone and hay presto the horn works now, coincidence i don't no with these cars!

 

A quick check of the radiator is to use one of those IR thermometers on the radiator at approximately the inlet and outlet ports. The cooling across the radiator should be something substantial like 20 degrees. If you're seeing limited cooling across the radiator it's likely plugged up in some manner either through the fins with bugs, sediment in some of the tubes or oxides at the solder joints for the tubes.