Oil Choice - Starting temps, vs ambient temps

Messages
576
Location
Madison, Wisconsin
While mowing the lawn the other day, I started thinking about my next oil change this fall and what I wanted to do. I know it's odd to think about cold weather oil in July, but it helped to pass the time... I've got a Briggs opposed twin in my tractor. I run Rotella 15w40 during the summer, and had been changing over to Rotella 5w40 in the fall. I'm considering going to the 5w40 year round, but it can be a bit tricky to find around here. Which leads me to consider the 15w40 as the year-round choice. And I know that will raise a few eyebrows... My tractor stays in a warm garage all winter. I get that lighter weights are recommended for starting in cool temps, but this thing is starting in 40-45 degree temperatures. Even a straight 30 weight might be OK for starting in that temp, according to Briggs' online oil charts. Not optimal, but OK. Obviously, it's a lot colder outside when I'm snowblowing but at that point the engine's running and warm. Any meaningful snowfall seems to work the engine pretty good, so it's not idling along by any means. My fundamental question here is this. Should one make an oil choice based on the temperature the motor is when it's started? Or the ambient temperature it's operated in? I'm leaning to the starting temperature, but would appreciate opinions.
 
Last edited:
Messages
8,859
Location
Texas
Both the oils you are talking about are the SAME (for all intents and purposes) at operating temp. The engine doesn't care whether its a 15w40 or a 5w40 in the crankcase when the oil is at 300 degrees F. The difference comes about when its cold. Given your usage cycle, 5w40 year round would be best, but with storage in a heated garage the 15w40 won't exactly be asphalt when you go to crank it up. It should be fine, just run at a high idle for 5 minutes before putting it under load.
 
Messages
6,638
Location
South Florida
These engines don't need 40 weight oil. Your climate sure doesn't support the need for 40 weight oil either. Why don't you try Briggs & Stratton's number 1 oil recommendation for ALL their engines, which is SYNTHETIC 5W30 (not conventional, it consumes). Then you don't have to worry about summer, spring, fall, or winter oil. Synthetic 5W30 can handle the heat fine and offers all the protection you need. http://www.briggsandstratton.com/us/en/support/faqs/engine-oil-recommendations Briggs states the following: Synthetic 5W-30 -20 to 120° F (-30 to 40° C) provides the best protection at all temperatures as well as improved starting with less oil consumption. Based on what they say, plus my experience doing over 200 oil changes per year on power equipment and customer feedback, I 100% stand behind Briggs recommendation.
 
Messages
6,638
Location
South Florida
Originally Posted By: abycat
I'd run a 40 wt in it. They get hot in the summer. 5 30 in winter and 15 40 in summer.
And the engine will run even hotter with a 40 weight. They run colder on a 30 weight, and even colder on a synthetic 30 weight.
 
Messages
2,008
Location
grande prairie AB
Originally Posted By: bubbatime
Originally Posted By: abycat
I'd run a 40 wt in it. They get hot in the summer. 5 30 in winter and 15 40 in summer.
And the engine will run even hotter with a 40 weight. They run colder on a 30 weight, and even colder on a synthetic 30 weight.
I don't think you could measure the change it would make without using decimals. my truck Guage doesn't change from a 20 wt to a 40. And that is a nice Guage with a big range. op may be different but temp is pretty much the same.
 
Messages
8,859
Location
Texas
Originally Posted By: bubbatime
Originally Posted By: abycat
I'd run a 40 wt in it. They get hot in the summer. 5 30 in winter and 15 40 in summer.
And the engine will run even hotter with a 40 weight. They run colder on a 30 weight, and even colder on a synthetic 30 weight.
Until I see temperature probe data, I want to see "allegedly" at least twice in the above post. What evidence do you hae that it runs hotter with a 40-weight? And I'll go right ahead and say that I flat out don't believe you'll EVER find evidence that it runs "even colder" on a synthetic 30 than a conventional 30.
 

TWG1572

Thread starter
Messages
576
Location
Madison, Wisconsin
Well, that was simple enough. Guess I was overthinking it while driving around the yard - but at least the overthinking passed the time. smile Starting temp it is....thanks! This is a bit entertaining because I almost put a last sentance in my post that I wasn't interested in debating the best oil types. I run Rotella because of the add pack and am not interested in shifting to a PCMO. If I can find a reliable local supplier of the 5w40 in quarts, I’ll run that year round. I can find the big jugs but they are a pain to measure out small quantities. I know I could fill empty quart bottles with the bigger or something, but it just seems like a lot of pain. FWIW, I did run the 15w40 through one winter a couple years ago. I didn't notice any difference in starting, etc.
 
Last edited:
Messages
6,638
Location
South Florida
Originally Posted By: abycat
I don't think you could measure the change it would make without using decimals. my truck Gauge doesn't change from a 20 wt to a 40. And that is a nice Gauge with a big range. op may be different but temp is pretty much the same.
How does a water cooled truck have any relevance at all to the discussion at hand, which is about air cooled small engines? Answer, it doesn't.
 
Messages
6,638
Location
South Florida
Originally Posted By: 440Magnum
Until I see temperature probe data, I want to see "allegedly" at least twice in the above post. What evidence do you have that it runs hotter with a 40-weight? And I'll go right ahead and say that I flat out don't believe you'll EVER find evidence that it runs "even colder" on a synthetic 30 than a conventional 30.
I've seen testing done on this very issue. 40 weight runs hotter, 30 weight a few degrees cooler, and synthetic 30 weight a couple of degrees cooler still. I'm not just spouting nonsense like so many others seem to do these days. I've seen the empirical data myself.
 
Messages
2,191
Location
VA
Originally Posted By: bubbatime
Originally Posted By: 440Magnum
Until I see temperature probe data, I want to see "allegedly" at least twice in the above post. What evidence do you have that it runs hotter with a 40-weight? And I'll go right ahead and say that I flat out don't believe you'll EVER find evidence that it runs "even colder" on a synthetic 30 than a conventional 30.
I've seen testing done on this very issue. 40 weight runs hotter, 30 weight a few degrees cooler, and synthetic 30 weight a couple of degrees cooler still. I'm not just spouting nonsense like so many others seem to do these days. I've seen the empirical data myself.
Can you point us to the empirical data? Otherwise I think you're spouting nonsense.
 
Top