flushing a 7.4 mercruizer with fresh water - Maxum Boat Owners Club

pascavone · 12-12-2010, 04:22 AM

were is the sea water pickup on the 7.4 mercruizer?

My system has fresh water cool heat exchanger.

dose it ue the outdrive, or is there a inlet under the transom on a 28scr maxum?

seapuppy · 12-12-2010, 03:30 PM

Pascavone..
what drive do you have......but overall...most of the time...your boat cooling system pulls the water up thru the drive to the pump...if you have an Alpha 1 drive...the pump is located in the lower half of the drive unit...
B2/3 drives pull the water up thru the pump mounted on the stbd/lower side of the engine...it then moves the water up to the heat exchanger and then to the manifolds,risers, and out of the drive.....
the heat exchanger transfers the heat from the engine to the water pulled up the drive...

SP

PS..I have just woken up so...my 2 little braincells didn't fire off properly, I should have read you have a big block engine...which means you have either of the b2/3 drives....which puts the pump down on the engine...

pascavone · 12-12-2010, 11:21 PM

yes, I put my garden hose and ears on the Bravo3 and expected all the hose water to zoom up into the engine.

Then i though the thermostat need to open first, then all the hose water would zoom up into the engine.

Then I figured I had the hose open to much, and that why all the water was squirting out the ears.

So, I was gettting steam out the top of the drive and my enging temp was at the 170, so me thinks it worked.

shrew · 12-13-2010, 02:21 PM

You've got it right, that should work fine. However it takes a bit longer than you'd expect to circulate the water through the engine and come out the the bottom of the transom assembly. I have the same problem with the muff. It looks like more water is coming out of the muffs than should be. I haven't found a good set of muffs yet.

pascavone · 12-18-2010, 02:59 AM

well, this is the way to flush the raw water system even with a fresh water cooling, but its not winterized.....

you still have to drop the hoses off the raw waer sea pump, remove the drain plug from the tranny cooler, pull off the end caps of the heat exchanger, and clean the tubs, and finally drop the hoses off the exhaust manifolds. Also says something about a fuel cooler but not sure i have it.

sounds like work.

shrew · 12-20-2010, 02:09 PM

Quote:

Originally Posted by pascavone

well, this is the way to flush the raw water system even with a fresh water cooling, but its not winterized.....

Very true. I was thinking 'flushing', not necessarily winterizing. A bit of an oversight on my part. It sounds like you've got things relatively in line. I think there should be some drain plugs pulled on the block somewhere on your list as well. I don't recall having an oil cooler on my 7.4.