THE INTERNATIONAL JAGUAR 'S'-TYPE REGISTER FORUM

lately my car has started to bellow smoke from the exhaust after about a 15mile drive!
it smokes for about a minute then stops,it doesnt overheat,the oil pressure is ok and it doesn't lose power
any ideas please?

What colour is the smoke?

White smoke could signify brake fluid being sucked up from the brake servo so you might have a small hole in the diaphragm. Check brake fluid levels.

White might also be steam. Only reason for steam is water getting into the bores. Head gasket? I would have thought this would show at start up more so than when the car is warm but check water levels. If in doubt do a radiator compression test for any leaks.

Blue smoke could mean oil in the engine either getting past the piston rings but this would be constant. Could also be oil creeping down past the valve guides although this would be again somewhat constant. Blue smoke at start up would also show valve seal wear as the oil would soak down over night in to the bores. A compression test on the cylinders might help. You are looking for around 160 plus psi on all cylinders. anything around 120 psi and you have a problem.

Black smoke would mean a rich running engine again this would be constant and show up more under hard acceleration. Have you checked the Auxiliary Enrichment device (AED choke) is switching itself off. Check the otter switch is not locked on. The otter switch is prone to seizing up when they get older. It is a Bi Metal switch which when cold creates an earth but as the engine warms up the Bi Metal switch opens and breaks the earth so the AED switches off. They can lock up either open or closed. If locked open ie no earth the choke will not work. If locked closed ie earthed all the time the choke will not switch off. You can test this when the engine is cold by disconnecting the wire on the top of the otter switch. With the ignition on but the engine cold, not running and the wire disconnected from the otter switch, tap the wire against the metal inlet manifold and you should hear the AED click open and close again when you remove it. If you hear a click repeat the process against the tab on the otter switch and see if it clicks again.
Now start the engine and get the car hot. Repeat the procedure above. The first part should be the same ie tapping the wire against the inlet manifold should operate the AED. This time though with the engine hot if you tap the wire on to the otter switch the AED should not work as there should be no earth through the otter switch. If the AED does operate then the otter switch is locked closed and your AED is staying on all the time. This might account for the extra smoke at 15 miles.

Can't think of anything else at the moment other that if the smoke is white you might have voted in a new Pope

That is about as comprehensive as you are going to get including a new Pope. The only other things that could contribute to blue smoke (burning oil) are blocked engine breathers or the most unusual of incidents where all the ring gaps on one piston align. Seen it precisely once in my long life on an Alfa that showed low compression on one cylinder.

Thankyou both very much for a very comprehensive reply!
i will let you know the outcome

You did not say what the colour of the smoke was!

sorry its black smoke and a lot of it!
the aed seems to be working ok on start up it settles at 2000 rpm and after a few minutes drops down to idle.

Likely SU carbs flooding if AED is OK. Check float levels, dirt in needle & seat, sinking floats (common) ~ check no fuel has leaked into them. Also only use genuine SU dampers of the correct type or they can stick.

Black smoke means no new Pope yet.

Not something I have come across but if the smoke is black and does not last long try starting the car and running it until warm then check the condition of the plugs. Might be one plug not clearing the chamber until it has warmed up. Is the engine running smoothly on all six?

Sorry for delay Cass not been able to explore the problem due to family problems
when i can i will update the forum
once again thanks to all for their input

Hi Cass
I've always felt the Otter switch was too long in switching off and installed a switch in the facia locker, breaking the earth circuit where I switch it off after a minute or two (It probably means the Otter switch isn't working properly, but one can always tell it's on with the sharp 'hiss' from the engine)
My car currently is struggling to rev without coughing when cold starting at the moment, which suggests some adjustment/cleaning needs to be done.
Barrie