Dear Forum,
I have been posting on this forum for some time regarding the occasional huge plumes of grey smoke pouring from my exhausts combined with a strong smell of burning rubber. One of the steps I have taken is to fit an Oil Catch Can between my PCV Valve and my inlet manifold. Yesterday I drove 140 kilometers (87.5 miles) and it collected 200 ml's (a little under 1/2 a pint) of oil!!

Apart from this, my 100,000 mile engine seems okay and to have plenty of power? Surely if this is being caused by blow-by this level of blow-by wear would result in poor performance?
Any ideas, please?
Regards,
Ray

 

That is a heck of a lot of oil Esray.

Have you done a compression test?

That would possibly alleviate piston ring/bore wear.

If no ring/bore wear then you possibly have very high pressure in the sump for some reason.

I should add that if a cylinder has low compression you need to inject some oil into it and if there is still low compression it is something to do with the valves and not the rings.

 

Thanks John - That'll be my next move.
Puzzling, though - there does not seem to be any power issues? I would have thought that piston ring blow-by sufficient to cause this amount of oil loss would also result in power loss? However, I do not know of any other causes of excessive blow-by other than valve seals and piston rings/bore wear? I will be interested to take a good look at the oil separator under that Cam Cover when I remove it (AGAIN)!
Regards,
Ray

 

I agree very puzzling.

 

My next big job (will have to be deferred until I sort this out one way or another) was to be replacing the Timing Chain Guides, because I think worn guides are the reason for my very slight engine 'tremble' at idle and for a 'whining' noise coming from the timing cover. Every now and then, I think my timing chain slips in or out of the 'groove' it has created for itself, and in so doing, alters the timing fractionally?

Is it possible that the effect this (possible) timing issue has on valves opening and closing (perhaps fractionally out of sync with the Camshaft Sensor) could be contributing to this excessive crankcase pressure?

 

I am curious to see what you come up with.

Our XJ8 with under 90,000 miles has been spitting white clouds of smoke when you step on it to pass or on freeway on ramps. I cannot seem to get it to exhibit this by stepping on it and it downshifting once. But when I bury the accelerator pedal and it kicks down two gears, causing the engine to rev higher than normal, I get a huge screen of white smoke pouring out behind me. I thought my head gasket was on the way out, but it has been doing it for a while. The car runs very well, in fact better than my higher mileage XK8. No rough idle or engine stumbling. I have not performed a compression test, but did just perform a coolant pressure test after repairing the thermostat housing. Attached is a picture of the excess oil I found in the intake manifold when changing the thermostat housing. Those reflections in the bottom are, yes, pools of oil. The car does eat slightly more oil than the XK8...between each oil change (ranging from 5-9,000 miles, I change once per year with Mobil 1 5/30 due to not putting on enough miles) it might go through .5-1 of a quart. Certainly not what yours is going through though.

Our other XJ8 has around 55,000 miles and while on the freeway on ramp the other day I was surprised to see what I thought should be more smoking than normal under heavier acceleration. After seeing the lower mileage car display something similar, I am becoming convinced this is a Jaguar 4.2 anomaly.

I will mention both the XJ8’s are driven primarily in town and very easy. The XK8, which doesn’t smoke, is driven in town but does get more of an engine workout. I replaced one XJ8 PCV valve and cleaned the other two recently. Two of the higher mileage PCV’s were fairly oily inside. I suspect a faulty valve is what is causing much of the exhaust smoke and intake manifold oil in mine.

 

For those who are seeking to add an oil catch can to their engine, please be aware that small diameter hoses (less than 1/2" id) can actually cause more oil to be drawn into the can and engine than with large diameter hoses.

 

I would think about replacing the PCV. I was getting blue smoke clouds on hard acceleration and start up and a new PCV fixed that. Three years and about 30-40k miles later, the same thing was happening again. I suspect the PCV becomes a wear-and-tear maintenance item the older your engine gets.

 

These days, replacing the PCV valve is a standard part of a tuneup, along with plugs, filters, belts, etc.

Cheers,

Don

 

XJ8JR & Don B, thank you for your responses. I have already replaced my PCV Valve. Any thoughts on my suggestion that a slack timing chain may be affecting my timing sufficiently to be a cause of excessive blow-by, please?

 

Blowby is the result of worn piston rings. Nothing at all to do with timing. The only determental effect of a worn timing chain is either poor performance or the valves crashing into the pistons (on an interference engine).

 

Please, does anyone have a 'ball-park' figure for what sort of compression I should expect to see from a 13 year-old Jaguar with 100,000 miles on the clock? What would be acceptable and what would indicate a rebuild required? Somewhere between what and what?

 

This will be a rough guide Esrayand is for testing at roughly idle. At higher revs the SC kicks in and will produce a higher psi:

If the atmospheric pressure is 14.7 psi and the compression ratio is 9:1, the equation to solve for the psi is (14.7*9)/1. Therefore, the answer is 132.3 psi. People use this method of calculation to determine the pounds per square a piston produces.

The atmospheric pressure can vary, but the standard atmosphere produces 14.696 psi at sea level. For more exact calculations, the altitude should be considered.

The compression ratio on my car is 9.1 so I plugged that figure into the above calculation and it gives a psi reading of 132.3psi.

Lots of other considerations but the above will give you a ballpark to be going on with.

I posted in another post that our cars are quite inefficient with a compression ratio of 9.1! My Range Rover Sport NA has a compression ratio of 11.1.

There is now a turbo charged engine with variable compression to counteract this inefficiency for charged cars at lower revs.
It works by extending the piston rod at lower revs.

 

Proper testing has to be done both wet and dry for compression. (and the difference between them) Cylinder leakage tests must also be performed at TDC for each cylinder. I am suggesting however, that the AJ8 doesn't normally suffer issues with excessive blow-by, and the normal operation of this engine, as with all engines, does have some oil usage. Moral of the story is, it is normal for some oil mist to pass into the intake under normal conditions.

 

Okay, the compression tests are in: 5 cylinders have 148 psi and three have 135 psi.
The mechanic I asked to conduct the test is saying that this is okay?

Any comments, please?

 

Everything I have read about compression tests would confirm those readings are all within accepted tolerances.

Did you do a "wet" compression test as well? With some oil injected into the cylinders.

Not absolutely necessary but interesting comparison.

 

Thank you John.
I have asked if a wet test was done. Communication is a little tricky, the mechanic is Syrian and does not have much English and I must admit, my Syrian is a little rusty; in fact, corroded beyond repair would appear to be a better description!

 

The issue obviously is that their is still no explanation for all of the oil you are getting thru the PCV valve.

 

Absolutely!
I am having the timing chain guides/tensioners looked at. There is a tiny miss; a 'tremble' at idle and occasional chain noise. My inexpensive Syrian mechanic (ex Jaguar Dealer employee here in Dubai) believes that the Timing Chain Tensioner Blades have a groove worn into them which allows the timing to fractionally slip from time to time, as it goes in and out of this groove. I have asked on this forum if this could cause excessive crankcase pressure through (say) a valve temporarily being miss-timed with regard to the Camshaft Sensor and (perhaps) allowing compression to escape into the crankcase, but was informed that there can be no link between timing and excessive Crankcase pressure.
I will keep you posted.

 

Dear Forum,
Just to end this post the problem was a 'Drum'? in the gearbox that was cracked nearly in two. When the trans got hot, the crack expanded, leaked oil and locked the third (I think) gear up. This intermittent 'seize-up was also what caused the billowing grey/white smoke out of my exhaust! I must admit, I still do not understand why a fault in the gearbox should cause smoke from the exhaust - But since the problem has gone away, perhaps I shouldn't care?