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merc 9.9 4 stroke cooling

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billyd2023

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hello! I have a 2007 merc 4 stroke that I bought used. put it on the boat and it will run for about 5 minutes under load then sputter and die out. after it rests for an hour or two it will start up and run for about the same amount of time before dying again. I hooked up the garden hose with the clamshell over the water intake port and ran it to try to figure out the problem. was surprised by what I saw: water coming out of 3 different holes near the lower unit and also out of a hole on the transom side of the shaft about halfway up. water out of the indicator hole on the back of the engine is not as strong as I've seen on other outboards.

I've never seen water coming out of so many places on an outboard! Is this normal for this engine? I'm thinking my running problem could be due to overheating; the engine block was pretty hot; couldn't keep my fingers on it. would think with the cold water coming from a garden hose it shouldn't have gotten that hot?

Any help would be appreciated!
 
I have a Mercury 9.9 HP outboard, 2006 model. I don't think you are having cooling issues. All those holes you mention are likely vent holes to permit any trapped air to escape from the lower unit when operating the motor. When using a clamshell and hose, you are pressurizing the lower unit, so water will come out of those vent holes. When the motor is running with the clamshell, simply put your hand in the stream of water coming from the engine and check its temperature. It should be slightly warmer than the water going into the engine. At idle, you will not feel a large temperature different between the water going in and what is coming out of the engine.
 
Thanks for the reply dougd1. Appreciate you taking the time to respond. I'm curious; have you ever hooked up the clamshell to your motor? your comment about vent holes to allow trapped air to escape makes some sense; just I've used this method on several other engines thru the years (including a 2007 25hp merc 4 stroke) and never seen anything like this. Also; as I mentioned; the water stream coming out of the "pee hole" is not as strong as I've seen on other outboards. to elaborate a bit further; the longer it runs the stream gets weaker. almost to a heavy dribble before the motor conks out. that's what gets me thinking the water bleeding out of the lower unit should be going to the engine. I'm thinking water pump and / or thermostat. Make sense?
 
I have starting problems of my own with my 9.9 HP Mercury, so I am always using a clamshell on the lower unit. The clamshell is hooked up to garden hose, supplied with water from my house. Please clarify your comment about your discharge water stream becoming weaker. Is that because the motor is slowing down to the point where it conks out? As it conks out, I can see the stream becoming a dribble because the motor speed is slowing down, thus the water impeller is slowing down as well. However, if the stream is getting weaker independent of the motor speed, then that is a different issue. When the motor is running, can you rev up the engine and when doing so, does the water discharge become stronger? If it does, then I would think your water impeller is ok. I don't have a thermostat that I am aware of on my 9.9 HP motor.
 
Just checked the Mercury web site - there is a thermostat on my motor. Have not had any issues with it, although I have only had the motor for a couple of years.
 
water stream is weak all the time. seems to get worse the longer it runs. near the point of stalling it's just a healthy dribble. increased engine speed doesn't seem to help it. same results whether using the clamshell or running in a water tank.

since you're using a clamshell; I'm still curious if you see water expelling out of holes neat the lower unit? 2 holes the expel water downward and one that expels it towards the front.
99 water leaks.jpg
 
When I use the clamshell on my engine, I get water spouts coming out of the lower unit when the hose is connected to the clamshell. I haven's specifically looked to see if there are three of them. When running the engine with the clamshell on, I get a steady stream of water coming out of the cooling water discharge hole. I would have a look at the water pump impeller to see if it needs replacing.

Doug
 
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