Small Block Coolant Drain Plug

[Larry M.]

There is a post which says this is part#3889330 (Joe Lucia). Then there is this link:

https://www.forums.ncrs.org/showthre...hlight=3889330

This is a discussion about plugging the exhaust manifold on non air cars for export which says the thread would be straight pipe thread and not NPT.

Should the coolant drain plug on C2 small blocks be straight or NPT? Is the 3889330 straight or NPT?

[Joe L.]

Re: Small Block Coolant Drain Plug

There is a post which says this is part#3889330 (Joe Lucia). Then there is this link:

https://www.forums.ncrs.org/showthre...hlight=3889330

This is a discussion about plugging the exhaust manifold on non air cars for export which says the thread would be straight pipe thread and not NPT.

Should the coolant drain plug on C2 small blocks be straight or NPT? Is the 3889330 straight or NPT?

Larry------


All Corvette small blocks I am aware of used a petcock for radiator coolant drain. These petcocks were all NPT thread.

If you are referring to the block coolant drains, those were also NPT thread. The plug was external hex head steel.

[Larry M.]

Re: Small Block Coolant Drain Plug

Joe, do you know the part number for the block plug? Is it the 3889330 or some other number? Sorry I didn't make it clear which plug.

[Joe L.]

Re: Small Block Coolant Drain Plug

Joe, do you know the part number for the block plug? Is it the 3889330 or some other number? Sorry I didn't make it clear which plug.

Larry------

3889330 is the part number. However, it's long-since GM discontinued. No matter, though, identical plugs are easy to find, either in a good hardware store or from a source like McMaster-Carr. Nothing special about these plugs, at all.

[Terry M.]

Re: Small Block Coolant Drain Plug

Larry------


All Corvette small blocks I am aware of used a petcock for radiator coolant drain. These petcocks were all NPT thread.

If you are referring to the block coolant drains, those were also NPT thread. The plug was external hex head steel.

Joe

For original 1968 to 1972:
We have observed copper/brass radiators with a bottom drain that have a 90* fitting (a male end is soldered into the bottom of the passenger side header tank) and the other end of that 90* fitting has a brass plug with a hex head. We also see copper/brass radiator with a side drain that use a petcock. So far we have been unable to establish a pattern to either style drain.

My early 1970 had the 90* elbow with brass hex head plug.