96 Yamaha 150 overheat

[robopitt]

I looked at a used boat today with a 150 TLRU. Hooked up the hose with the rabbit ears and started it up. It didn't want to idle so I gave it some gas and revved it a bit maybe up to 2500 rpm ( the rpm gauge wasn't working). It took maybe 20 seconds before I got a stream from the tell tale. Then the overheat horn came on and when I cut back to idle it quit. So we waited a couple minutes and started it again, this time at idle with out any throttle. It ran now at idle and again took about 20 seconds for a stream from the tell tale, the overheat horn still sounding all the time. We let it run maybe a minute and the water coming out the tell tale was not even warm until the engine was shut down and then the stream got warm as it continued maybe 5 seconds after shut down. The boat owner said he just had it out last week and got no overheat horn, and he blamed inadequate water supply from the hose.
My last outboard was 73 1150 merc with no warning systems, rip. So I'm wondering if it is unusual to get an overheat warning from this motor when running it from the hose and maybe I revved it too much to start, or if there are some cooling issues, be it thermostats, pressure sensor grommet or impeller.
Thank you to anyone that can shed some light.

 

[MBTundra]

Re: 96 Yamaha 150 overheat

From trouble shooting my motor I learned that the water is colder from my garden hose than any lake or river around here. Also the muffs will help push the water into the system. So both things, cold water and more pressure, does not put the motor in regular operating conditions.

Mine would never overheat on the muffs. Put it in the river or lake in gear and it does.

See my post "1996 P60 Idle Overheat" the problem is not solved yet.

 

[rodbolt]

Re: 96 Yamaha 150 overheat

how do you know it was overheat?
thats your first sign to walk away from this sale.

 

[robopitt]

Re: 96 Yamaha 150 overheat

We unhooked the 2 temp sensors and the alarm went off, hooked em back up and the alarm came back on. The alarm was on as soon as you turned the key on, once the motor got hot. What seemed so odd to me was the cold water coming out the spit of a hot engine. The boat is reasonably priced and the engine looks very clean, if the problem could be easily fixed it may be worth the effort.

 

[rodbolt]

Re: 96 Yamaha 150 overheat

run away run away
this motor has both running and rigging issues.
unless you wish to invest tools and time it may cost more to make it run than buying a running rig ready to fish.
the reason why the tell tale stays cool is its tapped off the block/ex cover at the point of entry and does not circulate through the motor on that model.
all it does is alert the operator that the pump is working, a trained operator can actually look at the stream and tell you if its working correctly.

 

[RUSTYHAMMER]

Re: 96 Yamaha 150 overheat

I have a 91' 150 that with the muffs on has a weak tell tail stream and it will over heat after a short time,but once I put it in the water it has a strong tell tail and it dosen't overheat!Best thing to do is put that boat in the water and take it out for a good test run and see how she runs! Muffs are really just to flush the motor,I was never able to get a good water preasure reading on the motor using a hose that was supplying 45psi of water