15w40 in a 10w40 application

Messages
7,550
Location
North Alabama
I've been curious about something for a while. From everything I've read here & elsewhere, it seems that from the 1960's thru at least the late 1980's, folks had all sorts of problems with 10w40 motor oil. Most of the complaints focus around the "fact" that it broke down early, leaving behind excessive deposits & sludge. On the other hand, an oil of similar viscosity, 15w40 HDEO, is constantly praised for the performance it has consistently delivered. My question is this: Have any of you BITOGers ever owned a car (with a known oil change history) that called for a 10w40 oil, but one in which you used a 15w40 diesel oil instead? If so, what were your observations using a 15w40 diesel oil over the gas-engine rated 10w40?
 
Messages
498
Location
N. Texas
Had a Pontiac with a 350 that called for a 10w40, that was my grandmother's before mine, she and I both used nothing but straight 30 weight in it back then (QS). Not sure how many miles were on it when I got rid of it in the 80's. But it was driven from Texas to Arizona to Missouri pretty regularly. Never heard of diesel oil back then either though.
 
Messages
6,388
Location
Washington St.
Modern 10W-40 oils are much better than the oils available at that time. 15W-40 oil with dual rating for diesel and gasoline engines are also very good...use either. Ken
 
Messages
441
Location
Toronto, Canada
I think you will find that the dual rated 15w40 HDEO are among the best conventional oils available. The only concern I would have about their use in an engine that likes a 40 weight would be in cold weather use. You probably don't have that problem in Alabama. I have used a 15w40 in summer in a Porsche. So have many others.
 
Top