The largest and best supported Jaguar cars enthusiast site on the Internet!

Serving Enthusiasts since 1993
The Jag-lovers Web

Currently with 3,166 members

Smoke Diagnosis

Smoke Diagnosis

Jan Wikstrom

The combination of (bluish) white smoke and black plugs indicates oil burning; too much fuel produces sooty (dry) plugs and black smoke, as well as "lumpy" running and overheating.

The problem is not a head gasket; in the V12, the oil would have to pass through the water to get into the cylinder. It's either worn/broken rings or worn valve guides. There's a simple way to diagnose:

  1. Bring the engine to normal working temperature.
  2. Let it idle for five minutes or so.
  3. Stomp the throttle and hold at about 4,000 rpm. If this produces a cloud of blue/white smoke, it's more likely rings. If the smoke doesn't taper off, it's *bad* rings.
  4. Keep the revs up around 4,000 until the smoke thins, then let the throttle snap shut. If this produces a puff of blue/white smoke, it's more likely the valve guides.
  5. If both tests produce a positive result, it's rings *and* guides.

Do a compression test, anyway. This is an easy job you can do yourself; I bought a compression tester from K-Mart for, I think, $15. It's a little awkward to reach in the V12, but worth the trouble. Take all the plugs out and test one cylinder at a time on the starter; it only takes three or four compression strokes to bring the gauge up to a steady value. The desired reading depends on the compression ratio of your particular engine. The main thing to look for is consistency; if one cylinder is much lower than the others, it has a damaged ring or piston, and if all are uneven beyond, say, 10%, you have a generally worn engine.

There's more info at

Looking for or selling Jaguar Automobilia? Then use our absolutely free Jaguar Collectibles Exchange! Got some pictures you would like to share with other Jag-lovers?
Then try our automated Photo Album and post some images!


Please help support the move to the new site, and DONATE what you can.
A big Thank You to those who have donated already!



Go to our Homepage
Improve your Jag-lovers experience with the Mozilla FireFox Browser!

  View the latest posts from our Forums via an RSS Feed!

Jag-loversTM Ltd / JagWEBTM 1993 - 2024
All rights reserved. Jag-lovers is supported by JagWEBTM
For Terms of Use and General Rules see our Disclaimer
Use of the Jag-lovers logo or trademark name on sites other than Jag-lovers itself in a manner implying endorsement of commercial activities whatsoever is prohibited. Sections of this Web Site may publish members and visitors comments, opinion and photographs/images - Jag-lovers Ltd does not assume or have any responsibility or any liability for members comments or opinions, nor does it claim ownership or copyright of any material that belongs to the original poster including images. The word 'Jaguar' and the leaping cat device, whether used separately or in combination, are registered trademarks and are the property of Jaguar Cars, England. Some images may also be Jaguar Cars. Mirroring or downloading of this site or the publication of material or any extracts therefrom in original or altered form from these pages onto other sites (including reproduction by any other Jaguar enthusiast sites) without express permission violates Jag-lovers Ltd copyright and is prohibited
Go to our Homepage
Your Browser is: CCBot/2.0 (, IP Address logged as on 26th May 2024 21:58:50