leaving a vehicle for very long periods can cause seals to fail, my c4 had this problem.

 

Maybe if the ambient temperature is high enough. But with an outside temp of 32 degrees or lower, it can take a very long time to get the exhaust hot enough that you can't put your hand on the mufflers. Remember, the amount of heat in the exhaust depends on the power being produced by the engine. At idle the engine is only producing sufficient power to turn itself over which is negligible. If I want to check the oil level in my dry sump I have to drive the car for 10 minutes or let it idle for 25+ minutes to get the oil temp up to 175 degrees and that is in shirt sleeve weather.

Bill

 

I think this is really interesting info from the OP's experience and especially the oil analysis. But there are a couple of things that I also came across in the posts. Condensation in the exhaust; I have many. many times seen cars w/ water dripping out of the tailpipe. Seems to me it can go on for quite a while so getting the engine up to temp would be a poor indicator of clearing the exhaust. I can also see that there could be low spots in the usual contorted pipes and they could take a long time to dry out and might need full throttle exhaust flow to do it rather than just getting up to a temp. Also we know the headers get hot fast, but that 'hot' fades quickly beyond the headers. How hot is the exhaust at say just ahead of the rise over the axles? Condensation in the oil would be similar. Getting the oil up to temp, and that means >212F, doesn't mean the water is gone. How long I don't know, but driving until the gauge hits 212 I think is far from evaporating all the water out of the oil. Finally, I don't track this, but how many times I have heard from trusted sources something like this, 'more engine wear comes in the first 30 seconds after it is started than in XYZ' gives me hesitation in adopting any 'start it and run it every XYZ weeks' while being stored program. I am lucky in living in southern Va so it is a rare month when my Stingray doesn't get driven. So this discussion is mostly academic for me but I enjoy it because it is still interesting.

 

I would not start the car; "twice a month." Unless I was going to drive the car some distance and time. No real advantage to that often of start ups, without driving.

 

[QUOTE=Getting the oil up to temp, and that means >212F, doesn't mean the water is gone. How long I don't know, but driving until the gauge hits 212 I think is far from evaporating all the water out of the oil.[/QUOTE]

Of the various engine components that are lubricated by the oil, some are hotter than others. The oil temperature sensor, whether it is located before or after the cooler, reads an average temperature of all oil that is returned. I assume that oil that has splashed on cylinder walls, and perhaps circulated through main bearings, gets well above 212 degrees. Thus, even though the oil temp gauge may read only 195 does not mean that oil has not gotten hot enough to boil out the condensation. Just my speculation.

 

Unfortunately where I live driving my car is not going to happen for about 6 months of the year due to salt and gravel on our roads, this is a long time so I will start my car once after 3 months and let it run for 20 minutes or so just to lubricate the seals. I had my water pump seal let go on my c4 with very few miles on it due to sitting too much.

 

The source of the water in both exhaust and the crankcase (via piston blowby) is the hydrogen which is contained in gasoline. Gasoline is 86-87%w carbon atoms and 13-14%w hydrogen atoms. During combustion, the carbon atoms end up as CO2 and the hydrogen atoms end up as H2O, otherwise known as water vapor. So the big cloud of steam coming out of exhaust pipes on a cold morning is simply the water vapor that started out as hydrogen atoms in the gasoline. Anywhere that the exhaust gas goes (mostly to the exhaust pipe but some by piston blowby to the crankcase), the water vapor goes with it. When the crankcase is cold, some of that water vapor condenses into liquid water on the cold metal in the crankcase and mixes with the oil. Similarly, when the exhaust pipes are cold, some of the water vapor condenses on the cold muffler and exhaust pipes, forming the bit of liquid water that dribbles out of the exhaust pipe.

Getting the liquid water evaporated out of the oil does not require the oil to reach 212F. Think about your clothes dryer. It doesn’t get your clothes anywhere near 212F to get them dry. The warmer it gets, the faster evaporation takes place, and the tumbling in the dryer helps too by making sure that liquid water isn’t hiding in stagnant zones. So by analogy, with all the turbulence in a crankcase, getting the oil to 160-170F is plenty to evaporate the liquid water.

 

Y'all are thinking about the mechanicals, but don't forget the tires. If you have all-season's you're probably fine, but the summer tires (like the Michelin Super Sports) shouldn't be driven at temps lower than 40F.