V12 overheating
 

Hello. I was searching this and other forums, but I still cant find answer to my problem. I bought an 96 XJ12. On my first trip to Viena I got stuck in traffic jam. Temperature was slovly raising, unfortunately it was impossible to stop the car. I had to repeately shut the engine down and start it to move to nearest available parking space. At the end I ended up with boiling water. I realised, that the electric fan in front of the radiator wasnt working at all (before the trip it was OK). So i refilled water and returned back home (on the open road the temperature gage showed normal temperature). Back at home we changed both thermostats, elcetric fan relay, temperature sensors and coolant. At first everything seemed OK. But then I took the car to a test drive, when immediately the temperature gage started raising to aprox 3/4 of hot, then returned back. We chcecked it, and the problem seemed to be air bubble near sensor. So I opened expansion tank, put the car on the hill, nose up, and started the engine and hoping to release trapped air. On the second test drive everything was OK, temperature normal, so I took the cars to the hills... It was OK, till I shut the car down. After three minutes I started it again, but temperature was above normal and then slowly returned back to N. When we opened expansion tank, water was boiling (allthrought temperature gage was showing normal temperature)... I realy dont know, what to do. My mechanic thiks, that the problem is head gasket, but there is no water in oil, no black smoke, hoses from radiator arent hard. Any ideas?

Hello, sorry for the late response. Have any developments been made?

My 96 XJ12 runs a bit hot only on the hottest summer days. Stop and go traffic on days like this makes me nervous. Mine hasn't ever overheated, however. My electric fans often run after the key is switched off, usually on low speed, but sometimes on high, which you will certainly hear; They are loud!

I've noticed the temperature rising after turning the engine off more than a few times. These are big, hot engines, and mine has the catalytic converters on the down pipes, so there is a LOT of heat under the hood that tends to warm the engine even after its turned off. You can feel the heat pouring out from the wheel wells after a drive on a hot day.

Have you tried a combustion gas test of the cooling system? It's also called a block test. The tester "smells" for combustion gasses in the coolant.

Mine has ALWAYS made bubbling noises in the coolant expansion tank immediately after turning the engine off. Not sure why. I'm not losing any significant amount.

If you replaced the thermostats, make sure you use OE Jaguar ones. The term "meets or exceeds OE" doesn't mean you get the same quality. Also, some suggest drilling a small hole in the thermostats, and orienting it up when installing them allows a passage for air to escape. These are supposed to be self-bleeding cooling systems, but every bit helps.

-Nick

Skipper sorry late to the thread did you ever get your issue sorted? I'm curious as to your XJ12 is it a short wheel base or long? All 96's are long wheel base in North America but not sure over there?

truth be known Jag V12 engine itself , engineering was not the best for an effiecent cooling of cylinder block and heads.

excerpt from TWR racing program.

Never had an issue with over heating but I am never stuck in traffic. With only 75,000 people in town it's tough to get a traffic jam going.

Its no secret that V12 cooling has always been an issue. But it seems like they got it as right as they could with the X305. I've never had a problem with overheating, even in the Arizona summer, with the a/c on, and in traffic. Soon after I got the car I replaced the radiator and all the hoses, and certainly that helped. I still always keep an eye out for the temp and the coolant low light. There is not much space between coolant loss and devastating overheating. With all the talk of cooling problems, I've never seen it in my car. Knock on burl walnut.

Of course I am not racing the car, certainly that would bring a whole new set of considerations up. I'd say that the Jag V12 isn't a great choice for a race car! But Group 44 and TWR did have some success with the V12 in the XJS.

Too bad Skipper gave up on the forums here. I suppose 3 weeks is too long to wait for a reply from us enthusiasts! I bet his car has given up too. Usually it is a lack of cooling system maintenance that ends up killing V12s.

Actualy I didnt gave up ;) And my car also. Summary so far - I have changed radiator, hoses, termostats. I did the combustion gas test - it was OK. After that incident anything worked fine for few years. Only one day ago, it was realy hot (33 dfg celsius) and I got stuck in traffic jam. Temperature was raising a little above N, so I have set heating on Hi and temperature stopped just a little bit above N. It seems to me, that the cooling system can work sufificiently in a realy hot day and traffic jam for about 45 min. After that it has enough. So, according to my opinion, after I have changed anything important in cooling system, it is a feature of the car, not a bug :D

The bubbling noise - My car does it too. But only after a drive, when the car was cold at the start. Bubbles come from the top hose of the radiator, and I think, that this is normal. When the coolant gets hotter, it comes throught this hose from the radiator to the expansion tank. However, this hose ends above the max coolant level (on a cold car). So when the car after a drive gets cooler, coolant retunrs throught this hose, and finaly ther is some air sucked throught that hose. On the next drive, coolant in the expansion tank rises from the bottom hose and the air is trapped in the top hose.

And it is a SWB car ;)

Three weeks, three years. It’s all the same :)

Get the radiator rebuilt. These cars shouldn’t overheat.

Jagsandmgs, they may not over heat in NH(new hampshire),, but in central Texas where summers get over 100+ F, for many days the Jag V12s are as close to overheat and BOILING after shutdown!

and if any coolant blows out ,when you drive away it will overheat worse! and its the coolant loss that forms bubbles in the cylinder heads and blows headgaskets!

The coolant temp switch control of one or both fans running is the same as in the inline 6 models

On the lower left aft side of the radiator is a 3 wire temp switch

Remove the connector and take one of the white wires to the black one and you will get one fan

Remove the jumper and take the other to black and you will get both fans

You can do this with a paper clip as it is a low current part of the system

The fan control relay modual do get water inside if no properly installed and the black colored X308 version does not work in the X300 / X305 ( white )

See page 101

http://www.jagrepair.com/images/Auto...s/jagxj1996.pd :icon_dance-disco:

a 6 cylinder engine is only half a 12 cylinder, so much easier to keep kool!!!!!!

Radiator is new, I am not sure about my catalytic converters. On an emission test i got higher CO level on one side. So maybe crowded catalytic converter might be my problem.

Sleek, was your car built with FORD engineering, after Ford bought Jaguar?

Ford R&D spent some time redoing the cooling of engine and cooling system!
ron

Yes Ron the last gen V12 was updated using Ford's money and tech to get the 305 OBDII compliant. That included the ignition system rework, cooling system changes, intake air control changes and basically the entire EMS. They did a good job and the distributorless ignition system is super nice. But i cant see how they sold enough cars to see a return on investment.

The cooling system changes only involved relocating the cylinder take-offs to 1 2 & 3 A and 1 2 & 3 B, plus a heater core take off at 6B. Thats one less take-off than the previous versions, including the 6.0L in the XJ81 and X27! Seems like if they really thought overheating under normal use to be a problem, they could easily have added coolant take-offs above every cylinder. Seems like a good idea, but they didn't. Some of them are still blanked off. Also, they never added an electric coolant pump to run after shutdown. I suppose they thought it unnecessary. Trust in their engineering. Right?

The 81 and 305 benefit to some degree* with the change to the twin electric fans out front.

I know some people (such as you Ron) have upgraded their cooling system, like with aluminum radiators and better fans. That is especially useful in the XJS, with its stuffed engine compartment, and particularly for higher output engines. For me and the 305, I'd just like to have some hood louvers. All V12s should have them. Like dual barbeque grills! Why only the R cars?

G’day Gents,

I am having a problem with my V12 getting a little hot under the collar lately. I’ve replaced both thermostats but I think one of the new ones is dodgy, more investigation after the Christmas period.
A question though, does anyone know at what temperature the electric radiator fans activate? I can’t find that info anywhere.

Cheers,
Jeff.

185F, 85C if memory serves me correct.

i have an adjustable fan temp switch, i set it around 175/180F , i want to start air flow before reaching 190F!
i dont want a boil to begin ,because once its going it is much more difficult to stop it!
ron

G’day Gents,

On the subject of our V12 cars, has anyone done any driving with a an OBD reader connected to observe the actual operating temperature during normal driving rather than stare at the meaningless temperature gauge?

My car runs at about 105degC however the temp gauge pretty much sits rock steady just under the N. At that temp the thermostats would be wide open you would think and the electric fans would be running continuously which they do.

According to the specs of the coolant I use the boiling point is 127degC with a system pressure somewhat lower than the relief pressure of the tank cap so I’m not worried about it boiling.

There is a manufacturer in Australia that produces a hi flow thermostat that has a much larger opening than the normal thermostat. I though that in fitting these the car would run cooler but there appears to be no difference.

I’d be interested to know whether anyone has any further info.

Cheers,
Jeff.

Jeff, what are the ambient conditions during your normal driving? City traffic with ambient temp of 37ºC? Or steady driving, no traffic, and 18ºC ambient? If the former, your 105ºC coolant temp might be as good as it gets. If the later, well, I'd be concerned....as the system should be able to maintain whatever temp the thermostats are rated or close to it under such conditions.

Does the temp stabilize at 105º or keep going up-up-up?

All this being said my experience is with the older 5.3 V12s.

Cheers
DD

G'day Doug,

The temps at the moment around here are in the high 20degC to low 30degC range so maybe I need to look further. The heater matrix was pretty much clogged with scale when I got the car and I had to replace it so perhaps the radiator matrix is suffering the same problem. I'll take the car to a workshop early in the New Year and have them check it out.

Cheers,
Jeff.