pressure testing crankcase
 

Recently, I took my 2002 e320 into the dealer for some radio work. When I picked up the car they told me that I had a small rear seal leak. I have not had any problem with oil usage. I do have a question about the advisability of their technique of pressure testing the crankcase. It would seam this would be hard on the seals as I do not believe that the crankcase is under pressure under normal operations. Does anyone have any experience with this testing technique?

Ofcourse it's hard on the seals! It is after all supposed to point out weak links, if the seals are otherwise ok than there is no harm.

Depending on how much blow by you have and the efficacy of your crankcase ventilation system, the crankcase can be under considerable pressure. I used to have an old Mercury that had so much blow by that it would actually push oil out the dipstick tube.

I do question the wisdom of pressure testing, since this could lead to failure of a marginal seal that could have continued adequately for months or years of continued service. If it isn't leaking under the use the operator puts it to, then it isn't broke, and doesn't need fixing.