Closed Cooling System - Freshwater Drain Plug Location on Exhaust Manifold 3.7 Liter

[frankttaylor]

All,

Well yesterday I finally decided to winterize my boat. I followed the owners manual that came with the boat and it states to only drain the fresh water side of the cooling system. It states to remove the plug from the exhaust manifold and according to the diagram it is about in the middle. The only plug I could locate is at the front and when I removed that one ant-freeze started to come out (obviously the wrong plug). The configuration looks different then my engine. I have one of the last generation 3.7 liters. Do you think that maybe the design changed and that they used an old book? Or am I missing something? I did successfully drain the heat exchanger. The last thing I need is a cracked exhaust manifold. Here are my specs.

1990 Bluewater
3.7 Liter
Engine# OC768011

Thank you!

 

[Don S]

Re: Closed Cooling System - Freshwater Drain Plug Location on Exhaust Manifold 3.7 Li

There isn't a drain on the manifold. It's antifreeze.

 

[Eric 3.7LX Alpha 1]

Re: Closed Cooling System - Freshwater Drain Plug Location on Exhaust Manifold 3.7 Li

There are 2 plugs on the bottom aft end of the heat exchanger. The one most to the rear is the one with sea water to be drained. The front plug will have antifreeze.

 

[frankttaylor]

Re: Closed Cooling System - Freshwater Drain Plug Location on Exhaust Manifold 3.7 Li

That is bizarre. I will scan page from book. I do not understand why it states there is a darin on the exhaust manifold. It even has a diagram. The plug looks the same as the anti-freeze plug on the manifold. So basically all I need to do is drain the heat exchanger and I am done draining the fresh water from the system?

 

[Don S]

Re: Closed Cooling System - Freshwater Drain Plug Location on Exhaust Manifold 3.7 Li

What manual are you looking at? It doesn't say Seloc or Clymer on the cover does it?

 

[frankttaylor]

Re: Closed Cooling System - Freshwater Drain Plug Location on Exhaust Manifold 3.7 Li

It is the original book that came with the boat. the poeple I bought from the boat kept everything surprisingly. I have to grab when I get home tonight.

 

[stonyloam]

Re: Closed Cooling System - Freshwater Drain Plug Location on Exhaust Manifold 3.7 Li

There is a drain on the manifold, however that is to drain the antifreeze, do not touch it!!! As Eric says, the ONLY drain plug that you need to remove is the AFT (the one nearest the transom) drain plug on the HEAT EXCHANGER!! That will drain ALL of the RAW Water from the cooling system. Do pick up a cheap antifreeze tester (less than $10) and check the engine antifreeze, should be about 50/50 automotive antifreeze.

 

[luckyluke]

Re: Closed Cooling System - Freshwater Drain Plug Location on Exhaust Manifold 3.7 Li

There is a drain on the manifold, however that is to drain the antifreeze, do not touch it!!! As Eric says, the ONLY drain plug that you need to remove is the AFT (the one nearest the transom) drain plug on the HEAT EXCHANGER!! That will drain ALL of the RAW Water from the cooling system. Do pick up a cheap antifreeze tester (less than $10) and check the engine antifreeze, should be about 50/50 automotive antifreeze.

Don't mean to highjack this thread but I have a 470 with closed cooling/heat exchanger and my sea water drain plug is very difficult to reach so all I did was remove the forward end cap of the exchanger (one bolt) and the water, of course, drained out. Anybody see anything wrong with this?

 

[Don S]

Re: Closed Cooling System - Freshwater Drain Plug Location on Exhaust Manifold 3.7 Li

Don't mean to highjack this thread but I have a 470 with closed cooling/heat exchanger...............................

Then don't hijack, just start a new thread of your own and ask your question. That's why there is a BIG RED "Post New Thread" button at the top of the forum.

 

[luckyluke]

Re: Closed Cooling System - Freshwater Drain Plug Location on Exhaust Manifold 3.7 Li

Then don't hijack, just start a new thread of your own and ask your question. That's why there is a BIG RED "Post New Thread" button at the top of the forum.

Woah, sorry.... Just wanted to make a suggestion on how to easily drain seawater but I didn't want to give bad advice in case this is not a good method.

 

[stonyloam]

Re: Closed Cooling System - Freshwater Drain Plug Location on Exhaust Manifold 3.7 Li

Don't mean to highjack this thread but I have a 470 with closed cooling/heat exchanger and my sea water drain plug is very difficult to reach so all I did was remove the forward end cap of the exchanger (one bolt) and the water, of course, drained out. Anybody see anything wrong with this?

I think that is an alternate method suggestion, rather than a hijack. That should work just fine, just try to get the exchanger level, or better yet pointed down to get all of the water out of it., and maybe have a spare gasket on hand just in case.

 

[frankttaylor]

Re: Closed Cooling System - Freshwater Drain Plug Location on Exhaust Manifold 3.7 Li

OK so here is the pages out of the book that I is confusing. I have read a few posts about cracked exhausts and want to make sure I avoid this. Also it states that I should inpsect heat exchanger by removing screws. Is this necessary?

 

[Don S]

Re: Closed Cooling System - Freshwater Drain Plug Location on Exhaust Manifold 3.7 Li

Turn the page and use the instructions for your 3.7. Those instructions are for the 2.5 and 3.0 GM engines.

View attachment 1989 4 cylinder 27.pdf

 

[frankttaylor]

Re: Closed Cooling System - Freshwater Drain Plug Location on Exhaust Manifold 3.7 Li

Turn the page and use the instructions for your 3.7. Those instructions are for the 2.5 and 3.0 GM engines.

View attachment 174248

So it is. Wow wasted a fair amount of time on something so simple. I feel like an idiot. Of course if I didn't ask then I probably would have messed it up. Thank you!

 

[Don S]

Re: Closed Cooling System - Freshwater Drain Plug Location on Exhaust Manifold 3.7 Li

Mistakes happen, at least you was using the manual. Most never do.

 

[stonyloam]

Re: Closed Cooling System - Freshwater Drain Plug Location on Exhaust Manifold 3.7 Li

I think the manual you have is #3 which covers all of the 4 cyl engines including the closed cooled GM engines, and "older style" 470's. This is the manual that you need for your late model 470: Boatinfo - Mercruiser Service Manual nr. 8 - 1985-1989 - Mercury Marine 4 Cylinder Engines So you are OK since the raw water is drained from the exchanger.

 

[Don S]

Re: Closed Cooling System - Freshwater Drain Plug Location on Exhaust Manifold 3.7 Li

You should have read the last replies Terry, he is looking at the owners manual, not as service manual, and he was on the wrong page.