Conventional 10W-30 or a diesel 15W-40?

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Feb 21, 2004
Is a thinner oil or a thicker oil more desirable for an OHC vehicle because I've heard that pushrod engines can run a little bit thicker oil than an OHC engine. Do you think I could use a 15W40 diesel oil in and OHC engine with 153,000 miles? I'm might try it to see if it cleans out any deposits and I've heard alot of people on here say their engines run so much smoother and quieter with a 15W40 diesel oil.

I just have a hard time putting anything in my engine other than the weight/specs of oil that my manual states. My manual says to use a 10W30 SL/GF-3 oil and I'm having a hard time deciding if I should use something other. I mean 15W40 is thicker than what the manual says and the diesel oils aren't GF-3 certified. I'd like to use Rotella 15W40, Mystic 15W40, Delo 15W-40, or another good one. Anyway what do you think?

Maybe I'll just stick with the SuperTech 10W30 and ST filter.

[ May 22, 2004, 10:57 PM: Message edited by: gtm245 ]
These heavy duty diesel (also rated for gasoline) type oils are available in 10w30 grade also. You will have to go to a truck parts supply to get it though, or maybe a truck stop, or through the net. So you can stick with the owner's manual recommendation (both in grade and that it will be SL rated for gasoline engines) and get the higher detergency and other goodies of the HD oil too.
We've run Pennzoil HD 15W-40 in all of our vehicles without any problems. This includes an 89 Taurus, '85 and '95 Honda Accords, 92 Cadillac deVille, and 97 Plymouth Voyager. None of these call for 15W-40, and none of them have had any oil related problems in at least 100,000 combined miles.
I am using 5w30 with 25% M1 for exactly the same reason you are thinking about 15w40 heavy duty oil.
I like Delo 400 but decided on thin oil because gas is too high now.
If you are not experiencing major oil usage with the 10w30 then why change from a good thing? Also, some 10w30's are thicker than others at operating temp while still delivering fast start-up lubrication. Do some research and find one at or above 11 cst@100C if you want a slightly thicker oil.
I am agonizing over a similar viscosity dilema. The 15w-40 oils seem too thick for my climate, but there are apparently no "absolutes" when it comes to ambient temperature and viscosity. Maryland pretty much has winter temps in the low to mid 20's (F), occasionally dipping to 10. Am I being overly concerned with 15w or 10w ?
I would like to run a diesel oil in everything for the detergency and convenience of a single oil type.
Currently I use Amsoil 10w40 (SL/CI4) in my farm tractor and landscape equipment, and 5w30 (gas)(SL/CF) in the autos (F150 V6, Villager V6, GrandAm 4) which spec 5w30.
Here is what I am considering as an all fleet choice: (in order as of today)

Amsoil 5w30 Diesel Oil SL/CI4
Amsoil 10w40 Gas/Diesel SL/CI4
Amsoil 15w40 Diesel Oil SL/CI4

My main concern is the winter use of 10w & 15W
Certainly I wouldn't use 15w-40 during the colder New York months, but it should be fine in Spring and Summer if your manual calls for the usual weights. I'd agree with TallPaul -- check out your local truck parts retailers for the less common 10w-30 diesel lube.
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