Many people think that using a 10w-60 is necessary in almost any modified car, especially ones with turbos; that is a very old-fashioned approach to lubricating a performance car. Many years ago, a thick mineral oil was necessary to cope with higher engine temperatures in powerful engines, now it's often better to up the quality rather than Ir, another option for one oil would be Rotella 10w-30 - I bet you could find that easily in bulk. That would be a great compromise between price, cold weather performance, hot weather protection etc. compared to 15w-40. I wouldn't want to be using 15w-40 in -30 degree weather in a Ford that specs 5w-20 Anything with VVT (variable valve timing If you need a 15W-40 diesel oil, Castrol® GTX® Diesel helps extend engine life, protecting against the wear and tear of severe weather, rough roads and heavy tows. As a 15W-40 viscosity grade, it flows like a 15 weight oil from start up in Winter, but provides the protection of a 40 weight once the engine reaches full operating temperature 5W-20. 5: This is the oil’s viscosity rating at low or winter temperatures. W: This stands for “winter,” and is part of the “5” rating. 20: This is the oil’s viscosity rating at high temperatures. What this means is that the oil industry scientists, in their labs, have created lubricants that flow better at low temperatures than This is very outdated and Im sure doesn't apply to current oils. 20 Years ago I ran Chevron Delo 400, Mobil Delvac 1300 and Shell Rotella T 15W-40 in a 1999 Cat 3406E in a dedicated route. With 30,000 mi drains (Max allowed with UOA) and 2 gallons of add oil (Roughly 20% of capacity) the TBN was at 50% of new and viscosity was slightly below At operating temp. The two oils are very close in viscosity. Good plan to change oil early. An early change gets all the break in metal too fine for the filter to catch out of the engine. Put a magnet on your filter to trap even more break in metal. Use magnet till about 3000 miles or so. 17,501. Location. Clovis, CA. Mar 17, 2014. #2. SAE30 is good above 40*F. Below 40*F, you may experience hard starting. 10W-30 may contribute to oil consumption. Check the oil level regularly. That's pretty much what it says in the Briggs & Stratton owners manual. K. 10W-30 is a synthetic designed for conventional engines and low-stress, extended drain intervals where it can be used in high concentrations for oil control. 15W-40 is a synthetic designed for higher performance engines, with more stress and heat. It can be used in lower concentrations for oil control. 10W-30 is the cheaper of the two oils. 10w30 vs 15w40. The key difference between 10w30 and 15w40 motor oil is that 10w30 motor oil does have a viscosity grade that flows like ten-weight oil when the weather is cold or even the engine temperature is low. It can also resist thirty pounds while the engine is at its maximum temperature. The viscosity of 15w40 motor oil is comparable to what is the difference between the two. I always run marine oil and a friend of mine uses regular oil from auto parts stores.his motor is a mercruzer 5.0 inboard outboard. he also runs a fram oil filter from auto parts as well he says it the same as a 305 smallblock chevy . A9QjfNH.