I am thinking of acquiring a 98 Jetta - it blows whitish smoke especially when accelerating ( but at idle it is may just barely be noticeable ) - smoke has a slight grayish or blueish tinge to it but most definitely white and I have been told that white smoke means unburned fuel -correct? However this AHU motor runs smoothly and when I separately crack each B-nut at the injector RPM drops and runs comparatively same as others did -
Is there any way to distinguish between whether it might be the rings or turbo that is allowing oil to bypass?
Everyone says do a compression check - well I have and in cylinders 1-3 I got a compression reading of 450 - in cylinder 4 I got a reading of 550 - so that seems odd - 450 should be good enough to run well and 550 even better but the 100 difference is not understood to be a good thing - now PO did do an in house hone and re-ring or engine bay ring job - I don't think hitting one of the oil squirters with hone would be cause for white smoke but would it be possible that they did not split or clock the rings ends correctly like at 120 degrees from each other? Has anyone ever had a diesel motor bypass oil through rings ends after a ring job without clocking them 120 degrees apart ( resulting in white smoke )?
This AHU motor is timed correctly (blue line) and IQ setting at 4.0 with VAG-COM
I did notice a bit of blow-by at the oil filler cap but nothing extra great and blow-by seen did seem to be a bit bluish there or maybe gray white - I could not tell - I should have had the owner step on accelerator while I watched blow at oil filler cap to see if it blew whitish smoke more or not - if so then I would assume that the problem would be with rings and not necessarily turbo - is the a correct assumption?
Of course it could be both rings and turbo but I am just looking for a way to distinguish between the two.
I also thought of disconnecting and capping the turbo oil line just for a few seconds while motor started and then rev motor to check for white smoke - thinking this might not cause harm just for a few seconds while it ran and accelerated. Everyone is probably going to say "NO" don't do it but if done right while engine is cold it may not be harmful - is this correct - has anyone successfully tried this or anything else before?
Any air entering the pump?
Do you experience a drop in coolant level whereas there are no obvious leaks?
When you did the compression check:
1) Was the motor hot?
2) Did you have a charger on the battery?
3) Were all of the glow plugs out?
4) Was the 550 hole the first one you did?
Any idea how many miles on the "in chassis" ring job?
Were they chrome rings, if the seller knows?
100 psi difference is too much, but faulty technique on a compression test can skew the readings. That being said, it seems likely that the extra 100psi is coming from extra carbon in the CC from the oil the rings are passing.
But maybe it is just that the rings are not fully seated, yet. It can take up to 10,000 miles to seat rings in a bore or bores that are not absolutely perfect.
I would beat the guy down savagely because of the obvious oil smoke (whether it real is oil or not. You must buy it on a worst case scenario) and the uneven compression. The stealership will tell you the car needs a motor on just the compression readings. If you can buy it cheap enough, take it home and run a couple of tanks of fuel through it and see what the mileage is and how much oil it uses. If oil consumption is reasonable and mileage is OK drive it for 6 month and redo the compression check.
FWIW, if there is any reason to suspect a failing turbo, check the function of the flapper valve at the intake manifold. If it does not close when the key is shut off and you lose a turbo you may be in for a VERY interesting day. Youtube "diesel runaway". Not so bad if it is a stick, but I had one on an automagic once.
Auto mkiii. Never happened.