Hello all, new poster looking for some advice regarding a potential purchase.
A particular XJS has caught my eye, partly because it has a '93 (i think) 6.0l in a '77 body & a trans conversion to a 5 speed getrag from a 6 cyl model. This engine caught my eye as it is both the larger 6.0l and I believe it has the one piece rear main seal (or did that come in in '94?)
I had the vehicle inspected and the tester noted that: “the vehicle blew some blue smoke from the valve cover/breather cap on start up, stopped when warm. However when the warm engine was revved up it blew more smoke momentarily on throttle lift” & noted that motor checked okay on a compression test with no abnormal values.
From my research this could be a load of different issues, my initial thought was a bad ring (although the good comp test suggests otherwise?), or blocked/malfunctioning PVC system, although I read that it could be a valve seal as the vacuum created on lift sucks oil past the valve seals.
However I would have thought that these faults would cause smoke form the exhaust too. Does anyone have any suggestions as to what could be the cause, and the best steps to diagnose the issue? I would hate to overspend on a car with issues, but would also hate to pass up on a good opportunity as a 6.0l conversion is something I would want to look into.
With worn valve stem seals you would have blue smoke on throttle lift, but it would come of the exhaust, as the vacuum in the cylinders sucks the oil in the cylinders and out the exhaust.
With worn rings you would have blow-by and blue smoke out of the breather, but more on throttle push than on throttle lift. Besides, you said compression test was OK.
It’s somewhat bizarre that you have smoke out of the breather on throttle lift, as at that moment everything is under vacuum… How did you determine this ? Did you have the PVC Valve out ?
With a bad PVC Valve at throttle lift the crankcase would see full vacuum and all the vapors will be sucked into the intake manifold, so maybe this is the case ?
Yes it does seem strange to me. Trouble is the vehcile is located interstate so I was not present for the inspection. The more I re rrad the report and research online the more I dont understabd how it can smoke from the breather on lift. As you said it should be in vacuum…
Im going to have to get back in touch with the mechanic that did the inspection and ask him to clarify exactly when it blew the smoke. In the meantime my understanding is that smoke from the breather is most likely a problem with the rings or the pcv system, right?
Blue smoke (oil vapors) are a combined result of hot oil and blow-by gases from the rings.
Even with a brand new engine there is a small amount of blow-by, witch increases as the piston rings wear.
The PCV valve just regulates the amount of vacuum the crankcase sees, so the engine doesn’t start sucking oil instead of just vapors.
On the other hand if the PCV valve is blocked or stuck closed then you would start having pressure instead of vacuum inside the crankcase and the rear main seal, especially but not only, will start leaking.
Aristides
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
5
Which valve cover/breather cap are we talking about?
The report doesn’t say. It just says valve cover/breather cap. I’m starting to wonder if the report is worth the paper its writen on. I might just have to get it checked again for more detail or fly over there to look at it myself.
This is a very strange combo. The body of the 1993-96 cars had most components galvanized.
In addition, most of the electrical connectors were Ford-ified. The 6.0L v12 had factory cold-air intake system, which was possible because of the redesign of the hood and probably difficult to transplant.
To me it would have been more sensible to put a moded flat-head engine from the pre-HE Jag in a face-lift body and do the manual conversion on it (the bolt-pattern on the 6.0L is not the same as the 5.3L and probably much more fabrication was required).
In any case, sounds like an interesting car. Where are you located? Are you planning on doing your own wrenching?
I’m located in Adelaide, South Australia. The car is in Melbourne.
I do plan on doing some of my own wrenching, although there is also a Jag specialist not far from me for anything I can’t manage.
The car is an interesting collection, which is why I’m interested, although now I’m starting to wonder if it is a factory 6.0l or not. I do have a load of pictures of the engine bay, so I may be able to work it out from that.
I got back in touch with the mechanic about his test results. The story now is the fumes came from a breather filter on the front left hand side of the engine (not sure if that is left from the drivers seat or not…) and it was white after 15 minutes of running.
His original report stared: “Slight blue smoke evident when hot and idling for a while after a quick rev”
He also stated he did not perform nay compression testing, and hasn’t done so for years despite his report containing the exact words: “Compression Result: Balance tested ok”
I asked what this line referred to but haven’t got any further answer yet.
Basically I have no useful information at this point.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
10
Looking to hear from other owners of 6.0’s. What breather are we talking about? The earlier 5.3’s had a PCV system at the front left, but it was connected into the LH air intake and the intake manifolds, there’s no place for fumes to come out.