My stock oil cooler has 3/8" lines (6.2 MPI - twins in a 29' Fountain Fever).
I replaced the port cooler with one that has 250-300% more area (moved from 9 to 12" length, 2 to 3" diameter)
yet saw little difference in oil temps between port and starboard engines. Is it possible that the 3/8" lines
do not flow enough to take advantage of the larger cooler? The new cooler is set up for 1/2" lines.
I would love to hear comments from those who have actually changed oil line diameters.

http://www.offshoreonly.com/forums/g...-hardware.html

I have 50+ psi oil pressure hot. Should be plenty of pressure for engines that spend the majority of their time in the 3000 r.p.m. range.

I did on a big block and saw immediate difference but small blocks dont need or pump as much oil so not sure? In my case I am positive the bypass relief was opening and pump bypass was prob also opening and oil was never getting to the cooler, Smitty

Pressure means little when chasing something like this in many cases. Volume is the important value you can't evaluate just by looking at pressure. As you are probably aware, oil pumps are producing volume, not pressure. I'm not saying oil pressure isn't an important value (obviously resistance to flow inside an engine creates pressure and it's necessary for an engine to live). If oil pressure is appropriate, in my mind you need to look at the items that would increase flow/volume.

Why not plumb larger oil lines and record your findings regarding oil pressure and temp?

I know the std BB merc stuff is real restrictive with lines, fittings and adapters, I changed all of mine and ran #10 line

BORGIE - Sorry, I now understand your comment. A high volume oil pump might make a difference, correct?

EZSTRIPER - I am leaning towards replacing all stock Mercury plumbing, remote filter adapter, block adapter, and lines with #10.

Well yes and no. A high volume pump wouldn't do anything for you with restrictive plumbing. Until you get the plumbing to where it needs to be, I think your issue will persist. My comment just highlights that most think of oil pumps as creating pressure. They DO NOT. They create volume and the resistance to flow in the engine, ie bearings and passages is what creates pressure. You can have good pressure and crappy flow. I think you will be amazed at what stepping up a size in oil line ID will do for you.

Thanks BORGIE

The new coolers are set up for 1/2" pipe plug. I'm not sure if that would be 8AN or 10AN lines. I will be looking into a block and remote filter adapters that will accept larger lines.
If someone has used a particular brand I would would love to hear about it.

i use -12 for oil lines.i would also add that the pressure releif valve in the oil pump also controles oil pressure.a stiffer spring will raise the pressure .