Jimbeau

I am going to replace the valve cover gasket on a 3.2 engine with HFM injectors. When I got the car a few months ago, the previous owner mentioned he had just had the valve cover gasket replaced, but recently it has started running oil out the right back corner (BTW, it is the valve cover and not the head gasket. From underneath, I can clearly see it flow down from between the head and valve cover interface). Apparently, the previous gasket replacement job was to simply use RTV sealant on the old gasket, and this has now failed. Regarding replacement of the valve-cover gasket (along with thrust washer and spark-plug tubes), should an RTV type sealant be used on the new gasket? The service manual does not indicate that a sealant is applied before assembly (just that oil is not applied), but if anyone has had experiences with installing the gasket, I would appreciate knowing the best approach. Thank you kindly...

lkchris

Very little use of sealant in German cars.

Especially if gasket is plastic rather than cork.

Kestas

I believe the engine has two half-round pieces at the back of the valve cover. Get yourself a mirror and inspect that area. You may be getting a leak from there.

But fixing a leak by adding RTV to the old gasket.... yecch! I suspect you'll need a new valve cover gasket.

Jimbeau

Sorry for the confusion. I already have a new gasket and it is plastic. The assembly also has the half-round pieces in the back where the leak is occuring. Having said that, should the new gasket assembly not use any RTV, or just a small film? Thanks

oliverb

When the valve cover gasket was replaced on my 103 (different but similar) by the P.O. (done at a dealership), RTV was used only in the area you describe. Over a few years a leak developed there as well as along the right side. When I replaced the gasket a couple of years ago, I thoroughly cleaned the area but did not use RTV. So far, after about 3 years, it is not leaking. I believe some mechanics use the RTV in this area because it is known to be a problem area for leaks as the gasket shrinks and hardens with age. By the way, the leak along the right side and rear was diagnosed as a head gasket failure - no oil in coolant, no pressure tests, etc., just seeing oil running down the engine. Very close and careful examination by me showed the leak source to be the valve cover gasket. Only leak now is the top timing chain cover and that is minimal.

Brian McL

That gasket doesn't need any sealant. The timing chain cover, on the other hand, should use Locktite 5900..hard to find...or buy it at the MB dealer under their label, same stuff. And it works.

Jimbeau

Thanks to all who replied. The manual seemed to imply to me that no sealant was used on the valve cover gasket, simply because the assembly directions didn't call for it. It was good to get confirmation on the issue, however. -- Jim

Kestas

I just dawned on me that you may be apprehensive about buying a new gasket when the old one looks okay. The old gasket probably got hard from the heat and cannot comply with the sealing surface. The new one will be more supple and will seal better.

Jimbeau

Kestas,
I actually had the new gasket, but was concerned that it might be counter productive to use a sealant on it. However, I think you are on track with the way the previous repair was made -- a strong bead of sealant was used to take up the irregularities in the heat-distortion gasket. I had the same thing occur periodically in a 1.8 L Mazda DOHC engine as it accumulated 200K miles. About 30-40 K miles was all a valve cover gasket would last before oil would begin leaking on the exhaust manifold. Gooping a used one up with sealant never lasted very long. -- Jim

Jimbeau

While removing the valve cover to replace the gasket, the problem became apparent when 3 bolts at the rear would not "spin up". These bolts had been overtorqued and had stripped the treads in the head, and apparently the quick fix was to goop the old gasket with RTV and send it down the road. I ended up using helicoils in the head to fix the problem. Important to note is that the compression of the gasket is limited by bolt sleeves that fit between the head and the valve cover. Once the valve cover is tightened properly, any further torque on the valve-cover bolts will have little alternative but to strip the threads, especially if the compression of the thrust washers has met their limit. (BTW, I also replaced the thrust washers). I can see where it would be tempting to simply try to fix a leaking valve cover by tightening the bolts if you were not aware of the bolt sleeves, but all that would happen is to rip the aluminium threads out of the head. -- Jim

Kestas

I suspected it had such a design. This design is getting popular. The force on the sealing surface is set with no possibility of overloading (much as the previous owner tried), and the force is even, unlike the previous designs where overtorqueing bolts could deform the valve cover lip. It also allows the seal to float on the surface to comply with thermal cycling.