I recently purchased this '86 XJS V12 knowing it needs work. Lots of white sweet smelling smoke barrels out of the exhaust while it's running, I assume it is a blown head gasket. Could it be something else?
The previous owner had purchased new valve cover gaskets because they leak and he said he didn't put them on because it was too involved. Any pointers for changing those? I will wait until the blown head gasket is confirmed before changing them. Can I change head gaskets myself or do I need a mechanic? I plan on having a buddy of mine help me do a compression test on all of the cylinders to figure out which head gasket to replace. This doesn't have aluminum heads does it, they don't look aluminum? This is my first Jag so any help would be much appreciated.

 

Nick, if it isn't a blown head gasket, then you are looking at either a warped head, cracked head, or cracked block. I would pray that it is a blown head gasket.

As for differentiating between a blown head gasket and anything else, you are not going to know. Everything is going to show up pretty much the same. So, your best bet is to simply dive in and see what you find. The cracked head/block is easy to see normally. A warped head is more difficult and if you have a 12" straight edge (preferably a metal ruler), you can due a pretty decent fairness check. Simply use a flashlight on the backside of the ruler and then look for any light coming through under the ruler. If you see light, you have a warped head.

As for whether you can do this yourself, I will leave that to someone that is more experienced with your year car. I would think so, but some times there are some funny things with these cars.

 

Sorry to say but yes 'Alloy Heads".

Mind you I remember reading about a transmission problem that can cause clouds of white smoke due to a faulty valve than allows trans fluid to be sucked into the engine.

Transmission Vacuum modulator valve, which controls the upshift points of the auto box. It has a diaphragm which can fail and then allow trans fluid to get sucked in, giving lots of lovely sweet white smoke.

Don't know if this might apply to your car, but certainly get it checked before opening her up. It is just a bolt on part.

Does your car overheat, use coolant?
Does it change gear OK or use trans fluid.

You really need to post this problem over in the XJS forum there are some great 'old' hands over there.

 

I never would have thought of the trans fluid being sucked into the engine, I will definitely check that first. Thanks.

 

I checked the vacuum modulator on the trans and it's fine. The oil doesn't look milky. It uses a lot of brake fluid and coolant but the brakes work fine, hmmmmm.

 

Could it be that your master cylinder is bad and you are sucking the brake fluid into the engine and that is causing your smoke issue? Just thinking. May want to try removing the line going to your master brake cylinder and try letting the engine idle and see if the smoke goes away. If it does, then that would confirm a bad master brake cylinder. Easy/cheap check.

 

I haven't had much time to spend on the car recently, but I will try that, thanks.