flushing raw water return through elbow. 3.7. backflow? overheat

raise10

Recruit
Joined
Aug 11, 2011
Messages
4
I was flushing out my exchanger and outlet lines after an overheat on my 88 merc 3.7 alpha 1. while flushing through elbow/exhaust I get a good bit of back flow. I have pulled the elbow and flushing through the hose fitting. I see the holes in the elbow the water flows back out from. Water appears to be flowing out good just not as fast as i am putting in I am using 3/4 inch hose with about 75 psi on it. I dont see how it could run out as fast. Should I have some backflow out of fitting or do I have a restriction. I have read on here there shold not be any backflow. If so, How do I clean the chamber inside elbow? The outlet holes are clear.

Also thanks to everyone who has already helped me tremendously as I am a new boat owner of a boat that didn't run.

I think that the thermostat is what caused the overheat. If I am testing right it will not open in boiling water. Impeller was shot but prob. from the overheat, could have been previous owner, or driveway testing on muffs. I didn't let it run long enough to get hot in driveway(lesson learned). The manual I got with boat says not to run full tap psi on muffs. I see no mention of that in the manual I downloaded from here. Is the old manual right? It doesn't make any sense to me not to run full tap psi.
Stern impeller replaced pressure checked out drive. Everything together and running good except elbow, shutter(I'm not looking foward too) and thermostat. Tstat and shutter spose to be here tmorrow.
Thanks
 

stonyloam

Vice Admiral
Joined
Mar 13, 2009
Messages
5,827
Re: flushing raw water return through elbow. 3.7. backflow? overheat

I think it should flow pretty freely, you might try running a brush or something through the water passage to clean it out.
 

raise10

Recruit
Joined
Aug 11, 2011
Messages
4
Re: flushing raw water return through elbow. 3.7. backflow? overheat

backflow is just emptying jacket back out through fitting(low point with biggest opening) when pulling hose off. Ran all day at 140 to 147 max temp according to boat gage. Hope I didn't get wrong tstat as it opens at 140 according to boat gage.
 

stonyloam

Vice Admiral
Joined
Mar 13, 2009
Messages
5,827
Re: flushing raw water return through elbow. 3.7. backflow? overheat

It should be a 160 degree thermostat, and the normal operating temp is 165-200. I never have a great deal of faith in gauges, so you could measure the temperature of the coolant in the reservoir and compare to the gauge.
 
Top