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A gentleman by the name of "Mark" sent me a PM - he is having a problem with his Yammie 150.
I wanted to post my reply so that other forum members may benefit:
I have a problem that sounds like this one. My overheat alarm goes off after 5-10 minutes of running over 4000 RPM's and seems to get worse when the motor is trimed up? I have replaced the impeller and housing. Even took it apart again to make sure the o-ring was not pinched. Then the overheat alarm went off constant unless I wiggled the key. I replaced the entire key switch assembly and it solved that issue but I still have the 4000 RPM problem. Could you give me some things to try and resolve this issue?
Thanks
Mark
Mark,
There could be several reasons for your overheat condition:
1)weak water pump (I am assuming not in your case - but could be) - really need a water pressure gauge to tell - should have about 5 psi at idle and 20 above 3000 rpm.
2)intake to pump restricted or too high in water column - with the boat up on plane and motor trimmed out for max speed, the cavitation plate should be just on top of the water - if your prop is sucking air, then the water pump probably is too.
3)pressure control valve is stuck open - debris can get stuck under the pcv and let cooling water dump out the relief holes at the top of the upper casing - you can observe this at lower rpms - there should be very little water coming out the relief holes until the system pressure exceeds 20 psi at the higher rpms.
4)thermostats could be stuck - you can remove and inspect and test in a pan of heated water and thermometer - should be fully open at 140 degrees f. - 0.120 inches.
5)head water jackets clogged with mineral deposits - remove and clean out.
6)faulty thermo switches - there is one mounted in each head assy - can remove and test in pan of heated water - should be able to measure continuity between two wires at approx 180 degrees f. - I have personally had one go bad and close at 130 and give me a false overheat alarm.
Hope this helps [img]smile.gif[/img] ,
Ken K
I wanted to post my reply so that other forum members may benefit:
I have a problem that sounds like this one. My overheat alarm goes off after 5-10 minutes of running over 4000 RPM's and seems to get worse when the motor is trimed up? I have replaced the impeller and housing. Even took it apart again to make sure the o-ring was not pinched. Then the overheat alarm went off constant unless I wiggled the key. I replaced the entire key switch assembly and it solved that issue but I still have the 4000 RPM problem. Could you give me some things to try and resolve this issue?
Thanks
Mark
Mark,
There could be several reasons for your overheat condition:
1)weak water pump (I am assuming not in your case - but could be) - really need a water pressure gauge to tell - should have about 5 psi at idle and 20 above 3000 rpm.
2)intake to pump restricted or too high in water column - with the boat up on plane and motor trimmed out for max speed, the cavitation plate should be just on top of the water - if your prop is sucking air, then the water pump probably is too.
3)pressure control valve is stuck open - debris can get stuck under the pcv and let cooling water dump out the relief holes at the top of the upper casing - you can observe this at lower rpms - there should be very little water coming out the relief holes until the system pressure exceeds 20 psi at the higher rpms.
4)thermostats could be stuck - you can remove and inspect and test in a pan of heated water and thermometer - should be fully open at 140 degrees f. - 0.120 inches.
5)head water jackets clogged with mineral deposits - remove and clean out.
6)faulty thermo switches - there is one mounted in each head assy - can remove and test in pan of heated water - should be able to measure continuity between two wires at approx 180 degrees f. - I have personally had one go bad and close at 130 and give me a false overheat alarm.
Hope this helps [img]smile.gif[/img] ,
Ken K