high oil consumption with only 80k

"George" wrote in message news:XP8Te.690$ snipped-for-privacy@bignews1.bellsouth.net...

Assuming your catalytic converter is still working, it will take care of the oil smoke once the car is warmed up. Do you get any blue or blue-gray smoke for a short time after a cold start? A black tailpipe is normal these days.

1 quart in 1000 miles is not all that bad. I don't know what Toyota claims is acceptable, but I am confident GM would say that is OK (but I would not be happy - it has been a long time since I had any car that used 1 quart of oil in a 1000 miles, and it was British). Howver, all car consume some oil. There is always a thin film left on the cylinder walls on each power stroke and at least some of this is consumed. Consider this:

I think everyone can agree that even the best oil control rings in the world must leave a thin coating of oil on the cylinder walls. They have to or the oil control rings would not be lubricated. Likewise the compression rings would be running dry and would quickly wear out. How thin do you think this layer would be? Maybe .0000003"? This is really thin, a single oil molecule is around 0.0000003" in diameter. A 1.8l Corolla engine has a 3.11" bore and a 3.60" stroke. This means that there is a cylinder wall surface area exposed to the incoming charge of 3.11" x 3.1412 x 3.60" x 4 = 141 sq. in. The total volume of oil needed to cover this area is perhaps 0.000042 cubic inches. I think everyone can agree that at least some of this oil is vaporized and consumed on the power stroke. For simplicity, we will assume that one half is consumed on the power stroke and none is lost on the exhaust, intake and compression strokes (this seems like a really conservative assumption to me). So, this means that around one fourth of the oil coating the cylinder walls is consumed for each revolution of the crankshaft, or around .0000011 cubic inches per engine revolution. To simplify things further, assume we only drive around in the top gear and never let the car just idle (again, a conservative assumption). For every mile, the engine will turn over around 3000 times. So for each mile the engine should consume around 3000 x 0.0000011 cubic inches of oil. This is .03 cubic inches of oil. In 1000 miles, this is 30 cubic inches of oil. 30 cubic inches of oil is roughly 0.6 quarts!

So you say - BS! Lots of engines don't use as much as 1/2 quarts of oil in three thousand miles. I agree, so where did I go wrong? Maybe the thickness of oil film is too thick. Cut it in half, so now you only use 0.3 quarts in

1000 miles (oil molecules aren't this thin by the way). Maybe only 10% of the oil is consumed (not 25% as I assumed), so now you only use 0.1 quarts in 1,000 miles. No matter how you cut it, your engine is burring some oil. And this doesn't include oil lost when you are idling (particularly when the engine is cold), or oil lost down valve seals (and you have 16 of those), or though the crankshaft seals, or through leaky gaskets, or by evaporation, or through the PCV system (look in the PCV valve and lines sometime...there is oil in there on its way to the intake to be consumed).

So why do so many people claim their engine use no oil. One reason - blow-by. Blow-by past the rings adds material to the oil in the crankcase. Some of this stuff evaporates and is consumed via the PCV system, but other components of blow-by stay in the oil (why do you think oil turns black?). We used to have an old tractor that actually "made" oil between changes - as long as you did not work it too hard. It you do a lot of in-town driving and never really get the oil hot, a lot of contamination can collect in the oil pan (unburned hydrocarbons, water, etc). This crap can make it seem if you are using very little oil around town. But then, when you take a long trip and get the oil hot, most of this stuff will evaporate and be sucked into the engine via the PCV system and burned. With the crap removed, it looks like you had a sudden increase in oil consumption. In reality you did not.

Read the following references:

I would not be thrilled if my car was apparently using 1 quart of oil in

1000 miles. However, I would not push the panic button either. Unless you get a steady increase, I'd suggest you just drive the car and keep the oil checked. I would suggest you have the PCV valve replaced and make sure there are no small leaks. As the Quaker State bulletin above points out, a very small leak can lead to significant oil loss. Not all leaks show up on the driveway. Some engines only leak when running and the leaks can be hard to find. Look for oil spots on the engine or under carriage. Particularly check at the bottom of the bell housing.

Ed

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