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Fresh-Water Intake Degrades at Speed

clohman

Member II
My informal assesment is that the stock 5/8" fresh water intake line for the Universal Diesel engine stops working correctly beginning around 6 Knotts. My guess is that at some point, the sea water passing by the throughhull at a 90 degree angle begins to suck water out of the line. At this point, the temp on the engine begins to climb. Backing off to about 5.5 Knotts solves the temp problem. RPM for this "test" is about 1800+ @ 5.5 knotts and about 2000-2100 for 6. Impeller is new. Water pump is the original Obendorf.

Any thoughts?
 
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Geoff Johnson

Fellow Ericson Owner
I think I have the same setup (M25 engine with Oberdorfer pump) as you and have not noticed this problem. There is probably another reason, such as a partially obstructed heat exchanger, or a hose lining that has come loose and causes an obstruction at high flows rates.
 

clohman

Member II
Thanks. The previous owner replaced the heat exchanger and I replaced all the hoses. It just seems to me that water passing by the intake at a 90 degree angle will begin to have a "sucking" action.
 

Geoff Johnson

Fellow Ericson Owner
Sometimes these obstructions show up only at high rev's. I had a maddening problem of my engine losing power as I increased speed and ultimately discovered that the flapper valve in the exhaust had come off and would obstruct the exhaust as the engine speed increased. During the diagnosis, my yard (which provides telephone consultation) had me remove the the hose which dumps the raw cooling water into the exhaust to make sure I had a good flow (be prepared for a lot of water). If you don't want to work around a running engine (who does) a more conservative approach is to remove the end caps from the heat exchanger to see if maybe there are some old impeller bits floating around. Another test would be to run your engine at high rpms with it out of gear (to eliminate the theory of water being sucked out of the intake) to see if the temp increases.
 

Tom Plummer

Member III
Running the engine with the boat stationary makes sense but I doubt if it will overheat out of gear. Most diesels have to be under a load to heat up. Suggest that you moor bow out securely tied to the dock and run the engine in gear at the rpm’s where you have the heating problem. :devil:
 

fgpericson

New Member
I have an E27 1971 with a Volvo 2 cyl. diesel. I have noticed this swing in the heat guage also. I have assumed that there is a defective thermostat which I intend to replace this weekend. I also have assumed that the fresh water heat exchanger could have debris in it that is clogging either the intake or the discharge but that does not explain the rapid heat drop. These thoughts you have expressed are interesting and I will let you know what I discover. Since I have never worked on one of these small engines before but obviously am intrepid, I may be in for an overhaul by the end of the weekend. I will let you know after I try out your thoughts.
 

Chip Lohman

Junior Member
See my post today on the replaced, larger heat exchanger. (Old one was clear.) Problem solved, or at least circumvented.
 
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