On 7/16/20 6:37 AM, Tim wrote:
Mike
Hi, I have a 40hp Mercury outboard that sounds an overheating alarm when revs, get over around 4500 rpm, this outboard is a US made 4 cyl 2 stroke 1996 mod,
first of all this outboard does not have a thermostat by design, so i replaced the impeller but the impeller blades were bent only and not realy damaged in any way so i am concerned that i have not fixed the problem, the engine is in very good condition for its age so i am wondering if any one else out there has had a similar problem with this engine and if so was it resolved and how.
regards Mike.
???

Mike you?re impeller could be bad to where ar high rpm, the canes are collapsing and not shoving water through.

I?ve seen this in an evanrude. Where the guy didn?t spring for an OE impeller and went for a cheap ebay replacement. It would collapse . Got an original and it worked fine.

Sounds like yours is getting weak.

Good luck

Once in a while the rubber impeller separates from the metal sleeve. You can
test this by trying to peel the impeller away from the sleeve. The bond
should not be broken.

On Sat, 18 Jul 2020 19:00:35 -0000 (UTC), Justan wrote:

On 7/16/20 6:37 AM, Tim wrote:
Mike
Hi, I have a 40hp Mercury outboard that sounds an overheating alarm when revs, get over around 4500 rpm, this outboard is a US made 4 cyl 2 stroke 1996 mod,
first of all this outboard does not have a thermostat by design, so i replaced the impeller but the impeller blades were bent only and not realy damaged in any way so i am concerned that i have not fixed the problem, the engine is in very good condition for its age so i am wondering if any one else out there has had a similar problem with this engine and if so was it resolved and how.
regards Mike.
???

Mike you?re impeller could be bad to where ar high rpm, the canes are collapsing and not shoving water through.

I?ve seen this in an evanrude. Where the guy didn?t spring for an OE impeller and went for a cheap ebay replacement. It would collapse . Got an original and it worked fine.

Sounds like yours is getting weak.

Good luck

Once in a while the rubber impeller separates from the metal sleeve. You can
test this by trying to peel the impeller away from the sleeve. The bond
should not be broken.

Good call. If you got the one with the brass insert, this happens,
probably because this is "New old stock" and may have been grtowing
old on a shelf for 20 years. I had exactly that problem with my 75 2
stroke when it was getting into middle age, along with the parts. It
didn't last 10 minutes until I saw the water pressure drop. It was
enough to pee but not enough to cool.