I was thinking of switching to Rotella 5w-40. I know that it isnt a true synthetic. How many people have switched to synthetic on a truck with over 100k on it? Should I just stick with the 15-40 dino oil? If I switch what are the chances that I will have oil leaks? The only reason that I am considering switching is it gets kinda cold here and I want the best protection when it is -10* and colder.

 

ive got 110,000 on the clock and ive been running mobil one since i got it. Dad's got 92,000 on his and hes beed running the same oil since 60,000 miles. there shouldnt be any reason for it to start leaking if you switch to synthitic.

 

There is another thread going on this same thing in the first generation section you might check also. https://www.dieseltruckresource.com/...ad.php?t=86806

 

The synthetics are better then conventional oil. They will weep out where conventional oil won't. But that is better for it flows easier. It is more likely that you may only have to tighten up a bolt a 1/10th of a turn. Use it all year round. Takes heat and cold better then conventional oil. Get who's ever oil you want and read their info on their oil products. I have been using it since 86 and wouldn't change.

 

Cummins only says one thing on the issue I think I can remember: Do NOT run synthetic oil in your cummins until the motor is fully broken in.


My hydraulics professor, when we went through the lectures on motor oil, said that the main difference synthetic will give you is an added 50 to 75 degrees or so before the oil will break down due to excessive heat.,In other words, if you have two parts that are kept from wearing themselves against each other, and they both run at 300 degrees, there will be no difference between the oils (synthetic or regular), HOWEVER, if you are running at 400 degrees (just a number I pulled out of my head, it's been 27 years or so since I was in his class in college so I don't remeber the exact numbers), the synthetic oil (depending on what kind it is and it's properties) may "keep on chugging", and the regular oil will stop lubricating and break down. In this case your synthetic oil would be worth it's weight in gold.

Anyway, my 2 cents worth, I'm sure nowadays, they have some real good synthetic oils that REALLY go to VERY high temps. before they break down. So if you have a modded truck and pedal to the metal, I'd say go synthetic after it is broken in,...Who knows how hot some of the parts in there get.
I know that they say the turbo is one of the places that has the highest heat.


Also, there is less strain on parts as the oil "warms up to temp" if it is thinner at colder temperatures, but I don't believe that would be much of a problem because most people who have cummins know to let their truck warm up before they tough the throttle.

 

Since you're looking at going from 15w-40 to 5w-40 rotella for viscosity change: go for it. The 5w40 is refined better. Hohn might pop up in a sec with pour points of 15w vs 5w, but the 5w is rated for colder temps and isn't a switch to syn, so the only difference you will see is price. At $14 a gallon I can't see why not go for the 5w,... except that Mobil 1 is a true syn and can be found for $20+ a gallon

I'm running Rotella 15W-40 in the bike and truck, but the bike has a little 5w- mixed in

 

On syn vs dino oil the differences I've found are:
-how well the oil sticks to metal after shutdown which will effect the amount of cold start wear
-Higher flash points of syns mean that the oil doesn't burn up as quickly as dino so you get better protection is extreme situations
-Oil change intervals are much higher for syn

I was reading some stuff of Bank's page and they say that syn won't mess up your turbo if you forgo the cool down- they say it doen't coke (if that's the right word) Interesting.

 

"Coke up" is also a word my hydraulics professor used.
Coking up is turning into a black mass of some sort (maybe like coal or hardened soot or something). In very high heat oil ducts, (i.e., like in turbos), every time you turn your motor off without cooling down the turbo, the oil ducts in the turbo become a tiny bit smaller due to the micro-layer of coke that is added to the duct walls. Times that by hundreds of shut-downs without cooling down first, and pretty soon your oil duct fails to do it's job and you get to buy a new turbo (or motor, in bad cases)...all because your 1/2" oil duct became a 1/8" oil duct over the course of time and added coke.

I think I remember that synthetic oil will also coke up, but at a higher temperature, ...higher enough that other parts will fail before the coking up of the oil becomes a factor....If I am remembering my classes right.

I don't tow, and I don't run my truck hard, so I've never ran synthetic in it.
I did have a chrysler turbo car in the early 90s, and I ran synthetic in it....there was an odd thing that would happen....Every now and again it would end up a quart low on oil. Without any kind of pattern to it. So I switched back to regular oil. I later found out my brother in law had a turbo car that did the same thing when he ran synthetic in it. I have never met anyone to explain to me what was happening. But I swear I am not making it up.

 

It is probably due the fact that syn's will creep and weep where conventionals won't. That 8% to 10% has advantages.

 

All I know is what I have researched....and when all done there is only a smidgen of difference between Dino oil and syn stuff...that's what I think I know and its only what I have read from bob the oil guy and the porsche sight and a few others.
I have to go with this a I have no means to set up a lab to start testing and would not know how in the second place

 

Another benny of synth is that it has better thermo conductive properties. The moleculles bind tighter to each other and objects so that it moves the heat away better. I forget the actual % but I thought it was like 35% of the engine cooling is done with the oil, mostly at the pistons and crank...........nothing really important
To my way of thinking Sysnth is well worth it. Every vehicle I've owned since 1981 Has run synth. I changed the 3 new cars I've owned right away. You used to have to let the bearings seat before you switched to the big slippery but now the tollerences are so good it doesn't matter if you start right out with synth. BMW, Mecedes, Porche and Vettes all do.

 

I believe ability to retain a film (what you said only in different terms) is part of the weight rating. EXCEPT the synthetic will retain this ability at 75 (just a guess) degrees higher temps. than petroleum oil. At "normal" operating temperatures, there should be little difference.(this is just what I learned in hydraulics 101 at USU a zillion years ago...if I am remembering correctly).

 

Well how many here had to rebearing the Getrag trans in the early versions on trucks? mine had 276,000 kms when I sold it. It needed to be done but all original so with that I would say the the Mobil 5w/30 did the proper lubercation of the input bearing.Which is were they usuall came apart.The layer of oil is thinner but holds the metal apart better. 15w/40 was over one and a half minutes and it still wasn't throught the engine, the 5w/40 was 12 seconds to go through the engine in testing. That says alot there how many of you don't even give enought time for the oil to circulate through the engine ????

 

synthetics beat dino everywhere but price, they retain viscosity longer, at higher temps, lower temps, it is slicker, but from my research I would not change my schedule for oil changes as the air filter has a lot to do with the silicon aka grit in the engine oil, enjoy the synthetics for the viscosity properties....not high mile intervals

 

When I got my truck, it had about 60,000 miles on it, and I switched it over to Amsoil. Now it's 5 years later and 145,000 miles on the clock, most of it pulling a 5er. I've got to go about 7 or 8k miles before it even gets close to needing a quart of oil, and all of it towing. Seepage? Hardly enough to keep things from rusting underneath.