New Volvo Manifolds..

Picked up some new 7.4L OEM manifolds from Volvo, and in the center of the water inlet tube (cast into the bottom of the exhaust manifold) is a threaded hole that enters the water jacket, anyone know what size plug should be here?
(The manifolds come with a brass nipple for the inlet end at one side, and a reducer and plug for the other/unused side, but nothing for the middle threaded hole..)

Re: New Volvo Manifolds..

Not sure what hole you are referring to, could you post a picture?

Is it pipe thread? Measure it with a ruler an post the size.

Re: New Volvo Manifolds..

a 1/4" NPT plug wont seem to fit, a 3/8-16 bolt does, but it feels loose, lemme see if i can get a picture.

Re: New Volvo Manifolds..


Just noticed my camera is dead, got it charging. Here is a previous picture I took. I circled the area where the hole is tapped into in the pic.
Edit: Ok, added a couple extra pictures, sorry they're not centered, hard to get in there with the manifolds already installed.

Re: New Volvo Manifolds..

Ayuh,... It should be 1/4 pipe for a drain plug by the looks of it...

Re: New Volvo Manifolds..

Seems to be the newer style manifolds. Have no idea what thread it is, but it doesn't look like pipe thread in the parts drawing because it has an oring seal.

Look here at 16 through 20
Exhaust 8.1OSi-J - 7747720 - Volvo Penta

Re: New Volvo Manifolds..

I checked it again, and its definitely not 1/4" NPT. Hard to tell, but from the first of the two pictures of the threads, the hole starts off tapered (no threads), and then goes to what seems like a 3/8" course thread. A course 3/8 bolt threads in, and then stops (so i would need a really short bolt if the threads are indeed 3/8-16) Maybe a 3/8 x 1/2"? Just dont understand why a bolt hole would enter a water jacket there, I figured it looks like the perfect spot for a drain, but the installation instructions from volvo, and the workshop manual make no mention of this threaded hole, and no plugs were included for this penetration.

Edit: Looks like we were typing at the same time, that's definitely the one for sure, now if I can find out what size plug that is, don't want to wait until next week to get this up and going, but If I have to..
Thanks Don, huge help as always.

Re: New Volvo Manifolds..

Update:

Marine shop called me back, said they spoke with Volvo - threads are 7/16-14.

Re: New Volvo Manifolds..

Just get an oring that will fit over the threads of a short bolt and see if it will hold. Do NOT use a washer or it won't seal.