P38A Radiator drain plug o-ring troubles

I'm having trouble with my radiator drain plug. Concerns my '99 4l v8 p38, bosch engine.

O-ring was squeezing out and thus leaking a bit. Had to drain everything to replace rocker cover gaskets and replace the coolant itself so as the old o-ring was mangled I fit a new one. When tightening the plug it squeezes out again from between rad and plug. Tried three different sizes, all squeeze out:

• 14x2,5
• 18x4
• 20x2

All standard circular cross section o-rings. Manuals says to tighten to max. 6Nm. At about 3-4 o-ring starts to squeeze out. Currently I've tightened it with the 14x2.5 ring to just before it squeezes out. When I google it on part number it seems to be a circular cross section o-ring same as I am using. Don't trust it as is to hold pressure.

What am I doing wrong? Or is this normal and is just hand tight 2-3Nm enough for this plug?

It is weird that they would have designed an o-ring seal without recess in the mating faces so I'm thinking about fitting a square section o-ring.

You don't need to tighten it much, just a bit more than a nip with the wrench and it'll be fine, so long as you've put some pressure on the rubber it won't come undone. Think like putting an oil filter canister on

I used a flat washer, not a round one

ar1g3 said:

I'm having trouble with my radiator drain plug. Concerns my '99 4l v8 p38, bosch engine.

O-ring was squeezing out and thus leaking a bit. Had to drain everything to replace rocker cover gaskets and replace the coolant itself so as the old o-ring was mangled I fit a new one. When tightening the plug it squeezes out again from between rad and plug. Tried three different sizes, all squeeze out:

• 14x2,5
• 18x4
• 20x2

All standard circular cross section o-rings. Manuals says to tighten to max. 6Nm. At about 3-4 o-ring starts to squeeze out. Currently I've tightened it with the 14x2.5 ring to just before it squeezes out. When I google it on part number it seems to be a circular cross section o-ring same as I am using. Don't trust it as is to hold pressure.

What am I doing wrong? Or is this normal and is just hand tight 2-3Nm enough for this plug?

It is weird that they would have designed an o-ring seal without recess in the mating faces so I'm thinking about fitting a square section o-ring.

Click to expand...

PTFE tape on the thread as an alternative?

Datatek said:

PTFE tape on the thread as an alternative?

Click to expand...

It's quite a loose and coarse thread, plastic on plastic, don't that would do anything more than a mess

Hand tight is enough for a rad drain plug, I've never used anything except a stubby screwdriver, on a slotted one.

I think I used a fiber washer and ptfe tape, the oring is useless

Thanks everyone! I tightened it up with a screwdriver and used a slightly fatter o-ring. Let's see!!

The system hold pressure, no leaks. Thanks for the advice!