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Mercury 150 running warm

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rjred

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My Mercury 150 at times runs hot but not hot enough to set the warning off. I have replaced the water pump, thermostats and poppet valve. Now I have no water coming out the tell tail. According to this flow graph in the manual it shows that the water has to go through the thermostats before it comes out the tell tail. Can someone explain to me how this is suppose to work because I know the thermostats haven't reached 140 degrees, to open within seconds of the motor having been started. If I can understand how the water flow is suppose to work, hopefully I can diagnosis the issue with my motor.
 
Pull the stats, leave the covers off and run the engine, see if you have water.
Check your popit, screw may be lose, stack up is wrong, the seat may not be all the way in...
 
My son had a late 90s 150 and his tell tale was also plumbed off the stats. Upon starting the engine there was no tell tale. As the engine warmed the water started to intermittently emit from the tube as the stats would open and close. After the engine had warmed sufficiently to keep the stats open (143F pellet stamping on his engine) he has solid flow.

I didn't like that setup so I changed the TT flow by teeing into to the tube on top of the engine that went down to the poppet. This tube was tied in at the top of the engine block and the block had to be full of water to get flow.....with that he had full flow within seconds of startup.

The OT alarm is 195F on my engines and I suppose it is the same on yours. Since water boils at sea level pressure and 212* if you are hot enough to set off the alarm you will start having steam with your TT.

My 2c.
 
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Texasmark said:
My son had a late 90s 150 and his tell tale was also plumbed off the stats. Upon starting the engine there was no tell tale. As the engine warmed the water started to intermittently emit from the tube as the stats would open and close. After the engine had warmed sufficiently to keep the stats open (143F pellet stamping on his engine) he has solid flow.

I didn't like that setup so I changed the TT flow by teeing into to the tube on top of the engine that went down to the poppet. This tube was tied in at the top of the engine block and the block had to be full of water to get flow.....with that he had full flow within seconds of startup.

The OT alarm is 195F on my engines and I suppose it is the same on yours. Since water boils at sea level pressure and 212* if you are hot enough to set off the alarm you will start having steam with your TT.

My 2c.
Click to expand...

Mine is setup like yours was, coming off the stats. What I'm trying to understand is how I always had tell tail water coming out within 15 seconds of starting the motor.
 
The water flow is like a 2.5 set up. It will not pee till the stats open. Throw the gauge away and install water pressure type as the needle/resistor type will have you chasing ghost problems.
 
Docksidemarineservices said:
All bets are off when you think you have better knowledge then the designing engineers. Plumb it back to factory and recheck your work.
Click to expand...

In answering that (non directed) statement I will just comment that the orders to/design objectives/management constraints/ bla bla that control the actions of designers has it's intended goals, having been one for over 30 years. As far as my stuff, I may, and a lot of times do, have different objectives. There may be a few times that subsequent actions/results caused me to return things to their original condition.

Case in point is my dash mounted temp gauge rather than a pressure gauge. For what I do its the perfect answer. Were I going out 30 miles into the ocean on a daily basis, or even going out at all, I would want a pressure gauge.................both of which aren't supplied by OEM design engineers on production equipment!!!!!!
 
Texasmark said:
In answering that (non directed) statement I will just comment that the orders to/design objectives/management constraints/ bla bla that control the actions of designers has it's intended goals, having been one for over 30 years. As far as my stuff, I may, and a lot of times do, have different objectives. There may be a few times that subsequent actions/results caused me to return things to their original condition.

Case in point is my dash mounted temp gauge rather than a pressure gauge. For what I do its the perfect answer. Were I going out 30 miles into the ocean on a daily basis, or even going out at all, I would want a pressure gauge.................both of which aren't supplied by OEM design engineers on production equipment!!!!!!
Click to expand...

The difference is... you are doing it from experience.....

Merc offers pressure and temp, the boat manufacturer determines what is installed... All options are available.
 
This afternoon I took the thermostats out and run the engine on a hose. Water did come out of both sides. So I put the thermostats and housing back together and hope to get on the water soon to see what temperature and pressure I get. My boat has both gauges in the dash. This is my 4th boat and this is the first one that the tell tail should not run right away. When I first got the boat a thermostat must have been stuck open because the tell tail ran right away instead of waiting for the thermostats to open. Although when I replaced the thermostats I did not notice one open. Thanks to all who replied and I will post my readings after I hit the water.
 
Docksidemarineservices said:
The difference is... you are doing it from experience.....

Merc offers pressure and temp, the boat manufacturer determines what is installed... All options are available.
Click to expand...
My 2002 Crestliner 1750 Fish Hawk came with Faria Beede instruments. The instrument panel had a blank in the center where an instrument could be installed.....but wasn't. Apparently they, the boat builders decided that this insturment (https://www.opticsplanet.com/faria-...ck-ss-2-water-temperature-gauge-100-250f.html) wasn't necessary!
 
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