I was getting prepared to mount and plumb my engine and tranny coolers when I realized the tranny coolers I bought from Eddie Marine have 3/4" NPT fittings for the water inlets and outlets, while the engine coolers have the standard 1" NPT water inlets and outlets. I was planning on plumbing the entire system with 1 1/4" Shields 250 hose and Teague 1"-1 1/4" stainless fittings.

The tranny coolers are the standard duty 2" x 12" core coolers, and the engine coolers are the heavy duty 3"x12" core coolers, one with a built in p/s cooler.

I was planning on routing the water from the sea water pump, through the tranny cooler, then through the engine cooler, and finally to the engine crossover. This won't work with the smaller cooler because it would create a restriction in the water flow and possibly lead to engine over heating due to reduced water flow.

I called Eddie Marine to see what they normally do, or if I should simply run heavy duty coolers for the tranny's too. I think the heavy duty coolers would be too much for the tranny's, and he agreed. He said they normally tee off of the main line somewhere, usually between the sea water pump and the engine oil cooler, or they feed water to the tranny cooler via a pressure relief valve set at something like 15 psi. I bought a pair of the new Merc pressure relief valves, but I believe they are fixed at 25 psi. So the tranny coolers wouldn't get any water flow through them until the water pressure exceeded 25 psi. I'd hate to trust my tranny's longevity to a pair of plastic overflow valves, as well as the fact they would only be getting water flow at higher engine rpms.

Another option he mentioned was adding one or two thru hull fittings and feeding water to the trannys coolers that way. I hate to put any more holes in the hull below the water line than I have too. He said one thru hull fitting tee'd off would provide sufficient water flow when under way.

Anyone have any preferences for the options I listed or other recommendations?

Oh well, I guess no one used this combination of coolers. There are aspects of all the plumbing options I didn't feel comfortable with, so I just went ahead and ordered 2 more of the heavy duty 3"x12" coolers with billet mounts. A costly oversight, but I figure I can always use the smaller 2"x12" coolers as fuel coolers. Tranny's last longer with lower fluid temps anyway....

If it isn't too late, use an adapter on the tranny cooler. The slightly smaller inlet and outlet will not have enough of a restriction to cause you any problems.
Gary

The problem is that I can't find a 3/4" NPT to 1 1/4" hose adapter...

I already ordered the other 2 HD coolers anyway.

3/4" pipe to 1" pipe. 1" pipe has an OD of 1 1/4".

Right. I found some that were aluminum or chrome plated brass, but I prefer to stay with stainless. Call me anal, I guess...

It's too late anyway, I should get the new pair of larger coolers next week. Thanks for your help and ideas though.

groco full flow cast bronze fittings maybe?/... DO NOT USE BRASS NIPPLES ON CAST BRONZE FITTINGS (ELECTROLOSIS)i had an 8 year old red brass nipple break off on a sea strainer. oops! s.s. is ok if you must .i'd use 316