The V-12 in my 1986 XJS overheats in the warmer weather. I've already tried a total system flush and running straight distilled water with the "Water Wetter" type cooling compound. This seems to help some but it still rises above the "N" mark on the temperature gauge on hot days. I've heard about putting an aluminum radiator in it too but reviews are mixed whether or not alloy beats the standard radiator for cooling (I believe it would be a waste of $$$) Both the regular fan and the auxiliary fans run and operate fine. It stays in normal range heat wise while its cruising but once your in stop and go traffic it gets too warm. I've also researched and found that this is common with these V-12's.

Any suggestions from any of you here where I can get this beauty cooled down without spending a bundle of cash?
Thanks!

 

How far above the N does it go?
Have you renewed the thermostats?
One trick is to pull the radiator and clean all the crap off it and the surrounds.
Whilst it is out it would probably be worth getting it re-cored; at least that way you will know that any over heating is not radiator related.
There is nothing wrong with the basic cooling system as long as it is well maintained; I'm on my 6th V12 and none of them have ever over heated.

 

Thanks Steve...My next solution was to replace the thermostats, I have pressure washed the radiator and found nothing blowing out when I did do that. I don't believe the radiator is bad but if the thermostats don't fix it I'll try that next.

 

When you Stop in Traffic and the Temperature starts to rise, does the electric fan cut in to cool her down?

If not that could be your problem.

 

Define "overheats"?

In a perfect world every car would hold a 100% steady coolant temp under all conditions, all the time. In the real world some don't. Some people consider *any* increase in coolant temp 'overheating'. I don't, personally.




How far above the "N" does it go?
What are the ambient temps when this happens?
Does the increase begin immediately on hitting traffic, or after a few minutes?
Does the needle climb a bit and hold, or just keep going up-up-up?
Have you checked your gauge reading against a handheld infra-red thermometer to a get a rough idea of *actual* temperature

What I getting at is that you might not actually have a problem.

Or maybe you do

Also, when you say the regular fan is Ok, how did you test it?

Cheers
DD

 

make sure you get *correct* thermostats. If they're the wrong length, you'll worsen and confuse the issue. This thread will help:

https://www.jaguarforums.com/forum/x...ostats-149202/


Also, make sure to properly bleed the cooling system. This is essential. We can give instructions if needed

Cheers
DD

 

DOUG; REPLIES BELOW

How far above the "N" does it go? Substantially over the 'N'
What are the ambient temps when this happens? 75F and above
Does the increase begin immediately on hitting traffic or after a few minutes? Slow increase the longer your stopped/idling the higher it goes
Does the needle climb a bit and hold, or just keep going up-up-up? Up, up, up and it was worse before I flushed and added 100% H20
Have you checked your gauge reading against a handheld infra-red thermometer to a get a rough idea of *actual* temperature No I have not
So darn hot I can hear it BOILING when I shut it down!
What I getting at is that you might not actually have a problem.

Or maybe you do Oh I have a problem Doug, and it's depressing because this car turns many heads here in America, it's rare to see one of these on the roadways.

Also, when you say the regular fan is Ok, how did you test it?, I simply observed the regular fan running, the other fan is activated automatically when the air cond. is on.

 

When was the last time the radiator was either re-cored or replaced? Did you (and any previous owners) flush and replace the coolant every 24 months? Do you know if any previous owners ever used tap water to top off or mix with antifreeze?

The car is 30 years old, and if you don't know the answer to the above questions for certain, at a minimum you need to pull the radiator and get it flow tested. Or don't waste the money on testing, and just take it to get re-cored.

On my '90 XJS which I've owned since it had 5K miles, and do know it's service history, and never used tap water... needed a re-core. IOW, I wouldn't recommend that you just assume it's good.

 

Ok, that's no good.



That doesn't confirm proper operation.

Get the engine fully warmed up....a bit hotter the normal, as you've been experiencing, is best. Now turn the engine off. Now, spin the fan by hand. You should feel a definite resistance and the fan should not spin more than 1 turn. If the fan spins easily, of if there is any doubt, replace the fan clutch.

A weak fan clutch can cause overheating in traffic for sure

Cheers
DD

 

Thank you Doug, I'll try the fan clutch trick.
Thank you Mac Allan but I hope I don't need to replace radiator, but as the cliche goes, "It is what it is"

 

Very good advice from previous posts .
My guess would be that it's likely lack of regular thorough maintenance by previous owners has lead to one is possibly several causes all contributing to marginal cooling that copes in cooler weather and when moving but in hot ambient temperature it's not able to cool adequately.

Would suspect fins (between water radiator and air conditioning condenser) clogged plus main fan viscous clutch not spinning fast enough at high temperature and maybe radiator internal passages clogged.

Also be aware of bleeding process for radiator

 

Nice looking Jag

Cheers
DD

 

This brings up another question. After the flush, or when you were experimenting with different coolant remedies, did you re-bleed the system?

If not, you could have air pockets in the engine block, so I would recommend you don't tempt fate and keep test driving until you have the cooling sorted.

 

A 'stack up' of faults wouldn't be surprising at all.

I'll also add the that slew of small hoses (from the expansion and overflow tanks, vapor pipes, filler neck, etc) should be removed and checked for clogs...or even just summarily replaced on GP.

Unless there's a known history of repairs to suggest otherwise, this would be a good candidate for the "do it all, do it once, do it right" method. Go thru the cooling system entirely....and then 'good to go' for many years. Hoses, belts, thermostats, fan clutch, flush and bleed again, professional radiator cleaning. Lots of work but easier than the ala carte method

Cheers
DD

 

Some LIGHT reading from Word Doc's I wrote many years ago.

Enjoy.


Cooling system upgrade.doc

Bleeding the V12 cooling system.doc

V12 thermostat fiasco explained.doc


The first one will have more scribing than you need, but you are smart enough to ignore what is not related to your car/issue.

NICE looking XJ-S by the way.

 

Do not mess about, boiling in the system is potentially a disaster. Pull out the rad, clean all the rubbish that will be clogging the oil and aircon coolers. This prevents air getting to the water rad. Do not delay doing this. Recore the rad if in any doubt at all about it's state. Definitely replace the fan clutch. Loads of stuff on the forum about bleeding the XJS V12 system, follow that on installation. Also a VERY good idea to replace the OEM electric auxiliary fan with an 11 inch modern one, no wiring changes needed.
All this will set you back less than 150 USD, unless you have to recore the rad. Get stuck in, you are on borrowed time!






Greg

 

Agree with Greg. Would also like to add, have you checked the flaps and ensured that the foam around the radiator is there?

From what you are describing, speeds above 45 mph or so push enough air through the radiator for heat transfer. When stopped, the only thing pushing air is the fans, and you clearly aren't getting enough air in the right places.

 

If his car is overheating, it isn't from some foam. My car has had overheating from a bad water pump, bad fan clutch, busted electric fan, bad radiator cap, and was the worst with bad thermostats.

Never had a problem with foam or bleeding the system. An aluminum radiator would definitely keep the system cooler, new ones typically have more rows and the thermal coefficient of brass is is lower than aluminum. You should find and fix a problem and not try to make up for it with extra fans or water wetter.

If it is only when parked then your fans may be the issue. If you electric fan is running then check the mechanical fans clutch.

 

I Have been attending to my cooling system. Mine has been running a little warm- with the needle sitting just on top on the "N".

I performed a flush and replaced the coolant to no avail. I broke down and pulled the radiator to clean all the junk the was packed into the fins. Since it was out, I took it to a radiator guy to give it a proper flush and possible recore. He inspected it, and determined it did need a recore. When I picked it up last night, I was informed that the bottom third of the radiator was filled with stop leak.

It is had to determine what someone did or didn't do prior to your ownership.


Paul

 

Hi Paul

Don't get too excited as if its been fill with that kind of stuff you might have to change all the Hoses.

Grant knows all about this, so I hope he will chime in and put you right.