Can "Bad Stuff" From Short Trips Be Burnt Off?

[Jelly]

Don't know if "burnt off" is the proper term or not, but it's something I've been thinking about.

Say you do two weeks of short trip driving where you know all sorts of good stuff have accumulated in your engine.

Can all that stuff be, once again, "burnt off" with a nice long highway trip?

 

[Ballbearing]

I would say the higher engine temps for a long period must burn off any moisture and unburnt fuel that accumulates with cold and stop start running.

 

[427Z06]

Pure conjecture on my part, but I think although the water and water are evaporated off, the oil does suffer some damage. Terry and Molakule should be able to answer this.

 

[pitzel]

quote:

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Originally posted by 427Z06:
Pure conjecture on my part, but I think although the water and water are evaporated off, the oil does suffer some damage. Terry and Molakule should be able to answer this.

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Check out Olympic's XD-3 0W30 oil analysis in the UOA section doing tons of short trips. A good long run at the end of the 10k km interval pretty much burned everything off and the oil was as good as new.

Of course its imperative to have your PCV system in good working order, or else all bets are off. And of course, modern fuel injected vehicles are substantially less susceptible to the issue of depositing a lot of stuff in the engine oil during startup.

 

[TomJones76]

quote:

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Originally posted by Ballbearing:
I would say the higher engine temps for a long period must burn off any moisture and unburnt fuel that accumulates with cold and stop start running.

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Moisture will burn off.
Fuel will not.
Your engine runs between 180 and 300 Fahrenheit depending on application. Your anti-freeze will boil at 265 Fahrenheit.
Water boils at 212 Fahrenheit.
Gasoline combusts at 536 Fahrenheit.
Motor oils may have flash points in the 400-475 Fahrenheit range.
If your motor oil is making it to 536 Fahrenheit, your motor won't last long enough for fuel contamination to be a problem. Also, the fuel contaminating your motor oil will likely burn off only AFTER the motor oil it is living in burns off.

http://hypertextbook.com/facts/2003/ShaniChristopher.shtml
http://www.amsoil.com/products/tso.html
http://www.shell-lubricants.com/products/pdf/RotellaTMG.pdf
http://www.neosyntheticoil.com/30w.htm

[Edited because I left out citation the first time.

 

[pitzel]

quote:

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Originally posted by TomJones76:
Moisture will burn off.
Fuel will not.
Your engine runs between 180 and 300 Fahrenheit depending on application. Your anti-freeze will boil at 265 Fahrenheit.
Water boils at 212 Fahrenheit.
Gasoline combusts at 536 Fahrenheit.
Motor oils may have flash points in the 400-475 Fahrenheit range.
If your motor oil is making it to 536 Fahrenheit, your motor won't last long enough for fuel contamination to be a problem. Also, the fuel contaminating your motor oil will likely burn off only AFTER the motor oil it is living in burns off.
[/QB]

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I think in this discussion, it should be emphasized that 'burning off' does not mean combustion, but rather, forced evaporation of the contamination components.

Oil temperatures in a fully-warmed up engine easily exceed 100degC which is sufficient to evaporate water. Petrol will evaporate at temperatures significantly less than that of water. The evaporation will take place in the crankcase and the products of evaporation will be discharged through the PCV system into the engine's intake for high-temperature combustion.

Of course, if you have glycol ingress, all bets are off. Glycol actively reacts with oil and damages it apparently.

 

[olympic]

Moisture can be burned off but short trips damage the oil in ways that can not be "repaired" such as oxidation, nitration and TBN depletion. Oil will last alot longer when the vehichle does strictly long hiway trips where normal operating temps are maintained for long periods of time and the engine is running at peak efficiency ie-it's not producing alot of combustion by-products that collect in the oil.

I made 10,000 hard driven city km on a quality syntheitic and the oil looked pretty good according to the UOA. But I'm hoping to quadruple that to 40k on my hiway vehichles. 10k(6200 miles) is nothing under the right conditions. That was my normal OCI with bulk dino oil and no bypass filter on my hiway vans. Never had a problem and the engines were spotless inside. Heck, the GM OLM say I could have stretched it out to 15,000km under these conditions but I never did.

 

[Russ]

What exactly constitutes "short trip"? Under 5 miles, under 5 minutes?

 

[olympic]

A short trip would be best described as a trip where your engine oil does not reach full operating temperature. In the summer 5 miles may do it. In winter it will be considerably more.

Warm up and cool down cycles also degrade the oil. A single 150 mile trip/week will leave the oil looking much better than ten 15 mile trips per week.