OK, we all know that oil in the anti-freeze, or antifreeze in the oil is usually a crack in the block, crack in the cylinder head, warped head, or bad head gasket.

Usually though, this results in what I refer to as oil emulsion stew in the oil pan, and occasionally some very small amount of oil residue might get into the cooling system.

I have always attributed this to the fact that since the antifeeze is under more pressure than the oil in an engine, the anti-freeze usually breeches the oil passages, not vice versa. I've wrenched a lot of cars but never seen it the other way until.........

My son comes in from outside yesterday morning and says "there's a puddle of goo under my car". I jokingly say "next time you come in at 2AM, come inside to puke, not on the street.....

When I went out to investigate sure enough there was a puddle of goo which had leaked from the cap on his coolant reservoir and the coolant reservoir itself was full of thick oil/antifreeze mix, popped the oil filler cap and creamy stuff in there also......what the heck?? I'm guessing cracked block but has anyone encountered this? And even if I long block the thing to cover the odds on both the block and cylinder head, how would I ever get the cooling system flushed sufficiently to put this thing back in service??

Admission.....this is not a Slant, but I thought it would make for some interesting conversation and you guys are my only wrenching buddies.

So in order to appease the moderators, my question would be....."has anyone ever encountered this on their slant?"

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63 Valiant 200 Signet Convertible 170/
63 Dart, 225/
68 A100 Pick-up 225/
2006 Mitsu Raider Quad Cab (Dakota) Mopar 4.7L
1992 Dodge Stealth RT (My Mid-Lifer) 3.0L 24V

Is the car an automatic? If so, the oil might be coming from the transmission cooler in the bottom of the radiator.

Think optimistic and prepare for the worst is what I always say.

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

To start, one of your assumptions are incorrect. While the engine is running, the engine oil is under greater pressure than the coolant. Radiator cap is approximately 15lbs, right? Oil pressure is higher than that, unless there's bigger problems in the engine.

What you have probably seen in the past is due to oil pressure dropping off as soon as the ignition is shut down, but the coolant retains a certain amount of pressure quite a bit longer, allowing coolant to bleed into the oil system and crankcase.

As was already mentioned, it could be a case of a ruptured trans cooler line in the bottom of the radiator, if an auto car. The other possibility is a really badly blown passage in the head gasket, but only between a coolant and oil passage.

I think I would try a good radiator pressure test as the first thing, then have a radiator shop check that trans cooler line. If those two check out, then it's time to pull the heads and look at the gaskets.

Roger

Roger

H'mm. I think the relative pressures will vary depending on where in the system we look. There are places where the oil's under little or no pressure, and oil pressure of less than 15 pounds is regarded as acceptable at hot idle (not that I'd be especially happy to see such low pressures, but according to the builders, it's not abnormal...). And there are times when the coolant's not under much of any pressure (e.g. a partial-pressure cap and a cold engine). And there are leaks/cracks when cold that close up when hot, and sometimes vice versa. And, as you mention, the cooling system maintains pressure long after shutdown, while the oil circuit doesn't. So really, whether the oil's going to leak into the coolant or the coolant's going to leak into the oil, or both, depends on where/when the leak is.

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