2000 C40TLRY Yamaha(2 stroke) Overheat Problem

[livin2fish]

Anyone ever have a overheat sensor which was overactive?

Lake water 45 degrees. Motor will run on plane fine at about 1/2 speed. When kicked up to higher speed, the overheat sensor drops speed down to idle within 1 mile. After a couple of minutes idling, back up to 1/2 speed, no problem.

Things already tried: Checked pee stream which appeared fine, new impeller installed, back-flushed system during impeller change, new thermostat (tested old thermostat in hot water with thermometer, opened at 140 degrees).

If a new overheat sensor is needed, does the head have to be removed for the installation?

[ausnoelm]

I think the head might need to be removed to clean the water cooling passages??

[TownsendsFJR1300]

Salt water lake or fresh water lake???? If salt water, was it flushed religiously after use?

How did the water passages look when the thermostat was out?


I'd check and replace that sensor BEFORE I pulled a head(depending on the above answers)...

Looks like the sensor is part# 11 and 12 and just screws into the head:

http://www.boats.net/parts/search/Ya...201/parts.html


If you have a shop manual, it has the spec's on checking continuity of the switch when immersed into heated water..

PM me for further..

[99yam40]

The switch with the pink wire will be the one that puts it into RPM reduction mode if it gets too hot.

I would check head temperatures at the location of the switch when problem shows up to see how hot the metal is getting.

On my 1999 C40 it looks like they might pull out without pulling any bolts or the head cover, but it may not. Consult your service manual to see what it says.

There should be special grease in there to make sure the heat is transferred between the motor and switch efficiently

There is a very good chance it will take a cleaning of the water passages to make this problem go away.
Might search Rydlyme marine descaler to see if a good flushing will help without pulling motor apart.

I have injected compressed air into the water going into the motor while flushing to help get more stuff out of water passages before. I might work for you too

[livin2fish]

Remove Heads to clean passages: Hopefully last resort!
Never Salt water
Head Temp.: Can place hand on top of head immediately after shutdown.
Shop Manual: Don't have. Available on line?
Thermostat Cavity: Not terrible. Outlet/inlet holes not plugged.

[bajakeith]

over heat

Ck and or replace the PRV also called a "poppet valve"

[99yam40]

I believe a 2000 C40 does not have one of those

[robert graham]

Did you inspect/replace the metal wear plate under the impeller?.... How about those black rubber grommets in the water pump body?....

[TownsendsFJR1300]

Remove Heads to clean passages: Hopefully last resort!
Never Salt water
Head Temp.: Can place hand on top of head immediately after shutdown.
Shop Manual: Don't have. Available on line?
Thermostat Cavity: Not terrible. Outlet/inlet holes not plugged.

PM sent about the procedure for checking the sensor..