15w40 oil


Well Known and Active Forum User
Non-VOC Member
Howdy Chaps,

Sorry for starting a new thread on this. During my lengthy absense from the forum (off sulking because I hadn't found a Shadow basket case), admin has changed my permissions - can't respond to posts, just start new ones. At any rate.....

Eddie - reason diesel forumulation was recommended for your Hardly Able-son was then/even more so now it contains more wear additives. Unbeknownst to most, we hear in the U.S. with vintage machines face a dilemma. More stringent emissions requirements are eliminating the key additives vital to flat tappet engines such as ours and that is ZDP and ZDDP (zinc and phosphate), in use since the 40's, which also inhibits corrosion. They are at .06% and dropping, minimum for motors of our vintage is .12-.14% and though still present in aviation oriented formulations, other factors make diesel formulations the way to go for us.

In lubrication-shear scenarios - cam lobe/lifter - modern engine designs take this into account by dispersing load over a greater area, lighter valve trains which permit less aggressive seat pressures, etc.., unfortunately our motors do not, but take heart, Indian Fours have a cam lobe like an inverted sharp "V" slapping lifters at 1/4lb each aaaand, they run essentially a ring and pinion in the form of bevel drive gears right in with the same engine oil!

If you're reading this and in the U.S., you want to look at the code circle on the bottle for API Service letter for "C" which denotes diesel and will likely read CF or CJ-4. Anything with an "S" prefix denotes gasoline and thus will lack these additives, in the interest of preserving your catalytic converter, of course ... but trashing your Vin in the process.
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Well Known and Active Forum User
VOC Member
I read the same about using Diesel rated oil so I bought a gallon of Mobil One 5-40 for Diesel Trucks. The oil is wonderful and the exhaust pipe is clean but it's too light and uses oil. My next plan. is to step up to a 20-50 rated for the same application. I went with the Synthetic oil because every engine I've ever seen that has used it is spotlessly clean inside and seem to run forever.
Cheers, John