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Flushing mercruiser 4.3l with external pump

J

Jewfiesta

New member
Hi! This might be a silly question, but here goes

Is it possible to flush the cooling system while the engine is off, with an external pump connected to the water inlet hose coming from the sterndrive impeller? Or does the engine need to be running to control the valves in the cooling system or something?
 
Your not going to be able to push much water past the pump in the leg

You could put a Tee on the intake hose and push it thru that way
 
Jewfiesta said:
Hi! This might be a silly question, but here goes

Is it possible to flush the cooling system while the engine is off, with an external pump connected to the water inlet hose coming from the sterndrive impeller? Or does the engine need to be running to control the valves in the cooling system or something?
Click to expand...
thermostat needs to be open as well, as mentioned wont get water past the impeller in drive.

Why are you opposed to running the engine while flush water is provided?
 
AllDodge said:
Your not going to be able to push much water past the pump in the leg

You could put a Tee on the intake hose and push it thru that way
Click to expand...
Yes I assumed pushing water through the impeller while it wasnt running, was impossible. So my idea was to attach the pump to the hose coming from the sterndrive impeller, thus bypassing the impeller.
 
Dieter said:
thermostat needs to be open as well, as mentioned wont get water past the impeller in drive.

Why are you opposed to running the engine while flush water is provided?
Click to expand...
I was gonna bypass the impeller by connecting the pump to the hose coming from the impeller.


Im considering making a flushing system for on-water use. It would make the plumbing less complicated if I could flush while the engine isn't running. If the engine isnt running, theres no need to add a second valve just for dumping the impeller water back overboard.
 
Jewfiesta said:
Can you explain to me in simple terms how this works? Im relatively new to boat engines
Click to expand...
It’s not different than automotive engines in respect to thermostat. Thermostat opens when engine is at temp , which is 140 f or 160 f for most marine engines with open cooling. Thermostat lets hot water out of the engine when open and cold in. Whether you are flushing or trying to winterize by sucking antifreeze in , unless thermostat is open engine block will not get fresh water.

To be honest you are making this more work than needed. Even if boat is slip kept put muffs on drive when all the way up by hanging off swim platform and run engine when at temp to flush salt water out .
 
Dieter said:
It’s not different than automotive engines in respect to thermostat. Thermostat opens when engine is at temp , which is 140 f or 160 f for most marine engines with open cooling. Thermostat lets hot water out of the engine when open and cold in. Whether you are flushing or trying to winterize by sucking antifreeze in , unless thermostat is open engine block will not get fresh water.

To be honest you are making this more work than needed. Even if boat is slip kept put muffs on drive when all the way up by hanging off swim platform and run engine when at temp to flush salt water out .
Click to expand...
Ok, thank you! I honestly believe it's more work to hang off the the swim platform with the muffs every time I've used the boat. I can easily put together some hoses and valves and just plug the slip's garden hose to it.
 
if you pursue your flushing concept to fruition, make sure you use high quality hardware...any leaks (in or out) won't be a good thing...
 
Engine needs to be running for an effective flush on a raw water i.e. no heat exchanger, engine,,, there is a circulating pump inside the engine..
 
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