What oil temp is needed to remove moisture?

[Patman]

I know that in theory they say that you need to reach 212F (100C) in order for water to boil, but does that mean my oil temperature must reach 212F in order to fully burn off the moisture?

I've been tracking the oil temperatures in my 98 Corvette since I bought it, and most days the oil temperature reaches a peak of around 200-205F, and this is after driving it for a full hour. It has been rare for it to go much higher, the absolute highest I've seen has been 221F, but only at the end of some brutal stop and go driving.

I'm kind of worried as to what will happen in the winter time, as I figure my oil temps might be 10-15F lower. So should I be worried in the winter if my oil temps just get up to 190F after driving the car for an hour? What would be the absolute lowest oil temperature I'd want to get up to before shutting the car down (if I want to make sure to get rid of all the moisture in the oil everytime I drive it)

[ August 29, 2004, 05:51 AM: Message edited by: Patman ]

 

[ToyotaNSaturn]

An intruiging question, Patman. If there's any contamination in the moisture, that would raise the boiling point above 100C, correct? If that burn-off temp goes above 100C, then would the moisture ever truly burn off on those cold winter days even after driving it for some??

 

[westex39]

Water does not have to reach the boiling point to evaporate. The heat built up by you driving for an hour would be enough for the water to evaporate. It would most likely evaporate at much lower temps as well. The air flow through the crankcase through the PCV valve will draw the moisture off too. The real danger is the condensation in the crankcase when making very short drives of 2 or 3 miles and letting the engine cool off and repeating this on a daily basis, never letting the engine come to full operating temperture and water will continue to collect.

 

[yannis]

Run a thiker oil..

 

[Gary Allan]

All the rhetoric that I've heard is that 180 is the target temp. It will vaporize at lower temps ..sure ..but this apparently falls into the typical event duration for effective purging. Naturally this school of thought, like most of my automotive knoweledge, is dated.

 

[Ugly3]

Put a measured volume of water in the oven at 150 degrees and check the volume hourly. Repeat at various temps.

While the relative humidity of the surrounding air is a critical factor in water evaporation rates, I think you will be surprised how fast the water evaporates.

I hear that swimming pools in Arizona must be covered to slow the evaporation rate.

 

[YZF150]

Sweat evaporates.

 

[QuadDriver]

Burn? Im not sure of the auto ignition temp of water (if one in fact exsists) but it will boil pretty well at 212F/100C.

 

[mountravlr]

If distilled water boils at 212F at Sea Level, then it boils at lesser temps at higher elevations. Anyway, boiling of moisture is not really at issue. As has been stated it is really a matter of evaporation, facilitated by circulation inside a hot engine.

 

[427Z06]

Patman, if there was a huge problem with water not evaporating out of the oil, just think how many UOAs we would see with very elevated water levels. I believe if your oil gets up to 180F on a daily basis and weekly it gets there and stays there for 30 minutes, most of the moisture will evaporate out.

 

[JohnnyG]

quote:

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Run a thiker oil..

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Now, what on earth would that accomplish?

For what it's worth, atmospheric pressure has a direct relationship to evaporation rate. Water will boil at a much lower temperature at high altitudes than at sea level. If there is a vacuum in your crankcase caused by the PCV system, water would vaporize more quickly.

 

[427Z06]

OK Patman, one data point of the experiment completed for ya'. Set my convection oven to 175F and let it stabalize. Put a 1/4 cup of distilled water in a metal pan. 30 minutes later, all but a few drops of the water has evaporated.

 

[XS650]

quote:

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Originally posted by 427Z06:
OK Patman, one data point of the experiment completed for ya'. Set my convection oven to 175F and let it stabalize. Put a 1/4 cup of distilled water in a metal pan. 30 minutes later, all but a few drops of the water has evaporated.

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You have somethng els working in your favor. The pan is where the oil is the coolest. As it gets flung around the inside of the engine. it is at a higher temperature surfaces and is exposed to more air because it's in droplet and thin layer form.

Back in the olden daze of the 1960s, engine running on the cruddy oil of the day did good with sump temps around 180F. If the sump stayed much below that, they sludged up worse than normal.

 

[Gary Allan]

quote:

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Put a measured volume of water in the oven at 150 degrees and check the volume hourly. Repeat at various temps.

While the relative humidity of the surrounding air is a critical factor in water evaporation rates, I think you will be surprised how fast the water evaporates.

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Sure ..no arguement .water will evaporate at 75* ..100* ...125*...yadayada

but if the engine oil only reaches 150 degrees ..the engine is NOT warmed up ..and the "duration" of the event is NOT long enough....

..and you will NEVER dispell the accumulated moisture.

Oil temp, in most situations ..tracks coolant temps (within 10 or 20 degrees +/-)
Now does my antiquated assertion of 180* sound a little more valid???

 

[kickster]

According to most Auto MFG. 90C is the set temp to born off water.

 

[moribundman]

I wonder what happens to condesation that is present in the oil. Does it sort of emulsify with the oil when forced through the oil pump? If so, how does that affect evaporation?

 

[JohnBrowning]

First water does not need to be boiled off. The idea is that you want it to leave the engine at a faster rate then it is accumulateing! I can sit a glass of water on the counter an never heat it at all and it is going to evaperate. Now oil might be hydroscopic and the combustion process will cause condensation.

The important thing I think is the total time spent at operateing temp as opposed to some magic temp.!!! Any temp. hotter then ambient temps is going to cause the water to evaperate quicker. The problem lies in short trips that get the vechile up to operateing temp. before just down that are short in duration. If you do not get rid of water faster then it is being absorbed you get acid issues.

 

[theguru]

Exactly what I was going to say.

 

[jaj]

I'm going to say what the others have said, but in a slightly different way. "Lets talk about vapour pressure".

Any fluid, water included, will maintain an equilibrium of liquid and gas in an enclosed and only partially filled space. The pressure of the vapour over the liquid is determined by the temperature of the system, and it's a constant at a constant temperature. If you remove vapour from the system, liquid will evaporate to compensate for the loss until the previous pressure is restored. That's how the PCV system gets water out of your motor oil without boiling it out.

Of course, when such a closed system is raised to the "boiling point" of the liquid, the liquid absorbs heat and converts to vapour until all the liquid is gone. This is "boiling off" the liquid.

To clean the water out of your engine oil without boiling, you just have to keep removing the water vapour from the space above the liquid (ie - the enclosed crankcase volume), and the water in the oil will continue to evaporate in an effort to re-establish it's equilibrium vapour pressure.

If your oil is at 200 degrees (F), the vapour pressure of water is relatively high, and your PCV system will draw the vapour out of the engine very efficiently until all that's left is a tiny amount of water vapour inside the crancase. That moisture will condense into the oil as the engine cools, but it will be a negligible amount.

There are two reasons you get creamy oil when running a cold engine:

1 - more water vapour condenses inside the cylinders in the first place (instead of being expelled) because the mass of the engine itself is cold. This means there is more input of water to the oil.

2 - the whole system is cool, so the vapour pressure of the water in the crankcase is quite low, so the PCV system can't extract it. The water's happy being a liquid and riding around in the oil, and until it feels the call of warmer temperatures, it has no inclination to try to support a higher vapour pressure.

So that's the way I'd answer the question - I knew that Chem and Phys honors degree would come in handy some day!

JJ

 

[QuadDriver]

quote:

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Originally posted by Gary Allan:

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Sure ..no arguement .water will evaporate at 75* ..100* ...125*...yadayada

but if the engine oil only reaches 150 degrees ..the engine is NOT warmed up ..and the "duration" of the event is NOT long enough....

..and you will NEVER dispell the accumulated moisture.

Oil temp, in most situations ..tracks coolant temps (within 10 or 20 degrees +/-)
Now does my antiquated assertion of 180* sound a little more valid??? [/QUOTE]

pan temp would give an average temp of all the oil, but the tiny bit of oil that just dropped in from a bearing or the underside of a piston is way way way above boiling. If every drop of oil gets a shot in the bearings every few minutes, it does not take long to boil off the water

In fact, I saw a study a while back that showed most of the heat accumulated by the oil comes from the friction of the fluid in the bearings rahter than via transfer from the heated metal of the block. Interesting seque of the evening, if we compare 2 venerable v8s, the small blck chevy and the windosr ford (definite competetors) you might notice that in most applications the chevy requires an oil cooler and the ford does not - the reason being the smaller oil passages of the SBC create a lot more friction in the oil galleries themselves - the oil pump is its own worst enemy