Originally Posted By: 5AcresAndAFool
Ive always wondered if you had a situation where a vehicle was run around the clock most of the time, such as vehicles serving police, taxi, or ambulance duty, if you would be better off using a straight 30 weight oil.
In practice, the taxis we ran were "on" almost around the clock, and this was the late 1970s on, using conventional 10w-30 for 10,000 km OCIs. Engines lasted hundreds of thousands of miles. I'm sure an SAE 30 would have done just as well. This was the days before HTHS talk, but my dad seemed to have an instinctual understanding of the concept, and contended that an SAE 30 (that thick expletive, he called it) would provide slightly poorer fuel economy than a 10w-30, which is always something to consider in fleet usage.
For me, in practice, I don't like switching by season, so grab something I know will word fine in the cold, and use it year round. And, as OVERKILL points out, some of the most capable extended drain oils on the market certainly are not monogrades. The real world isn't ideal, and I think when it comes to automakers, it's simpler and safer to specify one grade for year round use, particularly in a country with as diverse a climate as the States, and just let us strange BITOGers obsess about viscosity tweaking.
Merk: Our Walmarts carry SAE 30 in 5 gallon pails, and most oil company distributors do, too, I'd wager.