Join Date: May 2004
Location: Morganville, NJ
Thanked 19 Times in 16 Posts
Even though it sounds backwards, changing to a more viscous oil will not decrease oil consumption in these or many newer designed engines.
The low tension piston rings absolutely need the low viscosity oil, otherwise they are starved for lubrication, which causes them to overheat, and begin to microweld and eventually lose tension. This is first evident with the oil control rings, as the oil consumption will increase dramatically. Then the compression rings slowly wear and grind on the cylinder walls. This wear is most prevalent during cold starts when the oil just can't get to where it needs to fast enough. You wouldn't believe how fast the rings overheat, even at cold start, when they have no/limited lube.
You are correct about the oil causing the cat codes as it slowly poisons the converter.
All K series use oil, the harder they're run the more oil they use. The K20 engines that rev, like the type S engines and the Civic Si engines even when new use more than a quart in 5k if used a little hard, if beaten upon, the consumption goes up. On these motors they spec 5w30, mainly as a way to keep oil in the bearings at such high revs.
The early K engines seem to be prone to camshaft wear as well. It appears to me to be insufficient hardening of the cam lobes. Mainly exhaust cam.
Using the highest quality 5w20, in ones that spec it, you can does significantly reduce the chances of them becoming major oil users, save ever overheating them. All bets are off at that point.
I've seen it first hand with my sister's previous shoebox Civic Si, it used about a quart between changes. Which for her was 5 to 8k. I made her go and get oil, and the Honda filters to use during changes. She went and got some really cheap, VERY cheap Citgo 5w20 at one change at around 60k. After that change, its oil consumption went up to more than 2 quarts every 5k or less.
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