Freshwater to Saltwater

[tdappleman]

This looks different but the specs say OMC 3.8 at least.

http://www.go2marine.com/product.do?no=161230F

 

[Woody]

Don't be afraid of the salt. It can be managed easily as long as you're on top of things.
There is a few things that come to mind...
Engine temperature; with raw water cooling in the salt you'll want to stay down at about 140 degrees. Any higher and salt will build up in the corners of the engine castings. With a closed cooling kit installed you can run your engine at a higher temp... gasoline burning engines are more efficient at the higher temp. Merc's rwc engines are 140 t-stat and the fwc are about 165.
Not that you'll be needing a heater down there but if you have a closed cooling system you can install a hydronic heater.
The raw water pump; I much prefer the seperate belt driven pump like the bravo system uses over the alpha style pump in the drive. With the belt driven pump you can change an impeller with the boat still in the water and if you use a 'through-hull' pickup you can easily install a filter system too... all good things to have.
Keep your anodes in good shape. A lot of systems have zincs in the heat exchanger and risers too that tend to get forgotten. Electrolosis is your enemy.
If you research the closed cooling systems available both aftermarket and factory you'll see both types; one that has coolant in the engine only and another that has it in the manifolds too (which has a block-off plate between the riser and manifold). Choose the 'manifolds in' kit if you can then you'll never have to change them. Note some manifolds don't have the fittings cast in to them for this but I'd change them when (or if) you put the cooling system on.
That leaves just the risers... boats here in the Pacific ocean that sit in the water all year round need risers every 5 +/- years. I'm sure it's similar there.
Flushing; with closed cooling it isn't as important to flush it out. Do it anyways to get the residual out of there and give yourself a warm fuzzy feeling. Without the closed cooling you should flush it every time it comes out. Salt corrodes the cast iron quickly. You can tell with a simple test... flush it right when the boat comes out and there's clear water exiting... wait a day or two and flush... you'll have rusty water come out of your engine for a while.
Hope this helps.
Cheers :thumbsup:

I have rwc engines and I don't have a 140 degree thermostat. I did some looking through my Merc stuff and all I see is rwc 160 and closed cooled 170. I don't boat in salt water and don't understand the idea that it will leave salt deposits in a engine running a 160 degree t-stat but not in one that's running 20 degree cooler.:huh:

 

[jcjones]

tdappleman, thanks for that link too.

Still not the correct manifold, but at least that's one that specifically indicates a 3.8l engine. The risers on mine are just like the OMC V8 version that are at the very back of the manifold and connect to a rubber tube that then connects to a kind of "S" shaped cast tube then to another rubber tube and finally into the intermediate stern drive section.

If I went to V8's and kept the OMC stern drive units I would have to move the engine mounts forward far enough for the extra 2 cyl's on the back of the engine. Might have to do a little fabrication for that since the front hydraulic "Selectrim" mounts are right at the forward edge of the engine support platform in the engine compartment.

Damn... Why do I always wind up with the weird s**t?!?!?! LOL

 

[magster65]

I have rwc engines and I don't have a 140 degree thermostat. I did some looking through my Merc stuff and all I see is rwc 160 and closed cooled 170. I don't boat in salt water and don't understand the idea that it will leave salt deposits in a engine running a 160 degree t-stat but not in one that's running 20 degree cooler.:huh:

At least 3 of the rwc engines I've owned have had 140s... I googled "mercruiser thermostat replacement" and this is the top match: http://www.sterndrive.info/sterndriveparts/engine_thermostat_kits.html
It lists the 140 and 160...
As for the salt build-up at higher temps, that's the answer I got from my pal... he's a certified Mercruiser mechanic. That's what they say on the topic at the 'certified' trade school he attended. Maybe the salt stays in solution form more easily at lower temperatures? That's my guess.
Who am I to question Mercruiser? :smt001