Differnce between diesel oil and gasoline engine oil

[junker68]

Hello all,
When purchasing oil for my 240d, I've noticed the oil sold for diesel engines is remarkably cheaper in price than the oil refined for gasoline engines. And I'm not referring to sale prices.
A 5 dollar difference on average when purchasing the 5 gallon container.
Anyone know why?
Not synthetic, just basic everyday oil to each type of vehicle.
I bought Mobil Delvac for $13.99 - 5 gallon jug. Whereas the cheapest basic oil for gasoline engine was Quaker State was 18.99 - 5 gallon jug.
Also, not looking to turn this into a debate about which oil is better, etc.
Just wondering, is it refined less?
Thanks

[Mike D]

Refined less? Yes and no. Certain elements (Zinc for one) are removed from the "gasoline" oils. This is to protect the newer computer controlled vehicles' sensors. Of course this cost is passed onto the consumer.

Any car produced prior to the 2000 model year should actually use the "diesel" oil simply for the added engine wear protection Zinc adds to the system.

Same oil otherwise with the exception of the synthetics.

[BillGrissom]

I understand that "diesel oil" (CJ rated) has more detergents to better suspend carbon between changes. Oil gets black much faster because of more leakage past the rings at 20:1 compression, and the fuel droplets burn as a sootier "diffusion flame" rather than the ideal "pre-mixed flame" in a gas engine (assuming fine atomization/evaporation and mixing).

Many owners of classic gas cars use diesel oil like Rotella. They consider it better quality and the added zinc helps w/ flat-tappet cams, especially those using racing cams w/ stronger valve springs. Diesel oil used to cost more. Be happy. The fuel is even cheaper than gas currently.

[junker68]

Thanks to all.

Interesting, unfortunately, though gasoline is about 50 cents cheaper around me, NY.

Dwayne

[tyl604]

Diesel is higher cost than gasoline in Atlanta.

[flainn]

I've sure never noticed diesel-rated oils being cheaper than equivalent weight gasoline-rated oils. Are you sure the gasoline oil wasn't synthetic or partial-synthetic? And I assume you mean 5-quart, not 5-gallon.

[OM617YOTA]

Most "diesel" oils are actually HDEO - heavy duty engine oil, and most will indeed have a spark ignition rating as well and have to meet emissions and sensor requirements for gas engines if so rated. I run it in everything.

I've definitely never witnessed diesel rated oil for less cost than SI only oil.

[junker68]

My bad, 5 quarts, not 5 gallons.

I bought the oil at Advance Auto, but Autozone had the same price. They're next to each other so I'm sure they try to be competitive.

Definitely not mistaking the synthetic or partial-synthetic with the regular dino oil.

I've even asked the different clerks over the past two years and they can't offer an explanation. The point I'm trying to make is that if I was comparing the dino with the synthetic, they would have been quick to point it out.
Funny how I get more info on this forum than from the guys who sell the stuff, not surprising though.

As an aside, I know it's been brought up a few times, but it's amazing how little the clerks in these stores no about the items they sell.

[flainn]

I went to AutoZone's site and tried to price compare, but I can't seem to find gasoline-rated oil in a 4-quart jug -- all I can find is 5-quart jugs. Whereas the diesel oils are more commonly available in 4-quart jugs.

The prices I'm seeing are about the same -- meaning a 4-quart jug of Delvac is about the same price as a 5-quart jug of gasoline-rated oil.

Maybe you've got something going on locally, like close proximity to a refinery or something.

[mannys9130]

Originally Posted by BillGrissom

more leakage past the rings at 20:1 compression.

It's my understanding that the higher compression ratio actually promotes BETTER sealing compared to a gasoline engine. The piston rings are spring loaded in a sense, so they push out against the cylinder wall even at rest. During combustion though, the high pressure gets behind and above the piston ring, and pushes it down and out against the cylinder wall. Since the diesel has a higher CR and MUCH higher combustion chamber pressure, it seals VERY well. There will be blow by in any worn out engine, but it's certainly not because of the high CR.

[unkl300d]

Originally Posted by BillGrissom

I understand that "diesel oil" (CJ rated) has more detergents to better suspend carbon between changes. Oil gets black much faster because of more leakage past the rings at 20:1 compression, and the fuel droplets burn as a sootier "diffusion flame" rather than the ideal "pre-mixed flame" in a gas engine (assuming fine atomization/evaporation and mixing).

Many owners of classic gas cars use diesel oil like Rotella. They consider it better quality and the added zinc helps w/ flat-tappet cams, especially those using racing cams w/ stronger valve springs. Diesel oil used to cost more. Be happy. The fuel is even cheaper than gas currently.

^^^^^^^
This

[junker68]

Well, there's the answer right there, the two examples I have in my garage and pointed out by flainn...
The gas formulated oil is in 5 qt containers while the diesel is in 4 qt containers.
I didn't even notice.
Thanks!

[flainn]

Originally Posted by junker68

Well, there's the answer right there, the two examples I have in my garage and pointed out by flainn...
The gas formulated oil is in 5 qt containers while the diesel is in 4 qt containers.
I didn't even notice.
Thanks!

Good to know. I happen to think four- and five-quart containers looking very similar is deliberate on the part of the oil companies. In fact, I seem to remember hearing something about that a while back.

[Diesel911]

If it has not been mentioned the amount of Zinc in Diesel Engine Oil is supposed to be bad for the gasser Catalytic Converters.
It is going to depend on how much of the Oil Vapor in your Crankcase Vent System actually makes to combustion and the Zinc from that to the CAT.
Comparing Gasoline and Diesel Engine Oils