Yes - 1200 is a maximum SHORT TERM LIMIT. If you are hauling up a long mountain pass, then you should not see any more than 900 - 1000 continuous.

David

 

What is not in this equation is oil temp.
I was doing some reading on thermal breakdown of modern motor oil last night.

Modern dino oil is comprised of many different size oil molecules.
Viscosity is determined by the molecule size as well as several other factors.
Large molecules are a heavier viscosity than the medium moleclues are.
The smaller molecules are a lighter viscosity than the medium molecules are.
Oxidation of the oil is the result of the smaller molecules being burnt out of the oil which raises the viscosity.
If this continues long enough, a tarry sludge is all that is left of the oil.


Modern dino oil is relatively stable to 178 degrees F.
For every 18 degrees added to that base temp the oil oxidizes at twice the rate it did at the previous temp.
So oil running at 196 degrees oxidizes twice as fast as oil at 178 does.
Oil at 214 degrees oxidizes four times as fast as oil at 178 does.

Now consider the oil cooling jets are spraying oil on the bottom of a piston that is 1000 plus degrees on the bottom. The oil is also going through the turbo that is also at 1000 plus degrees which adds even more heat to it. There are 43.6 increments of 18 degrees between 214 and 1000 degrees. That does add a lot of oil oxidation to regular oil. I would venture a guess that over 1/2 the coolant temp rise when working a diesel engine comes from the oil cooler.

This is not a do not run it that hard post, but it does add a lot of meat to the argument about oil changes at higher mileage than 3000 miles. It also adds a lot of meat to the argument about dino versus synthetic oils.
True synthetic oils are made with molecules that are all the same size, so the oxidation is not near as damaging to synthetics as it is regular dino oil.

 

Sounds like you've really been doing your homework on oil properties, Dave.

Given that synthetic has uniform sized (large? medium?) molecules, why is it that an engine with a seepage using dino juice will turns into a leaky mess when switched to synthetic? Nobody has eve been able to explain that one to me.

Also, for NA engines I gather that the 1000-1200 degree temperatures are a non-issue (they just don't get that hot without a turbo). That being the case and severe oxidation is less of an issue, would it be safe to run them more than 3000 mile oil change intervals if you install a dual filter setup?

 

Dave, you could not be more right on this.

It seems that there is a huge bunch of people out there that think that all they need to do to get more horsepower is "turn the pump up" and this could not be further from the truth. I read a artical in a truck magazine where the magazine "modified" the engine for more power (approx 150). The aftermarket manufacture listed a 1550 degree exhaust temp as "ok" - WOW!

Now a little more research revealed that the exhaust temp was maxed out (1200) as delivered by the OEM manufacture. In other words, unless you were willing to sacrifice engine life and durability, the engine already had all the performance that was possible from the factory!

Food for thought -

David

 

I have never run a pyrometer on a NA engine.
But I have also found by experimentation that increasing the boost can cool the EGT.
I have also found larger exhaust pipes/lower restriction mufflers can cool the EGT.

My only rational thought on explaining this is the larger air flow lets more heat out of the engine faster.
Since I have never had a pyrometer on a stock NA motor I have to wonder what the EGT is.
It could very possibly be right up there at 1200 or more since the exhaust and intake are so restrictive as they come from the factory.
Also EGT is relative to engine speed, there are many times when running at lower RPM can shoot the EGT numbers through the roof.
This should be the same with a NA motor pulling a hill at lower RPM.