I use to work in an auto parts store and was told when I began working there that the rule was the higher the mileage on the engine the heavier the oil you use. For example, a New engine would require 5W20 where as an older engine with 100k+ miles on it would go 20W50. How true is this? I know this is a touchy subject and people have there own opinions and stick by them, but I wana know what weight oil you would use in a 4.9L L6 engine with 130k miles on it.

 

Just my preference, but i use shell rotella 15w40 in my 94 4.9l

 

15w40 for me also. Rotella, Delco Delvac, etc. Any of the good diesel oils. The extra additives in them vs conventional oils today is also helpful for our older motors.

 

Awesome, thanks for the info. I really appreciate the helpfull advice

 

there is no need to use heavier oil then the manufacture recommends unless your engine is worn or uses oil. Just because it has a certain mileage doesn't mean you should use thicker oil.

 

I run with either Rotella 15w-40 or Supertech 10w-40 HM. In either case, I would stick to conventional oil and not synthetic. Blended syn, would be ok, yet, some brands are higher than others, yet still lack higher amounts of ZDDP, Phosphoruos, and others additives. Yet, I also change my oil every 3K or 3months, simply because of hard driving, stop and go driving, and extended periods of no driving. I also use my dremel to cut the oil filter open @ each change to check for failures in the engine.

 

I would concure with this statement. Heavier weight oil will increase oil pressure but that does not increase the oil flow, and can actually decrease flow. The oil flow is what lubricates. In theory, to maximize the oiling system, you should run the thinnest oil possible that still provides adequate oil pressure. Regardless of mileage, as the engine wears and clearances open up, you may have to increase viscocity to maintain this pressure. Many performance engine builders use 10psi/1000RPM minimum and 75psi @ 6000 as the basis for determining the optimum oil viscosity for an engine.

At cold start (even 75*F), the lower the "W" viscosity the better. A 5W-XX oil will provide better flow and wear protection than a 10W-XX or 15W-XX. I can't say I'd ever run a 20W-50 (racing viscosity) oil in any factory assembled engine. Once the oil is at operating temp the second viscosity rating (i.e. -20 or -30) is what you should look at and use for determining optimum viscosity based on oil pressure. In other words, a 0W-30, 5W-30 and a 10W-30 provide the exact same performance once the engine is warmed up, but the 0W-30 will provide better cold start oil flow and wear protection.

To answer your original question, I would probably run 5W30 in your 300I6, unless you know for some reason it's very badly worn. Oh yeah, and I wouldn't recommend trying the 75psi @ 6000 rpm test on your I6 !!! Although, a good mechanical oil pressure gauge would be a good investment if you're worried about it.

 

I would run what the owners manual states, which I believe is 10w30. I don't believe in the whole running thicker oil in old engines philosophy, except maybe in something that is really worn out.

I run 10w30 in my 302 that has almost 290,000 miles on it. My friend is an I6 fanatic and he runs the same in his 300 that has over 250,000 miles on it.