Freeze plug question

[Dash01]

Suppose an M30 engine sat overnight in freezing weather, with inadequate or no anti-freeze mixed in the coolant water.

Upon startup there are no issues, freeze plugs are intact, and plastic tank on the radiator is intact. No leak apparent anywhere.

This a few hundred miles after a new headgasket had been installed, with all new head bolts, and a refurbished head that had been machined ~0.004" during rebuild.

A few weeks later, got low oil pressure warning on startup, so shut down engine instantly. Inspection of dipstick and oil filter show frothy mix of coolant and oil (coolant having been installed after the cold weather, and after installation of a new heater core).

In this scenario, since there had been no leak or other obvious indication of a cracked block or head after the cold weather, but a mix of coolant/oil appeared some weeks later, what is the likely source of the coolant/oil mix?

1. Cracked block or head from freeze, despite intact freeeze plugs and radiator tank?

2. Headgasket issues from HG failure or improper torque of new head bolts?

3. Other sources?

[632 Regal]

if it looks like a chocolate shake then id say a cracked block/head, if its just a slight bit then it might have been residual fom the head gasket repair...

good luck!

[Ross]

Do you suspect you improperly torqued the head?
Unless the cooling system is over pressurizing I'd say the gasket is more likely.

[Dash01]

Do you suspect you improperly torqued the head?
Unless the cooling system is over pressurizing I'd say the gasket is more likely.

There are 14 new head bolts in there, and I thought I was careful to install them in correct sequence and torque, including running the engine for awhile before final angle torque. That said, I would damn sure prefer to find that I made a mistake with leaky HG, as opposed to having a cracked head or block.

The frothy stuff on the dipstick and oil filter looked like whipped latte'. That tells me there was mixing of oil and coolant, but not necessarily the source of the mixture, be it crack or leaky HG. There was no oil in the coolant tank, etc. but rather coolant in the oil, which I suppose could be from heated coolant under pressure finding escape through a crack or leaky HG, then by gravity into the oil pan.

[whiskychaser]

Not sure about the set up on the 535 but I had a similar problem after re-installing the head on my 525. The head to block seal was fine - my problem was the timing cover seal around the waterpump (my fault!!) . It also leaked out so I spotted it straight away. Dipstick looked fine but I drained the oil and it looked like latte