Condensed blow by or oil at the bottom of the intake manifold?

I just noticed a phenomenon that I would like other Gen II owners to investigate.

I usually drive at about 65 to 70 mph for 25 miles on the Interstate on the way home from work.

Lately I have been checking for fluid at the bottom of the intake manifold to see if there's a correlation between the oil consumption of my 05 Prius and the amount of fluid that collects down there.

I have observed that there's a stark difference in the presence or absence of this fluid when the engine is hot or cold.

Upon opening the throttle plate to look down into the bottom of the intake manifold while the engine is still hot, I find there isn't any fluid pooled there - in fact, it's completely dry. I have checked this several times now - always dry.

After the car has been parked in the garage overnight, I check again when the engine is cold. To my surprise, I find there's a film or shallow pool of fluid at the bottom of the manifold after the cool down period. I have checked this several times already as well - always "wet" in the cold engine.

I had thought that this fluid was engine oil that had dripped down from the cylinder head through worn valve guides or valve seals but now I'm not so sure. I haven't noticed any smoke exiting the exhaust pipe in the morning at start up that would prove that oil that had dripped into the combustion chamber from the valve train.

I suspect that this fluid is condensed blow by vapor that stays in the hot engine after shut down. I'm sure that some of that blow by contains some oil mist too. I see vapor rising out the oil fill hole when I remove the cap right after I drive into the garage after my evening commute. Is this blow by? I really don't know.

My 05 is consuming about 1 qt of oil every 4500 miles which isn't too bad after 193K miles - mostly highway miles at that. It seems that a significant amount of this oil consumption might be due to blow by.

I am particularly interested in the observations of other Gen II Prius owners with less than 100K miles who have no oil consumption issues. Do any of you see a film or pool of fluid in your intake manifold after an overnight cool down after driving at highway speed for at least 25 miles the previous day?

Yesterday, I changed oil and poured in Pennzoil Ultra 5W30 SN for the first time. This oil is claimed to have a very low NOACK value (Walmart has discontinued it and Pennzoil had a rebate offer so I bought some for about $2 per quart which is a steal). I'm interested to see if there's any decrease in oil consumption after switching to PU from Mobil 1 5W30. In theory, if the problem is blow by, there shouldn't be any decrease in oil consumption. If it's oil evaporation, then I should notice a slight decrease in consumption over 4500 miles. I'll let y'all know what I found in a couple of months.

 

Since the fluid evaporates and gets burned during the next drive it seems logical that it's gasoline but it still might be engine oil. I'm pretty sure that the intake manifold temp gets high enough to evaporate oil too. Not likely to be water. I've managed to obtain a small sample of the fluid and it's not clear.

 

So Ed, does your 07 consume oil? If so, how much? Does the oil/fuel mixture evaporate from the intake manifold of your car when the engine is at operating temperature? That's what I'm asking others to check. Without success thus far since no one seems curious enough to do it. It's easy and quick. Remove the air filter box cover, turn the throttle plate, and look down into the manifold with a light source - takes less than 30 seconds each time.

I suppose I didn't make it clear why I want to know this.

There are many PCers who claim that their Gen II's don't consume any oil between changes - they say the level is exactly the same on the dipstick after 5000 miles or more. If this is true, these owners shouldn't have any oil at the bottom of the intake manifold after the engine cools down from operating temperature.

If it's a well known phenomenon, then ALL Gen IIs should consume some oil between changes - even if it's only 8 ounces per 5000 miles.

It seems to me that you think that I'm "beating a dead horse" - and you may be right.

Nothing else better to do during this three day weekend I guess.