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View Full Version : Need info on Fresh water cooling for GM 350/ Merc 5.7



doug hess
02-25-2002, 07:19 AM
I am putting in a new engine and looking for info and diagrams converting a seawater cooling system to a FWC half system, engine block only. Current system has thermostat housing with 6 hose connections and cannot be used in a split set up. Does anyone know what type of housing to use and what the connection are?
The engine is a 1992 with Alpa 1 drive.

Doug

avanti
02-25-2002, 08:37 PM
We have a 2000 Donzi 18 Clasic with a 350 Mag in it. We put a 1/2 FWC system on it. We just bought a kit from Mercruiser and it had everything in it that we needed. It was around 700 for everything. I think the thermostat housing that came with the kit has only one large hose that runs to the heat exchanger. If you look at the Mercruiser web site they probably have a diagram of the FWC system. Hope this helps you out.

doug hess
02-25-2002, 09:23 PM
Avanti, Thanks for the reply. I have looked at many of the FWC systems on the Mercruiser site but cannot get clear idea of how circuit goes with regard to the thermostat housings.

I have not seen any with the one big hose you mention which sounds similar to automotive type housings but was wondering about using one. Do you have a part number your systems or the housing.

Even better do you have the manual or instructions that came with it?

Doug

avanti
02-26-2002, 06:57 AM
I pulled out my stash of Mercruiser info and found the following part numbers. The FWC kit is 860427A7 and the thermostat housing is 861188A1.

doug hess
02-27-2002, 10:22 PM
Avanti, Thanks for the numbers.

After a lot of research on FWC for 350's with Alpha 1 drives I said the hell with Mercury kits. The Alpha has a modest capacity pump in the I/O which is marginal for FWC. Merc says flat out it is no good and you must put on a new engine mounted pump.

I use my boat for cruising rather than WOT speed. A much simpler alternative was a $600 complete FWC kit which uses a higher capacity heat exchanger. This avoids maintaining Merc engine mounted pumps at $400 to $600 each and $250 thermostat housings.

That is what really set me off, the $250 for #861188A1, a 3 pound cast iron housing with some simple machining!!?** I am sure they can explain their NASA pricing but I would rather use the money for gas.

Doug

avanti
02-28-2002, 07:21 AM
Just a note to say that Mercury is full of balony about the additional water pump. If you read the fine print you will see it says you require the additional pump for the full system only, not the 1/2 system you want. We run the 1/2 system all the time using just the Alpha's pump and it works just fine. The right price on the Mercruiser kit is around 700 and that includes all the pieces, hoses, clamps, etc. that you need. Hope this helps you out.

doug hess
02-28-2002, 09:25 PM
Yes, your information is helpful, thanks.

I am going full block and manifold cooling where capacity is more of an issue. In my prior life I was involved with heat transfer systems. Recently I spoke with directly 4 of the makers of these systems about the Alpha 1 application. To address it, while they were not specific I got the impression they add capacity using say a 454 size exchanger on a system for 350 engines.

One of the reasons behind my extra caution is that while this is for a new engine, the old manifolds are going to be reused after getting boiled out at the local auto radiator shop.