Why oil consumption while towing/working hard??

[Ponch]

Fellow "oil guru's".....from my many years of studying things online "oil related" and such on forums like this...I have one underlying question for you all? From what I understand about engines, and oil consumption related to piston rings..etc..it seems that while any engine is under a large "load" or being worked hard..that the force of combustion is supposed to force the rings against the cylinder walls with "greater" force than such an engine that is under a light load or idleing, and in turn "seal" better from the heat of the combustion?....I personally am referring to a duramax engine, and as I have noticed personally a greater amount of oil consumption while towing heavily in summer months..NO matter what brand or weight of oil used..whether it was synthetic or not! I can run say 7,000 miles or so unloaded compared to the same mileage (not completely loaded the whole time but worked hard by towing) but notice more consumption while working hard. Do any of you feel that the oil is being "evaporated" so to speak this much? Or do you believe it is getting burned up by passing by the rings? Give me your insight on this matter. Thank you all in advance!
-PONCH

 

[Gene K]

Oil is sucked past the rings at idle but it doesnt take a lot of load to seal them.

The primary reason for the increase while towing in my opinion is higher rpm. The same reason cars run at highway speed use more oil.

 

[Ponch]

At "Gene K" if I drive unloaded at 70 MPH at roughly 1600 RPM...and then drive loaded at the same speed and RPM then how does this compare?

 

[dave1251]

PONCH My theory is that there is not more evaporation but more oil is finding its way pass the rings because your engine is using more revolutions per minute because of the increased load. That is why there is more consumption per distance traveled. That is my simplistic theory on the matter. This should be a interesting discussion.

 

[Gene K]

Originally Posted By: Ponch
At "Gene K" if I drive unloaded at 70 MPH at roughly 1600 RPM...and then drive loaded at the same speed and RPM then how does this compare?


I cant really say as my pickup wont use Overdrive 2 when in tow/haul and wont climb 6%+ grades without dropping to 2nd.

Im just taking a "Swag" at why you are observing this.

 

[BoiseRob]

Towing/working hard puts the engine under pressure or "boost" more than running empty. This increase in boost/pressure pushes oil past the rings.

 

[Shannow]

I've often wondered the same thing, and observed a couple of different things.

A walking stick breather, totally illegal when I was using it, never saw blue smoke, except on severe over-run, and snatching a gear.

Have had a few heavily worn engines that blew lots of blue under load, and the longer and harder they ran, the more blue they blew.

So I've sort of developed Shannow's theory of oil consumption:
* High load consumption/smoke is probably due more to crankcase pressure sending oil and volatiles into the intake;
* snatch changes (often in high load hill climbs, or plain messing around) have thinned the oil with temp, and then high vacuum on the change down sucks oil in.

My E30 was wonderful at producing smoke on full throttle AND over-run.

 

[dnewton3]

Probably some combination of the following theories:

higher boost pressures
higher in-cylinder temps resulting in higher EGTs
greater heat load in the oil resulting in quicker evap (lower Noack oils)
crankshaft splash
etc ...

Generally, my Dmax uses almost no oil in winter and spring. My oil consumption goes up with heavy towing. Because my interestate speeds are fairly consistent regardless of load (empty versus pulling trailer) I don't think the rpm issue has merit.

GM's official statement on oil consumption for the Dmax is 1 qrt per 100 gallons of fuel used; anything up to that level is deemed acceptable. And any consumption less that that is "better". Note, that's not a mileage derivation; it's based upon fuel consumed. That makes sense, as the more loading you see, the more fuel you use, and the more oil is used as well.

Can I tell you with certainty which of the factors is the "Red X" contributor? No - I cannot. But I can assure you it's perfectly normal and not worth worrying about. Even under my heavy summer loads, I don't see oil consumption up to 1 qrt/100 gallons. I used about 475 gallons of fuel over my last OCI, but only 2 qrts of oil; I'm well within the limits. And I was BRUTAL on my engine last year on purpose, to see how hard I could push it and the dino 10w-30 oil.

Track your fuel and your oil consumption. If you are "better" than 1 qrt/100 gallons, you're fine.

 

[Shannow]

dnewton3,
a bit off topic, but that's why I consider a bit of 2 stroke isn't a problem (in the absence of good)...1:100 seems to be OEM measure of "OK"

 

[Ponch]

Great info fellas!

 

[artificialist]

Originally Posted By: Shannow
dnewton3,
a bit off topic, but that's why I consider a bit of 2 stroke isn't a problem (in the absence of good)...1:100 seems to be OEM measure of "OK"

He said 1 quart of oil after burning 100 gallons of fuel, not 1 gallon of oil.

That would be a ratio of 1:400.

 

[dnewton3]

Correct - GM's official stance is that any Dmax engine that uses 1 qrt oil per 100 gallons of fuel (or less than that) is acceptable. That would be 1:400 as viewed oil to fuel in gallons to gallons. But GM states it in quarts of oil to gallons of fuel ... Same concept, but stated differently. Changes the aspect ratio and magnitude based upon the units measured, but the physical rate of consumption does not change.

Even under my heavy towing loading in heat and mountains last year, I didn't see that kind of consumption.

 

[Shannow]

Sorry, yes, my bad (I live in Litres, and occasionally imperial gallons).

Still 1qt per 1,000 miles being acceptable on a new passenger car is still a fairly significant ratio...depending on miles per gallon.

 

[Silk]

Mitsubishi drag that one out when ever someone complains about their engines using oil. My 4D56 powered Pajero did about that much - 2 litres in 5,000km...I'd put a litre in at 3,000km and change it at 5,000km. I built the engine rebored with new pistons and never considered it an oil burner....and of course being a diesel it didn't blow blue smoke. Ran a catch tank breather for a while to see if it was going that way - an egg cup full every 5,000km oil change.

 

[skellyman]

Probably some combination of the following theories:

higher boost pressures
higher in-cylinder temps resulting in higher EGTs
greater heat load in the oil resulting in quicker evap (lower Noack oils)
crankshaft splash
While the above are some factors , base oil and additive package do affect oil usage.

 

[benjy]

diesel's are usually on boost, when more boost is used carrying loads more cylinder pressure is made, boosted diesel's make some serious cylinder pressure for sure, this causes oil consumption, exactly where i goes, prolly lots of places, at 25 lb boost was the only time my gas vw turbo used oil, not stock of course