Jul 05, 1997
RAY: You have an old heap, like a nice 1974 Chevy Caprice and it's starting to burn oil at an alarming rate. You go to the gas station. Every time you go in you say check the gas and fill up the oil. At any rate you go in this one time --
TOM: I don't see anything puzzling about any of this yet.
RAY: Hang on. We're getting there. Butch, the chief mechanic at the gas station says, "No wonder you're burning oil. You've got this wimpy little 10W-30 motor oil in here. You need the oil that conquered Mt. Kilimanjaro. You need 10W-50 or 20-50. You need some nice thick oil, because the oil pump is pumping the oil past the rings."
TOM: Sounds reasonable to me.
RAY: Anyone that has a package of Lucky's rolled up in his T-shirt sleeve must know what he's talking about, right?
TOM: Are his knuckles scraped?
RAY: No. They're manicured. Anyway, Butch changes your oil and puts in 20W-50. You drive away and notice that you can't see Butch in the rear view mirror due to the cloud of smoke that's behind you. But, you're not worried. You figure it'll take a while for everything to work.
Many weeks go by and you notice that you are burning oil at about twice the rate that you were before.
The question is, what happened?
RAY: Here's the answer. Putting 20W-50 into the oil crankcase won't necessarily slow down your oil consumption if it's getting by the rings, because there are three rings in every piston, and the bottom ring -- called the oil control ring -- is supposed to scrape the oil off the cylinder as each piston descends.
Now, if the oil scraper ring isn't working, that oil won't get scraped off. Instead, there'll be a thicker film of oil on the cylinder wall. And, the engine will burn up that oil as it would the thinner viscosity. In fact, it'll burn it up faster, because the film is thicker.
TOM: It's twice as dense as the lighter oil.
RAY: Exactly. And Butch is twice as dense, too. That's why sometimes using heavier oil, although, intuitively it seems like it should reduce your consumption, will in fact increase the consumption because it's leaving a thicker film on the cylinder walls.
Instead, it comes out the tail pipe as pretty, billowy blue clouds.
TOM: It is kind of pretty, isn't it? Especially when it's sunset and the sun is coming down through those clouds into your cloud of blue smoke. I think it's rather nice --
RAY: Poetic, actually.
TOM: You don't see that anymore.
RAY: Thank God!