TexasYamaha
Cadet
- Joined
- Nov 24, 2003
- Messages
- 6
My son and I have been struggling to correct an overheating problem on his 2000 Yamaha 150 OB. <br /><br />He bought the boat and motor used and has had the overheating problem to some extent since he's owned the boat. We replaced the water pump last summer hoping to fix the problem w/o any change.<br /><br />We have the Clymer manual and after reading I felt that either the thermostats or pressure relief valve were causing overheating. Overheating primarily occurs at low speeds w/ loss of indicator stream usually, but not always. Water pressure at idle is low, almost zero on instrument panel gauge. <br /><br />We removed the pressure relief valve and although there was a little sand around the rubber seat, it really didn't look bad. The rubber seat was recessed ~ 1/8" inside the cavity. We did not remove the seat but cleaned w/ toothbrush, removed sand, and re-assembled. <br /><br />We removed the thermostats. Again some sand but not too bad. We cleaned them in vinegar overnight and verified they began to open in hot tap water, probably 120-130F. <br /><br />We verified overheating was real by measuring the closure temperature on the temp switches. Both were w/i spec of 183-194 F. <br /><br />After reassembly, the problem remained w/ same symptoms. Next we removed the thermostats entirely on advice of some locals, who advised my son that removing thermostats was first thing they did on Yamaha's. It initially seemed fixed and my son took off on a fishing trip. He got stranded and had to pull the boat quite some distance thru Laguna Madre shallow water to Intercoastal near Corpus Christi. He got a tow from a passing boat.<br /><br />From searching and reading previous posts on this subject, the consensus seems to be the pressure relief valve. Our current plan is to replace the pressure relief valve seat, valve, and spring w/ new parts. I read of some backflushing through the thermostat openings down to the lower unit pump outlet w/ lower unit removed. Is this worthwhile? <br /><br />With all the unsuccessful repairs, I'm looking for some guidance that we're on the right trail to a fix. It has been a frustrating experience, especially for my son. <br /><br />Thanks in advance.