At operating temp, why does outside temp matter?

[OVERKILL]

Originally Posted By: Vikas
PSA:

If you want to brag about your instru///Mentation display, don't do it if the check engine light is on!




That's the EVAP solenoid CEL and it has since "fixed itself", LOL!

 

[OVERKILL]

Originally Posted By: weasley
Holy c***! Did you really get through that much fuel in 6 km?!


60Km. The car has the typical E39 cluster dead pixel issue, there's a whole other number there that's missing

 

[Quattro Pete]

Is there a number all the way on the left that may also be missing?

 

[OVERKILL]

Originally Posted By: Quattro Pete
Is there a number all the way on the left that may also be missing?

Now now, LOL! No there isn't, but I'm pretty sure you can see that for yourself

 

[RamFan]

Originally Posted By: MolaKule
Quote:
Say in one case it's 70 degrees outside. Say in another it's 105 degrees. An owner's manual might spec a xW-30 versus an xW-40.



Keep in mind most of the oil temperature charts are for conventional oils verses ambient temperature, with a built in margin of CYA.

Just in case you drive through Death Valley and are using mineral oil, you might need an extra margin of safety to keep the oil from thinning out too much when going across the desert at 100 MPH.

Warmer ambient temperatures simply mean that the coolant and oil will heat up faster, that is, the rate of change of temperature will be faster in hot weather than in cold.

Once the coolant reaches operating temp after thermostat opening, the engine coolant temp should stabilize unless air flow is somehow restricted through the heat exchanger or radiator, or the cooling system was somehow underdesigned for the intended operating temperature and driving conditions.


Oil and coolant temps differ with vehicle and engine size, but as a rule of of thumb the oil temperature is about 20F above coolant temp.





Given Synthetics generally higher VI in addition to not thickening as much wouldn't that also suggest that they thin out quicker with higher heat? So why do synthetics claim to protect better in higher temp conditions?

 

[OVERKILL]

Originally Posted By: RamFan
Originally Posted By: MolaKule
Quote:
Say in one case it's 70 degrees outside. Say in another it's 105 degrees. An owner's manual might spec a xW-30 versus an xW-40.



Keep in mind most of the oil temperature charts are for conventional oils verses ambient temperature, with a built in margin of CYA.

Just in case you drive through Death Valley and are using mineral oil, you might need an extra margin of safety to keep the oil from thinning out too much when going across the desert at 100 MPH.

Warmer ambient temperatures simply mean that the coolant and oil will heat up faster, that is, the rate of change of temperature will be faster in hot weather than in cold.

Once the coolant reaches operating temp after thermostat opening, the engine coolant temp should stabilize unless air flow is somehow restricted through the heat exchanger or radiator, or the cooling system was somehow underdesigned for the intended operating temperature and driving conditions.


Oil and coolant temps differ with vehicle and engine size, but as a rule of of thumb the oil temperature is about 20F above coolant temp.





Given Synthetics generally higher VI in addition to not thickening as much wouldn't that also suggest that they thin out quicker with higher heat? So why do synthetics claim to protect better in higher temp conditions?


Resistance to low temperature thickening does not mean a base oil is going to thin more under high temperatures.

 

[supercity]

A higher VI would indicate the viscosity will change less with temperature, so it should thin out less than a oil with a lower VI, not more

 

[RamFan]

Originally Posted By: OVERKILL
Originally Posted By: RamFan
Originally Posted By: MolaKule
Quote:
Say in one case it's 70 degrees outside. Say in another it's 105 degrees. An owner's manual might spec a xW-30 versus an xW-40.



Keep in mind most of the oil temperature charts are for conventional oils verses ambient temperature, with a built in margin of CYA.

Just in case you drive through Death Valley and are using mineral oil, you might need an extra margin of safety to keep the oil from thinning out too much when going across the desert at 100 MPH.

Warmer ambient temperatures simply mean that the coolant and oil will heat up faster, that is, the rate of change of temperature will be faster in hot weather than in cold.

Once the coolant reaches operating temp after thermostat opening, the engine coolant temp should stabilize unless air flow is somehow restricted through the heat exchanger or radiator, or the cooling system was somehow underdesigned for the intended operating temperature and driving conditions.


Oil and coolant temps differ with vehicle and engine size, but as a rule of of thumb the oil temperature is about 20F above coolant temp.





Given Synthetics generally higher VI in addition to not thickening as much wouldn't that also suggest that they thin out quicker with higher heat? So why do synthetics claim to protect better in higher temp conditions?


Resistance to low temperature thickening does not mean a base oil is going to thin more under high temperatures.


So the high temperature protection associated with synthetic is attributed more so to the base oil rather than VI properties? Great thanks.

 

[OVERKILL]

Originally Posted By: RamFan

So the high temperature protection associated with synthetic is attributed more so to the base oil rather than VI properties? Great thanks.


Yep

And no problem.

 

[Garak]

Originally Posted By: OVERKILL
And this car has an oil cooler. These swings would be far greater on a car that doesn't have one.

I think that's somewhat application dependent, Overkill. The old Audi with the giant oil cooler would peak at temperatures like your last picture, when it was around 35 C out and I flogged it with full boost for about an hour. I found that in normal driving conditions (i.e. steady state highway), I wouldn't have much more than a 10 degree difference between summer and winter. As per mechtech2's post, a large amount of city driving in the summer, too, would get the oil temperatures to the observed peak.

Note, though, that on the taxis, there was a marked difference in oil temperatures (noticed on my hands during my inevitable oil change messes) between winter and summer. In the summer, I could find the oil draining right after shut off to be uncomfortably warm (not scalding hot, though). In the winter, the "uncomfortable" side of the equation would be gone.

 

[Jim Allen]

It's very much application specific but oil temp is always less in winter than summer ... whether that be by a little or a lot. In the case of my trucks, it's alot. I've been watching oil temps for years. On these 30 degree days, with the high capacity cooling option, the 5.4L at it's unloaded weight can only generate a stabilized oil temp of 165F, with coolant at 185-ish. At 70F ambient, the coolant runs 192-ish and oil temp is in the 185-ish range. A 100 degree day might see coolant a bit over 200F and oil temp about the same. This is a V8 with a large oil capacity, no oil cooler, and fairly low power density. Change that equation in any way and you are likely to see a change in operating oil temps.

All these temps are why my 5.4L engine does best with a light oil. At my winter oil temps, the 10W30 in the crankcase is running in the 50 grade (23 cSt) range according to Widman's viscosity calculator. Plus, it takes 15-20 miles of driving to get it even that high.

 

[OVERKILL]

Originally Posted By: Garak

I think that's somewhat application dependent, Overkill. The old Audi with the giant oil cooler would peak at temperatures like your last picture, when it was around 35 C out and I flogged it with full boost for about an hour. I found that in normal driving conditions (i.e. steady state highway), I wouldn't have much more than a 10 degree difference between summer and winter.


Was your cooler air/oil or water/oil? Mine is air/oil IIRC, which is likely why the difference.

I assume we are in agreement with respect to my point about cars without an oil cooler though, correct? As your taxi example seems to support what I'm saying here.

 

[Garak]

I'm not sure whether it was air/oil or water/oil, Overkill. I no longer have the vehicle to actually physically check it. At the very least, it had to have been thermostatically controlled. If it were neither thermostatically controlled nor a water/oil cooler, the oil temperatures would have been ridiculously low on a highway run in the winter, given the size of the cooler and the 4.5 L sump, and that wasn't the case.

Yes, we are in complete agreement. My taxi example isn't exactly scientific, but I do know the difference between uncomfortably warm oil and oil that just nicely warms up my hands.

It was definitely significant enough to notice.

 

[il_signore97]

Originally Posted By: OVERKILL


Was your cooler air/oil or water/oil? Mine is air/oil IIRC, which is likely why the difference.



That right there makes all the difference, as well as no oil cooler at all. In my Benz, there is a very large oil to water heat exchanger that does an excellent job of keeping the oil very close to the coolant temperature (whatever that may be). Granted, it does take a bit longer to get the oil warmed up in the winter (almost 9 qt capacity), but it still does get there and stay there.

What's most interesting (as a sidebar) is that a side effect of the large oil to water cooler is how it affects the warmup of the coolant temperature. In the winter especially, the coolant warms very quickly to about 70 C, but then takes quite a bit longer to settle in at the normal 85-90 C operating temperature. This must be a result of the large amount of oil that needs to be heated by the coolant prior to the opening of the thermostat (plus the large amount of heat being blown into the interior to warm it up until it gets comfortable).