1996 C150 Overheating

[Fin Addict]

I'm having som trouble with my c150 overheating. I can run at idle speed for long periods of time w/o any problems but once I go full to almost full throttle the engine will overheat after about 1-2 miles distance. I just got the boat from the shop where they replaced my water pump & thermostat's but I'm still overheating.

When my rev limiter cuts the RPMs and a go to idle the water sitting out is not even Warm it's much like the temp of the water i'm in.

What else could be causing the overheating if my water flow seems to be in order? Could the thermoswitch's be bad or the alarm sensor?

Any tips would be greatly appreciated.

[jb123]

how long have you had the boat, did the issue happen beofre the repairs ?
i would suggest replacing the prv parts, very cheap, to rule that out.

[Ken]

FA,
Could be a bad temp sensor, aka thermo switch.
You can remove both and test them in a pan of heated water - the contacts should close and you should be able to measure continuity between the two wires on each switch at around 180 degrees f.
I have personally experienced one closing at 130 degrees and giving me a false overheat signal.
The pressure control valve, aka pressure relief valve, aka "poppit" valve, is designed to open at around 20 psi and relieve over-pressure in the cooling system. Debris can get stuck under the valve/seat and prevent the valve from closing completely, and thereby allowing cooling water from the water pump to pre-maturely dump out the relief holes.
You can remove the pcv fairly easily and inspect.
You might want to replace it with the new "mushroom" syle valve that is less prone to sticking open from debris.
The water that comes out the water pump pilot hole on the Yamaha outboard, aka pee-stream, is water that has not gone thru the water jackets yet - therefore, it will be only slightly warmer than the water that the lower unit is submerged in.
Good luck [img]smile.gif[/img] ,
Ken K

[Fin Addict]

I've had the boat for about 4 years now, the overheating started the beginning of this summer.

Ken, the shop told me that my poppit valve was sticking and they cleaned it out but did not replace it. I'm not sure why the mechanic did not replace it if it's inexpensive and he did see it sticking. I will replace it myself to see if it makes a diff.

Thanks for the tip on testing the thermo switch.

FA

[Fin Addict]

One thing I did forget to mention that I do have days or long periods of time when my engine will not overheat.

Some times after the first overheat it will not overheat for the rest of the day under the same driving conditions. Others it will overheat multiple times.

[jb123]

not sure what rpms youre gettin out of it but you might want to try lowering the motor one hole, ensuring waterflow over the intake.

[protagy311]

what you need to do is take the water jacket off the back of the heads and look for any corrosion around where the temp sender is.(this was the problem with mine) also look at the bottom of the exhaust plate and remove the spring and poppet valve. make sure the valve moves freely.