Valve guides, seals probable cause of oil loss

Hey there, time traveller!
This article was published 23/06/2006 (7138 days ago), so information in it may no longer be current.

QUESTION — I’ve encountered a problem with my 991/2 VW Golf, (new style), that has me baffled. The car is a 2.0 litre, manual transmission with 91,000 kms on it. We’ve had the car for less than one year and recently noticed that it is going through about one litre of regular 5W30 oil in about three weeks. The car is driven daily but not hard and I haven’t seen any blue exhaust smoke at any time. Neither is there any evident oil leak on the engine or any oil puddle on the driveway. Obviously, the oil is going somewhere except I don’t know where! Would you have any advice or knowledge if there are any known problems with this vehicle? I haven’t contacted a dealer about this yet and thought I’d write you first. Thanks for your help.

ANSWER — With no oil leaks, the engine oil must be going out the tailpipe. It can get into the engine’s combustion chamber and be burned two ways. It can leak past worn valve guides or it can be coming past piston rings. If the oil is being consumed during stop and go city driving, the valve guides or their seals are the probable culprit. The seals can be replaced without having to remove the cylinder head.

Broken, stuck or worn rings will typically cause higher oil consumption when the vehicle is driven at higher rpm such as cruising on the highway. Remove the spark plugs and look at the top of the pistons. If the edges of the piston top are cleaned of carbon, this is caused by oil coming past the rings and you will need to have the engine disassembled to determine what needs replacing.

You may not see the oil going out the tailpipe but it is undoubtedly there. Sometimes, another driver following you will be able to see or smell it easier than you can.

QUESTION — I noticed when I pulled my 1985 Firebird T5 Borg Warner transmission apart to install a new second gear that the angled roller bearings and their races on the input shaft and output shaft have wear lines on them. Nothing that I can feel with my fingernail, but the colour changes on a couple of them when you rotate it in the light. These only have about 3,000 to 5,000 kilometres on them since the rebuild last summer. The needle bearings that go around the end of the output shaft where it fits in the input shaft seem fine but then they are not under the same pressure as the input/output bearings since there is preload on those. I think I had .002" preload on them, so is this worn look normal to a degree?

It was grinding a bit when second failed again and you can see a small amount of material on the magnet so maybe something got in there but then wouldn’t all the bearings be worn? In the light, the fluid possibly had fine metal particulate in it too, but then I have seen that look every time I have drained that transmission. I am wondering if I should now change those bearings again? Driving it home from storage, there didn’t seem to be any more noticeable noise, but in my opinion they may look a tad worse than the original ones with 190K on them (although they did not seem to be too bad).

ANSWER — Normal wear on bearings will cause a frosty grey appearance on the races. This should be uniform with no lines or small pitted marks. Your bearings have very little mileage on them so they would normally be fine. The small lines are probably caused by excessive pressure on the bearings. Normal preload for the mainshaft bearings on this transmission are zero to +.001 inch preload. You had slightly more than that. (The countershaft bearings are zero to +.004 clearance.)

The fine metal particles are almost certainly coming from wear on the gears as they mesh and shift. This would be considered normal, especially on new gears. Since there was no noise coming from the transmission before you disassembled it, the bearings are most likely fine. As you are doing the work yourself, labour cost is low. If you had to pay a professional to do this, I would likely replace the bearings, because the cost of replacing the bearings is much lower than having to pay for overhauling it again later. If it was my transmission, I would likely reuse the bearings.

Jim Kerr is an experienced mechanic, instructor of automotive technology and member of the Automobile Journalists’ Association of Canada. You can e-mail questions to Jim at the address below.

kerr.jim@sasktel.net