M20 twin turbo cracking heads. Please help

[Bubbles]

I think that the turbos will be OK even without the coolant lines as I used to have a m20b23 with TD04HL turbo and I used it without the water for about an year without an issue.

This does not mean that turbo cooling is not necessary. The oil does a lot of cooling for the bearings, but if the bearing housing is built with a water jacket, it SHOULD be used. Especially with a twin turbo setup, since you just have a T in the oil feed line, one turbo could potentially be starved of oil. You need to have separate coolant passages otherwise you're heating up the second turbo in line instead of cooling it. The turbine housings and bearing housings are meant to withstand that kind of temperature. A normally NA engine might not have been designed to withstand that temp. I'm not saying this is the root of the cause for a cracked head, but you will definitely destroy your bearings in your second turbo over time.

As to the actual head cracking, have you done a coolant flush and/or inspection of the coolant passages to look for blockages? Hot spots can cause more thermal expansion and cracking. just an idea.

good luck

[CorvallisBMW]

^ I would be tempted to agree on the sequential vs parallel routing. I would aim for parallel routing on coolant and oil if at all possible.

[mikebloco]

I would go bigger single and make life wayyyyy easier

[barbierij]

almost a year later...what did you find out!?

[zoomer]

I got tired of destroying 885 heads, so I installed m20b20 with 731 head and removed the water cooling from the turbos. And voila - no cracked heads so far (although I had several blown gaskets but thats another story)
By the end of the month I am planning to install the m20b28 engine again with a fresh head. Hopefully the issue was with the water cooling (my theory is that since there are 2 turbos the coolant gets too hot and when it goes in the back of the block it goes directly to the head, so the front of the head is nice and cool and the rear is very hot and it cracks)