Coolant mixing with oil

[1981 e21]

Substantial coolant loss. Dipstick showing coolant mixing with oil. Car is no longer ovrrheating but radiator losing coolant. No extrernal leak. Water pump relatively new. Could it be head gasket? Blue liquid test showing no cumbstion gasses in radiator. Could head gasket still be the culprit? One more thing. No white smoke in tail pipe. Where else could coolant be mixing with oil? Oil cap does show a bit of creamy stuff but could it be because the car is driven only on short ride and only couple of times a week. Irrespective of that, coolant loss seems to be substantial. Pls help.

[Jeroen]

Significan sludge build up is a sign of a head gasket failure, the coolant must be going somewhere. In the oil system (sludge build up), being burnt in one or more combustion chambers (may cause discoloration on one or two spark plugs), or due to a coolant leak that may only be present while driving (higher pressure or temperature).

You mention that the car is "no longer overheating". Overheating may be a sign of a blown HG as well and may at some point no longer occur when air in the cooling system prevents the thermostat from opening, or overheating may have been the cause of the HG failure, may even have caused the head to crack (usually near one of the cam bearings and therefore hard to identify).