Dear Tom and Ray:

We drive a 1990 Dodge Caravan with a 3.0 liter V6 engine. Two months ago, the oil light came on as we pulled into a gas station. We had just driven 250 miles on the interstate in below zero weather and were stopping for gas. I quickly discovered that oil was literally pouring out under the car and pooling onto the ground, although there was no oil at the top of the engine. To my horror, the dip stick showed "empty," even though it had showed "full" when we left four hours earlier. The Caravan had never burned a drop of oil in 40,000 miles. Fortunately, there was a Chrysler dealer across the street. The service manager suggested I pour in some oil, see whether it was running right out, and, if not, drive the van over. I added three quarts to reach the "add" mark. None appeared to be running out, so I drove to the shop. The perplexed mechanics ran the van for 45 minutes without being able to find any leak. They did find water in the PCV valve, and dried it out. We drove 200 miles home without incident, and I immediately had our Chrysler dealer recheck. He, too, could see that there had been a catastrophic oil leak, but was unable to determine its source. He replaced the PCV valve and put dye in the oil. 500 miles later, he rechecked for leakage, and was as baffled as ever. He told me he called Chrysler directly, and the engineering people there were baffled, too. My dealer is convinced that the PCV valve is not the culprit, particularly since Chrysler changed the design to correct a PCV-valve freeze-up problem on earlier models. This incident has destroyed our confidence in what has until now been a very reliable vehicle. How could we have lost all that oil so quickly? And why should it be so hard to figure out why? Help! We're stumped and worried.
Robert

RAY: Pardon me for a moment while I put on my Sherlock Holmes hat, Robert. My brother will put on his "Watson" hat, too, although it takes him a little longer since he has to take off his dunce cap first.

TOM: I think the PCV valve WAS responsible, Robert. That's not where the oil came out, but I think it was responsible for the leak.

RAY: He may be right. Here's what may have happened. The temperature was below zero. There was water in your PCV valve. The water froze, plugging up the valve.

TOM: With the PCV valve plugged (for a couple of hours, perhaps), and vapors unable to escape, a tremendous amount of pressure built up inside your crankcase.

RAY: And when the pressure got to be too much, something had to give. And what probably gave was either the front or rear crankshaft seal. It's possible that one of those seals deformed long enough to release the pressure, and then returned to its normal shape once the pressure had dropped. That certainly would spray oil all over the place, and if it really returned to its original shape, there would be no evidence that the seal had leaked.

TOM: The PCV valve would have unfrozen while you sat at the gas station scratching your head. And since the dealership across the street dried out the water, you had no problem for the remainder of your trip. And since you had the PCV valve replaced with a new (and perhaps upgraded) one when you got home, you haven't had any more trouble.

RAY: Another, similar possibility is that the oil pressure relief valve got stuck during the trip. Again, that would have caused tremendous pressure to build up in the engine, and could have caused something like the oil filter gasket to deform and leak catastrophically until the pressure returned to normal. So I'd have the pressure relief valve checked, too.

TOM: Elegant answer, Ray. Sherlock Holmes couldn't have done it better himself!

RAY: Sherlock Holmes never spent any time in the engine compartment of a '90 Caravan.