JagExp

The XJ Forum (6/12/Series)

12 cyl XJS overheating

AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor

memotor Guillermo T
juarez, Mexico   MEX
Hello;
I own a Jaguar XJS, 1988, 12 cyl engine with only 57k miles on it.
Of lately the car has develop overheathing problems that I've being taking care of, with the usual tasks of rad cleaning, new thermostats, several new hoses, etc.
but still the engine feels way too hot in normal driving even though the temp gauge marks below the "N".
I suspect air in the system, or thermostats not working properly. I still need to check this.
But what throws me off is the gauge reading, it does travel up but to me is obvious that is not reflecting what is really happening under the hood.
By the way the engine runs smooth as silk, but is generating way too much heat for my taste, wich didn't happen before.
If anybody out there has an idea of what is happening with my S, I'd much appreciate the feedback.
Thank's in advance for your help.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
Orlando, Florida, USA   USA
replace the Temperature Sender and see if the gauge reads different.

If no change, replace the Temperature Gauge.

Worst case scenario is that you have a blown head gasket.

is there any oil mixed with the Coolant when you check the oil ??



1965 Jaguar S type
1984 Jaguar XJ-6



Edited 1 time(s). Last edit at 2017-08-08 04:36 PM by Jose A..

memotor Guillermo T
juarez, Mexico   MEX
Thank's Jose, good points;
Currently I'm out of town but I'll get to check what you suggest this coming weekend.
Much appreciated.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
PeterT Peter T
Oxford, Oxford, UK   GBR
If the instruments are measuring correctly, go back to the radiator. Make sure the air flow is not blocked by rubbish collected between the rad and air con condenser. V12 radiators get blocked internally and due to the peculiar design don't flush out easily. Be prepared to buy a new one.

Remember Jaguar V12 engines are immensely strong but they really don't tolerate overheating.

Orlando, Florida, USA   USA
does the car have an electronic auxiliary fan in front of the radiator? The XJ-6 Sedans do.

if yes, have you tested the fan to see if it works, and if it does, is it coming on as it should?

if it does not come on, there are two possible causes:

1) the auxiliary fan relay, (should be replaced first before messing with the next item).

2) the thermal switch at the bottom right or left corner of the radiator.



1965 Jaguar S type
1984 Jaguar XJ-6

bburton123 Bruce Burton
Ball Ground, GA, USA   USA
After you figure out the overheating check that your distributor mechanical advance is not frozen...springs should cause the distributor to snap back when you twist the mechanics. I had mine rebuilt by Advanced Distributors in MN. They all go bad apparently. Mine was frozen and causing overheating. Vacuum advance on mine was toast too. High heat under the hood cooks the vacuum advance bladder.

Hope that helps - not that it fixes your current problem.

memotor Guillermo T
juarez, Mexico   MEX
Thank you all;
The good news are that there's no sign of oil mixed with water at all.
Jose, my car doesn't have the extra auxiliary fan, but I'm thinking of putting one on.
I think my friendly radiator shop did a good job of cleaning it, Peter, I was there trough the whole process, but I read somewhere that is a good idea to put an extra wide rad, and I'm thinking of going that route, plus the auxiliary front fan.
I guess I should mention that I live in the Mexican desert, Juarez, and this summer has being particulary HOT! I'm talking 108 degrees plus for two months straight, and driving the car a couple of times I noticed the situation that I described, so I stoped driving it.
I guess I should check the vacuum advance mechanism, not a bad suggestion at all Bruce, just to make sure is working properly.
I totally love my three Jags, but sometimes it feels good to go back to my '63 Spitfire and enyoy the simplicity of it.
Again thanks for your help, much appreciated guys.
SALUDOS!

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
PeterT Peter T
Oxford, Oxford, UK   GBR
Guillermo,

V12 XJ radiators are extremely difficult to flush out well. It's due to the peculiar double pass design. The tank on one side of the radiator has an inlet at the top and an outlet at the bottom; on the other side there's just an inlet at the top. The design is such that water from each bank of the engine enters the top of each tank of the radiator. From the tank with both an inlet and an outlet, the water passes through the top part of the heat exchanger to the tank on the other side and mixes with the hot water from the bank on that side. The mixed water then passes back through the bottom of the radiator back to the tank with the outlet. The (hopefully) cooled water then goes to the water pump. The tank with an inlet and an outlet is divided (again hopefully) about 2/3 or 3/4 the way up (forgive my memory). It's a complicated scheme and not nice thermodynamically or practically.

Flushing has to be done from the side with an inlet and an outlet. My own feeling is that if a V12 radiator needs flushing, it may be better to buy a new replacement, preferably the hot weather/high duty version. If you have it re-built, make absolutely sure the tank with inlet and outlet is properly divided. When I bought my XJ12, I strongly suspect that it wasn't and it overheated on cold days in northern Europe!

There's lots of discussion on various internet sites about methods to improve the system. They include different fan arangements, filters to capture dirt that blocks the radiator (and engine), alternative radiator arrangements that eliminate the double pass ... . If I lived in Mexico, I'd look into them. On the other hand, my car survived a year in Houston, TX without overheating.

If the vacuum advance isn't working, it's not surprising in your hot climate. If you replace it, make sure the replacement is working (try sucking through it). Repairing vac or centrifugal advance should also give you a good improvement in fuel consumption/performance.

Orlando, Florida, USA   USA
Saludos Gullermo,

someone must have removed the auxiliary fan? all 1980's Jaguars have it. ESPECIALLY the V12. That thing runs hot like a nuclear submarine.

But you can mount a "PUSHER" fan in front of the radiator, behind the grille, or a "PULLER" fan behind the radiator if you have the room.

I have a number of electrical parts from a 1986 XJ-S V12 Coupe. Let me know if you need anything.



1965 Jaguar S type
1984 Jaguar XJ-6

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
memotor Guillermo T
juarez, Mexico   MEX
Wow! Now I know for sure that we didn't flush properly Peter. Not as simple as I thought.
Definitely I need to go back and redo that process.
I'm going to check around for a replacement, and add the extra fan, just to take care of the problem completely.

Jose if you have the fan that we've being talking about, I'm thinking "PUSHER", let me know.
I'll try to find one locally, but I'll consider yours as an option, if.
By the way, I'm looking for a nice clean front grille, for a 1988, mine has been repaired.

It's a pleasure to hear from such knowledgeable Jag lovers like you guys.
Thank you very much!
SALUDOS!

Orlando, Florida, USA   USA
Guillermo,

I sold the fan I had from a 1986 V12 XJ-S.

I have a grille from a 1986 V12 XJ-S Coupe. It is not cracked or repaired but the chrome is starting to
peel, and the V12 emblem is not very good.

For cooling fans for the V12 XJ-S, Wolfgang is your guy: here is his website:

http://www.v12s.com/



1965 Jaguar S type
1984 Jaguar XJ-6



Edited 1 time(s). Last edit at 2017-09-01 04:08 PM by Jose A..

dberghoefer David Berghoefer
Yulee, Florida, USA   USA
All good advice. One thing no one has mentioned though is verifying the actual temperature. Gauges are good "indicators" and when everything is going well we feel good seeing the needle in the Normal area. When the needle strays from it's normal position or we sense some other reason to doubt it's accuracy it is good to check all the possible causes. I might suggest a radiator thermometer and maybe an infrared temperature gun to see what the temperature actually is. Then you will know for sure if your engine is running hot or you have an electrical issue in the indicator circuit. Keep in mind Jaguar V-12's make a lot of heat under the bonnet, so feeling lots of hot air on a summer day is not necessarily indicative of a problem. On the other hand, a gauge that shows below normal all the time is not accurate either.
Happy hunting!

memotor Guillermo T
juarez, Mexico   MEX
Thank you David, you're right.
For a while, the xjs was my daily driver, summer driving included,and I never noticed this hood and fender temperature, HOT, while the gauge read below normal, like everything's ok, no boiling sounds or anything. Maybe my car is running ok, but I don't remember it being that way.
I stoped driving the car for about 6 months, with start ups every once in a while, and that's when I noticed this new situation.
Nobody has mentioned the thermostats and their role in all of this.
My car has two brand new ones, but maybe one is not working properly.
I guess removing them is not a good idea, right?
Then there will be no way of controlling temperatures.
Thank's again for your advise.

memotor Guillermo T
juarez, Mexico   MEX
Thank's Jose I'll check the site for the fans.
My grille is pretty clean just that it had one crack that has being repaired and it's not that visible.
I'll keep it in mind.
Gracias!

dberghoefer David Berghoefer
Yulee, Florida, USA   USA
You're right. The thermostats are there for good reason. The infrared thermometer I mentioned is good for checking their operation. Thermostats are simply a temperature operated flow valve. As the engine warms up you should see the temperature on the engine side climb while there is little change on the radiator side until it nears opening temp. (around 180F) when you should see (or feel) the hose leading to the radiator get hot all of a sudden. That is when your thermostat opened. Keep in mind that if you do replace them or drain the system for any other reason, you need to bleed the air from the system according to the shop manual. Air pockets trapped in the cooling system will not allow the system to work properly.
Cheers,

. Hide banner ads & support this website by becoming a > Gold Supporting Member <

To add your reply, or post your own questions

Members Sign In   or   Create an Account

Registration is FREE and takes less than a minute!


Having trouble posting or changing forum settings?
Read the Forum Help (FAQ) or contact the webmaster