Oil - Another "why" question

[Beltzington]

I have read literally hundreds of articles and reviews on oils and still can't seem to get my brain around the logic of using a heavy weight oil for hotter outside air temps. Why would you use 10w-30 for -20F thru 100F and 15w-40 for -10F thru 120F? I understand the lower cold startup winter weight however the operating weight makes no sense to me as the engine operating temp is well over the outside temp once the engine warms up to, let's say, 180F for discussion. If 10w-30 is ok for a warm engine why recommend 15w-40? My guess is it was nothing to do with outside air temperature and more do with them hedging against the quality of chemicals used to modify the viscosity to increase the span between winter and operating weights. SO, based on this assumption my take-away is if you always use a high quality oil "Brand X" than 5w-40 is the best choice for all situations.

Anyone see this differently?

 

[Oldpath05]

Heavy weight oil is recommended for tractors because it gives more ballast, keeping the front end down.

 

[dickfoster]

Heavy weight oil is recommended for tractors because it gives more ballast, keeping the front end down.

Is that to keep the front end down on your way to the snipe hunt?

 

[Oldpath05]

Is that to keep the front end down on your way to the snipe hunt?

Think you need to use synthetic oil for that.

 

[bdog]

I too wondered the same thing until I had a truck with a digital oil temp gauge. Your oil gets hotter than your coolant temp and your oil does in fact get hotter when it is hot outside than when it is cold.

I don't remember the exact numbers but on my diesel truck my oil was significantly cooler after several hours on the road in 30-40 degree temps than it is while driving in 100 degree weather. It wasn't 60-70 degrees warmer but more like 10-20 if I remember correctly. I can see at 100+ temps the oil being thinned out enough to necessitate the 15-40 vs 10-30.

 

[namesray]

I have read literally hundreds of articles and reviews on oils and still can't seem to get my brain around the logic of using a heavy weight oil for hotter outside air temps. Why would you use 10w-30 for -20F thru 100F and 15w-40 for -10F thru 120F? I understand the lower cold startup winter weight however the operating weight makes no sense to me as the engine operating temp is well over the outside temp once the engine warms up to, let's say, 180F for discussion. If 10w-30 is ok for a warm engine why recommend 15w-40? My guess is it was nothing to do with outside air temperature and more do with them hedging against the quality of cstophemicals used to modify the viscosity to increase the span between winter and operating weights. SO, based on this assumption my take-away is if you always use a high quality oil "Brand X" than 5w-40 is the best choice for all situations.

Anyone see this differently?

This seems like a interesting topic to me. Good question. Your theory makes sence. With 5w 40 you get the best of all the operating conditions and ranges. I too ask a lot of questions about oils. I have asked on tbn here, mechanics where I work, equipment dealers, even kubota corporate. I never get a in depth detailed answer.

I can tell you this. I work for the state highway dept. I have been told (and believe) by the mechanics that ALL equipment and vehicles get the same oil, 15w 40 diesel oil. This means the big trucks, loaders, exevators, graders, down to the gas engine pick up trucks and cars stating 5w 20 oil, and even the lawn mowers and push mowers stating 30 weight oil. The bigger equipment of course. The pickups and cars all last over 100,000 miles with never an engine failure. And the lawn mowers through out the years always work too. This all happens in the northern Pennsylvania climate, both summer and winter.

The only issue I have ever heard they had was with the new tier 4 engines in the big equipment/trucks. They were using the older class of engine oil with higher ash contnt and it was clogging the regen dpfs quicker then should have.

So I am thinking it is all a hoax. As long as it has oil, it'll work better then no oil! So my search for more info on oil types goes on. I am contemplating if it would be ok to switch from kubota oil to shell rotella t oil for my tier 4 tractor engine. Save about $10 per gallon.

 

[3930dave]

I have read literally hundreds of articles and reviews on oils and still can't seem to get my brain around the logic of using a heavy weight oil for hotter outside air temps. Why would you use 10w-30 for -20F thru 100F and 15w-40 for -10F thru 120F? I understand the lower cold startup winter weight however the operating weight makes no sense to me as the engine operating temp is well over the outside temp once the engine warms up to, let's say, 180F for discussion. If 10w-30 is ok for a warm engine why recommend 15w-40? My guess is it was nothing to do with outside air temperature and more do with them hedging against the quality of chemicals used to modify the viscosity to increase the span between winter and operating weights. SO, based on this assumption my take-away is if you always use a high quality oil "Brand X" than 5w-40 is the best choice for all situations.

Anyone see this differently?

Up until not that long ago, most charts like you posted were created with conventional oil in mind - vehicle manufacturers knew that many consumers did not want to be forced into buying synthetic oil.

The xW40 option on the old charts was to give people hauling heavy in extreme heat a way to minimize oil consumption. Modern synthetics have low volatility at high temperature, but the easiest way to reduce consumption with older conventional oil was to bump up the viscosity.

A good quality modern 5w40 is a versatile oil, that will cover many applications.

Rgds, D.

 

[KubotaToy]

The same as namesray stated about the highway department, my father has used bulk 15w40 on the farm from the cheapest wholeseller he could find since 1974. 15w40 was used in every tractor, truck, utility vehicle on the farm, never experienced a problem. I used 5w40 in all my equipment and will in my truck when the warranty ends. Bottom line, use whatever oil that makes you feel good but keep oil in it and change it on a reasonable basis.

 

[Beltzington]

Thanks for the comments, I always go through this every time I due my annual service on the tractor. I think I may have asked my question poorly, so let me try again.

If I know I will never be operating below 0F or above 105F is there a best weight oil? Synthetic 5-40, 10-30, or Dino 15-40. Or should I just stop worrying about this and start thinking about problems I can solve like global warming

 

[Oldpath05]

"(Or should I just stop worrying about this and start thinking about problems I can solve like global warming)"<<<Yes exactly, get rid of your diesel guzzling tractor and switch over to a battery powered tractor and we can all live in harmony, sit around the battery powered camp fire and sing Kumbaya, no more worrying the brain numbing kunfusing motor oil numbers and diesel fuel color., I'll be behind you all the way..............