WOT. too much rpms?

[fishinhardwater]

is it possible that i can 'overheat' an outboard not having the right pitched prop? could not find numbers on prop, all i know is its aluminum. and i dont know the rpms the engines turning. I have a 1988 Mariner 60 HP on a 1988 16' Starcraft Mariner 160 aluminum boat. the overheat alarm goes off at WOT only, no where else. i have tried fixing all the mechanical stuff, now turning towards prop questions. any suggestions where to start? if not i guess im just gonna take the overheat sensor off and hope it dosent burn it up. I took the engine off a 1975 duranautic 16' aluminum if that makes any difference... thank you

 

[crb478]

Re: WOT. too much rpms?

If you are turning too many rpm's you can and will damage the motor. When was the last time you changed your impeller. It could be that you are not over reving, but not getting enough water to the motor to cool it. I would not disable the alarm unless you want to buy a new motor.

 

[Silvertip]

Re: WOT. too much rpms?

Although the wrong prop can damage an engine from over reving or lugging (inability to reach recommended WOT rpm) I doubt that's the problem. You said you "fixed all the mechanical stuff". Did that "stuff" include the thermostat, bypass valve, and impeller? The bypass valve sticking or being non-functional will cause high rpm overheat as will the impeller. The overheat system is obviously working and is trying to tell you something. Disconnecting it is akin to outboard suicide. Fix the problem. Look for prop numbers on the hub behind the prop nut.

 

[steelespike]

Re: WOT. too much rpms?

What repairs have you made?Have you checked the sensor or replaced it.
Prop numbers are usually on the barrel or under the prop nut.Has this allways
had an over heat problem? We will need to have the prop size,present max rpm and speed.Sometimes if the motor is mounted really high it can cause cooling problems.Is the antivent plate even with the bottom if the boat?
Is there anything on the bottom or transom that could disturb water flow past the motor?Is there a foil on the motor?Have you checked the water intake?Are you sure the water tube is properly seated in pump and powerhead?Have you checked the water passages.

 

[fishinhardwater]

Re: WOT. too much rpms?

Mariner 1988 3 cylinder 60hp serial number ob248347.

i have read alot of posts concerning the same exact problem, and lots of suggestions out there to help them, but no one seems to post their conclusion on how they fixed the problem..

-if the antivent plate is the thing that my hydrofoil mounts on, it sits about 2'' above the bottom of the boat (but never had alarm in the past with it like that)
-learned that my motor does not have a thermostat or poppet.
-my motor does have a hydrofoil, but i have taken it off and put it back on and the alarm goes off either way.
-bought motor used.
recent fixes-
-carberator rebuild. no alarm
-fuel diaphram rebuild. no alarm
-new plugs. no alarm
-new plug wires, when wires were installed, the very next time i used in salt water is when the alarm started, but put old wires back in and alarm still goes off. maybe a hint?
- new impeller, better water flow, still overheat alarm at wot.
- bought new sensor, the one that screws in next to top spark plug. still have alarm at wot.
-back flushed tell tale, now alarm takes about 15-30 seconds before it goes off at WOT, as before it would just go off as soon as i gave it WOT.
-out of ideas, now thinking prop or rpms is wrong, ill have to get the numbers
-maybe im not running enough oil? (50:1 is what i run) ill try putting extra oil in tank and see what happens.

if i think of anything else ill let you know. thanks

 

[crb478]

Re: WOT. too much rpms?

sounds like you need to clean your water passages real good and probably put in a new impeller jus tto be on the safe side.

 

[fishinhardwater]

Re: WOT. too much rpms?

did that already