Effects of Extreme Cold on Engine Oil

[anyoldname]

I'm involved in a project where we will be running a gasoline engine in a very cold environment, think -60degF/-50degC or colder.

Please ignore all the usual issues of getting the engine started, it will be started and warmed up in a warmer environment and while the engine is running the oil will be kept warm.

What I am trying to figure out is what will happen to the engine oil if the engine has to be shut down in this very cold environment. Will the oil simply get very thick while it is cold but then recover fully once it is warmed up again?

Or will some of the elements in it be damaged by the cold compromising its lubricity?

Or will it possibly freeze similar to diesel, with some elements forming a wax or solids that will block filters, damage pumps etc?

Or is there some other failure mode that I haven't thought about yet.

Thanks.

 

[patprimmer]

It simply gets thick when cold and thin when hot. To much heat causes oxidation as well. To cold slows down any reactions



Regards
Pat
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[ivymike]

I'm not aware of any permanent damage that could occur to the engine oil itself. Since it's a gasoline engine, I imagine you're talking about a very low budget operation, so continuous oil and coolant preheating (kim hotstart or similar) are out of the question?

In the environment you've described, you'll have to pay attention to the possible accumulation of water in the crankcase. The blow-by gases which escape past the piston rings into the crankcase contain a significant amount of water vapor, and if this vapor is allowed to condense then water will accumulate. Besides the general unpleasantness of having a small amount of water in your lube oil, after shutdown and cooling, this would of course become ice.

Depending on the engine design (if for example it has wet cylinder liners, which a few gasoline engines do but not many) you may also have trouble with internal seals getting very cold and allowing coolant to dribble into the engine oil.

 

[romke]

the oil gets cold and can even more or less solidify. it is not unlike diesel fuel - the same phenomenon (wax crystals forming and interlocking) can occur and. just like diesel fuel the effect is fully reversible when warmed up.

actually i am far more worried about the gasoline itself and the coolant. if the engine would be stopped and those fluids would be allowed to cool down to -50 deg C the gasoline may become solid and the coolant will be solid - maybe destroying parts of the cooling system in the process.

 

[anyoldname]

Thanks for the responses everybody.

Romke, we've still got some work to do but hopefully the fuel and coolant will be ok, it helps me that there is a reasonable amout of data on the properties of these fluids at low temps but I'm struggling to find any data on the oil at extremely low temps as these temperatures are outside of the normal operating condtions.

One point is that you say diesel oil fully recovers when warmed up..... I know a enough to realise that winter grades of diesel vary greatly with location but my experience of UK winter diesel is that once you get it properly cold then it will form wax that does not disperse once the temperature increases. In fact, I have seen wax still present in the fuel filters of agricultural kit months after winter has ended.

 

[drwebb]

For engine oils, usually the parameters most important for low temperature performance are crankability and pumpability. The latter is estimated from ASTM D4684 Standard Test Method for Determination of Yield Stress and Apparent Viscosity of Engine Oils at Low Temperature. The method is normally run down to -40C, but no reason in theory candidate oils couldn't be tested at -50C.

Alternatively, you could specify an SAE 0W oil with viscosity <15,000 mPa*s at -40C by this method, utilizing the assumption that viscosity increases by a factor or ca. 2 for each 5C drop in T, and the viscosity limit for engine pumpability is taken as 60,0000 by SAE specs. This second approach doesn't ensure -50C performance (e.g. absence of gelation), but may exclude from consideration oils less suitable for starting in that extreme environment.

 

[romke]

it is true that diesel fuel, once wax crystals have been formed, will not become fluid again immediately when the temperature rises. one of the reasons for that is that wax crystals, when formed, tend to sink to the bottom of the tank and thus the composition of the fuel will vary - heavy waxy components at the bottom, more fluid components on top of it. under those circumstances it can be very difficult to get the wax fluid again.

if however the wax crystals are removed and heated separately they will eventually become fluid again. it is not only heat that is needed to do that, you also need a means to break up the interlocking of the various crystals that have been formed.

in service that interlocking of crystals is prevented by adding a small amount of cold flow improver to the diesel fuel, the pourpoint depressant in a engine oil has the same effect. those substances do not prevent the forming of crystals but prevent strong bonds when the crystals interlock - for a certain time that is. if you let it settle for a prolonged period of time the heavy parts will solidify.

with normal use of diesel fuel that will not easily happen when using the appropriate dosage, but if you leave the equipment stationary for a prolonged period of time flow improvers are no lonnger effective.

 

[dicer]

In the old days, gasoline engines that were operated in very cold environments, at shutdown time gasoline was mixed with the lubricating oil, to keep it more fluid. It must have worked just fine as it was used for aircraft. The system was called an oil dilution system.