what size is coolant return hose fitting to block?

[Xtrempickup]

I gotta make a quick fix, close off the coolant return on the back of the commonblock 2.5 i have. I need to buy a cap to screw in. Anybody have an idea what size i need to plug the return hole? I dont have the hose off yet or il have a big mess. Gonna run the mitsu oil cooled until can get around to pulling it off and fixing the problem. Wna be able to drive to car without a huge coolant leak.

[cordes]

The actual hole on the block in the back is 1/4" NPT. The fitting at the head is 3/8ths NPT. The block is actually the feed and the head is the return.

[Xtrempickup]

Ok sounds good i might actually have what i need to plug it then