closed cooling system

[ericcarr2000]

Ok, I just pulled the trigger on purchasing a new to me 87 sea ray sundancer 268 with the 7.4 mercruiser in her. What I have in mind of doing is installing an aftermarket closed cooling system on her. My question is this, Ive found that there are two different kinds of systems I can get. One that cools just the block and one that cools the manifolds and block. If I were to purchase one that cools just the block, what all is involved in winterizing the manifolds?

 

[Bt Doctur]

Re: closed cooling system

draining the manifolds and fiiling them with A/F

 

[ericcarr2000]

Re: closed cooling system

So that's all there is to it, draining the manifolds and adding antifreeze in them, pretty quick huh?

 

[agallant80]

Re: closed cooling system

It won't work. Well it will but the issue you will have is the years worth of crud in the block will plug things up in the closed cooling system and cause constant overheat issues. The motor has to be pretty new to add closed cooling. Unless it was replaced very recently you are going to spend a tonne of money on something that will be a constant headache.

 

[Walt T]

Re: closed cooling system

agallant80 is right. I've seen that before. You somehow have to clean the daylights out of it.

 

[Scott Danforth]

Re: closed cooling system

you also have to drain the raw water side of the heat exchanger and the power steering cooler that is in the line as well.

However as many have pointed out, your motor is a 1987. even if it has been in fresh water only, the block will have a lot of sand and gunk in it. that needs to be cleaned out.

 

[tpenfield]

Re: closed cooling system

Yes, tell us a bit more about the boat and engine's history. I added closed cooling to the twin 7.4L on my 1996 boat that was run in fresh water it whole life. So far, so good. If the engine has been run in salt water, there is probably way too much iron flake/scale in the water jackets, and it would tend to clog up the heat exchanger.

 

[ericcarr2000]

Re: closed cooling system

Well, as far as ive been told the motor was rebuilt in 2004, and there have been only a couple hundred hours put on the rebuild. Also it is a fresh water ONLY motor from the great lakes.

 

[thumpar]

Re: closed cooling system

I remember reading that after 100 hours it is not recommended to add closed cooling to an engine. Even if it was rebuilt it is the same parts.

 

[ericcarr2000]

Re: closed cooling system

I understand that but if I were to give her a good flush a few times everything should be fine you'd think though.

 

[thumpar]

Re: closed cooling system

Maybe but why? My old 1983 boat had the original engine and never had an issue with cooling. The only real advantage I see with closed cooling would be if you are running in salt and maybe a tad easier to winterize but you also are adding more parts to fail and weight.

 

[ericcarr2000]

Re: closed cooling system

That's exactly what I'm trying to make easier, the winterization. My current boat has the 3.7 mercruiser motor and has the closed cooling system and is extremely easy to winterize her.

 

[thumpar]

Re: closed cooling system

I have the 5.7l and have no problems draining it.

 

[ericcarr2000]

Re: closed cooling system

So to winterize the motor and risers is all I have to do is to take some hoses off and dump some antifreeze down them?

 

[thumpar]

Re: closed cooling system

Skip the antifreeze. Just take the plugs out. I am guessing you have an engine driven seawater pump so pull the hoses off that and the circulation water pump. The power steering pump should have a drain. If you have cool fuel (not sure when they started that) drain that also.

 

[ericcarr2000]

Re: closed cooling system

What the heck is cool fuel, lol?

 

[ericcarr2000]

Re: closed cooling system

So I guess I really have to find out where these drain plugs are in the motor then.

 

[thumpar]

Re: closed cooling system

It is a fuel cooler that is inline after the seawater pump.

 

[thumpar]

Re: closed cooling system

Boatinfo - Mercruiser Service Manual nr. 9 - 1985-1988 - GM V8 Engines

 

[Silly Seville]

Re: closed cooling system

You're on freshwater...you don't need a closed cooling system. I have the near identical boat/powertrain as you. I can drain my engine in less than 3 minutes. AIR DOES NOT FREEZE! Why do you want to spend money on the complexity of a system that was designed for saltwater boats? Especially given that in spite of the claim that your engine was rebuilt ten years ago, it may still be the nasty, rust scale filled block from 1987. If you wanted to do this "correctly", you would need to have the block, heads and intake manifold stripped and sent to a machine shop to be boiled, baked and blasted clean. That is the ONLY way to get the rust scale out completely. So at that point, you are effectively rebuilding the engine. What you are considering start to finish is a $4,000 exercise in futility for the sake of what? Easier winterization? If you are that averse to winterizing yourself, pay a marina to do it. For the cost of a rebuild and closed cooling system...you could pay to have that thing professionally winterized for a decade or more.

Just open the drains, pull the appropriate hoses, and let it air out.