Honda, BF90DK2, 2012

by Derek
(Brisbane, Queensland, Australia)

Honda, BF90DK2,

I've two 2012 Honda 90's on the back of a 6.3m aluminium cat, less than 500hrs on each. I have the following problems with both engines, it is intermittent but getting progressively more regular
Problem 1 - the overheating alarm goes off after a prolonged (20min) cruise at around 4500 revs. Engine shuts down and after a cool-off period we are good to go again. Depending on how long the cool-off was dictates how far we then get before it goes off again - normally after this happening I'd keep the revs below 4000 which seems to prevent a reoccurrence
Problem 2 - After a period cruising at 3500-4000 revs (such that the engines are operating temperature) and wanting to come to a halt I'd slow the engines down; when they reach 1000 revs the overheat alarm goes off and engine shuts down.
Now the above doesn't happen every time but enough to be an issue. I'm not sure if it is the same issue causing both scenarios or different issues.
A Honda marine mechanic has carried out a full review, this included using Dr H diagnostic system, acid flush (although engine is clean of build-up - see photo), new impellers and even had the cylinder heads machined as there was some suggestion of exhaust gasses escaping into the cooling water and super heating it.
What appears to be a rare occurrence is happening to both engines.
Any help or suggestions would be great as we are about to enter another round of investigation