Too Cold Oil Temperature??

[Majik]

I've heard this several times that "Cold oil will cause engine damage"

I've yet to find any data to back this up though. The only specs I've found said that if temps were below 20F then warm the engine and oil up. With todays multiweight oils, I just can't think of something that cold oil (ie 85F) is going to hurt an engine. I'm not saying that cold oil like 0F can't hurt the engine. I've had customers tell me this for years that say that an oil temp at 130F will hurt an engine and 180F is the minimum you should run in an engine. Any truth to this?

 

[patprimmer]

Cold oil will not directly cause engine damage.

The oil being at to high a viscosity can cause engine damage by the pressure going to high or the flow being to restricted.

The pressure to high causes broken oil pump drives and blown oil filter canisters. This then causes a total loss of oil supply to the engine. I have seen this happen. The engine in question was driven quite a few miles after the canister burst. It was driven to a stall at WOT in low gear on a flat road. The result was not pretty. We recovered the cam, inlet manifold, exhaust, ignition system and the heads after a lot of repairs on the heads.

The restriction causes the oil to be lost out the pressure relief valve instead of circulating to all required areas. Damage results from oil starvation even though the gauge shows very high pressure.

A co-incidental cause is that if the oil is real cold, the engine internals are also cold and clearances might be so far out from suitable running clearances that damage results, eg, piston to bore is to big and the pistons slap hard enough at WOT high rpm that they crack the skirt off behind the oil ring grove.

It is impossible to associate this with a specific temperature as it depends on engine internal clearances, grade of oil, size of oil pump, strength of oil pump drive system. oil gallery layout, rate of warm up and temperature profile across engine components, strength of oil filter canister etc etc.






Regards

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[Majik]

Thanks Pat for the info. thought it was kinda a little bunky myself.

 

[TheBlacksmith]

I think Pat nailed it. The rest of your vehicle; transmission, bearings, tires would appreciate a slight warm up also before being pressed into hard service. That's why most recommendations today are to start driving slowly as soon as the engine is started. Warming the engine for several minutes wastes gas, can dilute the oil and pits a warmed engine against still cold and stiff parts.

 

[drwebb]

It sounds like you are referring to cool oil under running conditions in which case the oil will do it's job. Extreme cold-start conditions are a different matter, when the engine can be starved for oil under certain conditions long enough to cause damage, and this scenario is well documented. The SAE -W viscosity specs are meant to guard against this but are only tested on fresh oil, and formulators have realized over the past 5-10 years that cold flow properties can become very degraded in used motor oils. How much attention is paid to this parameter probably varies from one marketer to the next.

 

[Majik]

It's more that you must run a thermostat on your oil cooler because if you don't "The oil cooler will cool to much and the colder oil will damage your engine". Such as if it's a brisk day out my engine runs a low temp just driving around. But alas it will take hour or so to even begin to get to 180f. If racing on a circuit then it maintains steady oil temp up in the lower part of the gauge. I just hate adding in another piece (thermostat) that could fail on a mission critical system and prevent the cooler from even working properly. What was confusing was the use of heaters in drysump systems seemed to confirm that there was a problem with low temp but it might be one of those everyones doing it things.

 

[Zapster]

It is my understanding that if oil temp is too cold that condensates will not evaporate. The problem condensate is water vapor from the air. In addition, raw gas may run past the rings during startup and this too can collect in the oil if the temperature is too cold.

 

[patprimmer]

Majik

You just asked a completely different question.

If the normal operating temperature is to low, water builds up in the crankcase or sump and contaminates the oil. If the normal operating temperature is close to water boiling point, the water will be flashed off, thus cleaning the oil of the water contamination.

Use of the site google feature would have shown you that this has been already discussed in detail in previous threads.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Majik]

ahh sorry... the google one works much better than the other one.

 

[Knap]

Would low oil temperature be an issue re cavitation and additives not being as effective, as well as not maximising power output?

 

[romke]

normally it would not because the time an engine is run with too low an oil temperature will not be that long. some of the additives in the oil will be more effective within a certain temperature range (antioxidants, anti wear additives) but when the oil temperature is really low you do not need the antioxidant and since oil viscosity is much higher you do not need the antiwear additives either. as soon as normal operating conditions are reached the additives will be there up to their respective tasks.