Closed Loop Cooling in Mercruiser 3.0l question

[atm0029]

Hi fellow boaters,

Im a new boater, but have a sharp edge in automotive applications. Ive just rebuilt my mercruiser 3.0l engine and added a heat exchanger (ebay heat exchanger - the one thzt costs ~$200). I wanted to have a closed loop system because salt water in panhandle Florida ruins engines and everything it touches.

My question (theory): If I cool the engine and exhaust manifold together with the heat exchanger, and the heat exchanger is appropriately sized, what antifreeze circuit should I run?

I have a coolant passage block off plate between manifold and riser so that the salt water lives in the riser, and antifreeze lives in the exhaust manifold. The salt water dumps into the riser from the 1" fittings that ive installed in the riser.

Where Im at: my circuit is completed with this pathway:
Antifreeze: Starting with the heat exchanger, then antifreeze flows to the water pump that pushes it thru the block and cylinder head and then reaches the thermostat (Im running a 160 degree thermostat). After the thermostat, I have antifreeze enter the manifold, once it flows thru the manifold it then exits and returns to the heat exchanger.

Salt water: Gets picked up by the impeller in the foot, and pushes thru the heat exchanger (that is completely separate passage from the antifreeze) and then I have the salt water dump into the riser and it then goes out the exhaust bellows.

My worries: Being that the antifreeze is being held back by the thermostat, that means I have stagnant antifreeze sitting in the manifold. I dont like the thought of having stagnant antifreeze in the super hot manifold. Though, its heat would conduct through to the block and then bring the block temp up, thus allowing the thermostat to open.

I have an alternative methodology for antifreeze flow: There is an output on the water pump that I could use with the exhaust manifold so that the manifold is always getting moving antifreeze, but then engine antifreeze could still be controlled by the thermostat. Would this pathway work? My only concern is that if the antifreeze is always moving through the exhaust manifold then there might not be adequate amounts of time for cooling in the heat exchanger. Its supposed to exchange, but if the antifreeze is always moving then the heat exchanger cant really do its job..

Is my current circuit okay?

Thanks folks

 

[Scott Danforth]

you need to have constant flow thru the exhaust manifold.

that is why there are different thermostat housings for HX cooled vs raw water cooled.

the thermostat is used as a mixing valve in this application

the isnt enough copper in a $200 ebay heat exchanger for a full system on a 3.0

plumb it like the merc or volvo HX cooled units.

 

[achris]

... Ive just rebuilt my mercruiser 3.0l engine and added a heat exchanger (ebay heat exchanger - the one thzt costs ~$200). I wanted to have a closed loop system because salt water in panhandle Florida ruins engines and everything it touches....

If you rebuilt from an engine that has previously been in salt water, don't put closed cooling on it.

The block will have scale and salt in the pores of the metal and if you enclose that, it's going to clog up the new heat exchanger and cause more problems than it solves.

The history of those engine is that they run perfectly well in salt water, and giving them a 5 minute flush at the end of the day doesn't hurt. I've seen salt water run 3 litre engines that are more than 30 years old and have no problems. I wouldn't fuss about it.

Chris....

 

[nola mike]

Not to hijack the thread (but I'm kinda going to hijack the thread), my buddy just got a new boat with a VP and a port for a hose to flush when done. Does this exist on mercs, and if so, where does it plumb into? Seems simple enough to just tee it off, and the advantage over muffs would be that you could flush while on the water. Don't know if you'd need the engine running, in which case you'd need to shut off the seawater input...

 

[achris]

Not to hijack the thread (but I'm kinda going to hijack the thread), my buddy just got a new boat with a VP and a port for a hose to flush when done. Does this exist on mercs, and if so, where does it plumb into? Seems simple enough to just tee it off, and the advantage over muffs would be that you could flush while on the water. Don't know if you'd need the engine running, in which case you'd need to shut off the seawater input...

You would need to run the engine as the thermostat needs to open. And second, you'd need to have a 2 way valve so the water coming up from the drive pump could be redirected. The pumps hate being 'deadheaded'.

As far as I know, Merc don't offer any system like that on Stern Drives. I know they have flush ports on the outboards, have done for more than 20 years now, and I have a vague recollection of something like that on the inboards. I suspect they don't offer it on Stern drives because it would take a few SECONDS of running an engine with the valve handles in the wrong place for a LOT of damage to be done. And we all know, if it can be messed up (or another more appropriate word ), it will be! :facepalm:

Chris.......

 

[nola mike]

Yeah, those were my concerns about the impeller. Wonder how it's done on the VP. Seems like a nice feature, and AFAIK there are no valves. If the engine were off, maybe it could be done if water could enter after the T-stat? I don't have a plumbing diagram handy to see if you'd miss anything doing that.

 

[achris]

.... If the engine were off, maybe it could be done if water could enter after the T-stat? ....

I can see that working well. :facepalm: Someone forces a heap of cold water into an engine immediately after doing a hot run. How many cracked blocks can you count?

Chris......

 

[nola mike]

I can see that working well. :facepalm: Someone forces a heap of cold water into an engine immediately after doing a hot run. How many cracked blocks can you count?

Chris......

Work with me here! Was originally going to say that the t stat would be open immediately after running anyway, but then thought it would be tough to get the water in that quickly. I think you'd have to work hard to crack the block. Dunno that 70' water in a 150' block would do it.