Pretty simple question here.... I have been using the Rotella 15w40 for a while now and during my last oil change I realized that I had two different bottles, one said "Heavy Duty Engine Oil" and the other says "Heavy Duty DIESEL Engine Oil." I'm pretty sure they're the same thing but thought I'd throw it out there to see if there was any difference. Anyone?

 

Diesel oil is thinner, and it has a lot more additives, almost as much additives as back in the day which is why its highly recommended for older gas engines (like Fiats and MG's). I would say that mixing and matching 1 quart in with the rest of the gas combustion oil isnt that big of a deal, but if you got more then one bottle you should probably change your oil again because of how thin it is compared to what you would normally throw in there.

 

I understand the difference in diesel oils but what got me is that both jugs had the same sku number and were identical except for adding the word diesel. They were mixed in together on the shelf when I went back and looked again.

 

You're fine, its the same oil.

 

No diesel oil is NOT thinner than regular oil, the numbers on the bottle mean the same for diesel oil as every other motor oil.
Diesel oil is a heavy duty oil full of detergents and can take tons and tons of abuse for cheap.
All motor oils have less of the "bad" additives and more of the "good" ones now because the "bad" ones are bad for the environment, your O2's and cats.

 

Your right Spike, I meant to say that it is thicker. Not thinner, I dont know where my mind was. (generally) In this application, you are correct though. The viscosity should be the same.

Butttt..........

No Spike, your wrong. It is not the same oil as gas engine oil. There is a reason that one is for diesel engines, and one is for gas engines. (on modern vehicle's) I know I just kind of contradicted myself there but with old *** engines its a bit of a different story.

"Diesel engine oil has more additives per volume. The most prevalent are overbase detergent additives. This additive has several jobs, but the main ones are to neutralize acids and clean. Diesel engines create a great deal more soot and combustion byproducts. Through blow-by, these find their way into the crankcase, forcing the oil to deal with them. When you put this extra additive load in a gasoline engine, the effects can be devastating to performance. The detergent will work as it is designed and try to clean the cylinder walls. This can have an adverse effect on the seal between the rings and liner, resulting in lost compression and efficiency."

Like I said, if you put this in your engine, you should probably change it.

 

That's interesting. Where did you find that info on diesel oil?

 

Maybe I should ask my question a different way.... Is the same oil in these two differently labeled jugs? The reason being is because the barcode is EXACTLY the same on each of them. I don't want to be mixing oils. I appreciate your guys insight!

 

from : Comparing Gasoline and Diesel Engine Oils-

Which is another web opinion from a person who firmly believes in their approach. IMHO, the soot management quality of the diesel oil make it keep small particles in suspension, so our better quality filters can trap it. The extra cleaning is certainly needed by a late 1950's design, which has been pushed to 150,000 miles plus by a variety of owners. The idea that material is bypassing the rings because of breakdown of the seal does not seem to hold. Here are three pix, the reddish one is factory oil change intervals and about 50,000 miles as I recall from the OP. The super sludged one is infrequent changes with who knows what oil. The clean one is 190,000 on Castrol and switched to Rotella many thousands back. Frequent oil change intervals are a must. Not running overheated helps oil as well.

Meets spec CJ4 S/M. Which means it has less ZDDP than once formulated, which helped maintain the flat tappet engine design. That is a drawback, and there are some oils that still have high levels of ZDDP, but few. Modern engines don't need as much ZDDP, but there is nothing modern about a Rover 3.9 - 4.6 liter v-8.

The 40 on the end means Rover says it will work for temps over 95F (in the D1 manual). The watered down 10W30 from iffy lube is only for up to 95F ambient. So if you run a lower weight oil, don't clean out your PCV, run oil for 7500 plus miles, you are not doing the engine any favors. But many of us drive pre-owned piles of previously posh sheet metal, and it is hard to reverse the prior owners lack of routine service. Rotella is cheap enough to change often and readily available.

As for lack of compression, I have not seen a bunch of posts about drop in mpg after going with Rotella, or codes, or sudden drop in performance. Would be interesting for someone who is making the change to Rotella to run a compression test before and after.

But every thing is a compromise in some way or another. And no "magic" oil changed every 30,000 miles will make your overheated Rover last 450,000 miles.

 

Old stock and new stock.
You can mix oils all you want, different brands, types, viscosity, whatever you want to do its all good.
Yes it is best to use the same oil brand weight and type but they are all made to work together.