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Engine oil for GM 366 gas truck engine

A

andy r

Member
Interested in what weight oil you guys would recommend for a 1980 Chevrolet 366 gas engine. Gross vehicle weight about 26,000 lbs. Oils have changed so much over time I didn't know if the owners manual would actually recommend the best oil from what was available today. I do not operate the truck in the winter. Thanks.
 
I'd run the same 15w-40 that I run in my diesel tractors. No reason to have more different types of oil laying around.
 
I did the 15W-40 diesel oil thing in my 366 in my 92 C-70, shortly there after it started absolutely drinking oil, like a quart every 20-30 miles. Coincidence??? maybe it just wore out all of a sudden(250K plus).

I had been using cheap 10W30 or 10W-40 in it.
 
Years ago GM came out and said NOT to use 10w-40 oil as it was making the tops of the pistons carbon up. They said use 10w-30.
 
i use 15-40 rotella in everything but the wife's new jeep, i have it around here for the heavy stuff, never had any engine problems, ive heard from several places that the lighter new oils designed for the newer engines dont have some of the additives that the older engines need, dont know if its fact or not, but since i own only older vehicles by choise, i use the heavier oil
 
(quoted from post at 06:58:57 03/23/16) I did the 15W-40 diesel oil thing in my 366 in my 92 C-70, shortly there after it started absolutely drinking oil, like a quart every 20-30 miles. Coincidence??? maybe it just wore out all of a sudden(250K plus).

I had been using cheap 10W30 or 10W-40 in it.
Click to expand...

I'm guessing the Diesel oil had a much more aggressive detergents package than your cheap oil.
It cleaned out the sludge and ring area.

Diesel 15/40 rotella is all I have ever used in everything here
From the crawlers to the lawn mower, including cars and pick-ups
Never a problem

Tom
 
ran 10w30 in all chevy grain trucks back in the day 350s 366s 427s what ever was in the operation at that time. never had engine issue. still using dodge pickups and same oil still in it today. and always have 200,000 plus miles on the stuff before scrapping or selling, current unit is at 120,000. if you don't run it in the winter then throw in 30wt and us it. worst thing for any vehicle is sitting.
 
I would use the same bulk 15-40 oil that I already have here anyways for use in my diesel tractors. When I worked at the power company during that period of time we used the same bulk 10x30 that was used in all our gas engines their.
 
Andy I owned several of those trucks, put over a million combined miles on them, used 15w40 oil in all of them. never had a problem with it.
 
Back in the 80s the company that I drove used nothing but Rottela 15-40 in all the gas powered trucks. At that time half of the fleet of truck(50 trucks) were gas powered Chevy 327s-427s with maybe 6 powered with 366 engines and no problems.
 
(quoted from post at 05:12:29 03/23/16) Years ago GM came out and said NOT to use 10w-40 oil as it was making the tops of the pistons carbon up. They said use 10w-30.
Click to expand...

One engineer over there also said "10-40 oil never should have seen the light of day".Yet today B&S recommends it on at least one of their engines for warm weather use.Go figure.
 
If you check the YT archives, this question gets asked several times a week with about the same range of answers. Most of the motor oils available today are better than any available 35+ years ago. Any oil recommended in the 1980 owners manual will still be adequate to use today and will not cause any problems. If you are looking for the absolute best or optimum oil for that engine, in the condition it is in today, I would ask this question on the manufacturer's website. How many miles are on the engine?
 
I use Kendal 10w40 in my 1979 Chevy C-70 with 20,000 original miles on it. I tried 15w40 once, and maybe it was just me, but I felt that it did not like it.
 
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