coolant in oil, no oil in coolant

[Dash01]

'90 535ia M30 engine gets coolant in oil, but no oil in coolant.

Head and block have no no apparent crack, headgasket looks OK, with no obvious streaking or other signs of leakage or seepage between oil and coolant holes. Cylinders and plugs are dry. Freeze plugs all OK, as is plastic coolant reservoir and plastic radiator tanks. Car runs fine and does not overheat, with temp gauge pegged at 12 o'clock position.

Put in new oil and filter, and within a few miles the oil starts to get frothy with coolant mixing in.

Head was rebuilt and resurfaced only recently, and placing a mechanic's straightedge along the head and also along the block indicates no warping of either.

Where else could coolant find its way into the oil?

[Ross]

Headgasket or a crack, that's it.

[whiskychaser]

I dont know the M30 but on the M50 you can have a perfect seal between the head and block and still get coolant in your oil. The leak can come from either a bad seal between the head and the timing chain cover or the timing chain cover (behind the water pump) and the block. No prizes for guessing how I now

[Barney Paull-Edwards]

Water in oil, no oil in water? Water at 2psi,oil at 40 psi,gotta be combustion pressure forcing oil into water but no overheating and normal on gauge? If it was a crack surely there would be pressurization of one side or another?

[Dash01]

How about various screw plugs, etc.? I did not mess with any of these, but rather am trying to understand how the coolant could get into the oil, but no oil in the coolant. Head, block and headgasket appear to be OK.

Anybody know more about the potential for a passageway or seepage around the water pump or thermostat housing into the oil? I've looked down the front chain cover, but cannot see any likely signs of seepage. Whiskeychaser, can you tell us more about how that happens on your engine, or your engine and the M30 535i engine compare in this respect?

[Dash01]

Water in oil, no oil in water? Water at 2psi,oil at 40 psi,gotta be combustion pressure forcing oil into water but no overheating and normal on gauge? If it was a crack surely there would be pressurization of one side or another?

No overheating, has normal coolant temperature, and no oil in coolant. Coolant in oil, instead. And, when I unscrew the cap on the coolant reservoir (on the firewall), it hisses briefly, telling me that it is still airtight there. I am losing coolant at a slow pace, but there is no sign of water in the cylinders or on the plugs or white clouds from the tailpipe, so I think the coolant is escaping and running down into the oil pan, where it is mixed and recirculated with the oil. Low oil pressure light flickers on shutdown once the oil becomes milky or froth appears on the dipstick or oil filler cap. (I assume that is because the oil/coolant mix has lower viscosity than just oil, and/or the frothy mix causes cavitation registered at the oil pressure switch.)

No sign of cracked head, block, or telltale seepage marks on headgasket, which suggests that is not the source of the trouble.

[ironie]

a leakdown probably would have provided your answer, at least in regards to which cylinder is forceing water into the oil. My bet would be the head gasket either way. or you have a true fluke and it is a casting defect. The leakdown might have pointed it out one way or another. I can't picture a crack between water and oil jackets without some freezing. Even a plain old compresion test probably would have been useful.

[Barney Paull-Edwards]

How about looking at only oil/water interface I can think of,tranny cooler in radiator or engine oilcooler? Some cars have cooler/heater in circuit to heat oil in cold climates,took mine out ages ago for the reason of potential contamination.

[Bin_jammin]

How about looking at only oil/water interface I can think of,tranny cooler in radiator or engine oilcooler? Some cars have cooler/heater in circuit to heat oil in cold climates,took mine out ages ago for the reason of potential contamination.

Mind if I throw my hat in the ring? I've seen this type of thing happen more often than you might think, and first of all let me just say DO NOT DRIVE THE CAR. DO NOT EVEN RUN THE CAR, until you figure it out. If engines were made to use coolant as a lube they would, you're going to do massive damage to your bearings running with coolant in your oil

Now, so far as the no oil in your coolant, that's an easier one, oil doesn't milk coolant up like coolant milks oil up. The oil may be sludged in a high point in your engine, but it is possible that you don't have any oil in your cooling system, sometimes you can have a leak that works one way but not the other.

Like a head bolt. I've seen them leak coolant plenty of times. Pull your valve cover and look for wetness around your head bolts. Did you re-use the old head bolts when you pulled the head? And please, for god's sake, tell me you put a new gasket on....

[Dash01]

Mind if I throw my hat in the ring? I've seen this type of thing happen more often than you might think, and first of all let me just say DO NOT DRIVE THE CAR. DO NOT EVEN RUN THE CAR, until you figure it out. If engines were made to use coolant as a lube they would, you're going to do massive damage to your bearings running with coolant in your oil

Now, so far as the no oil in your coolant, that's an easier one, oil doesn't milk coolant up like coolant milks oil up. The oil may be sludged in a high point in your engine, but it is possible that you don't have any oil in your cooling system, sometimes you can have a leak that works one way but not the other.

Like a head bolt. I've seen them leak coolant plenty of times. Pull your valve cover and look for wetness around your head bolts. Did you re-use the old head bolts when you pulled the head? And please, for god's sake, tell me you put a new gasket on....

Well, since oil floats on water and since coolant is mostly water, if there were oil in the coolant it would be at least somewhat discolored and there would be oil floating on top of it in the translucent bucket into which I drained the coolant. None. Looks normal, smells normal, indicating no oil in the coolant. Before removing the head, a sniffer test revealed little or no indication of exhaust gas in the coolant, which tells us the cylinders are not compromised. (Upon removal of the head, cylinders and plugs were completely dry. A mechanic's straitedge laid on the head and on the block at various angles showed no daylight, so presumably the head and block are not warped. If they were warped, telltake leakage streaks or discoloration would presumably show on the removed headgasket, but it looks OK.)

The oil drained from the pan, however, started with water coming out, being heavier than oil and therefore at the lowest point. Then came milky oil. Some frothy latte' stuff was on the bottom of the oil filler cap and on the dipstick, on the oil filter, etc..

Again, the headgasket shows no signs of leakage or seepage between oil and coolant holes, toward the drain galleries, etc.. It is a new Reinz headgasket installed with new bolts, torqued to spec. If it were the source of the compromise, there presumably would have been coolant in the cylinders or white smoke from the tailpipe, but there was not. All freeze plugs are intact, as are the plastic radiator and coolant reservoir parts, which hold pressure, with a brief hiss when the reservoir cap is removed. No external signs of leakage or seepage, either.

Somehow, coolant is getting into the oil, but apparently not via past the head gasket.

How does a head bolt leak coolant in an M30 engine?

Can anybody direct me to a good schematic that shows the passages for both oil and coolant in the M30 engine?