V12 Jaguar

I have a 1994 Jaguar XJ12 with 74k on it. Anyways, yesterday I was driving on the highway and got stuck in a traffic jam with a solid hour of stop and go with driving at walking speed. I noticed the oil pressure started to drop down low, and the engine temp was going up high. I was able to get going at normal speeds soon after and everything returned to normal, but what do you guys think is wrong?

The first thing I would want to know is if the oil and coolant levels are ok and what weight of oil is being run in the car.

I checked the coolant and oil levels and they were fine. I just bought the car a few weeks ago and I had a mechanic inspect it, and he said it all checked out. I’m not sure what weight of oil is in it though.

You might want to change the oil now to make sure it has the correct blend. When was the oil changed last? If you don’t know, change it now. That’s $50 of cheap insurance.

Oil pressure at idle always drops. Your guage likely has no numbers on the dial face. So you can see the needle is lower, but what does it mean? As long as the pressure registers about 1/4 of the way up off “0” you are OK. Perhaps as the car got warmer the oil thinned out a bit and the pressure seemed a tad lower.

If you are concerned you can have a mechanic get real oil pressure readings with an accurate guage. Perhaps the oil in the crankcase is too thin. If you live in a hot climate you may need an oil change and go with a thicker weight oil.

Oil thins as it heats, so if the engine was getting hot, you were getting lower oil pressure at near-idle conditions. Have you driven at, say, 70 mph for an hour? Does it handle that fine? If so, then it was the combination of low speed and warm temps. If the cooling system continues to show signs of problems, you’ll need the mechanic to check out all the things on an XJ. You might want to join a Jag forum, the maintenance on these is extensive and specific.

Sounds like you might have a bad thermostat. I have had 6 12 cylinder jags over teh years and when they are set up correctly the temp barely moves when sitting in traffic on a hot day. I remember one 5.3 which I spent a fortune on trying to sort out the cooling system before determining the problem was a PO put a non Jag temp sender in it! At any rate, have your mechanic check the thermostats are working, (I think the 6.0 litre has 2 like teh 5.3), If it is getting hot then the oil pressure will drop. BTW, These cars will go 200k+ miles with a little bit of care. They are actualy not that tempramental and miles ahead of the 5.3 engine… After all, Aston Martin still uses the 6.0litre in their top of the range cars.

Good Luck,

  • D

I know nothing of this particular engine, but in general, when an engine gets warm while sitting still, but returns to normal when it starts rolling again, I look for reasons why the car is not pulling sufficient air through the radiator. - Bad fan clutch, bad electric fan, bad thermostat on electric fan, possibly blockage in the radiator air fins (plant debris, bugs, pet hair, etc.), possibly poor flow pattern inside radiator due to silicate or mineral deposits.

As Douglas M stated, you might have a bad stat - note that the V12 has 2 stats, 1 on each side of the engine.

The V12 will run a little hot under those driving conditions, it’s very tight under the hood without terrific cooling air capacity when moving slowly.

1 question though : Did the electric cooling fan come on ? The V12 has a standard viscous coupled fan but also has an auxiliary electric cooling fan to cope with these conditions. If that fan isn’t working then things will start to heat up pretty quickly. If you’re not sure get it checked, that all alloy V12 is the last engine in the world you would want to overheat.