E34 (M50) Overheat Issues

[cammons3]

Let me preface by saying that I’ve been working on this overheat issue for nearly four months… Saga begins with coolant usage, steamed exhaust, water in #4 cylinder, but no oil in cooling system or coolant in oil pan.
- Suspected head gasket
- Pulled head
-- machine shop inspected/surfaced/gave clean bill of health
-- ordered gasket kit
-- replaced gaskets/installed head
Overheat issues begins
- Bled system per Bentley
- Steamed exhaust continues
- Excessive air pressure in cooling system
-- checked water pump (good)
--- aftermarket w/ steel impellers
--- replaced with loaner pump anyway
-- replaced thermostat
-- found water in #4 cylinder (again)
Pulled head
- R&R head gasket with 0.3 mm thicker gasket
- Put old water pump (steel impellers) back in
- Steamed exhaust continued
- Overheat continued
- water in #4 cylinder continued
Pulled head (third time)
- Returned head to machine shop: found crack at #4 water jacket
- Sent head in for overhaul (not same machine shop)
- Installed remanufactured head
Issues:
- Idles w/out overheating (heater works fine)
- Cannot drive around block (overheats)
-- Cooling System seems to:
--- “over-pressurize” when under load
--- blows out coolant when relieving pressure via bleed screw (on radiator)
-- Just prior to overheating heater blows cold air
- Still no oil in water or water in oil
Additional maintenance:
- Bled more times than I can count
- Performed block tester to check for exhaust gas in radiator
- Purchasing expansion tank cap today

Apologies for this being so long, but it’s been a long four months. Car has gone through a tank of gas, and only driven a total of 20 miles! Can’t figure this one out, but we can now R&R a M50 head in less than four hours!

[cammons3]

Oh, did I mention replacing the fan clutch? Yup, did that too...

[Bill R.]

crack in the head or the block itself. Over pressurization under load is a giveaway for this...And you can have a poor sealing head gasket that will only leak gas one way, As in combustion cylinder pressure which is right around 200psi will force itself into the cooling system passages through a bad area in the gasket or head, but the 20psi liquid side of the cooling system won't leak across into the cylinders.. I've seen this on a number of customers cars. If you put a cooling system pressure tester on it and just rev the engine a couple of times you can watch the gauge jump up on the pressure tester as the high pressure gas goes into the cooling system.
Then when that happens the pressure gets high enough that it makes the cap release and it vents out the pressure pushing coolant out of the radiator
At this point the car isn't overheating its just pushing all the coolant out due to the overpressurization... When enough coolant is pushed out you lose the heater due to lack of coolant flowing through it... And then since there's not enough coolant in the system anymore it overheats. Something is still wrong with one of the basics of the job, the head gasket itself, the head warped, the head cracked or the block cracked.

Let me preface by saying that I’ve been working on this overheat issue for nearly four months… Saga begins with coolant usage, steamed exhaust, water in #4 cylinder, but no oil in cooling system or coolant in oil pan.
- Suspected head gasket
- Pulled head
-- machine shop inspected/surfaced/gave clean bill of health
-- ordered gasket kit
-- replaced gaskets/installed head
Overheat issues begins
- Bled system per Bentley
- Steamed exhaust continues
- Excessive air pressure in cooling system
-- checked water pump (good)
--- aftermarket w/ steel impellers
--- replaced with loaner pump anyway
-- replaced thermostat
-- found water in #4 cylinder (again)
Pulled head
- R&R head gasket with 0.3 mm thicker gasket
- Put old water pump (steel impellers) back in
- Steamed exhaust continued
- Overheat continued
- water in #4 cylinder continued
Pulled head (third time)
- Returned head to machine shop: found crack at #4 water jacket
- Sent head in for overhaul (not same machine shop)
- Installed remanufactured head
Issues:
- Idles w/out overheating (heater works fine)
- Cannot drive around block (overheats)
-- Cooling System seems to:
--- “over-pressurize” when under load
--- blows out coolant when relieving pressure via bleed screw (on radiator)
-- Just prior to overheating heater blows cold air
- Still no oil in water or water in oil
Additional maintenance:
- Bled more times than I can count
- Performed block tester to check for exhaust gas in radiator
- Purchasing expansion tank cap today

Apologies for this being so long, but it’s been a long four months. Car has gone through a tank of gas, and only driven a total of 20 miles! Can’t figure this one out, but we can now R&R a M50 head in less than four hours!

[632 Regal]

might be cracked block around the headbolts from them being hydrolocked with fluid during one of the many R&Rs for the head.