MT - What Is the Optimum Engine Oil Temperature?

[buster]

I never knew there was a specific temp.

"For a dual-purpose car, engine oil needs to be at least 220 degrees F to burn off all the deposits and accumulated water vapor."

https://www.motortrend.com/how-to/engine-oil-temperature/

 

[racer12306]

Interesting.

Makes the whole "drive it once in a while to burn off the water" a bit of a farce. My truck never sees 220* oil temps (if the sensor is close to accurate). 212-215* max, iirc. I have seen the Pacifica touch 220* but not often.

 

[Kira]

They don't say what a "dual-purpose car" is.

 

[Slow Car Sport Mode]

Sounds more like coolant temps to me... at least crawling in traffic, maybe. Might be between 185-190s otherwise.. depends on the vehicle. Chevy fans used to kick on at 220 if I remember right. We are entering the summer months, so, fluid temperatures should be up.

As mentioned, never heard of a "dual purpose car" unless they mean a work truck or car you use for both work and personal.

If I remember right, coolant temperatures stay more the same whether it is hot or cold out, but oil temperatures can go up significantly with the ambient temperature of the outside air? That oil temps will vary more than coolant temps?

What about burning off fuel that might accumulate due to a cold start, water is mentioned but when does that "burn off" and what is the temperature a NOACK reading would come into play in a normal passenger car ICE engine. So many questions, I know.

And will thinner grades not heat up faster?

 

[racer12306]

And will thinner grades not heat up faster?

This is a "simple" fluid dynamics question.

Viscosity is the resistance to flow, more viscosity = more resistance. Resistance, whether it is fluid or electricity, should mean more heat.

However, then you have the thermal conductivity of the fluid come into play.

 

[Kira]

However, then you have the thermal conductivity of the fluid come into play.

Which is why I use "oil wetter".

 

[billt460]

Out here in the dead of Summer, the highest oil temperature I ever saw in my 2015 HEMI was 240 F driving from Phoenix to Lake Havasu. That was with 120F ambient air temp, at around 80 MPH on I-10.

Most of the time going to town and back from a cold start, (say 15 miles round trip), it will get up to 214 F going up the hill home. Water boils at 212 F, so if there is any water in the oil, (which I doubt with a single digit outdoor relative humidity most of the time), it's not going to last long.

 

[dnewton3]

I think something many people misunderstand is how "moisture" can move from phase state to phase state.

As we all know, ice is frozen water; that happens (assuming "pure" water) at 32F.
Water exists between 32F and 212F (at sea level; less at higher elevations).
Steam exists above that boiling point of 212F.

HOWEVER ...
Moisture will evaporate at well below the boiling point. An oil does NOT have to be at/above your boiling point to rid itself of moisture. The rate of evaporation is dependent upon two things:
- relative humidity level in the immediate atmosphere; the greater the disparity the quicker the evaporation
- relative surface temperature where evaporation occurs; the greater the temp delta the quicker the evaporation

The boiling point is the temperature (depending upon system barometric pressure) at which you can force a phase state change for all the mass, given enough time. But we can still rid the liquid of moisture by having temps which induce evaporation. If evaporation didn't work below the boiling point, then human sweating would pretty much be a fruitless venture ...

Moisture will leave the engine oil via evaporation, it just does it quicker when the oil exceeds the atmospheric boiling point.

 

[wpod]

Remember the oil temperature [between the parts ] is higher than in the sump.

 

[John_Conrad]

easy enough,,, bring on winter for 6 plus months and in particular jan-feb depending on where you are and engine operation temp may not reach 150 at least in my case on some drives and my wife's car as she only drives 5 miles one way! but i watch my oil change intervals carefully depending on these factors and add a little protection to the cold winds coming in the front of the grill if necessary to help out.

 

[The Critic]

Interesting.

Makes the whole "drive it once in a while to burn off the water" a bit of a farce. My truck never sees 220* oil temps (if the sensor is close to accurate). 212-215* max, iirc. I have seen the Pacifica touch 220* but not often.

I was running errands around town yesterday. If I was in traffic, mine went as high as 224F.

 

[twX]

"Even on a short-duration, drag-only combo where oil is frequently changed, you would not want to routinely see oil temps under 200 degrees."

Here in the north, there are vehicles that wouldn't see oil temperatures above 170 degrees F for months at a time. On my Subaru, in cold weather, the oil is heated by the oil-coolant heat exchanger, and it still won't exceed 190 F in really cold weather, even with a grill block.

I doubt it's much of an issue, so long as the engine reaches steady state temperatures regularly. Water and fuel don't need to hit their boiling points in order to evaporate, and any oil hitting the pistons will get quite a bit hotter than the sump temperature.

From a study on piston ring wear at low engine temperatures, wear doesn't seem to be very accelerated unless oil and coolant temperatures are quite low. Wear seems to increase when the oil temperature is dropped below 35-40 degrees C, then stabilizes again once it's heated to beyond this temperature. Of course, this only shows the short term effects of cold oil operation, and eventually sludge would become an issue if these temperatures were maintained indefinitely.

 

[WobblyElvis]

Oil quickly cycles around the engine. The underside of the pistons and the area of the head around the exhaust valves must subject some oil to fairly high temps even before the entire engine is up to temp. I read somewhere that if the oil sump reaches 140F, water in the oil soon evaporates.

 

[edyvw]

Regularly I see in Atlas 198-234, depending on conditions, uphill etc.
In BMW, 220 is regular, up to 250 on track since installing radiator-type oil cooler.
Before that, I would see 300f on track.

 

[buster]

My truck doesn't provide oil temp unfortunately.

 

[Jimmy_Russells]

Both of our vehicles have normal operating range of 90-97C (194-207F). They'll go higher than that under certain circumstances obviously, but just driving around normally, that's the range they stay. I have to imagine if the oil temp "needed" to reach 220F on a regular basis, that these vehicles would have been designed to do so.

 

[Nesterenko]

And will thinner grades not heat up faster?

No, I believe it's the thicker oils that heat up quicker. Not exactly sure why but it could be more energy is needed to move it, therefore more friction created. Maybe member @kschachn could chime in.

 

[ZeeOSix]

No, I believe it's the thicker oils that heat up quicker. Not exactly sure why ...

More force/energy is needed to shear a thicker viscosity oil, which means more heat is generated.

However, one thing that people don't realize is that the thinner the MOFT, the more shear rate there is in the oil film at the same speed between moving parts, which can also heat up the oil. With all factors held constant, a thicker oil between moving parts really doesn't heat up much more than a thinner oil would.

 

[AZjeff]

How is moisture getting in the oil to begin with? Is the PCV system letting it in?

 

[ZeeOSix]

How is moisture getting in the oil to begin with? Is the PCV system letting it in?

Combustion blow-by (which contains water) past the rings and into the crankcase.