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Stumped

805HD, I just read back through all of your threads.
While this may wrinkle the feathers of the Merc aficionados (and no offense intended), why don't you consider doing this:

1.... abandon the use of the A seawater pump.
You will still need to keep it active as it provides A drive upper unit cooling. You can route this water over-board.

2..... install a thru-hull pick up system.

3..... install a crankshaft pump if you have the necessary space in front of the harmonic balancer.

This would at least eliminate the potential issue of not enough seawater from the A drive seawater pump!

Crankshaft pump 5.jpg


4..... if you cannot install a crankshaft pump, go with the Merc style belt driven seawater pump.

Either the crankshaft pump or the Merc belt driven pump will provide more seawater than what the A drive pump is capable of.


.
 
UPDATE***
Apologies for continually digging up a old thread.

Okay so I got an update for you guys who have all been so helpful, I ran the water volume test and passed with flying colors.. A little over 4.5qts in 15 seconds @ about 8-900rpm. I then verified the same amount before and after the thermostat housing (thermostat still out of the housing)

The boat IS getting enough water. I have eliminated the impeller and any restrictions up to the circulating pump that might be slowing down flow. I am now hoping the circulating pump on the block which is a Napa brand automotive and not marine is the culprit. Going to replace with a OEM.

I mean what the heck else could it be?!?!
Will report back!
 
In your video at the 5.05 mark you say the tstat fits on top of the housing, that is incorrect, the t stat goes inside the housing and the brass collar goes on top. Pretty sure
 
Last edited:
Bt Doctur said:
In your video at the 5.05 mark you say the tstat fits on top of the housing, that is incorrect, the t stat goes inside the housing and the brass collar goes on top. Pretty sure
Click to expand...

you are correct, when I got the boat (which had no overheating issues) the thermostat was on top of the brass collar. I tried it both ways with the same results. Also replaced the thermostat housing. Same results.

The circulating pump is automotive and not marine, at this point it is the only variable that has not been assessed. That’s my next step.
 
Definitely would replace with a marine circulation pump - marine will have a bi directional impeller and be made of corrosion resistant materials. Likely the automotive unit is corroded inside if u don’t have closed cooling
 
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