Having recently bought a vintage vw...a ‘58 Karmann Ghia...I’m in the process of checking out the condition of the Flat 4 engine.

Having carried out a compression test, cylinders 1, 2 and 3 all come out well with readings of 125-130psi. However cylinder #4 reads 100psi which is outside the usual accepted 10% tolerance. This, it seems likely is due to sticky rings.

The question is; what would be the best way to tackle this. A friend has suggested removing the spark plug and add a couple of table spoonful of Marvel to #4 and leaving it for a couple of days. The only trouble with this, as I see it is that the VW engine is a horizontal engine and just the bottom of the rings would be immersed leaving the top of the cylinder dry.

Sounds like the enine is operable, so drain 1-quart of oil out of the crankcase and replace it with 1-quart of Marvel Mystery Oil.  Run the engine for 20 - 30 minutes to circulate the oil and get it up to temperature.  Do this for a couple of days, and you should see improvement in compression as the sticky ring is starting to be cleaned.

Thanks Rich,

I’ll do that and report back.

John.

I ran the engine for a week with a Quart of Marvel in the crankcase. In an aircooled VW incidentally a quart is too much for normal use as the crankcase capacity is only 5 pints...a pint is more like it.

After a week I pulled the plugs and did another compression test but sadly the readings were the same...still down on cylinder #4. With the engine out and the heads off it’s now apparent sticky rings weren’t the culprit but worn bores and valve guides. No amount of MMO would have made a difference in this case but I think it’s still worth trying...it might well help others avoid having to tear down the engine.

Sorry about recommending the quart of Marvel Mystery Oil.  Our normal recommendation is to repalce 10 t0 25 % of your crankcase oil with Marvel Mystery Oil.  With a 5-pint crankcase, you are correct that 1-pint of Marvel should be used (20%).  I was just assuming a 4 or 5 quart system.

Not to worry Rich. I realised after I’d poured the MMO in but as I was going to be driving the car for 30 minutes a day for 5 days at the most I thought it wouldn’t do any harm.

I kept a watch on the oil pressure light, (no luxuries such as a pressure gauge on a vintage VW) and it only came on at idle when fully warmed up.

I don’t know if it’s possible to use a leak down tester on your engine but I used it to verify the rings were leaking on my #3 Cyl Toyota 22re Engine. You just hook it up and listen to the crank case for escaping air for a ring problem. I put a couple tablespoons of MMO in it through the spark plug hole and have been letting it soak. I hope it helps.