Thermostats 1996 150hp s150txru

[imjus4u2nv]

First time changing thermostats - new part isn't exactly like the old one. Fits in no problem and all back together, haven't run her long enough to test and wanted some input first.
Part I am using is attached

 

[Doc Stressor]

As long as it fits that's all that matters. They have changed the design over the years.

 

[seasick]

If one has the time, I like to pre test new t-stats in a pot of water. Drop them in, turn up the heat and at a minimum watch to make sure that they open up all the way Turn off the heat and as the water cools you will see the stats close. If you have a kitchen thermometer, you can place that in the water and note at what temp the t-stat opens. There aren't too many things more annoying then installing a bad 'new' t-stat.

When I can't pre test, I use an infrared thermometer. With the new t-stats installed, run the motor on the muffs and take temp readings of each t-stat housing. In a short period of time, the temps will start to rise and if all is working OK, will settle at some temp after 5 minutes or so ( depends on how cold your supply water is)

The third check method is to use your hand to feel the head temperature. You really can't judge what the temp is but you can pretty easily tell if one side is hotter or colder than the other. Unfortunately the fact that one side temp is a lot different than the other, only tells you that something is amiss. It could mean that a stat is stuck open ( that side will be cooler) or one is stuck closed ( it will be hotter).
If you use the hand test a few times, you will get an idea of what 'normal' is. If I forgot to pack my IR thermometer, I always do a hand test on spring startup just to make sure that the stats are working.Remember that both stats may be too cool or two warm but that is a another story.

One caveat: If you have overheating problems, be cautious doing the hand test since the heads can get quite hot

 

[imjus4u2nv]

Very helpful, thanks all. I will do the test on the old thermostats to see what temp they open up at (ran last season with these so this will he good baseline) and will check next time prior to putting in.
Many thanks.

 

[Topjimmy]

This is what I used on my 1995 saltwater 150 https://www.ebay.com/itm/2X-YAMAHA-...134427?hash=item25ebef8b1b:g:5lQAAOSwSVJaa5qh and it works as it should only problem I had was snapping off 1 bolt DAMN! and I was REAL care full and also I replaced the Poppet valve while I was at it

 

[imjus4u2nv]

This is what I used on my 1995 saltwater 150 https://www.ebay.com/itm/2X-YAMAHA-...134427?hash=item25ebef8b1b:g:5lQAAOSwSVJaa5qh and it works as it should only problem I had was snapping off 1 bolt DAMN! and I was REAL care full and also I replaced the Poppet valve while I was at it

I am gonna check these against what I bought, what is the puppet valve. Thank goodness no broke bolts (I am a pro at that lol).

 

[seasick]

The poppet valve is a device that open at high water pressure and allows some flow to bypass the heads. Normally it is closed at lower revs and opens at higher revs. If it gets suck open, the most common result is over heating at idle or low revs. Revving up the motor usually will clear the over heating condition and fairly quickly. A bad water pump can also cause overheating at low revs are any revs for that mater but you can often tell a weak pump by a weak telltale stream (assuming it normally works!).

My opinion is that if you don't have low rev over heating issues, the poppet is probably OK. I go by the "If it ain't broke, don't fix it" philosophy. If you decide to check or replace anyway, make a note of the orientation and order of the components so that you get everything back correctly.

Now you got me thinking about what symptoms you might see if the poppet sticks closed.. That would result in a higher than normal water pressure at higher revs but I am not sure if there would be obvious symptoms. It would add extra load and therefore wear to the pump impeller and higher pressure at the t-stats. But will that be obvious? I really don't know

 

[Doc Stressor]

Poppet valves, at least the ones I have seen, have a small hole in the center that allows some water to flow even if the valve sticks in the closed position. Water can also escape through the thermostat when operating at high rpm. But the flow rate is reduced so you generally overheat or at least run hot at high rpm if the valve sticks in the closed position. If a poppet valve sticks in the open position, you get overheating at idle because cooling water drains out before it can reach the top of the cylinder head. Poppet valves are located at the bottom of the block, thermostats at the top. They usually fail in the open position, but I have had one stick in the closed position over the years.

When operating in saltwater, it's not a bad idea to replace the poppet valves after 10 years if they hold up that long.