Recently bought an '89 XJS, very happy with my ride.
BUT... only to discover clouds of white smoke emitting from the exhaust when I've been driving for a while and the engine is nice and hot. No smoke during start-up.
A few interesting points though...
It would seem as if the smoke comes primarily from the one exhaust only - right side.
Not much smoke either whilst driving/cruising, but especially so when I pull away from a stop street or traffic lights.
Has anyone had similar problems?
Any insight or assistance would be greatly appreciated.

 

white exhaust smoke usually indicates a leaky head gasket letting coolant seep into a cylinder.

Darker smoke would indicate burning oil.

 

Hi TWR

You've got an 89 XJS so I'm taking an educated guess by thinking you have a Marelli, though if you have a Lucas Car (That has a small square

black box on the inlet manifold with a Lucas sticker on it) then this will not apply.

In basic terms the V12 engine on a Marelli Car, is like Two Six Cylinder Engines joined together.

And under the right (or should that be wrong) conditions, the 'A' Bank or the 'B' Bank side of the V12 Engine can run on its own.

As in just running on Six Cylinders on one side of the Engine only.

In the event that should happen, the side of the engine that isn't running will be Pumping Raw unburnt Fuel into the Hot Exhaust, which could

result in what is known as a 'Marelli Fire' and while I'm not suggesting that is about to happen.

It could be worth bearing in mind.

Maybe the White Exhaust Smoke could be an early indication of something going wrong in that direction.

If you've only just bought the Car, then its definitely worth checking the 'Spinner in the Dizzy' and if there's any signs of burning then replace it.

In the event your Car decides to Stop unexpectedly, then switch her off as quick as you can and grab a Fire Extinguisher just in case the worst happens.

But on the other side of the Spectrum, it could be what Brad said, so do a check on the dipstick for any signs of water in the Oil.

Or maybe its just Climatic with the prevailing Weather conditions that you have at this time of the year but no real way of knowing, without seeing the Car.

 

Whote smoke is also from:


Trans fluid, via the transducer vac line to the RH Inlet maniflod end plate.

Brake fluid, from the cars with a brake vac booster, that also takes vac from the rear of the RH Inlet manifold.

 

those would be better outcomes than a leaking head gasket.

 

For sure, time will tell.

 

Thank you for the feedback guys, appreciate.
Coolant seeping into the cylinder sounds about the most plausible cause, especially after speaking to a UK mechanic who suggested that the auxiliary air valve [situated on the water rail] might be leaking coolant into the intake manifold.
I'm really hoping I dont have a bust head gasket... will have to embark on a process of elimination.

 

Hi TWR

Much more likely to be what Grant said, as he has the kind of in-depth knowledge that mere mortals like myself can only dream about.

He's not called 'The Wizard of Oz' for nothing and so I reckon he has gone and nailed it!

This is the thing that Grant was talking about.



Vacuum inlet manifold on 'A' Bank

 

Thank you Grant, I'm talking all advice to heart as I really need this problem to go away as cheaply as possible.
Few questions:
By "Trans" I'm assuming you mean transmission fluid?
Why does the smoke only appear when engine is hot?
How do you repair the issue re transducer vac line?

 

OK,

Many reasons, few theories.

One drop of ATF (Auto Trans Fluid) will produce MUCH smoke, so when the vacuam modulator diaphragm fails, the vacuam of the engine sucks that fluid into the RH inlet manifold.

Car starts to smoke, so owner shuts it down, and there it sits.

That fluid "soaks" into the alloy casting of that manifold.

Years later, one of us types rescues the car, and DRIVES it, alloy gets hot, the fluid is leached out, and mixes with more comong up from the transmission, coz that diaphragm is still broken.

End result, SMOKE.

Same scenario with brake fluid.

I would raise the car, safety PLEASE, coz the Jag will hurt you if it falls, and reach under the RH side, and between the exhaust pipe and the trans case you will see/feel, the modulator. It has a 90deg rubber elbow attached. Pull that elbow, CAREFULLY, and look for RED fluid in the modulator spigot, and/or the elbow. If there is the slightest sign of fluid, the modulator is dead.

It is a standard GM item, nothing special at all.

As for that AAV leaking coolant into the inlet system, NEVER, EVER seen one do that. OK, nothing is impossible, its a machine, but in all my dealings with the V12, NOPE.

Same for head gasket failure, rare in the big scheme of things. However, an overheated engine will cause those gaskets to fail at some time. Dropped valve seat is usually first.

 

Hi Grant

If the Modulator dies, how does that affect gear changing?

What difference would you notice from one that is working properly?

 

OB,

When they start, not much, except the smoke.

A real switched on driver, take that as you may anyone please, may detect slight changes in the upshift, but the smoke is now over riding all normal brain processing.

Once they let go, upshift is very delayed, but not many get to that, due to the smoke.

At the age of these things now, I would simply change them as you do any service item. They are cheap, PITA to get out, but well worth it in my opinion.

 

Hi Grant

Cheers!

I'll just add that to the list of things I didn't know.

 

For the OP, here is a photo of the modulator. It is held in by one small bolt on the forward side of the unit, that fixes a small fork-shaped bracket round the unit's base.
Greg

 

That is waaaaaaay too clean for a V12, you sure thats your car, hahahaha, just kidding mate, well done.

 

An appreciator of true automobile art, thanks Grant. Taken a few years back, just after fitting my lovely Moroso TIG welded ally deep pan. Nothing like as clean today. I hope you all feel pangs of jealousy and need having seen the twin magnetic drain plugs, AND they are at the down-sloping correct end of the pan!
Greg!

 

Gotta get another XJ-S, DAMN.

 

loving the look of that Moroso transmission sump.
on the want one list.
After the new radiator, air conditioning repair and tackling the oil leak

 

Interesting discussion. But, a minor point leaves me perplexed. If he engine is ingesting
ATF or brake fluid, why does it smoke out one pipe, not both?


Whereas a coolant leak on one bank would result in smoke on one pipe.


Perhaps inducing a smoke mode and holding a white paper into the smoke would catch some residue for simple or complex analysis.


Carl
Carl

 

Hi Carl

I would think it Smokes out of one pipe because any oil from the Transducer (however microscopic) gets heated up in the 'A' Bank Inlet Manifold, as that's the side that has got the Vacuum inlet on it.