Oil Cooler or Head Gasket?

[MurphsLaw]

OK, 2001 V70 XC, 313K miles, (burns ½ qt. oil every 3K miles), owned since 233K miles. Never overheated on my watch. Now rapid coolant loss with no sign of leak. Cold engine shows no sign of coolant on oil dipstick. Slightly warm engine shows dipstick oil full of tiny bubbles but no foam (yet). No sign of oil in coolant reservoir. Anyone ever heard of one-way (coolant to oil) oil cooler leak?

[Xfingers]

FWIW, make sure there's no moisture on the front carpets inside the cabin. This would indicate coolant leak from the heater core.

[Astro14]

If there is a coolant leak - the oil turns into a chocolate milkshake quickly as the coolant is emulsified into the oil.

Doesn’t sound like you have either a head gasket or oil cooler leak (both are rare on this engine). As Xfingers says, coolant leak from the heater core is common. Usually the orings that seal the coolant pipes to the core are what fail.

Take off the trim under the driver side dash and have a good look at that core.

[BrickDriver]

Hopefully it's not the head gasket, but it is possible that a failed head gasket can cause similar symptoms. When mine failed, exhaust gases were pressurizing the overflow tank and there was significant coolant loss without obvious sign of a leak or coolant in the oil. If you rule out other causes (heater core, etc.), you may want to get a combustion leak test kit to check for combustion gases at the overflow tank. I used the Block Tester BT-500. It was an easy test and provided clear results.

[MurphsLaw]

Thanks for your responses! I had not smelled coolant in the cabin so did not explore heater core leak. Bubbly oil sent my mind in other direction. Passenger side floor is a little wet. Can't determine if it's coolant. I'll have a look at that core and keep the BT-500 in mind.