m42 leaking coolant under intake - NOT water pipe!

[misterTT]

Alright, so i've got a coolant leak that developed over the last month, which is coming from under the lower intake. I assumed this to be the fault of a coolant hose or the water pipe / O-ring that connects to the head. I completed the 'mess under the intake' bypass a couple of years ago.

Today I removed the upper and lower intakes, removed and inspected the water pipe (OEM unit which was still good) and hoses, replaced the O-ring, and buttoned everything back up. I saw no problems with any of the pieces, but assumed that the O-ring & water pipe might not have been seated correctly, causing the leak. That was not the case, apparently:

After getting everything back together, I refilled with coolant, and to my dismay could see (and hear) coolant leaking from the same area but on closer inspection it is coming from behind and above the water pipe on the block itself. I'm assuming this is a failed gasket, but which one?

See pic below (which I stole from one of the mess under the intake threads and added the area of leakage that i'm seeing). Any bright ideas? Input much appreciated!

BTW: I have found no oil in the coolant nor coolant in the oil. I don't think they are mixing, if that helps to narrow it down. However, there was some gross milky gunk in the intake bellows, which seems relatively common for cars in cold weather and lots of short trips.

[misterTT]

so I guess this is a blown head gasket, isn't it?

[bmwman91]

Bad o-ring on item 6/7?

[misterTT]

Bad o-ring on item 6/7?

Good thought - i'll poke around and see if that's it.

It did look more like a long line of moisture coming down though, rather than just beneath one of those connectors.

[roguetoaster]

Check the heater core hose outlet at the back of the head. They have a tendency to corrode through.

[bmwman91]

I know what you mean about a "line" of coolant. Fluid tends to follow its surroundings though, so if it leaks down onto the head gasket line it will run along there. I had a small leak at the rear heater hose outlet once and thought it was the HG too since it was wet along the gasket line.

[misterTT]

Just to update, you were spot on about the heater hose. I assumed incorrectly that since I had replaced it previously while clearing up the mess under the intake, that it was not likely the culprit.

I had originally used an oversized hose and clamped it down really tight. Looks like cold weather makes it brittle enough to leak. Replaced with a much better solution now, all is well. Thanks for the tip!

[roguetoaster]

Glad you got it sorted out! Despite the cost the BMW hoses seem to be the best bet to replace the heater core hoses, although I found mine to be a bit long and in need of trimming.

How did the outlet flange look while you were there? No or limited corrosion means someone has been diligent about using BMW coolant and distilled water. The original head on my daily looked like the picture below, but that head was scrapped anyway with a crack or two.

[jrobie79]

BMW doesn't make their coolant...its regular phosphate/nitrate free coolant with blue dye...as long as you use phosphate and nitrate free with distilled water you will be GTG

[roguetoaster]

Interesting, hadn't heard that about BMW before, but did realize the need for no phosphate/nitrate. What readily available coolants meet those requirements/what do you use?

[misterTT]

Happily, the outlet flange looked fine!

As for the phosphate/nitrate free thing, I do recall reading that somewhere, although I've been guilty of using whatever green stuff the local parts store has on hand. Not sure the phosphate/nitrate situation there.

[jrobie79]

prestone green shit is nitrate/phosphate free....just look on the back, it will say it