I know this sounds stupid but I cannot find what the factory spec is for engine oil for the 08 LMM, numerous searches only come up with a bazillion hit on recommended oils not on factory spec oils, I did not get an owners manual with my truck.
08 LMM oil spec
- Thread starter Mogman
- Start date
No there is an industry standard that should be recommended by GM like SI-4, FA-4 CK-4 etc as a minimum required spec. just cuz it says turbo diesel oil for example does not mean it is recommended by GM, or even suitable for the Duramax
You're not running after treatment system on the h2 right? Just buy whatever C rated diesel oil you can find, don't have to worry about the "higher zddp" oils affecting the exhaust. That being said, the Dmax being a roller cam won't be picky in that aspect. The new ck oils are supposed to be backwards compatible with older engine. You're over thinking it
I am a little cautious about using a full synthetic, with 300K on the engine I am afraid it may start leaking, with the low oil pressure I am thinking of switching to 20W-50, being TEXAS and summer I always thought 15W-40 was a little light anyway, I think the manufactures recommend thin oil for fuel economy.
15w-40 is NOT a thin oil. Understanding the low pressure issue you have, find a 20w-50 diesel spec and have at it.
You ever looked at the factory bearing clearances? There is a reason for 15w-40.
Running a thicker oil just heats it up to a higher temp and will fall to the same viscosity and pressure as the thinner oil did before. It’s going to look like it did something till everything get hot and you are driving it for a while.
I find it odd you are looking for a specific spec for “duramax/gm rated oil” but yet you are trying to bandaid an oil pressure issue without actually diagnosing that all the way, makes no sense on a engine that could possibly already be hurt.
There are plenty of 1000hp trucks running 15w40 with good oil pressure
I noticed my 200k+ mile LBZ was running lower oil pressure than I would like to see (hot idle was mid teens and cruising at 17-1800 was mid to upper 30s with no load at full temp) which prompted me to start running 20w50 to see if it would help. 40k miles later, the oil pressure is up (low 20s hot idle and mid 40s cruising) from what I was seeing with 15w40, and oil temps are no different. I know its a band-aid, but it seems to be working for me so far.