Does ambient air temp matter /that/ much for weight?

[Pskhaat]

Living in AZ, this summer I expect to see my daytime highs no less than 105F or so with a few 115F+'s thrown in here an there until well into October.

Now I traditionally have run M1 15-50 in my Toyota 1FZ-FE engine (~100k) and my Ford Probe 4cyl (~160k) during the summer months due to traditional logic of higher outside temp == higher viscosity.

Is this flawed thinking? The engine will operate roughly at the same temperature once warmed regardless of outside temp assuming my cooling systems are working fine.

That said, the manufacturer's both mention 5-30 as the recommended weight though non-US specs say 10-30 and 10-40, and I do feel that with my moderate mileage and higher temperatures 5-30 is a little light.

Thus, is a synthetic 15-50 an appropriate application in my higher temperatures or am I pushing the envelope; does the outside air temp really matter that much except for truly cold starts?

 

[Steve S]

That is how the selection of viscosity is done .

 

[JHZR2]

Most areas of the world provide a viscosity chart, not a one-size fits all.

A lot of it has to do with driving profile. If you never do more than 15 miles, your oil is rarely at temperature, and so the actual value at 100C doesnt matter as much!

Without an oil temperature gauge, its harder to tell if the heat transfer between the water/air and oil/air is sufficient to keep the oil temperature in the sweet spot of just above 100C. Inefficiencies in the systems due to age, coupled with a slightly lower delta T may cross the line, that the step up is worth it.

The easiest way to see if its a good choice is to gauge consumption and get a few UOAs done.

Even if I lived in AZ, Id probably be running a 40wt oil in an everyday vehicle that wasnt used in a condition that relaly heated it up (like low speed heavy hauling/towing). I might use 15w-40 diesel grade oils, but would more likely choose a 5w-40 synthetic.

JMH

 

[eljefino]

quote:

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Originally posted by Pskhaat:
The engine will operate roughly at the same temperature once warmed regardless of outside temp assuming my cooling systems are working fine.

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Since you're running at approx. thermostat temp (~190F) you probably don't need to go thicker. Going one grade up, to a xw40 weight, might make you feel better. I assume you do mostly highway driving; do you see any major hills that make your temp climb?

A scantool to the computer will tell you if you're running above thermostat temp better than the numb gauges they install these days.

Make sure the spoiler under your bumper and all the air ducting up to the radiator and A/C condensor are working 100%. These get ripped off on curbs, etc.

 

[MGBV8]

A view from down under

http://www.penrite.com.au/techbulletins/38_PENRITE_AND_LIGHTER_OILS.pdf

 

[Al]

I personally think a 50 wt. is too high. I would either do a 40 wt (max) or put a mix of 30 and 50 wt. I think a 30% to 50% 15W-50 with the 10W-30 M-1 would work great.

 

[Bryanccfshr]

I would run the recomended viscosity and not even blink. I think running higher viscosities vor ambients is bunk. A relic from from the old single grade days. If your worried about heat and volatility run a synthetic, the greater natural VI will actually cause the oil to thin less as it heats above 100c. The fluctuations in ambient temperatures(really 80 or 115 is not that much diofference) has minimal impact on oil temp and operating viscosity.

 

[Pskhaat]

quote:

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I assume you do mostly highway driving; do you see any major hills that make your temp climb?

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The Probe sees 95% highway driving and dusty roads. The Toyota (Land Cruiser) sees significant off-road, towing, loaded, and dusty conditions more often than you might think.

 

[Blue99]

If the air temp is 110F in AZ on a summer day & the pavement temp is 125+, I can certainly imagine the oil in the crankcase running 20 degrees F warmer.

While the cooling system temp may be 190F, oil returning from the high heat zones of the engine is much hotter and gives up heat to the oil in the crankcase, as it re-circulates.

At 220 F, M1 5W-30 becomes a 9.0 cSt oil, so I'd pick a 40 weight oil to handle the heat. I like Al's idea of a M1 10W-30 & 15W-50 blend.

BTW, I plugged some numbers into the viscosity calculator & VI index has such a minimal effect at temps around 100C, it isn't worth mentioning.

 

[Ugly3]

I would use what is says in the manual adjusting the viscosity upward for high miles on the engine if consumption is a problem.

 

[Pskhaat]

Generally I would agree on the weight suggestions in the manual, but for my Land Cruiser (for instance) it is sold internationally and different locale's see a graduated suggestion in their manuals whereby in the US we see simply 5-30; prior to 1995 the identical engine was graduated at 5-30 and 10-30 dependent on temperature.

Just as a point of conversation, non-US suggestions run from 5-30 through 20-50. The only thing that I can see different would be the US's smog stuff. Which manual suggestion do I then follow? (Rhetorical really

just curious...)