Onan 5500 oil 351ds

[jcw]

Just had my first oil change on both the v10 (4300 miles) and genny (67 hrs) before a 10 day trip. Dealer put 15w30 in generator vs 5w30 listed on the generator housing. I mentioned to the dealer and they stated they used Onan spec'd oil for the 5500. Should I be concerned?

[oldgold]

I don't think there's any issue with running 15w30, especially in the summertime. It's thicker starting out but when hot, both oils are the same viscosity. It may take a little longer to warm up. If cold weather camping I would lean towards the 5w, but onboard generator in the summer I just don't see an issue with 15w. You can always split the difference and use 10w.

Essentially, the lower the first number the thinner it is when cool.

I was running Honda 2000 Companions until we recently upgraded the camper. Now we have the onboard 4000 Onan and I am about to change the oil for the first 20hour service. I was leaning towards 10w40 synthetic.

Someone correct me if I'm wrong.