WE USE SAE 40 VALVOLINE FOR BREAK IN AND I DONT CARE IF ITS EXPENSIVE . I DONT RECOMEND TO USING SAE30 BECAUSE THE OIL TEMP AT BREAK IN IS GOING TO BE CONSIDERABLY HOTTER AT THIS TIME THAN ANY OTHER EVEN IF ITS NOT UNDER HEAVY LOADS SO RATHER THAN HAVE THE OIL BREAK DOWN SPECIALY HOW A CHEAP OIL WOULD I USE SAE40 THE OIL TEMP USUALLY WILL COME DOWN AS MUCH AS 40 DEGREES.
HOPE THIS HELPS YOU OUT LAZ MESA WWW.MESABALANCING.COM

Reed, maybe you should do a little research on aviation oils.
One more thing about aircraft engines; They typically have wider clearances because of the cooling medium they use, along with the low rpm usage, typically redlining at 2700 rpm's. Some of the geared engines spin faster, in the neighborhood of 3500. Show me any other application where you are virtually guaranteed 2000 hours of usage between overhauls.

That aviation oil you are talking about isn't 100 W, it's 100 grade. That is the same viscosity as you call 50 "weight". Aircraft engines are usually air cooled. One of the properties of engine oil is cooling, remember that oil cooler? The clearances on an aircraft engine are much larger, different coefficient of expansion. The aircraft oil must cool the engine more than your liquid cooled engine.
"Weight" is not a term the oil industry uses, they use "viscosity index". As best as it can be traced, the term "weight" entered laymen usage when the public couldn't or wouldn't use or understand viscosity index. Then the letter "W" showed up on oil cans. That "W" was for winter. What that meant was the oil was formulated to have a pour point of 0 degrees. But that "W" further cemented the term "weight".

Hey MKast... thanks for the info... Like I said... that was information passed on from my pilot buddy... I have a general understanding of aviation engines and air cooling... and I understand viscosity... I thought when he said 100 weight... that there must have been a misunderstanding... I can remember in the early days of oil grading when you used to see on the cans.... 30-30W.... and I am aware that the W stood for Winter.... I use some non-detergent turbine oils in transmissions... Shell calls it Turbo T-68... there is no "weight" but the viscosity is close to 20 w . Now we have API labels with S and C ratings SD SE SF etc are for Spark ignition CC CD CE etc are for compression ignition ( diesel)...

I have always use the 30 w for break in.Then after the first pull to seat the rings I changed to my regular oil and ck the oberg filter.

On every motor that I have dynoed never saw any oil temps over 200.I would think if it had a high temp it would mean a clearance prob?

Hey Guys,
I am in the process of changing heads and cam on my engine, not touching the shortblock. I ran 20-50 synthetic last season.
Should I run for a short time with regular SAE30 before going back to the synthetic?

I don't see the need; rings and bearing are already broke in :cool:

If it is a roller cam, no use what you have been. If it is a flat tappet, then use a conventional oil for break in and another 20 hours.

Chris

Thanks Guys!
It is a roller cam engine. I go right to the synthetic then. :)