My truck pings real bad under hard acceleration. It's been running the same 10w30 for like a year and a half now, cause I've just not gotten around to changing it. As I'm setting up a schedule for semiannual oil changes, I realize I'm getting close to my set winter change.

Today at the shop, I was working on a different truck that called for 10w30. The other guys at the shop said to just use 15w40 diesel oil instead, that the older engine would prefer it. When I pulled my truck in for a quick after-work check, the same guys said the same thing, that I should top it off with 15w40. The Haynes book, my bible for this truck, says 10w30 for the winter. Who should I trust?

 

The manual.

 

The Haynes book does not and in most all cases NEVER states required. The choice of any motor oil should be first what the OE specification is (not the viscosity) and then consideration is mile on the engine and overall engine condition and then what is the operating environment mostly the normal daily ambientes. This has always for decades been the proper way to choose motor oil with few exceptions. So technically speaking both guys in your first response were somewhat correct.


Or if totally confused go to the original Owners manual as Meb posted
Hayne Chilton Clymer etc., generally speaking at least prior 20 years ago before they all sold to one publishing printing company get a majority of specification directly from factory service manuals. the days of them literally tearing a vehcle down for their own pictures is gone with very few exception..

 

This is for the 1986 truck, but I would think that the earlier 1984 engine would be close to the same as this.....

 

That chart is Old School accurate. Funny they that is auto manufacturers “dumbed” up the what to use oil because to many DIY and even service shops (even today) get it all wrong about what is the best viscosity to use.


I was lmao on the owners manual page 6-12 , service section 1 in your post . How perfect is that ..