Rebuilt Powerhead Temperature Observations

[boatmon345]

Rebuilding 1997 Yamaha 150HP Salt Water Series II S150TXRV 2 stroke 6 cylinder powerhead.<br />( Click here to view updated blog with new pictures )<br /><br />I finally started the rebuilt engine last night and she ran like a beauty. <br /><br />I am a bit paranoid with the paint application I applied to the water passages, and so I am now wanting to take temperature measurements with a laser temperature tool (that I have yet to find). I'm thinking to take idle operating temperatures at the tops of both heads, and perhaps other places.<br /><br />Also, I had some sea water slip out the top of the stbd cylinder to head joint. The water bead was about 3/4" long by 1/8" wide, so not much but enough to be concerned. I found that a head bolt was not tight (odd, I torqued all of them). Hopefully that was the reason water slipped out.<br /><br />I read about using thermomelt sticks, but not sure I want to go this route. I'd like to get accurate reading that I assume a laser temp tool would produce.<br /><br />I have yet to determine if my overheat alarm works properly (I suspect it does not) so that will be the next order of business.<br /><br />Have any of you taken temperature readings this way and if so perhaps you can share some of those readings?<br /><br /><br />Thanks.

 

[Texasmark]

Re: Rebuilt Powerhead Temperature Observations

On my engine the stat is stamped 120F. The overheat warning device grounds out at 190F and resets at 170F. Would assume the top cylinders would run hotter than the lower because of circulation; maybe by a few degrees.<br /><br />I have used "thermal dots" on equipment where I used to work and used them effectively. I also was aware of a Laser, but never used one; saw one used however; rather expensive as compared to the dots.<br /><br />Best I can do.<br /><br />Mark

 

[boatmon345]

Re: Rebuilt Powerhead Temperature Observations

Does the engine need to be running for the alarm to sound in an overheat condition? <br /><br />I shorted both temp sensor leads with ign on (eng off - I'm not running it right now for other reasons) and did not hear an alarm. In fact, I have never heard an alarm. Where is the alarm located? I see some kind of buzzer under the console. Maybe this is it...

 

[rodbolt]

Re: Rebuilt Powerhead Temperature Observations

with the key on engine off dissconnect the pink lead from a temp sensor, take the harness side of the lead to ground. horn should sound and the temp visual on the multifunction guage should illuminate.<br /> to test the oil alarm insure the remote tank is full, carefully remove the water trap tube from the bottom of the engine oil tank with the key on engine off. drain the engine tank contents into a clean container. when the oil level gets about 2-3" below the lower level mark in the tank you should get 3 bars flashing,audible and oil transfer.<br /> tank should refill and shut off in 180 seconds.<br />that test should actually be done every 200 hours or once per year.

 

[boatmon345]

Re: Rebuilt Powerhead Temperature Observations

I found the alarm underneath the console, and it is not functional (no sound when connected directly to 12v). I will be replacing that then running the tests you outlined above. <br /><br />I don't have a multifunction guage on my console. No warning lights. Perhaps I should look in to getting one.

 

[boatmon345]

Re: Rebuilt Powerhead Temperature Observations

I have purchased an infrared temperature meter at Harbor Freight tools for $40 on sale, which has become very handy.<br /><br />For some temparature observations, ran the rebuild tonight at 1500RPM for some time then increased to 2000 (all while in neutral). <br /><br />While running 2000 I observed the hottest readings of the whole engine on the starboard lower cylinder (the oversized one) at up to 170F. I took this temperature aiming at the cylinder toward the crank (back of cylinder). Remaining cylinders varied from 135-150 or so.<br /><br />Is this OK. Here I am at 2000RPM, no load, and running 170F, just 25F or so short of overheat alarm. However, overheat alarm for that side of the V is on top outter area of cylinder head where it was about 135F or so.<br /><br />Although I am unable to get a clear path to the port side lower cylinder, I think it is running much cooler based on what I could measure. Why the imbalance?<br /><br />I can't imagine what this temp will be at 4000 or 5000 RPM under load.<br /><br />HELP. Could a rich fuel / air mixture cause an increase in temp like this?

 

[boatmon345]

Re: Rebuilt Powerhead Temperature Observations

OK I took the boat out for it's maiden test voyage last night. So far so good but really need some guidance on this temperature isisue.<br /><br />I really really really would liike to hear from someone who has knowlege of powerhead temps at various locations on the powerhead.<br /><br />After running 3200RPM for about 4 minutes I measured 190F around lower rear area of stbd bottom cylinder (#5), while thermostat area measured 125-130. Want to make sure I'm not burning this motor up.<br /><br />HELP. Sorry for flooding the forum with questions lately. I hope to help others as I gain knowledge in some of these areas. Thanks.

 

[Texasmark]

Re: Rebuilt Powerhead Temperature Observations

My Merc 3 cyl has a 190 degree temp alarm switch. It's located in the water jacket in the side rear of the block. Should be sensing water right at the head..... If that helps you to understand what you are reading. My thermostat pellet is stamped with 120 F for opening temp. <br /><br />If you measured exhaust temp with your laser it would probably read 190.<br /><br />Mark