Does Dirty Oil Effect Mileage? - PeachParts Mercedes-Benz Forum

Diesel911 · #1 08-30-2012, 05:35 PM

Does dirty Oil effect Mileage? Yet another Oil Thread

I had not thought about this before or read any info on that.
I got an Email from thedieselstop.com that I became a member of but do not spend much time there on the subject.

Some of the Members said their miles per-gallon drops lower when their Oil is dirty.

I think you may need to be a member to view the site and it is very slow to open even after you log on.
http://www.thedieselstop.com/forums/f24/dirty-oil-effect-fuel-mileage-306789/

I just changed My Oil yesterday and I think it has been in there over one year maybe even 1-1/2 years. The car does not go far, mostly in Town driving.
The old Oil definitely looked Thicker
I have seen even worse on the Diesel Generators used on Refer Units. And, the oil on them is changed after X amount of hours and you put a sticker on the Door of the Control Box so they can tell when to change the Oil next.
The Carrier units also have a By-pass Oil Filter but it is about 5 nominal Microns.
Those during operation units go from idling a long time to full load.
That Oil looks thick when it comes out.
So My own though is dirty Oil is thicker and that is what decreases the Fuel Mileage.
However, it looks like the particular Thread was more about Ford Pick-up Diesels.
I assume those Engines have Hydraulic Lifters. Not sure if dirty Oils effect on the Lifter would translate into loss of Fuel Mileage.
Does anyone have any experience or comments on the new to Me Subject?

vstech · #2 08-30-2012, 07:57 PM

plenty of new oils are advertised to save gas and increase MPG...
it does make sense that thicker is harder to pump, and push through the passages, so certainly some economy is lost. the ford truck diesel engine uses a 2000psi oil pump... thickness certainly would affect that sucker...
I doubt it makes and measurable difference on 61x motors, aside from wear and tear that is. the 60x motors have hydrolic lifters, so thicker oil could reduce the lifter travel... it could also raise it... I'm no expert...

whunter · #3 08-30-2012, 08:20 PM

The question can not be answered as asked...

Define dirty = micron particulate, chemical contamination, abrasive load...

The black color of diesel oil has NO effect.

Many companies make millions selling extreme filtration systems, logical for class 8 trucks, but not most cars.

I average 9k mile oil changes with synthetic, no MPG change.

Very few members run oil long enough to exceed modern oil life, and experience potential SLUDGING = dirty oil.

I see seriously dirty oil dozens of times per year, when it drains out in clumps and clods = this will have a detectable impact on MPG.

.

rscurtis · #4 08-30-2012, 08:28 PM

The answer to your question is "yes". Years ago, I had a friend who had one (actually two) of the rare Mitsubishi turbo diesel pickups. His PM habits left something to be desired. One truck got to the point that in order to start it, the battery charger was hooked up, a space heater put on the oil pan, and it would eventually start, even with 4 good glow plugs. Turns out, the oil hadn't been changed in 30-40,000 miles. It also inhibited the turbo. I changed the oil twice, the truck picked up about 50% more power, and would now start in the cold unassisted.

Diesel911 · #5 08-30-2012, 08:58 PM

Quote:

Originally Posted by whunter

The question can not be answered as asked...

Define dirty = micron particulate, chemical contamination, abrasive load...

The black color of diesel oil has NO effect.

Many companies make millions selling extreme filtration systems, logical for class 8 trucks, but not most cars.

I average 9k mile oil changes with synthetic, no MPG change.

Very few members run oil long enough to exceed modern oil life, and experience potential SLUDGING = dirty oil.

I see seriously dirty oil dozens of times per year, when it drains out in clumps and clods = this will have a detectable impact on MPG.

.

I was sort of aiming the question at anything with a Diesel Engine.
I have never noticed any mileage issues but as you said I tend to change the Oil often.

I have had vehicles that subjectively seem to run better right after the Oil Change but after driving the Car several times afterwards I noticed no difference. They were Vehicles with Hydraulic Lifters.

Speaking of better filters below is a pic of part of My By-pass Oil Filter Element. It has a coating of what one of our Members said was Soot on it; and it looks thick.
I don't have the Money to spend on an Oil Analysis to know how well they By-pass Filter it is really working and I was surprised to see anything visible when I pulled the Element out.

I left the Filter in the Picture in for 2 Oil Changes.

Diesel911 · #6 08-30-2012, 09:02 PM

Quote:

Originally Posted by rscurtis

The answer to your question is "yes". Years ago, I had a friend who had one (actually two) of the rare Mitsubishi turbo diesel pickups. His PM habits left something to be desired. One truck got to the point that in order to start it, the battery charger was hooked up, a space heater put on the oil pan, and it would eventually start, even with 4 good glow plugs. Turns out, the oil hadn't been changed in 30-40,000 miles. It also inhibited the turbo. I changed the oil twice, the truck picked up about 50% more power, and would now start in the cold unassisted.

This is the type of evidence I was looking for.

JHZR2 · #7 08-30-2012, 10:04 PM

Dirty? Not likely. If so soot laden that it causes a viscosity increase, then that could be possible.

Generally what one is interested in is oxidative thickening, which can definitely take an oil out of grade to a more viscous grade which will have an effect.

Diesel911 · #8 08-30-2012, 10:47 PM

Quote:

Originally Posted by JHZR2

Dirty? Not likely. If so soot laden that it causes a viscosity increase, then that could be possible.

Generally what one is interested in is oxidative thickening, which can definitely take an oil out of grade to a more viscous grade which will have an effect.

Is this more likely to happen with multiviscosity Oil or single grade/weight Oil?

JHZR2 · #9 08-30-2012, 10:55 PM

Multi-viscosity oils that use a lot of viscosity index improves and pour point depressants can be prone to shearing out of grade to a thinner grade. Oxidative thickening is a kinetic process (chemical reaction), dictated by time at temperature, oil base stock and antioxidant chemistry used.

zu! · #10 08-30-2012, 11:43 PM

I always thought oil got thinner and not thicker with age?

Having said that, I help out my buddy at his shop and quite often, I've seen people come in with noisy gas engines. Drain the oil and I can't believe it...so MANY of them just release literally a teacup of oil!!

Some of these jokers drive their little toyotas and nissans over 10,000 km between oil changes. One guy boasted that he only changes oil when the engine "sounds like your car" (My 300D). 300k and that bloody Toyota is still running.

JHZR2 · #11 08-31-2012, 08:34 AM

You can shear to a thinner grade or oxidatively thicken to a higher one. HD diesel oils are pretty resilient to shear out of grade (and thickening too).