150 Merc heating up

[Destroyer]

Check your thermostats to make sure they are opening. A lot of times they jam shut with salt or just old age. A quick test is to take them out, put them in a saucepan on the stove under water, turn on the stove and watch them... if they don't open by the time the water boils it's time for new ones. If they do open, then do the same test again, but this time put a thermometer in the water and check the temp that they open at. It should be the same or very close to what the engine specs call for.

If they opened, then check all water passages for salt or sand or something that got ingested by the intake and passed up into your engine.

Also, you say that the horn is going off but you don't say anythng about the actual engine temp. Is there a water stream coming out of the engine? (is it pissing?) Is it really hot or is just that the alarm is sounding? What is your temp guage reading? I have a 200 Merc of the same year as yours that had a problem, and it turned out to be a bad heat sensor on the port side of the engine.

If the problem is your t-stats DO NOT be tempted to just run the engine with the t-stats removed. They are there for a reason. Your engine needs a certain temp to help burn off carbon.. you can ruin an engine by running it for a long time with the stats not installed. It's ok to do in order to get back to port, but install new ones at your earliest opportunity.

[wellcraftinmass]

The water starts out of the tube but then it turns to steam about the same time the engine buzzer goes off. I will check the thermostats today. Thanks again for the info. Now on top of everything else, the oil pump drive shaft appears to have busted the gear, because the motion sensor is buzzing all the time and the oil is not feeding from the upper resevoir. This motor is driving me nuts. Now I mix the oil in the tank. now back to work thanks again.

[Destroyer]

Sounds like your pump is ok, since the pisser is pissing... (god, where do we get these names from...lol)...Anyways, since you are getting water flow my bet would be that one of your thermostats isn't opening. Remove them from your engine, put the covers back on and then try running your engine again. (Don't worry, you won't do any damage to the engine for that short a run) If it runs cool and the water doesn't turn to steam you've found your problem. If you still get steam then it's a good bet that you have blocked passages or hoses. To narrow it down even further, you can check where the problem is by just putting your hand on the heads of the motor after it heats up. If one side is cool and the other is really hot then the side that is hot is the side with the blockage.
My bet would still be on the stats though until proven different.

[phatdaddy]

If you have a harbor freight nearby, pick up a handheld laser thermometer. very useful for all kinda of jobs.

http://www.harborfreight.com/non-con...ter-96451.html

[wellcraftinmass]

I pulled both thermostats and the engine is running cooler, but its hard to tell now because its only running on the hose and muffs in the back yard. But the heads both ran cool the entire time it was running in the back yard. I am hoping that was the problem. Both stats were dirty and I ran the test you had mentioned and they both opened, but seemingly not very far. I am hoping thats the heating problem.

Now the trim problem. I ordered a used trim unit off ebay, basically to get the tilt piston. The tilt piston is leaking from the top packing. I wouldlike to get a complete rebuild kit for all three piston if I could. Does anyone know the best place to get "O" rings or packings for a 1989 Merc 150, 3 ram, side fill T&T unit???? Thanks again.