Engine/Transmission (1998.5 - 2002) Is cj4 a better oil than ci4+ for a 98.5 engine

[ESwartzer]

I,ve read other threads regarding this issue but they always seem to veer away from the original question. I,ve been running Amsoil 15w40 for years with good results, but I know that running a lower viscosity oil like a 5w40 or 5w30 will give somewhat better mileage because of less drag on the engine. With diesel prices over 4. 00 per gallon fuel mileage is a top priority. The 5w40 is a cj4 oil and the 5w30 is a ci4+ oil, and I assume that both would deliver a bit better mileage than what I currently use. I tow frequently in both California and Arizona and The 40w cj4 would likely give better protection in the heat than the 30W ci4+. But is it the correct oil being that it was formulated for newer engines? Any "informed" opinions would be appreciated.

Thanks ES.

 

[Vaughn MacKenzie]

Given that you tow in hot climates the "best" oil for you I feel is what you have in there now. The 5w30 is too thin for hot climates/towing and the new 5w40 formulation for 2007+ trucks doesn't have as good of additive package. I did try 5w30 Series 2000 in my '01 once and the wear metals went up quite a bit and I saw no noticeable MPG improvement. The oil "seemed" too thin in that I did have some oil consumption and noticeable blowby (this was on a well maintained 40,000 mile truck). In the time I ran the 5w30 we saw temps up to 110F and I'd never run it again as long as I live in this region, I would if I was a cooler climate.

 

[ESwartzer]

I had a feeling that the mpg improvement with the 5w30 would be miniscule. I think you are right in that I should stay with the 15w40 in this climate.

Thanks Vaughn

 

[Vaughn MacKenzie]

You are welcome ESwartzer

 

[AABEN]

The CI-+4 is the best.

 

[Mikey-KE7LBB]

https://www.turbodieselregister.com/magazines/Issue_057.phtml



Read pages 56-61 and it should clear things up