Mercury not peeing stream at high speed

Author Message   Robert Morgan Posted on Thursday, January 09, 2003 - 12:25 pm:    My Mercury 175 pees fine at idle, but when it's under a load it doesn't pee a stream, it only sputters water out. When I pull back to idle it starts peeing a stream again after a few seconds...Should the engine pee a steady stream regardless of the speed and load the engine is under, and if so, any ideas on what to fix? Thanks!   Jon Posted on Thursday, January 09, 2003 - 01:53 pm:    Robert, It should pee a stronger stream as the RPM's increase. It might be possible that what you are seeing has something to do with the lower unit moving through the water, but it shouldn't work that way. The first thing I'd check is to see if the key that prevents the water pump impeller from spinning on the driveshaft is in place. My guess would be if that key was missing or something has gone wrong, it might spin at a low speed, but just slip at higher RPM's. Jon   sparky Posted on Thursday, January 09, 2003 - 05:38 pm:    Motor might be mounted too high on the boat allowing air into the system. Without seeing the unit we can only make assumptions.   IwanLane Posted on Thursday, January 09, 2003 - 10:07 pm:    I had similar problems with little 4 horse Johnson. The problem was what sparky has outlined. The peeing worked well in a bucket but when I tried it in the boat, no peeing. Make sure that the cavitation plate is 1 to 2 inches below your hull.   Tonyob (Tonyob) Posted on Friday, January 10, 2003 - 10:09 am:    Robert, If the engine is at the proper height, you probably have a problem in the water pump. It could be a worn impeller, or a bad gasket under the base plate. Make sure the screen is not clogged. Likewise the water channel which leads to the pump. Tony   Bubba Posted on Friday, January 10, 2003 - 07:01 pm:    Is the motor overheating? The tell-tale stream is very difficult to see when the boat is running at high speed. See if you have a big gush of water coming out of the exhaust relief holes when you are running. If you do, your pump is working. It might be a good idea to test your overheat warning horn. With the keyswitch on, take the tan wire going to the sensor on one of the cylinder heads and short it against the block - the buzzer should sound. It wouldn't hurt to put an infrared heat gun on the thermostat housings while running if you know someone who owns one. Temperatures should be between 140 and 170 degrees F.   Robert Morgan Posted on Friday, January 10, 2003 - 10:11 pm:    Thermostat says it's running hot...my dad (I bought the boat from him) said that he had someone put it in a pool and said it was fine that the sensor was bad or something like that. He ended up cutting the wire that lead to the buzzer because it "was annoying". I'm worried that the engine is shutting down to protect itself, but I don't know how to verify if that is the case. I've been told that with the older model engines that at high speed/rpm the water is vaporized and comes out the exhaust, but I'm concerned because I don't want to hose up a $10,000 engine because my dad said he had it checked out. I'm 34 and I know my dad, he wouldn't lie, but I sure would hate to have to replace the engine because it locked up due to heat.   sparky Posted on Saturday, January 11, 2003 - 07:26 am:    Do a compression test . Blown head gaskets will cause overheating.Disconnecting sensors is a mystery to me. As they say outboards rarely wear out,they end up on the workbench because somebody made a mistake.   Tonyob (Tonyob) Posted on Saturday, January 11, 2003 - 11:25 am:    Robert, I'm not sure what year your engnine is, but there is a good chance that it has chromed cylinder bores instead of steel sleeves. These engines will not stand for very much overheating, so you had better be careful. Even if it has steel sleeves, overheating can cause serious damage in a short time. Based on what you have said, I don't think you have a serious cooling problem; if you did, the engine should have destroyed itself by now. If the head gaskets are bad enough to cause the problem it should be obvious. You would see thick deposits on the spark plugs due to water mixing with fuel. If you decide that the head gaskets are okay, I would advise you to remove the lower unit and inspect the pump. While you have it off, attatch a water hose to the water uptake tube. Turn the water on and see if the water seems to circulate freely. Do this with the spark plugs out. Look for any signs of water in the cylinders. Water could get in through the exhaust system as well as through the head gaskets. If everything seems okay, replace the spark plugs and run the engine with the hose hooked up as before. See if it cools properly. Look for hot spots, which would indicate a blockage or some other problem. If the engine cools properly when you do this, you can be sure that the problem is in the pump or lower unit. Tony   Robert Morgan Posted on Sunday, January 12, 2003 - 11:44 am:    Thanks for the info guys. I'll tear the lower unit apart and change the pump and the impeller. This website posting forum is the best!

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