XJ XJ12 ( X305 ) 1995 - 1997

V12 overheating

 
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Old 08-29-2016, 02:10 AM
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Default 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?
 
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Old 09-19-2016, 08:15 PM
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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
 
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Old 10-14-2016, 05:49 AM
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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?
 
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Old 11-03-2016, 06:37 PM
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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.
 
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Old 11-04-2016, 02:42 AM
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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.
 
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Old 11-29-2016, 02:27 AM
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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.
 
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Old 06-14-2019, 03:28 PM
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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

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
 
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Old 06-15-2019, 06:04 PM
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Three weeks, three years. Itís all the same

Get the radiator rebuilt. These cars shouldnít overheat.
 
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Old 06-15-2019, 06:46 PM
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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!
 

Last edited by ronbros; 06-15-2019 at 06:50 PM.
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Old 06-15-2019, 11:15 PM
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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
 

Last edited by Lady Penelope; 06-15-2019 at 11:28 PM.
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Old 06-16-2019, 09:30 AM
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a 6 cylinder engine is only half a 12 cylinder, so much easier to keep kool!!!!!!
 
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Old 06-16-2019, 02:40 PM
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Originally Posted by Jagsandmgs View Post
Three weeks, three years. Itís all the same

Get the radiator rebuilt. These cars shouldnít overheat.
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.
 
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Old Yesterday, 05:19 PM
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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
 
 
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