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3.0 closed cooling troubleshooting

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Boaterdustin

New member
Hi,

I have installed a half closed cooling system on my mercruiser 3.0 LX. I used a heat exchanger from a 3.7 marine ford engine and vented it out through the manifold. Put it in the water today and am having heat issues. My manifold and riser, circulating pump and thermostat housing are all new. New hoses and the heat exchanger was very clean when installed. The impeller is moving a ton of water and the raw water lines seem to be functioning properly. I have removed the thermostat. The engine coolant lines are hot and I am not sure if it is circulating properly. It is possibly air locked. I am also wondering if the water pump on the engine is large enough to move a larger volume of coolant? Does the position of the heat exchanger effect coolant flow. I mounted it inside the engine house and is sitting low in comparison to the engine. About even with the oil pan. Any information or advice would be appreciated.

Thanks

Dustin
 
I just looked at my 4.3 manual, and can see that seawater cooled, and closed systems are completely different critters with different thermostat hsgs. Was this engine originally set up for seawater, or a closed system? Beyond this I'm out of intelligent questions. I'd suggest you get an engine manual for your 3.0L and look at the two different system flow diagrams. If you dig deep enough on Google, you may come up up with a .PDF manual. But after what you're already sunk into this project, an official Merc. manual is peanuts.
 
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Boaterdustin said:
Hi,

I have installed a half closed cooling system on my mercruiser 3.0 LX. I used a heat exchanger from a 3.7 marine ford engine
Would that be from the Merc 3.7L engine...... the Merc designed aluminum cylinder block engine with the Ford 460 cylinder head?

and vented it out through the manifold.
What does "vented" mean?
Are you speaking of the "spent" seawater being directed to the exhaust manifold and elbow?

Put it in the water today and am having heat issues. My manifold and riser, circulating pump and thermostat housing are all new. New hoses and the heat exchanger was very clean when installed. The impeller is moving a ton of water and the raw water lines seem to be functioning properly. I have removed the thermostat.
I would leave the thermostat installed. It is there for a very good reason.
It will open up and flow coolant as temperature dictates.

The engine coolant lines are hot and I am not sure if it is circulating properly. It is possibly air locked.
A marine thermostat should have a small air bleed hole in the base frame that should allow any air to become purged in short order.

I am also wondering if the water pump on the engine is large enough to move a larger volume of coolant?
That would be the engine coolant "circulating pump" (aka "circ pump") .... and yes, it should be capable.

Does the position of the heat exchanger affect coolant flow. I mounted it inside the engine house and is sitting low in comparison to the engine. About even with the oil pan. Any information or advice would be appreciated.
Although we will see vertically mounted H/Es, and Off-Engine mounted H/Es ...... most applications place the H/E near the level of the engine's highest water jacket.
You will want to be able to remove the pressure cap and yet not have coolant escape.

Thanks

Dustin
Click to expand...
 
Last edited:
harringtondav: great point on the circulation pump and thermostat housing. I am using stock components meant for raw water. I know there is additional opening in the new circulation pump that was blocked off with a threaded plug. I'm hoping if I change the cooling hoses around I might get better circulation. And yes I should get a manual.

Thanks

Dustin
 
Ricardo
I don't know exactly the make and model of the heat exchanger, I got it from a friend that has a large 4 cylinder with closed cooling. By vented I mean "spent" raw water. I removed the thermostat and have intentions of putting it back in when I get it flowing cooler. Thanks for the info on the circulation pump and location of the exchanger. I don't think it is air locked, just not flowing properly. I'm going to re route my hoses ANF keep you posted. Thank you

Dustin
 
Bt doctur,

I made a new cover for my thermostat housing out of 1/4" plate and welded in a radiator bung with pressure filler cap. I'm going to reroute my hoses tomorrow so it will flow like the diagram you posted. If I can't get it to
Work I will try to find a proper thermostat housing for a closed system. Thank you!
Dustin
 
Problem solved. I had it hooked up for raw water thinking it would work but did not function properly. By moving the lower hose from the thermostat housing and hooking it directly to the circulation pump it now works like it should. I used a çouple of short pieces of hose, plugs and lots of clamps to block off the two outlets on the thermostat housing. It is not pretty but it got me and the kids out on the water today. I should invest in the proper closed cooling thermostat housing. Installing the thermostat tomorrow now that I know the coolant is flowing properly. BIG THANKS FOR YOUR REPLYS to my post. You have been very helpful.
Dustin
 
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