Overheating Yamaha 115 (2 Stroke) V4

[alt]

Trying to help a friend out here....

Running around 4500RPM - Engine runs all day long!

At WOT (5400RPM), after about 5-6 mins the over-heat alarm comes on and goes into limp mode. Leave her idle for 30 seconds and the buzzer goes out. By the time I get to the engine and take the cover off, the heads are not too hot to touch.

So, things to check....
Impeller (first thought... asked was it changed, waiting on an answer)
Thermostats (What temp do they open at?)
Popper Valve
Temp Senders themselves....

So, questions!!!

What temp do the thermostats open at?
What temp (with an IR gun) on various parts of the heads / thermostat housings should I be getting worried at?
Any idea on resistance readings of the temp senders?

I'm guessing that this is a dud impeller, however I thought it would over-heat quicker.

Thanks all!

[charliee]

cooling ducts blocked with sand/salt etc won't help either so it would be worth a good flush with salt away.

[alt]

Originally Posted by charliee

cooling ducts blocked with sand/salt etc won't help either so it would be worth a good flush with salt away.

Forgot to mention this is fresh water. I'm sure in a previous life it was used on salt water, but my friend has had this RIB for a year and the issue only cropped up 2-3 weeks ago.

[davej]

I have just changed the thermostats on my dive club 115, as at Tickover on the muffs the overheat buzzer came on.

I believe they open at 52 C

Also have a look at the impeller and if In any doubt change it. Nothing about these yams are cheap and from BHG marine with new gaskets they were about 80£

It was fine after and actually may have been caused by an inadequate supply of water through the muffs, however after a good 10 Yrs it was time to change them anyway.

I love the engine, plenty of torque And simple to work on.

[alt]

Asked my friend about impeller "Guy took it off, said it looked like new so put it back on" - i'm speechless. Who wouldn't change an impeller regardless after dropping the gearbox?

I'm going to insist he changes the impeller and see where we go from there.

After that it'll be temp removal of the thermostats to see if that solves the issue (If it does, change the thermostats).

If still no joy, i'll look at the temp senders - remove 1 at a time and see how it goes.

Final check would be the pressure relief valve.

[HDAV]

Does motor behave like overheating? I had a temp sensor issue, tested in in spec and everyThing was putting motor into limp mode Changed sensor been fine since I hp was testing thermostats etc all test were fine, replaced sensor not cheap and bingo until another sensor went then next month don’t hink the v4 has diagnostic interface see if you can get a copy of The service manual lots are online in pdf and that has specs for thermostat Opening, resitiance of sensor at different temps etc (kitchen non sauce pan of water the rotors and multi meter required and if you value your life a wife out for the day