Type of oil in a 165

"I've got a 165 L6, and th

"I've got a 165 L6, and the manual says to use straight weight 30 or 40 oil. Would it hurt anything to use multi viscocity oil? Like a 10-30 or 10-40."

"What year is this 165? I thou

"What year is this 165? I thought all reasonably current Mercs in the last 30 years or so were recommended to use Merc 25W50.
You can definitely use a multi-vis anywhere it is recommended to use a straight grade, but for marine use I wouldn't use anything less than a 10W-40.
Rod"

"The Model year is 76. The se

"The Model year is 76. The seloc manual says straight weight oil is recommended, but I think I'll switch to 10W-40 if you think it won't hurt anything."

"Graham, Stick with the straig

"Graham, Stick with the straight weight oil, or use Mercruiser 25-40 oil. Automotive-type multivis oil is not good for your motor. Check any mercruiser website."

"Hey, Chris, do you REALLY thi

"Hey, Chris, do you REALLY think automotive oil isn't virtually the same as the higher priced "marine" oils?

"Automotive multi-vis oil" is not only good for marine and any other engines, it's a marvel of chemical science. Thin when the motor is cold--to keep from wearing out the oil pump/ camshaft gears--and thicker as the motor warms up! Great stuff.

Jeff

PS: I know that a few marine manufacturers recommmend staight weight oil, but they gotta have a stick in the mind attitude to neglect the advatages of multi-vis oils."