I have been using Rotella 15W-40 for a while in my 4.9. It has been very good (feels like less noise and use of oil seems to be also less). Well, I was asked why it is good for a 4.9 and I could not tell the logical reasoning besides saying that a GM engineer said so. I understand what my friends think; GM recommended 10W-30 for 4.9, why do you think heavier 15W-40 for diesel engines is better for a 4.9???

What are the good reasons to use Rotella 15W-40 in a 4.9? I do remember it is good for distributor system or something. But I just don't remember details... By the way, does this also apply to LT1, too, since it is also an OHV engine?

Thanks a lot!

First of all, Rotella is not just for Diesels. If you look at the label it says something like "heavy duty oil for Diesel and gasoline engines".

It is better than standard oils because of extra anti-friction additives in it (ZDP?).

If you search this forum for Rotella, you should find plenty of threads which explain in detail why this oil is good to use in our engines.

Peteski

The Rotella/Delvac/Delo diesels oils are "better" because of the higher concentration of the ANTI-WEAR additive ZDP.

Normal "gasoline engine" oil on the shelf (with the ILSAC star burst label on it saying "for gasoline engines") has lower levels of the anti-wear additive and it also has quite a bit of friction reducer additives...i..e...fuel economy improving additives.

The friction modifiers don't really hurt anything but the lack of high levels of ZDP is not good for older engines like the 4.9 with distributor drive gears which are heavily loaded. The distributor drive gear in the 4.9 engine is what needs the extra anti-wear ZDP to live.

Thanks!

peteski, you are right. But when I checked information on this topic, there are a lot, really a lot. And as I read more, I get confused.

Typical questions that came in my mind were:

(1) 15W-40 is thicker than recommended. Why is that and what are the consequences?
(2) Rotella (or other CI-4 plus (am I correct?) oils) contains more ZDP than typical oils for gasoline engines and that is one good point about it, then why isn't it good for other engines like N*s?

Well, chevelle cleared some of questions in my mind. But if you guys don't mind, would you please answer these two questions above and one more: I thought that a distributor is almost not loaded at all (just a little rotor on the other end), why do you say it is heavily loaded? Is it because 90 degree twist gear arrangement (?) itself is not particularly good for gears?

I thought (for some reasons) this oil is good for old OHV engines. But it sounds to me that this oil is good for any old engines with conventional distributor system... Does this mean a LT1 may not be one of them, since it does not use 90 degree twist gear (optispark), which I am not sure to be honest...?

Ah, this topic is really deep, I think. Hope I can learn more from people like you guys...

Again, thank you!

The thicker viscosity isn't really required or necessarily "better" but it won't hurt the 4.1/4.5/4.9 engine at all. You might loose a little bit of cranking speed due to the thicker oil in the winter if you live way up north where it gets to -20 and below...otherwise, it won't hurt a thing.

Generically speaking, as an engine ages and miles pile up and some wear occurs bearing clearnaces open up slightly and the slightly thicker oil helps compensate for that, especially on the 4.9 which can often have the main bearing thump from the front main bearing with high miles.

The added ZDP is better for all engines, not just the 4.9 or pushrod engines. You have to look at the specific engine design to see if it really needs the added wear protection. The bad thing about ZDP (which contains zinc and phosphorus) is that it does poison the catalytic converter over time. Phosphorus in particular can reduce the efficiency of the cat so modern oils tend to have less and less ZDP in them to reduce the effect on the cat. As a result, modern engines are designed to run with lower and lower levels of wear protection...i.e..roller rockers, roller lifters, gerotor oil pumps, crank driven oil pumps, etc. The amount of ZDP in the oil is deliberaterly reduced and controlled in the ILSAC starburst "gasoline engine" oils to reduce the catalyst contamination. On an individual basis on one car the ZDP doesn't really affect the cat that much even over 100K but on the whole vehicle fleet (millions of cars) it does have a little effect on emissions so the reduction in ZDP is more for the common good than anything. On older engines, designed to run with oil with more anti-wear protection the new oils are not the best protection. The Rotella/Delo/Delvac is NOT rated by ILSAC for "gasoline engines" so it has much more ZDP in it since it is purposefully blended for "diesel engines" but you can use it in your gas engine with no problem.

The distributor gear drives the distributor AND the oil pump. The distributor doesn't require much force but the oil pump requires a lot of load which is what can wear the distributor gear out over time without adequate wear protection. Most cam-in-block...i.e pushrod...engines are like that, they drive the distributor and the oil pump off the cam shaft distributor gear. You are also on the right track with the gear design. A right angle drive gear is heavily loaded because there is a lot of sliding contact on the gear teeth so as the load goes up from the oil pump the distributor gear loading is increased dramatically. The distributor gear relies on the anti-wear additives in the oil to live. Same with the sliding bearing rocker arms in the 4.1/4.5/4.9. More modern pushrod engines have the oil pump on the crankshaft itself, a gerotor oil pump gear instead of spur gears, roller lifters and roller rocker arms.....all to reduce friction and reduce the engines dependency on ZDP depleted oil. This is also good in that it allows modern engines to go much further on oil changes since the oil is not depleted nearly as much and the engine is fine with the depleted oil that didn't have much ZDP to begin with. If you want more insurance against wear, though, feel free to use the Rotella/Delo/Delvac oils.

The diesel Rotella/Delvac/Delo oils are available in weights other than 15W40 (such as 10W30) but they can be hard to find as most of the class 8 diesels that the oil is specifically blended for are set up to use 15W40. Modern 15W40 oils do not have the poor viscosity improvers of past generation oils so they are fine to use. Plus, modern 15W40 oils that meet the diesel specs and the API SM performance specs have a lot of synthetic content and synthetic viscosity improvers so they are not a concern compared to the 10W40 and 15W40 oils of 20 years ago which were not desireable.

chevelle, your reply is really great! What a nice write-up about this matter. Thank you very much!

Just for my curiosity, how heavy can a normal engine (say recommended oil for that is 10W-30) use without any mechanical damage or problems?

I have heard that heavier the oil, better for lubrication (or preventing metal to metal contact due to oil film break-down) within certain range. I think using 10W-40 in a car requiring 10W-30 is this case. But I don't think I can use like 80 weight gear oil. My understanding is that as oil weight increases (by the way is my use of word "weight" for oil correct?), an internal losses due to higher viscosity also increases, which would heat up internal components and reduce fuel economy. What would be the limit for increasing oil weight (of course, within common sense, which may be difficult to define sometimes...)? Maybe 40 is the upper limit? Is this why I don't see 15W-50 or 20W-50 oil often?

Thank you very much. I learned a LOT today.

There are many factors involving the weight of the oil used in an engine including the operating temperature of the engine/oil, how the engine is clearanced when it is designed/built, what features are in the engine such as roller followers, etc.

Generally speaking I would never recommend any heavier oil than 40 weight in a passenger car engine. There are many caveats and nits to pick with that but there is really no reason to increase the oil viscosity beyond what the manufacturer recommends.

Increasing the viscosity of the oil does not necessarily lead to less wear. It can lead to more wear when the engine is cold if the oil cannot flow well. It can overload the distributor gear as mentioned if the heavy oil cannot be pumped when the engine is cold and is revved up too high. Too thick an oil can cause oil filters to blow off when the engine is cold and revved up due to excessive oil pressure.

On the other hand, air cooled motorcycle engines that are run hard will often use 50 weight oil or heavier because of the clearances in the engine opening up due to the high heat and the oil thinning excessively due to the high oil temps often seen with air cooled engines.

Understand that multivis oils such as 10W40 are basically 10 weight oil base stock with a viscosity improver package added to "thicken" the oil as it heats up so that it is the equivalent of hot 40 weight when hot. The viscosity improvers are long chain polymers that coil up when cold and stretch out when hot thus improving the viscosity. The bad thing is that the viscosity improvers, if not of very high quality, can break down in high heat areas and cause severe deposit build up that sticks rings in the piston ring grooves. This was a huge problem with multivis oils back in the late 70's and early/mid 80's with the SE and SF oils of that era. Oils with large viscosity spreads (such as 10W40) require large percentages of viscosity improvers which made them particularily bad for deposits back in the old days. That is why 10W40 oils were not recommended in many applications, why diesels never recommended multi-vis oils at all until recently and why 10W40 oils are really not recommended nor particularily desireable even today.

The viscosity improvers of today in the SL and SM rated oils are pretty much all synthetic and do not cause deposit formation problems anymore. Even so, mulit vis oils that meet the highest diesel performance specs are of the 15W40 variety which require less VI percentage than a 10W40 would....i.e..it takes less VI to make a base 15 weight oil the equivalent of a hot 40 weight than a base 10 weight oil.

In any case, it doesn't hurt much to increase the oil viscosity a little in most cases but the best approach is to use the recommended oil viscosity for the engine and not try to second guess the engineers that developed the engine. Most current production engines are recommended for 10W30 and lately 5W30 for improved fuel economy. The engines are designed for that and substituting thicker oil will not help durability at all and it would definitely hurt the fuel economy.

In the winter, cold cranking speed is governed by the oil viscosity. If you were to use 50 weight oil in very cold weather the engine would never start due to the fact that it would likely barely crank over. In cold weather 5W30 and 0W30 oils are common for cranking purposes.

Thank you very much, chevelle! Your explanation is awesome!

If you don't mind, one more, a simple question.

Why do oils for diesel engines have more ZDP? Sounded to me that for emission purposes (I mean, to maintain a catalytic converter healthy), concentration of ZDP has been reduced. Then, why oils for diesel engines are not following the same trend? Have they been exempted from reducing ZDP concentration to save catalytic converters? Or maybe the converter for a diesel engine is different from that for a gasoline engine and is more tolerant against ZDP (zinc part, pｈosphor part or both?) contamination?

Thanks much!

Thank you very much, chevelle! Your explanation is awesome!

If you don't mind, one more, a simple question.

Why do oils for diesel engines have more ZDP? Sounded to me that for emission purposes (I mean, to maintain a catalytic converter healthy), concentration of ZDP has been reduced. Then, why oils for diesel engines are not following the same trend? Have they been exempted from reducing ZDP concentration to save catalytic converters? Or maybe the converter for a diesel engine is different from that for a gasoline engine and is more tolerant against ZDP (zinc part, pｈosphor part or both?) contamination?

Thanks much!


Diesel engines don't have catalytic converters to worry about contaminating so the ZDP is of no concern to the diesel manufacturers.

When we say 'diesels" think class 8 18 wheelers, big Cat, Cummins, etc. and off road construction equipment....not just on-road passenger car and light truck diesels.

Diesel manufacturers have their own sets of performance requirements. Read the oil cans. See the API diesel specs such as CC and CD and many others. For diesels these specs supercede any gasoline performance specs such as SL and SM you see on oil cans of oil for "gasoline engines".

Diesels put a lot of soot in the oil so the oil is more heavily contaminated by soot and other combustion byproducts and blowby. Due to the nature of diesel combustion the engines produce more soot (the black smoke you see) and the high compression of diesels (22:1 or more) pushes some of the soot past the ring pack and into the oil. Soot is carbon which is very hard and very abrasive.....sooo...diesels oils have much more ZDP to prevent wear so as to be able to pass the diesel specific wear performance requirements for the API diesel specs.

Used to be the oils for diesels had to be very specific and wouldn't be desireable in gas engines. With the high performance oils of today the diesel oils are very good and very good for gas engines, too.

Manufacturers test for EPA fuel ecoomy performance with friction modified oils to improve the economy. The EPA wants you to be using those types of oils. That is why there is the "for gasoline engines" ILSAC starburst symbol on most common auto oils. They also spec reduced ZDP in those oils to reduce the possibility of contaminating the cat. The best oils, though, for wear and ZDP concentration are the current diesel oils and it doesn't hurt a thing to use them in gasoline engines.

Oh, I didn't know that those diesel powered trucks don't have a catalytic converter! That big cylindrical thing must be a silencer, then...

It is interesting to know that the technology is not necessarily advancing toward the direction to prolong the life of a car or to improve the performance of a car, but rather being more friendly to environment while trying to minimize negative effects to a car...

Thanks again for sharing these information with us. Your explanation is really great!

Oh, I didn't know that those diesel powered trucks don't have a catalytic converter! That big cylindrical thing must be a silencer, then...

It is interesting to know that the technology is not necessarily advancing toward the direction to prolong the life of a car or to improve the performance of a car, but rather being more friendly to environment while trying to minimize negative effects to a car...

Thanks again for sharing these information with us. Your explanation is really great!
anymore "paticulate filters" are what diesels have where we would have a cat conveter....Tho from what i understand its strictly to keep that black soot from spilling out the pipe , VW/AUDI are pretty much on the forefront of this , but there also in the pickup diesels ...hell there pretty much everywhere now with the new epa standards .....all of them made from some werid ass ceramic by 3m

All I can say is "WOW!" Thanks Chevelle!

Watch some Amsoil dealer now invade this thread. :-)

Peteski