The Diesel Stop banner

5W-30 or 15W-40

6689 Views 3 Replies 4 Participants Last post by  newtodieseling
This has probably been asked a more times than anyone can count but - I am installing a Amsoil by-pass and they are telling be to use 5W-30 Amsoil HD Diesel oil. I have been using 15w-40 motorcraft until this point and it has worked fine. What is the difference in the two weights? I live in Southern California so weather is fairly nice all year around. Thank you in advance and I did use the search portion of this site with little luck prior to the post /ubbthreads/images/graemlins/vulnerable.gif
See less See more
1 - 1 of 4 Posts
One of the"problems" with a 6.0 is that it "shears" oil. Its starts out 40 weight & in about 3000 its 30 weight. If you change oil on a fairly quick time frame (most guys here go 5k), its not that big a problem. However, you just spent +/-$500 and are going to use oil thats twice as expensive. If you don't need the lower viscosty because of surging or cold weather starting, you are seriously wasting a pile of money.

There is no doubt that a by-pass filter is a good thing, but synthetic oil is wasting money unless its needed. If you are going to go synthetic, go find some Schaeffer's 9000 5W40. Its one of two that are VERY shear resistant in the 6.0, and if you take OA's on a regular basis, (5k, 7.5k, 10k, 15k, 20k) to determine when to change, you'll recoup the cost of the by-pass and more expensive oil. I'd be surprised if you can't get 20k out of the Schaeffer's. The AMSOIL will shear just like dino & be 20 weight in a few k miles.

I've used regular Delo 400 15W40 year around, and change at 7.5k intervals. It shears to 30w, but the truck runs fine - no surging, no smoke, fires right up & runs smooth. My OA's have shown the oil working well at 7.5k. It costs a bunch less than synthetic too.
See less See more
1 - 1 of 4 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top