Yamaha 70 two stroke runs cold

[chismac01]

Hi

My 2002 Yamaha 70 two stroke runs cold. I tested the old thermostat and it seemed fine but I replaced it anyway thinking it may have been opening too early. A new thermostat made no difference and the engine still runs at about 45 deg C (110 F). I figure that 45C/110F is way too cold for good engine performance and engine life. I believe the temperaure should be around 85 C (180 F)

Can anyone help?

Cheers

[jeffersondodson561]

After verifying Tstats the next place to check is an damaged pressure relief valve.

[chismac01]

Thanks, that makes sense. Where is the PRV located - the manual I have doesn't show anything about a PRV

Cheers

[jeffersondodson561]

I dont recall on the inlines but the V blocks are sort of circular on the back of the powerhead maybe someone else can tell you.

[99yam40]

What temperature did your old thermostat and the new one open and close at when you tested them?
My C40 manual says 118-126 deg F to start opening and full open at 140.

What temperature is the water you are running in ?
how and where are you getting the 110 deg reading on the motor?
Have you looked at the parts break down of the motor to see if you could find the PRV ?

[chismac01]

I really appreciate your help

What temperature did your old thermostat and the new one open and close at when you tested them? My C40 manual says 118-126 deg F to start opening and full open at 140.

Started to open at about 120 and fully open at about 140

What temperature is the water you are running in ? About 70-75 DegF.

How and where are you getting the 110 deg reading on the motor? Infrared thermometer and an engine temp guage which I calibrated against a known thermometer.

Have you looked at the parts break down of the motor to see if you could find the PRV ? Yes but unable to find anything. I will talk to my parts man today to see what he can find on the official Yamaha parts breakdown.

I checked the Thermostat again yesterday and made sure it was sealed properly and that no water could bypass around the thermostat body. I have yet to test it in the water to see if that was the problem. My manual does not show it but I assume there must be some channel for the water to pass from the water pump to the discharge when the engine is cold and it would be in this path that some sort of PRV must be located. When the engine is up to temperature the thermostat would direct the water through the engine for cooling.

Again, thanks for your help

[99yam40]

I did not see a PRV on the parts break down either on a 70 TLRA if that is your model # as you have not given it.

Maybe shoot another motor with the temp gun to see what you get. you may be chasing ghosts
motor should not be running 180 in my opinion probably 140

[jeffersondodson561]

Me either saw one on the 75 but how did you test the tstat? I would float test the tstat!

[99yam40]

Thermostats do not float very well