Oil for Royal Enfield Himalayan

Feb 21, 2013
West Michigan USA
I just purchased a 3000 mile pre-owned '21 Himalayan (413cc air cooled single cylinder thumper with air to oil cooler). The manual states to use synthetic blend 15W50. About two years ago I bought a bunch of the Delvac 1 ESP 5W40 full synthetic that were on sale with big rebates (I think they ended up being about 10 bucks a gallon) and I have at least 8 gallons left. I use that oil in all of my small engines, mowers, generators, motorcycles and Can Am side by side. I'd like to use it in my Himalayan so I wanted to check with some oil experts here to see if this would be a good application for the Delvac. As I understand, a full synthetic oil can withstand much higher temperatures and shearing than conventional oils. With Delvac being a proven product over the years for OTR diesel trucks, and being a synthetic, I would think that it would likely outperform a 15W50 or 20W50 synthetic blend or conventional oil in an air cooled motorcycle. I have no problem buying those thicker oils, but since I already have lots of the Delvac 1 ESP on hand, I'd prefer to use that. I also like the idea of the Delvac being thinner so that it gets to the valve train faster to reduce cold start wear and tear. I live in West MI where riding temps are typically between 60 and 85F.
It would probably be OK, but why temp fate?

15w50 semi-synthetic probably was specified with something like 15w50 Motul 5100 4t motorcycle oil in mind. Not saying you have to use that, but you might compare the properties with your Delvac before choosing to use it.

Nice bike. I'd sure use what the manufacture recommends. I'm sure you can find a recommended oil at Walmart that is not too expensive. Ed
I also own a 21 Himalayan and used Motul 7100 15W50 at the first oil change interval. The first OCI is at 300 miles then the next is at 6000 miles. I picked up of Shell Advance Ultra 15W50 for $12.99 a quart at Advance Auto for my next OCI. Is that Mobil oil JASO MA2 approved?
A lot of times it seems like the manufacturers like specifying an oil that is bit of an odd viscosity just so you come back to them for the oil, most of the Japanese bikes are 10w40 for water cooled but the larger cruiser style bikes recommend 20w50, I know my friends Indian actually calls for 15w60 so good luck finding that unless you go back to the dealer. I don't have any experience with Royal Enfield bikes to know whether they have a dry or wet clutch but I would use an Xw50 oil, whether it's 10w50, 15w50 or 20w50 for that air cooled motor I really don't think it would matter that much and most times if there is a problem it affects the shifting quality first and you can just change it out for something else.
I'm no engineer, but it seems to me that a parallel twin would get very hot between the cylinders since it's solid aluminum. Twins do have space between them and are surrounded by fins which does help cooling. A single also is "open" on all sides with fins. I also think that a 50 weight oil should be specified when oil temps can reach very high levels in certain circumstances, such as being stuck in traffic in Phoenix or climbing big mountain hills with a passenger. In any of my single cylinder air cooled bikes, I have yet to see any oil temps above 200F. My '18 Passat normally has a 215F oil temp and it uses 0W20. I realize that the motorcycle transmission gears do a good job of shearing the oil molecules which means that a 50 weight will go down to a 40 weight over time, miles and heat. But if a bike is ridden at moderate speeds and loads at ambient temps below 90F, with the oil temp never exceeding 200F (mostly 170-180F), it would seem that a 15W40 conventional or 5W40 synthetic would be more than enough protection. My guess is that RE calls out 15W50 to make certain that the engine isn't damaged even in 130F temps under heavy loads and uphill climbs.
In the second sentence I meant to say that most air cooled "v-twins" do have space between the cylinders that are surrounded by cooling fins vs parallel twins and 4 cylinder engines that do not have fins between the cylinders.
A friend of mine owns a much older one. He dumps castrol conventional in it. Has about 10 cases (I don't think they even make it anymore) and does it once a year. Most peoples heads would explode, but it's been running great for years and years.

Oh, and oil filter. Whatever fits and is on the shelf at O'Reillys. Seriously.