The Stovebolt Site Forums The Shop Area Engine Shop oil recommendation?

Well after an hour or better in searching all over the web, I cant seem to find a straight answer on what oil is recommended for 1963 GMC 305E motor? Any help is appreciated?

In the past, I have always used 20-50 conventional in my 51 GMC 228.

Ive thought of that actually. Was concerned about the lack of zinc. I have a 62 261 that I run 20/50 Valvoline VR1. A bit pricey tho. Wasn't sure if it was a concern in this particular motor. Seems like straight 20 weight was the oil recommended when new?

How many miles/hours are on the engine? the 305 is a heavy duty industrial type engine, and it's probably got a little wider clearances than most similar-sized automotive engines. I'd recommend something like high detergent straight 30 weight DELO. If very low winter temperatures are encountered drop back to 20W-20 during the winter. That's what was recommended for most commercial engines from the 1940's and 50's.
Jerry

The guys over at the ecj5 forums recommended using the 15w40 rotella for the old Buick motor in my cj5. They specifically mentioned the higher zinc content since the oil is meant for a diesel motor.

Hours? probly a ton sitting at idle.. Miles? less than 11k

I didn't realize that diesel oil has a higher zinc rating. 15w40 Rotella is what I use religiously in my tow truck. IT is a diesel by the way.

Everything I run gets 15W-40- - - - -tractor, cars, trucks, lawn mowers, even my Harley soft tail! 5-gallon pails from the local farm store makes it cheap and simple to change oil. None of our vehicles have the microscopic clearances that require the super-thin oils, and they've all got high mileage which translates to wider clearances. Running the same oil an engine needed when it was new and close-toleranced after it's got some age and wear is sort of stupid.
Jerry

Ok Im sold 15w40 it is. Thanks

I'll agree with Jerry. You can't go wrong. I looked through my manuals and I don't have that year GMC. I have vintage Motor's and Chilton's, but they only give quantity specs, just like 60-66 GMC guy's site. I believe you'll find viscosity recommendations in the owners manual, if you can find one!

FYI, diesel oils have recently been changed to reduce zinc and phosphorus content. I run Delo 400 15W-40 in my F250 and have used oil analyses the reflect the reduction over the past few years.
But a diesel oil is still a good choice.

Thanks for the quick input. Much appreciated.

I have several flat-tappet motors in bikes trucks and cars. After DELO dropped the zinc etc additive I started using an additive that cost about $12 at the FLAPS. Then I discovered valvoline racing oil with zinc so now I'm using that. It's a little more expensive but not $12 more per oil change.

yep Valvoline VR1 is what I use in my 261. I just changed da oil today and put in 15w40 Rotella in the 305E. Actually got it started for the 1st time since piecing together. Far from done tho. Idled at 55 psi oil pressure. I was impressed to say da least. So whats the thought on a zinc oil additive?? Needed or not? I know it wont hurt, But NEEDED is the question???

Using oil with high ZDDP will not hurt a normal Stovebolt six engine.

However, while it should be used during break-in, high ZDDP is not needed after break-in.

Awesome. good to know. Everything I got is definitely broke in...