At my workplace we have an older 4-stroke quad that calls for 10W40. We keep plenty of 10W30 gas engine oil and 15W40 diesel engine oil. Which of these 2 types would be more suitable. Thanks in advance.
The 15w-40 diesel oils don't contain friction modifiers, so that would be the better choice for a wet clutch ATV. You can also find 10w-30, CH-4 rated diesel oils (Chevron makes one) for cold weather use.