Do they have to be US Coast Guard Approved, too? I can't get the Merc replacement lines any more. Theses lines are 25 years old with 4 rebuilds/failures. I have a new cooler and was going to use 10an oil lines & maybe include an in-line oil stat + gauge. Hydraulic hose shop the answer?

i never heard of oil lines being uscg approved,the answer is no.

Ayuh,...... Nothin' Marine 'bout oil lines,.....

Just the fuel, 'n electrical systems,....

Good. I'm replacing the hoses anyway, so I'll make it happen with 10AN plumbing & include a 215 degree in-line stat from Summit (Improved Racing)...wish it had a port for easy oil temp tap like Earl's, but I guess 180 degree is the only option for those. Anyone use these?

go with -12an.i believe you will be fine at 180 deg oil temp.