How to cure GMC Savana’s chronic oil leak

Hey there, time traveller!
This article was published 31/03/2006 (7161 days ago), so information in it may no longer be current.

Q I have a 1997 GMC Savana van G2500 with a 6.5 diesel. The oil pan leaks and it has been repaired five times. The last time a full gasket was used. Should they be using any specific silicone? Why is this happening?

Any suggestions?

A. This should be a fairly straightforward procedure. The factory does not use a gasket for the sides and front of the pan but there is a rubber half-circle seal at the back end. When resealing the pan, it is extremely important to clean any old RTV silicone off the surfaces and wipe the sealing surfaces clean with a degreaser such as alcohol or a brake parts chemical cleaner. If there is oil on the surface, then the RTV silicone does not stick and a leak develops.

The biggest problem doing this job is keeping the surfaces oil-free while installing the pan. Oil tends to run down the inside of the engine block onto the pan sealing surface. It works best if it can be left sit overnight with the pan off so most of the oil can drain. Then wipe the surface clean. If the shop can schedule the job so it can be done like this, there is less chance of a leak.

Place a two to three millimetre bead of RTV silicone GM # 12346286 on the sealing surfaces and install the pan. This RTV sealer is resistant to oil and specially designed for engine sealing unlike most household RTV’s. All the pan bolts except the back two are torqued to only 89 inch pounds.

This isn’t very much, and I would bet they have been overtightened, bending the pan sealing surface and possibly creating a leak.. The pan bolt flange can be straightened with careful use of a hammer. Finally, if you do use a gasket, don’t use RTV on the gasket too. The RTV will allow the gasket to slide out of place.

Q. I have a 1984 Motorhome Class “A” on a P-30 chassis with a 454 cu in. engine. The gasket between the exhaust manifold and the cylinder head is burned off leaving a gap from which I get exhaust leaking out and noise like a piston slap when idling in park. The local muffler repair centre says that I do not need a gasket there anymore. They will take the exhaust manifold out, clean out the old gasket and replace the exhaust manifold without a gasket. What is your opinion?

A. This engine did not use a gasket between the exhaust manifold and cylinder head when new, but most aftermarket engine gasket sets include them in the kit. Originally, the manifold sealed directly against the cylinder head, but when removing a manifold after many thousands of kilometres of driving, the manifold typically warps slightly. This can prevent it from sealing again unless a gasket is used. You may get lucky and not need a gasket, but I would probably use one.

Continuing to drive with an exhaust leak can erode both the cylinder head and manifold surfaces. If the leak has been there for some time, you may even have to replace the manifold and have the head exhaust ports resurfaced. Often, this can be cleaned up with a file and the additional use of exhaust system gasket cement to help fill the voids, but it can be difficult to assess how bad the problem is until the manifold is off.

If your repair shop says they can fix the leak without a gasket, then I would let them try. If it still leaks, then they will probably install a gasket. A leak should be noticeable within a few hundred kilometres of driving, so take the motorhome on a short trip before venturing out further.

Jim Kerr is an experienced mechanic, instructor of automotive technology and freelance journalist. You can e-mail questions to Jim at the address below.

kerr.jim@sasktel.net