Overheating at High RPM's

B

bayhawk14

Cadet
Joined
Aug 13, 2005
Messages
19
I have a 1998 Yamaha C115 that will not run over 4K RPM's without the buzzer going off. I can run at 3500 all day with no problems. I've changed the impeller, thermo's, checked poppit valve(replaced spring). I heard it's probably time to pull the heads & clean the corrosion build up. I have a little mechanical skills but worried about trying this myself. How hard is this? Is there a chemical you need to use to clean the salt corrosion, etc.<br />Any help would be greatly appreciated. I'm in New Orleans & it is weeks before a mechanic could even look at this thing. They are busy fixing boats that sunk, rigging new boats for people that lost theirs in the storm.
 
J

jim dozier

Lieutenant Commander
Joined
Jan 8, 2003
Messages
1,970
Re: Overheating at High RPM's

Before you pull the engine apart, what is the max rpm your motor will turn normally loaded? I had a similar problem with an OB a couple of years ago. After fixing everything possible on the engine related to cooling, much of which did in fact need servicing, the engine still overheated at high rpm. Then I bought a tachometer and found that the engine was not reaching its rated rpm. If your engine is lugging because of a too large prop or other conditions that prevent it from revving to its proper rpm it will overheat.
 
B

bayhawk14

Cadet
Joined
Aug 13, 2005
Messages
19
Re: Overheating at High RPM's

jimd, thanks for the response. Indeed, my prop is too big. I'm running a 21 pitch & should be at 19. I have a 19 on order right now. I just bought this motor last year & ran it 5 or 6 times with the larger prop with no problems. Wide open throttle I was at 5K RPM's where I should be around 5400 to 5600. The 19 should take of that. Thanks for the advice, before I take it apart I am going to wait for the new prop to come in than give it a run. Hopefully I don't blow anything!
 
R

Ray Neudecker

Lieutenant Commander
Joined
May 25, 2004
Messages
1,656
Re: Overheating at High RPM's

Normally pulling the heads and cleaning is not difficult. I always draw up on salt water exposed motors due to corrosion and the chance of breaking a bolt. Having a service manual would help and a torque wrench is a necessity. A good scraper will do most of the corrosion removal.
 
You must log in or register to reply here.
Top