Drain plug dripping

[David H.]

This issue is actually of a friend of mine that owns a '61 Corvette. I have been helping him with some small issues on this car that belonged to his father and now is his. He has spent the last fourteen years in the restoration process and last summer finished and drove it for the first time.
It is an absolutely beautiful car. (pictured)
One issue we cant seem to cure the easy way is this:
The drain plug was dripping ever so little and he decided to "fix" it.
He got an oversized plug and tried to tap the hole out to the new plug.
Unfortunetly he did not get the tap straight and now the plug goes in tight on one side and a slight gap on the other of about a fingernail thickness. Everything we have tried does not cure the drip. We have tried nylon washers, metal washers with rubber centers, compression washers, multiple washers and combinations of all of the above. No luck.
Short of removing the pan and replacing the backing nut, does anyone have any ideas of how to correct this issue? Thanks in advance.

[Bill I.]

Re: Drain plug dripping

Dave, think you said the proper answer. If oil gets to the last threads on the plug, it's gonna leak. Do the pan job. Bill

[Joe L.]

Re: Drain plug dripping

Dave, think you said the proper answer. If oil gets to the last threads on the plug, it's gonna leak. Do the pan job. Bill

Bill an Dave------



Yes, he made a BIG mistake trying to tap it for an oversize plug. Just what did happen is what often happens if this is attempted.

What needs to be done now is to remove the pan and replace the flange (nut plate). Even this is not so easy. An alternative is to weld up the hole in the flange and re-drill and tap with the correct size using something like a Lassie tapping machine to ensure you get it straight. However, I would not recommend attempting this with the pan on the engine and it would be impossible to use the Lassie machine with the pan on the engine.

One advantage of welding up the hole and re-drilling and tapping is that the weld will be very hard material, so the threads will be "immortal". The downside is that it will be hard to tap.

By the way, a slight amount of leakage from an original style oil drain plug is just about impossible to eliminate. Personally, I've NEVER seen it done, regardless of the type of gasket used, be it nylon, copper, aluminum, or the tin-elastomer composite type gaskets. However, GM finally did solve it by going with a special, torque limiting style drain plug and semi-captured sealing washer. Unfortunately, by the time they did this everything was metric. So, if he wants to convert to metric 12 X 1.75 thread size, he can get a plug and sealing washer that should solve the oil leak. Of course, a plug of this size is not going to have a head configuration like the one originally used for C1 Corvettes.

[David H.]

Re: Drain plug dripping

Thanks very much Joe. Your response was very helpful and he wants to try the "a special, torque limiting style drain plug and semi-captured sealing washer. Can you expand on what this is or what it looks like or where we might find one? Is it GM over the counter part?

[William C.]

Re: Drain plug dripping

Much easier to but a 60's pass car pan and used the thread plate, just swap it into the existing pan. At least gets you back to a known starting point, and the pan is very easy to drop on a solid axle as compared to any of the later cars.

[Terry M.]

Re: Drain plug dripping

Thanks very much Joe. Your response was very helpful and he wants to try the "a special, torque limiting style drain plug and semi-captured sealing washer. Can you expand on what this is or what it looks like or where we might find one? Is it GM over the counter part?

Here is a picture that should give you an idea of what they look like. The black gasket is replaceable, but you have to buy a package of 10, unless the dealer you get them from stocks them. There is also a blue colored gasket, but I don't know that part number. The blue is alleged to be superior, but these don't leak. I use a torque wrench, but one of my job titles is analyst, and I am. The threads are metric, so you will have to figure out how to overcome that hurdle -- unless Joe knows of some with English threads -- but I doubt those exist. A search on the C6 part of the Corvette Forum will yield you part numbers out the wazoo. It is past my bed time.

You will not get the drain plugs with the magnet from GM -- they discontinued the magnet. Speculation has it that was due to people going ballistic over the "fuzz" you see here @ 2830 miles on my Z06. I am sure that cost was also a factor.

[Joe L.]

Re: Drain plug dripping

Thanks very much Joe. Your response was very helpful and he wants to try the "a special, torque limiting style drain plug and semi-captured sealing washer. Can you expand on what this is or what it looks like or where we might find one? Is it GM over the counter part?

David------


The GM magnetic plugs are all discontinued and I can't find the part number for the non-magnetic plug. The GM part number for the gasket is 3536966, though. But, you need the correct plug to use this with.

You can get a magnetic plug from Dorman or Motormite, though, that is exactly the same as the GM magnetic plug. This is Dorman #090-091 or Dorman/Motormite #65372. This plug is supplied with a gasket but extra gaskets are available under Dorman #097-119 or Dorman/Motormite #66451. The latter 2 numbers are the same as the GM #3536966.

In order to use the above you would have to make up a flange (nut) plate with metric 12 X 1.75 thread or do the welding and re-tapping I described previously. Also, the area surrounding the drain plug (i.e. where the gasket seats) needs to be relatively flat and regular.

[Terry M.]

Re: Drain plug dripping

This is the drain plug for C6 -- 24241872 - Plug List is $22, but I see on-line prices of $13 to $15. This is for the GM part that no longer has the magnet. Many of the C6 drivers are going for the aftermarket parts Joe cited.