10w30 or 15w40

[William F.]

I know this has been discussed before, but I'd like a clear choice:My summer daytime temps are never below 80 and often in the 90's; I don't have to worry about cold starts in winter. For best engine longevity in the summer(not worried about slight improvement in milafe or power) which is BEST for my 67 300hp with moderate to high milage-10w30 CJ-4 or 15w40 CJ-4?I can get either one. Will the 10w30 which is recommended in the 1967 owners' manual be too thin during these hot summers?

Thanks

[Joe L.]

Re: 10w30 or 15w40

I know this has been discussed before, but I'd like a clear choice:My summer daytime temps are never below 80 and often in the 90's; I don't have to worry about cold starts in winter. For best engine longevity in the summer(not worried about slight improvement in milafe or power) which is BEST for my 67 300hp with moderate to high milage-10w30 CJ-4 or 15w40 CJ-4?I can get either one. Will the 10w30 which is recommended in the 1967 owners' manual be too thin during these hot summers?

Thanks

William-----


As you mention, the 10W-30 was the Chevrolet-recommended engine oil viscosity in 1967 and it's still the one I would recommend that you use today.

[Michael H.]

Re: 10w30 or 15w40

William-----


As you mention, the 10W-30 was the Chevrolet-recommended engine oil viscosity in 1967 and it's still the one I would recommend that you use today.

...........

[Stuart F.]

Re: 10w30 or 15w40

Did I tell the one about the Pontiac 389/421 engines?

Stu Fox

[Duke W.]

Re: 10w30 or 15w40

Don't forget to pick up some Mil-L-2105D oil that the owner's manual/service manual recommends for the transmission and axle.

Duke

[William F.]

Re: 10w30 or 15w40

What about the Pontiac 389/421's?

[William F.]

Re: 10w30 or 15w40

Duke et. al.

Just want an answer ,not "either one". Must be a reason why they make BOTH10w30 AND 15w40. My engine probably has 100K miles, at least on lower end(had top rebuild).

Will appreciate help.

[Stuart F.]

Re: 10w30 or 15w40

Bill;

We just hashed this same subject over a week or so ago and that brought in the 389 and 421 Pontiac engines of the early 60's, and all the problems they had with bearings - that was fun. Another simplistic conclusion was some of us like higher oil PSI readings on our gauges and some of us don't. Most posters had good results with one multigrade or the other, a lot dependent on the use you intend for your Vette. With your L-75 engine, just for normal year around driving, the 10w-30 will probably be fine. You already have the "flat Tappet" wear concern covered if you have the CJ-4. As for me, having an L-76 SHP and living here in central Florida (as well as having stocked up with 15w-50), I find the latter works well for me. And besides, I like higher oil pressure readings as I recall back in the day I sweated low readings idling in traffic with 10w-30 or the old 20w oils.

Stu Fox

[Michael H.]

Re: 10w30 or 15w40

Don't forget to pick up some Mil-L-2105D oil that the owner's manual/service manual recommends for the transmission and axle.

Duke

My reference to "90W gear oil" in a previous post was meant in jest. If you want to make it sound like I REALLY don't know why we shouldn't use 90W gear oil in our engines, that's ok.
I don't know all there is to know about motor oil but I know I'll stick with recommendations from people that DO. From your 15W40 recommendation, I don't include you in that group.
If YOU want 15W40 in your engine, go for it. But don't try to convince the rest of the world that it's the ONLY oil to use. Most know better.

I try to respect everyons opinion here but no one likes it shoved down their throat.

Edit: There. I added a smiley face.

[Duke W.]

Re: 10w30 or 15w40

Get a grip! My reference to Mil-L-2105D in this thread is to point out that there are recommended service fluids in 40 plus year old owner's and service manuals that are no longer available.

Likewise, there are products available today that did not exist over 40 years ago.

As I stated in the last thread on this subject, virtually any available multi-grade (and even straight SAE 30) C-category oil is suitable for typical vintage car use in mild to hot temperatures and 15W-40 is the most commonly available grade.

The obsession with this topic has beome pathological.

Enough!

Duke