Checking the Compression on a VW Jetta Diesel Engine

I think 1/2 qt per 5k is normal

To check your compression, you will need a compression guage.

A compression guage screws in place of the spark plug on a gasoline engine (glow plug on yours). You simply "bump" the engine with the starter a few cycles (make sure you disconnect all spark/glow plug wires prior to this, you dont want the engine to actually start) and the guage records the max cylinder pressure obtained. Repeat for all cylinders and compare these values to manufacturers specs. If you find one or more cylinders are below spec, pour a little oil into the cylinder through the plug hole, wait a minute or two, then try again. If the compression goes up, its probably bad piston rings or badly worn cylinder walls, as the oil provides a temporary seal between these two surfaces. do not be too alarmed if you see some small deviation between each cylinder, not every one will be at exact factory spec. You're just looking to see if any of them are way off. Do not use a compression tester for a gasoline engine on a diesel, as the guage cannot handle the higher compression.

If you're in the US, try going to local auto parts stores like Autozone, they often have compression testers (and many other tools) you can rent for free (just pay a security deposit you get back when you return the tool).Otherwise, do a google search for "diesel compression tester" and you can find ones to buy online.

The racing you hear is due to the engine burning the carbon cleaner, which is usualy a volitile solvent (sometimes its just kerosene). Although, I wouldnt worry too much about 1/2 qt per 5k mi, you should probably be changing your oil that frequently anyway.

Make sure that the compression gauge is designed for diesels, not just for petrol engines.

I think what happened is the following:-

1) The mechanic had you on, there should be NO carbon in an intake manifold. Even an exhaust manifold seldom needs carbon removal.... Also, the mileage is too low to do anything, these engines run for a LONG time without anything other than good oil and original oil filter. Maybe when its got another 200,000 miles on it you might need some work done, not before. I seriously doubt that this was a VW dealership, if it was, you should report them to VW asap.

You were 100% conned. I have been driving VW Diesels for over 10 years, sometimes with very high mileage, I have never been offered such a service, if I had I would have refused it and gone somewhere else.....

2) The cleaner has removed all the nice carbon seals from the piston tops, they will take another 10,000 miles to reform and then your oil consumption will fall some more.

3) I do not think the engine is damaged, but with such an idiot mechanic one cannot be certain. If it drives otherwise OK, you are probably fine.

4) P.W.B.S.W.A.F.S. = Problem was between the steering wheel and the front seat!!

The advise about doing a compression check are right on but I don't think you need to do one. Your oil consumption is about right and the person that stated waiting for few miles to replace some of the carbon on top of the pistons has some merit.

If any damage was actually done, broken ring or cracked piston, you would have a lot of oil usage and additional noise from the engine. At 85K you have another 200K or more miles left in it.

Don't do any more carbon cleaning and if you really think you need to then use some just plain water in a spray bottle squirted into the intake as it is running at about 1,000 RPM. The steam generated scours out any problem carbon and can't cause the engine to race. I am unaware of any acceptable carbon cleaners for diesels. Those for gasoline engines are not safe in a diesel.

Good post, I have given you a GA point.