Oil Grade vs. Temperature - another aspect of the issue

[Primus]

Discussing questions of preferable SAE grades or chosing the right one we often refer to or at least try to be as much as closer to OEM recommendations. These recommendations mainly consider Grade vs. Ambient temperature. However, they never consider an eventual impact of a road temperature. In summer days, as you may notice, the temperature of an ashpalt paved road is usually 10-20 C higher than that of an air. Thus, expecting that the temperature would not exceed 30-35 C, your car, in fact, is passing hours in a traffic jam or rolling over a highway stressed by 40-50 C heat coming out from the pavement.

What do you think about this impact ?

 

[Jim 5]

My thought is the Grade vs. Ambient temperature consideration already takes into account whatever the pavement temperature adds to ambient temperature.

My guess is that when the manufacturers made those recommendations, they were aware that they were designing a machine that would be operated over pavement around 99% of the time.

As such, it is likely that the testing giving rise to those recommendations was likely completed in various ambient temperatures. In every case, my thought is that those test cars were being driven on pavement.

 

[XS650]

They know what the oil temperatures in the engine run under various driving conditions and that's what they design for.

 

[bruce381]

Ambient is the temp at the point of use so if 30C in the air but on the "road" is 40C then ambient is 40C.
bruce

 

[mechtech]

What else is the vehicle supposed to drive on?

 

[Titan]

Look at it this way, ambient air temp has less to do with the internal engine operating conditions than you might expect. That's why I never understood why one neighbor would run a 5-30 in the winter and a 20-50 in the summer...in a passenger car with no towing...and they live below the Mason-Dixon line!

 

[jorton]

When motor oil get's a little beat up, it's due to engine design, driving routine, and climate so temperature of the pavement is indirectly related.

When pavement is 40-50C the engine is not in warm up loop for very long and that's good for the oil.

 

[Ray H]

quote:

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Originally posted by Titan:
That's why I never understood why one neighbor would run a 5-30 in the winter and a 20-50 in the summer...in a passenger car with no towing...and they live below the Mason-Dixon line!

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Old attitudes, passed down through who knows by what passed for expertise, die hard. That's probably the same reason that until 2005, Hyundai continued to preach the gospels of St. 10W-30, St. 10W-40, and St. 10W-50 for temperatures above -10 degrees F. in their owner's manuals. (By the way, though - did that neighbor ever suffer premature engine wear to your knowledge? By no means am I implying you're wrong - just noting that engines seem capable of thriving on a surprising variety of viscosity grades.)

 

[TallPaul]

Ambient seems to have a large effect on my '95 F150 4.9L. In winter I can run 10w30 and rarely drop below 40 psi oil pressure at 2000 rpm. In summer that same oil will run around 35 psi at 2000. So I run 10w40 summer and it stays above 40 psi. Now this is more a function of my typical trip being 15 to 20 miles, which generally does not get the oil as hot as a longer trip will. On longer trips I suspect the engine ambient temperatures would have negligible effect on oil temperature (and hence pressure).

 

[Raven18940]

SAAB recommends 15w50 or 20w50 for summer use, 10w30 , 10w40 or 15w40 for normal use and 5w30 or 5w40 for when the temp gets below -20 C.

 

[javacontour]

I've always suspected that cold was far more critical than hot when selecting the oil.

Why?

Because you have to wait longer for cold oil to warm up.

In the summer, there is just a smaller difference between ambient air temps and temps inside the engine.

Since most cars have a thermostat that keeps the coolant at the same temperature winter or summer, I don't really understand the need for most folks to use a "summer weight oil. For the most part, their engine will be the same temperature internally running on Feb 1 as it will on August 1.

TallPaul says above he sees some difference. I wonder if that not more of a cooling system issue than it is an oil issue. Either too much cooling in the winter, or too little in the summer?

Of course, YMMV, every vehicle is different.

 

[Gary Allan]

javac - you'll see oil temp vary from summer to winter. Your peak temp will vary a good bit. In the warmer months ..you've got a "step up" toward 100C temps ..but your peak probably takes about the same time to reach in many engines. It may be 220F in the summer ..or 185 in the winter. It will mainly vary with load ..but will be somewhat indexed for ambient temps. The heat is going to go somewhere ..the colder it is ..the faster it will escape through whatever medium is between it and the cooler environment.

 

[Titan]

RayH wrote: By the way, though - did that neighbor ever suffer premature engine wear to your knowledge?

I don't know why his cars always seemed to have some sort of trouble, and they tended to smoke a bit out the exhaust. Could have been the Make, could have been the way he didn't take time to ease out of the driveway to give them time to warm up. He could also never understand how my cars got so much better fuel mileage than his, given that he felt I drove faster than him. Truth is, I may have cornered faster, but take-off speeds were moderate compared to him, and I also didn't wear out my brakes as often as he did. So, our styles were very different, that's all I can say about that.

Too many varibles to place any blame for his complaints and increased troubles on viscosity alone.

 

[javacontour]

So a 35 degree difference in engine oil temps and a 60 degree difference in ambient temps. Hmmmm.

I really don't know as I've not had a car with a real oil pressure gauge in some time, and never one with an oil temp gauge.

It would be interesting for someone to use the same oil, same car, etc and take a couple of similar drives that last an hour or more along the same route during each of the four seasons, recording both ambient temps and oil temperatures to see how much variation there really is.

I wouldn't have expected that big a difference in oil temps.

 

[Gary Allan]

It's not easy to reason ..other then to say that the load your experiencing at the moment will determine your oil temp. The ambient temp will effect that reading depending on how much heat the pan ..and even the filter can (and whatever else it comes in contact with), can reject.

I imagine if you had an exhaust temp guage that you would find some parallels.