Engine Oil Question

I want to make the switch to synthetic oil in my boat but I can’t find the exact weight and viscosity that the manufacture recommends. I have a model year 2000 LTR engine in my boat that calls for 15/40 oil. All I could find in synthetic is 15/50 Mobil 1. I decided to go with it. Is that okay? I can’t imagine that it’s not but I wanted to throw it out there and get another opinion.

Thanks in advance.

I can't answer your question but I can offer some advice. Walmart was by far the cheapest place I found for Mobile 1 oil.

That Mobil 1 would be fine. You can find 15W/40's but they are fewer. I'd run a 5W/40 as choice before the 15W/50. That will give you the same viscosity at operating temp and a lower viscosity when you cold start so the engine gets oiled quicker. You will have no trouble finding a 5W/40.
Amsoil makes a 15W/40 Marine oil but I'm not a fan of their products, and I have used them.

i use the mobil one 15/50 in my 02 Xstar LTR, the only 15/40 i could find was penzoil, and id rather run the engine with out oil before i use that!! you could use the 5W40, but usually the engines are not used in "cold" weather. when you put your boat in the water, its usually 55 derees or more? unless you use your boat in very cold weather id use the 15w50 the mobil one is a very good oil.

Thanks for the responses. The information has been very informative. As I said, I went with the 15/50 Mobil One which I am now confident was the correct choice. However, as a footnote, the engine sounded really weird when I first fired it up after the oil change but it quickly reverted to its normal sound.

I gave it quick clean, drained the block and I’m guessing it’s going to be seven months before it sees the water again. Oh well, hopefully we’ll have an epic winter in the Sierras.

Again, thanks for the information!

Amsoil has a 15/40 Synthetic. Might want to take a look at them.

Matt that sound was most likely the lifters-dry? Did you fill the oil filter, at least partially, with oil? Also did you crank the engine without starting the engine to get the oil pumping through? The oil pump will be sucking air initially after a change, till it all gets pumping. I usually try to crank 2 times without starting.

Wow, that's probably it. I will keep both of those suggestions in mind the next time I change the oil. Thanks.

Virtually ALL synthetic oil meets viscousity grades from 5-50 without any problem. They put a range on the oil, but it really does not matter all that much. I use the Wal-Mart or NAPA oils and they work great. As long as you have sufficient oil pressure, you are fine.