Over cooling (Yamaha 4-stroke; 115hp; 2002)

Petgun

Recruit
Joined
Aug 5, 2012
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1
Hello there,

First post, new thread. I've looked into the issue in other threads and a decent service manual (Clymer's Yamaha 75-225hp; 2000-2003). Error code 49 means 'over cooling', i.e. the engine does not reach its appropriate working temperature & thus might stall at certain revs and/or when the throttle is adjusted. Our engine is run in saltwater only, no trolling, mostly cruise & idle, in water temp. 10-20 Celcius. Normally, removing the salt build-up in/around the thermostat once every season has normally fixed the problem, but not this time. So I thought I'd remove the thermo and go about the procedure for testing it as the manual prescribes. My results were: Opening begins at app. 65 Celcius. Max. opening at about 80 C. Maximum travel app. 3.18mm. These are all a long way from specs, but more significant: The thermo did not seem to begin closing when I put it in running cold water. That error accords well with what we've seen: Engine runs well on cruise (app. 4000+ revs); but at lower revs it soon over cools with a thermo that won't close.

I'll begin with a new thermo, of course, but what I'd like to ask is this: Would anyone please tell me where the water pressure relief valve is located? Is it part of the water pump assembly (impeller etc)? The service manual makes a point of this valve with respect to cooling issues and this particular model (only one thermo, as opposed to the bigger engines), but it does not specify exactly where the valve is to be found.

Thanks in advance to anyone who can provide understandable information to a novice like myself. :)
 
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