Pro-V 150 Thermoswitch testing?

[bassboat1]

After 3 days on the water, I think I got it solved. 2-stroke oil from the motor-mounted tank had dripped, over the years (decades!) on the in-line (glass) fuse holders below, softening the one that appears to power the ignition switch (clamp shown added for temporary testing). The molded-in rib wasn't strong enough to hold it together reliably. Since the picture, it's been replaced with an ATC-type. No overheat warnings, and it passed the Tempilstik testing recommended by Texas Rig. Thanks!Untitled.png Two problems killed with one stone!


I've been trying to troubleshoot an intermittent warning and the subsequent rev limit activation with this motor. (Q: Is there another system that activates the overheat alarm horn?) I fished for a few hours on Sunday - putted out of the shallows and ran a mile down the lake WOT with no issue. Fished for 30 minutes and ran back up - the horn started up about halfway in, and it immediately started choking out (rev limiter?). To date, I've replaced the thermostats and impeller (wear plate looked OK, didn't have a replacement). I pulled the heads to inspect for crust, as I have reason to believe that it's spent some time in salt. No problems inside... I R&Red and tested the pressure gauge, I'm reading about 10 PSI at WOT. The motor pisser runs strong at the lake and on muffs. Oil tanks are full. Is there a simple test for the thermoswitches (I understand testing the 4 stroke ones involves having some resistors handy?)

A (likely) unrelated issue is an intermittent fail-to-start (three times this season, out of a couple hundred starts). Nothing happens when the key is turned (I don't hear the starter solenoid or relay). On Sunday's most recent occurrence, I fiddled with the kill switch to no avail, then noticed the battery was reading 12.1V on the graph, turned it off and it started immediately. FWIW, it was fresh off the charger, where it read 13.4 fully charged with the onboard charger still connected (on float mode?)

[Texas Rig]

I believe overheat alarm is only activated by the water cooling system. You may have a water passage blockage on the engine. Per my Clymer manual, you need to check the temps of each cylinder's water jacket at warm idle in gear and at WOT. The manual references thermomelt sticks (125 deg F & 163 deg F) to mark each water jacket. The engine should melt the 125 mark at warm idle in gear and not melt the 163 mark at WOT. Lake water should be below 80 degrees F.

[bassboat1]

Thanks for the info! Nothing in the Yamaha shop manual about it The water passages around the cylinder walls looked fine, due to their relatively clean appearance, I chose to not pull the head covers off. I can use an infrared thermometer for the idle temp check, but I don't think I'll risk it for the WOT! . Off to find some temp sticks! Update: Ordered straight from Markal $33 shipped. If anyone needs these down the road, hit me up.