Oil burning 4.2

Hi all,
18 months ago I bought a non-runner project that I’ve just got going . It’s a reasonably well looked after 80,000miler ( genuine mileage it seems) Hasn’t been driven ( maybe even started) since 2013, so drained fuel etc and got running. Has clean oil, clean anti freeze coolant, runs good oil pressure and doesn’t overheat even idling for long periods. BUT, blows lots of blue, more white really, smoke when revved. Ok at idle. Also was lots of oil burning off the pipes from the region of the passenger, which eventually burned off. There are no drips on the floor unbelievably, so don’t think the external pipe burning is engine oil, maybe overfilled trans. Trans works ok BTW. There is some blowby from the breather. I vaguely recall that sometimes oil burning via the exhaust can be caused by a failure of a diaphragm in the transmission somewhere. Or could this be stuck rings from sitting too long, and may come good with a few miles? Or just wishful thinking? PO had spent some coin on this machine so I think it has been well maintained in the past, and 80K seems a little low to need rings. Any suggestions, thoughts welcomed, please.

Could well be stuck rings, have you preformed a compression test? Possibly wouldn’t hurt to take the plugs out and drop some ATF and Acetone mix into the bores and leave for a day or two, turn the engine over with the plugs out to expel any excess before trying to start again.

Yes. If the car has a BW12 it also has a vacuum signal coming up from the unit on the back RH of the trans. It’s known that if the diaphragm fails fluid can make its way into the induction system and burn white. Paul.

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Thanks Gents,
Gives me cause for optimism. Might try both methods and see what happens; would rather not strip the engine unnecessarily. Have already overspent on what I planned, ( who hasn’t ?) If engine has to come out , might end up going back in with a 4 speed behind it. Probably be the only 4 speed 4.2 Sovereign in the world.

Kevin, perhaps you could block the rubber pipe that connects to the modulator at the back of the trans and run the car? It just pulls off the back of the modulator. One crude way to isolate the trans (and any problems) from the engine. Paul.

Could it be valve stem seals? I have replaced my stem seals twice in 76,000miles. First time was at 65,000 and 22years old. Oil consumption was very high, but no idea whether it blew smoke. Next time was at 75,000miles and after 19 years in storage. Seals were cracking up so i replaced them while the engine was out.

I doubt it.
Valve stem seals would leak badly only on overrun (high vacuum). Easy to check.

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Yes, design tolerances are tight even without seals as I understand it. Indeed the older cars didn’t have them. Paul.

Thanks for the input Guys. I’ve disconnected the trans vacuum line, no improvement, sadly. Plugs are very sooty and carbs not well tuned, so need to address that first, I think. Smoke is white, and more like condensation than what I think is oil burning, like when a car is first started on a cool morning, except it doesn’t go away when the car is warm. Cooling system doesn’t build up pressure or overheat, so don’t think it’s a head gasket issue. Maybe " Italian Tune-up " is required! Doubt it’s valve seals as does it when revved

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Which nominally means the system is leaking, Kevin - which should be detectable by coolant loss…

Like Robin; I strongly advise a compression test. It may reveal a failed head gasket, but more importantly - it will reveal a ring/wear problem and overall state of the engine. It will focus your work in the right direction…

Frank
xj6 85 Sov Europe (UK/NZ)

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Thanks Frank,
What I meant was it isn’t building up excessive coolant pressure as it would if exhaust gases were getting into the cooling system. Doesn’t seem to be losing coolant either. Blown gasket would lead to bubbles in the radiator or header tank , I believe.
Plugs very sooty and carburation way out, so need to remedy that first.

Besides the compression test I would run it hard for at least twenty miles after a few nights of atf in the bores. If you only idle it the plugs might just not burn off the carbon, keep that in mind while going over the carbs.
It could be valve stems but in my case after the first time acceleration that oil is gone. It could be oil in the manifold that is still burning off, but since you have visible blowby at the breather the rings are involved.

Brake fluid from failed servo sucking into inlet manifold?

Just a thought.

Frankie

One clue:

Drive the car up to at least 50 mph. close the throttle. Blue smoke from the pipes? High vacumn sucks oil past the rings or through the valve seals… Wet and dry compression tests speak volumns.

A couple of decades ago, we had a red 71 Mustang. Nice sorta car. Badly abused Oily engine, but started and ran very nicely… Good set of pipes sounded nice…

Carl

Kevin,

as David wrote it’s always easier to assess an engine that has been used in normal operation. If the car is roadworthy and driveable, then drive it by all means. I’d be a bit more concerned than David when it comes to pushing an engine that is not running well in the first place and has been sitting for 7 ys. Instead of tempting fate with an Italian tune-up I’d keep the ball low, get it on operation temp, check for overheating, leaks, re-analyse the smells and fumes, maybe have someone drive behind to really check the exhaust fume colour.

White smoke (i.e. steam) should not occur on a warmed-up engine. Usually it is caused by condensation in the exhaust during warm-up. So maybe you still have a few litres of water in your exhausts … Apart from that white smoke is either a blown head gasket or ATF or brake fluid. Your symptoms don’t exclude a head gasket issue. Check oil filler lid for “mayonnaise”, exhaust smell in coolant and bubbling while engine is running.

Sooty plugs (overly rich mixture) would rather suggest black exhaust fumes than white. As others have written - a compression test on our XK engines is so easy that it is really the thing to start with. Then check ignition, then tune carbs, then get back to square one:-)

Good luck

Jochen

75 XJ6L 4.2 auto (UK spec)

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Fluffy soot is rich mixture, Kevin - ‘hard’ soot is burnt oil…from whatever source.

Do a compression test; it’s straight forward on a xk - and tells the truth. It confirms or rejects engine itself as a source of problems. You cannot adjust away an engine problem…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)
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Good morning Gentlemen,
Thanks for all the input, much appreciated. Here is the current situation,
The smoke does not look or smell like engine oil burning, so don’t think it’s oil rings.
There is no oil in the coolant or vice versa, nor any other indication of a blown head gasket
The smoke is there from start up, billows under load or when revved, but not on the overrun, so not likely valve guides or seals,
Discounted transmission servo
When purchased, car came with spare p\s pump, brake servo and carbs, plus various unused engine gaskets. There was indeed a steering problem, although it ultimately was not with the pump. There are certainly issues with the carbs. Did the PO diagnose a problem with the brake booster, hence the spare?
The engine bay is remarkably clean and the engine exterior spotless, unusual for a 50 year old XK, suggesting to me that ( hopefully) the engine has recently undergone some work.
So the plan du jour, is to build a decent pair of carbs and dial them in, then do a compression test and investigate the brake booster angle. With any luck, the blow by, which is not excessive, may be caused by stuck compression rings from sitting years without use. Hopefully they can be freed without stripping the engine.
Will keep you posted, and thanks again for all the help.

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Can’t fault your plan, Kevin…

When you do the compression test; do it first ‘dry’ - then ‘wet’; adding a spoonful of engine oil to the bores. Two factors; the first being even compression between cylinders - the important bit; within 15% is ‘acceptable’. The second is actual compression pressure; which varies with compression ratio - and of course degree of wear. As evenness is a factor; each cylinder should be tested using exactly the same procedure - and do note each reading…

The ‘wet’ test reveals bore and ring wear/anomalies; the compression will increase will the oil added, sealing blowby - the greater the increase the greater the blowby…

Frank
xj6 85 Sov Europe (UK/NZ)
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