Rear Main Seal

Is That Oil Leak From My Rear Main Seal?

Many Classic Thunderbird owners are plagued by oil leaking from their rear main seal area. This particular oil leak is costly to eliminate. Many owners have gone to great lengths to fix this leak. Some have gone as far as having the engine rebuilt only to have the leak reoccur within a few days, weeks or months of operation. Today's mechanics, many younger than your car, are not familiar with the workings and design of the Thunderbird engine. In addition, many engine rebuilding kits have unfortunately provided us with poor fitting or inferior goods. Any "regular" mechanic who is familiar with today's cars would not necessarily be knowledgeable as to what parts, supplied in certain rebuilding kits, do not work in our cars. The result of this loss of information is a misdiagnosed leaking rear main seal.

If your car leaks oil where your engine is bolted to your transmission housing, you have a leak which may be due to a bad rear main seal. Your leak, however, may not be from the rear main seal but from the gasket located behind the oil filter plate which bolts to your engine block. The gasket is part number 6838. This gasket is supplied in engine rebuilding kits but has been determined by many Thunderbird experts, our own Ken Smizinski being one of them, to be too thin to prevent oil leakage from behind the oil filter base plate. This leaking oil migrates down along the oil pump housing and drips down at the exact location where oil will drip from a leaking rear main seal. If your oil leak is caused by this gasket, you are a lucky individual. The cure can be done at home, the cost is less than $2.00, and you don't even have to change your oil!

Prestige Thunderbird has made available a special oversized oil filter base plate gasket. This part is still numbered 6838, so you have to specify the "oversized" version when ordering. A diagram of your oil filter base plate and its assembly is located on page 26 of your 1997 Prestige catalog. It, however, does not show the base plate gasket.

To change your gasket you will need to remove your oil filter or your canister and filter element if your car is not equipped with today's "spin-on" oil filters. After removing your oil filter, clean up any oil that was spilled on the block or floor. In the center of the oil filter base plate is a nut. It is numbered 6890. Once the nut has been removed, you will be able to remove the base plate, part number 6751. Clean the back of the plate off making sure you remove any old gasket pieces or silicon sealant. Clean off the section of the engine block where the plate was attached in the same fashion. Install the new gasket from Prestige using silicone sealant on both sides of the gasket. Reinstall the base plate making sure that the section labeled "top" is located in the top position relative to your engine block. Reinstall your center nut. Do not overtighten this nut. You may warp your base plate if you overtighten this nut. Reinstall your oil filter or canister and filter element. Add oil to replace that which you spilled on yourself or your car, if any. Start your engine and check for leaks. if your lucky your problems will be solved! Good Luck.