340,000 kilometers is about 211,000 miles, and that is a significant amount of miles if you are still running your original valve guides and / or valve seals.

I think your mechanic is right in that oil might be leaking down your valve seals and you are simply burning oil.

If the usage is more than 1 quart of oil / 1,000 miles ( you do the quart / mile to metric conversion), then it's time to replace the valve guides and / or valve seals. Valve stem seals and valve stem guides will wear - it's just a matter of when they are worn out and how the wear takes place.

The question is this: how does your mechanic know whether the problem is worn valve guides or valve seals?

The primary wear areas are between the valve stem and the valve guide, and between the valve and the valve seat.

Every valve moves up and down: once for every two revolutions of the crankshaft. The valve stem is lubricated by a light film of oil that gets by the seal at its top.

Depending on your driving technique, it is not unusual to have to replace valve guides as early as 75,000 miles to as much as 150,000 miles. If you use large throttle openings at low rpm's, the valve gets hammered into the seat, which is what causes premature wear.

Your mechanic should first do a compression test and a cylinder leakage test, to make sure whether or not your problem is due to cylinder bore wear.

The cylinder leakage test requires pumping air into the cylinder with the piston at top dead center, and then measure how much air leaks out. Your mechanic should also remove one valve spring and valve stem seal, and wiggle the valve in the guide to see how much free play (wear) exists. An experienced mechanic can tell whether or not the guides are worn.

If the valve stem guide clearance is within specs, the engine may need only valve stem seals. In this case, you are in luck, because the head does not need to be removed to replace the valve stem seals. The head does need to be removed to replace valve stem guides.

Putting in new seals may keep your engine another 75,000 to 100,000 miles, depending on how you have taken care of the engine. This is where frequent oil changes pays off. The more you invest in oil changes, the less you'll pay for engine repairs.

If your guides are worn, then the head comes off, and it is probably a good time to look at all the other parts of the head: timing chain, timing chain sprockets, timing chain rails, timing chain tensioner, cam lobe wear and bearing surfaces, rockers, followers, lifters, valves, valve springs, etc.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".