Dinosaur or partial synthetic?

[a64pilot]

Originally Posted by Compass790

I wouldn't sweat it too much. We have a 1982 Yanmar YSM8 & use mineral 15w-40 in both engine & gearbox because of the cold start advantage & the price. I worried less tho about oils after reading this :Consumer Reports:Truth Motor Oils- July 1996.
I still change it according to the recommended hours as agree with other posts about carbon buildup.

Go back and read that test, in it they plainly state since the cabs did neither cold starts, nor high speed, high temp driving that the advantages of synthetics of holding their viscosity better at temp extremes was not needed.
However as they were plainly honest in pointing that out, I give them kudos for being as honest as they could.

Synthetics ARE better, and especially if I had a turbo motor and ran it hard, I would certainly use synthetics, but as my 4JHE is the lowest power output for that engine block, and I run it almost always at 2000 RPM + or - 200 RPM and change oil every 100 hours, I do not think Rotella T6 would do anything for me.
For whatever it’s worth, I ran T6 for the first couple of years.
I do run Rotella T6 Diesel oil in our Turbo Miata, and in the wife’s Cadillac CTS-V. One reason I was using it was it’s an excellent oil for four stroke gas motors too, and it made it so that I only had to carry one oil for the generator, outboard and main engine.

Statistically, automobiles that use expensive synthetics exclusively do show less wear with extensive mileage, however it’s probably very likely that the person who spends the extra money on the high dollar oil simply maintains their automobile much better and doesn’t skip oil changes and other scheduled maintenance like the average person does, so how do you account for that? Maybe it’s a factor of keeping rigidly to the maintenance schedule and not the oil?

[Compass790]

Actually I'm aware of what they said re cold starts but his engine isn't a turbo & I imagine straight 30 weight CD mineral oil was the original factory recommendation for the 2qm20. Yes I too would use synthetic in a turbo. Doubt that he does high revs & high temps in his 2QM20. The point of the consumer test is that any oil that passes the relevant API standard should be fine synthetic or mineral.

[jacktheflyer]

Originally Posted by Cheechako

My opinion is you want to change oil often in a diesel to get rid of the carbon etc that builds up. So no point in paying for synthetic.

Engine oil is spent when it is either too full of carbon/contaminants or its additive package has been used up. The advantage of using synthetics is in its tighter viscosity specification over mineral oils and higher resistance to shear stress. As you say there is absolutely no advantage to using synthetics in internal combustion engines where there is no requirement for high shear stress lubricants. Synthetics come into their own in gearboxes and will make a noticable difference resolving gear noise.

[LakeSuperior]

Originally Posted by a64pilot

I wouldn’t use either of those oils.
Never heard of them, I’d stay with Rotella as it’s widely available or Delo, both excellent oils. If your in Europe seek out a good well known truck oil.
The key is frequent oil changes moreso than synthetic oil. Our oil doesn’t break down, but gets loaded with soot, you could go with a good bypass filtration system and then syn would make sense, but it’s tough to beat a good straight grade oil and change it often, and the older the engine is, the more often if needs changing due to increased blow by.
However Rotella T6 is an excellent oil, you can’t go wrong with it either.

Full synthetic oil produce way less soot and less wear products and therefore does not have to be changed as often.

[a64pilot]

Originally Posted by LakeSuperior

Full synthetic oil produce way less soot and less wear products and therefore does not have to be changed as often.

Don’t buy into extended oil change intervals. It’s a trap and a good way to a slow death for a Diesel.
If you want to extend Oil change intervals, install a very good bypass flirtation system.
Very, very little to almost none of the soot comes from oil, if you burn a half a quart in 100 hours, how could it? Almost all of the soot comes from the fuel itself.

Jacktheflyers post is spot on, there are other factors of course, but his post pretty much nails it.

[LakeSuperior]

The way I understand the soot problem is as follows.

The oil ring smears a thin film of oil on the cylinder walls on the up stroke. The cylinder wall temperature gradient increases moving toward the combustion chamber. The temperature gradient is a function of load and rpm.

At some point moving toward the combustion chamber the cylinder wall becomes hot enough to burn the oil producing burn products that are washed into the oil sump by the rings on the next stroke.

Regular motor oils are a mixture of many different sized molecules. The smaller ones burn at lower temperatures than the larger ones.

Pure synthetic oil is comprised on a single sized molecule with a uniformly higher burn temperature. Therefore it starts to burn closer to the combustion chamber thereby producing less burn products than regular motor oils thus extending the drain intervals.

[a64pilot]

If soot came from the oil, then gasoline engines would make as much soot as a Diesel, and they don’t.
Plus modern engines essentially consume almost no oil.
Soot comes from blow by, the older the engine, the more blow by and therefore more soot.
Reasoning for extended oil change intervals for synthetics is it doesn’t break down nearly as fast as mineral oil does. Actually as has been stated already it’s the additive packages that actually break down, not the oil. The first of the additive packages to break down are the viscosity improvers, the stuff that make 15W 40 oil so broad a temperature oil, reason straight weight oils won’t break down nearly as fast.
Good synthetics I don’t think need viscosity improvers, they meet the specs without being improved upon, so no additive to break down, so it will go for many more hours.
However it’s soot build up that causes us to change our oil, so to get the real benefit out of synthetics. You need to very finely filter the oil.
You can’t finely filter the oil with a single pass filter, it would be too restrictive, so you have a bypass filter, that filters only a fraction of the oil pumped, but over time of course it all gets filtered.
With a very good bypass filter and very good oil, you could go hundreds, maybe thousands of hours between changes, just change the bypass filter every so often, best to have a restriction meter like many of us do on our fuel filters.

Oil bypass filtration and good syn oil was the rage in the 80’s, along with pre-lubers.
Amsoil I believe was a big player in bypass filtration and extended intervals.