Engine oil viscosity

I have always used Kendall oil in my bike engines but I found that after building my LTD it would not stay clear for very long. I talked with the guy I buy oil from about adding some 20W50 to it and he said up to one liter for an oil change would be good as when I ran 20W50 alone the engine would take forever to warm up in the spring and fall. Years ago I think it was in a black quart can and was called Supreme which they stopped making about eight years ago and is now called GTX. I have had no problems to date on my '74 900 and ran a mix of 3/4 liter to an oil change of the 20W50. I have heard nothing but good things of the Shell Rotella oils. Considering what has been going on with gasket changes I would not ever consider using synthetic. Have you ever asked your dealer for a synthetic rated oil filter for a Z1 or KZ1000?

I've used full synthetic oil (Mobil 1 Racing 4t 10W-40) since 2006 (about 15,000 miles) and have not had any problems with leaks. I've never needed to have any engine work done since buying the bike new (about 56,000 miles) so it still has the original head & base gaskets and seals. I doubt that oil filters care what oil they process since they only filter out particulate matter. I happen to use K&N oil filters. Ed

Bountyhunter said
No. I use 10-40 in the winter and in the summer I use a 50-50 blend of 10-40 and 20-50. But 10-40 alone is adequate. The most important thing is to change the oil and not push it. factory spec is 3000 miles, I change it sooner.
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I like the idea of blending them, but was advised against that by the Brad Penn distributor I bought it from. I don't recall the reason, but I'm going to check into that again, since you mention it.
Any additional input from forum members on this would help as well...
Another thing...what do the numbers 10, 20, 40, 50, etc., and letter "W" mean when choosing oil?
daveo

Joe Gibbs Racing oil, now named Driven Racing Oil in 15W-50 Synthetic, after breaking in a newly built motor with his Break in Oil.

A trifle expensive, but it's running in expensive over 180 hp liquid cooled ZX motors.

The numbers mean a couple of things, including tests that were done. In a nutshell, though, the lower number means it will flow better (thinner) at lower temps, but as the engine warms up it flows like a thicker oil. Best of both worlds. follow this path for a complete explanation:
www.upmpg.com/tech_articles/motoroil_viscosity/

Hmmm.... I could be wrong here but I don't think 10-40, 15-40 or 20-50 oil gets thicker when warming up. I think it is supposed to protect wear surfaces like 40 or 50 weight when hot.

missionkz wrote: Hmmm.... I could be wrong here but I don't think 10-40, 15-40 or 20-50 oil gets thicker when warming up. I think it is supposed to protect wear surfaces like 40 or 50 weight when hot.

A multi grade oil like 10-40 does not get thicker as it warms up, it gets thinner. But it is 10W base oil with viscosity increasers that make it the viscosity of 40W oil at a higher temp (I think it's 100C?) which means multigrade oil's viscosity is more stable over the operating temperature range. The fact it's like 10W oil when cold means it protects a lot better when starting up cold but still acts like 40W oil when hot.