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1997 Mercury 40 water scalding from pee hole

S

swill936

New member
I have a 97 4 cylinder 2 stroke mercury 40 that is confusing us. The oil injection has been removed and I mix the gas at the tank. Otherwise stock. The motor has always been used in salt water but has been flushed after each use. While running up the intercoastal waterway, the water-pump stopped pumping water...had steam coming from the pee hole. Limped to the dock on the trolling motor.
Replaced the entire water-pump assembly. Back flushed thru the pee hole with free flowing water from the foot. Water from the pee hole runs with a broken stream and is scalding hot. My mechanic thinks the problem is exhaust in the cooling system from a leaking gasket between the power head and the drive housing. The bottom 3 cylinders are cool to the touch and the top one is hot but not burning my hand. I removed the foot and placed city water onto the water-pump discharge pipe and have the same symptoms when running the engine. The motor runs like new. Starts quickly and idles perfectly.
Can there be a blockage I'm not getting to flush?
Is there a best practice to backflush this engine?
HELP!! The fish are starting to bite and I'm on the dock!!

Sonny
 
Hi Sonny,
When you replaced the impeller did you notice if any of the impeller vanes were missing? If one breaks off a piece can take a ride up the watertube and get stuck in a cooling passageway that impedes the water flow. This may mean removing the block cover and or exhaust cover and removing the powerhead to find blockage. This will be a bear of a job to remove the exhaust cover bolts without breaking them from salt water use.
 
fitz73222 said:
Hi Sonny,
When you replaced the impeller did you notice if any of the impeller vanes were missing? If one breaks off a piece can take a ride up the watertube and get stuck in a cooling passageway that impedes the water flow. This may mean removing the block cover and or exhaust cover and removing the powerhead to find blockage. This will be a bear of a job to remove the exhaust cover bolts without breaking them from salt water use.
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The impeller looked new, but I changed it as a precaution. That impeller had only been in the outboard a short while. We ran into a sand bar in Lumber River a few weeks before and damaged the upper housing. There was no visible damage to the impeller, only gouging of the steel liner in the upper housing and I changed the upper housing and impeller but not the lower housing. We fished and tubed several times between the two events without incident.

Thanks in advance for any advice!
 
I'll remove it Saturday. Other than rusted exhaust bolts, are there any potential complications I need to be aware of?

SLW
 
Get a Mapp gas torch and a truck load of patience. Each bolt will be stuck. I've delt with this for almost 50 years. The goal is to expand the metal around the steel bolt and under constant heat walk the bolt in and out. It may only be an 1/8 of a turn each way until the salt starts pop out of the threads. If it doesn't want to come out after it starts to move, leave it alone and go on the the next bolt, let it cool and come back later. Use a 1/4 inch ratchet with the socket and palm the the top of the ratchet back and forth working the bolt out. You can easily break the bolt by man handling it. Yes, the ratchet will get very got doing this so stop and let things cool and start over.
 
Among the things mentioned, I find that "impact" does wonders without breaking bolts. Rather than brute force type torque, I use a small #F air impact wrench in the back and forth method. The 250 #F butterfly is perfect as it has "butterfly wings", bidirectional levers on both sides and back and forth motion is immediate. If you have a larger impact then reduce the impact intensity with the control knob....just enough pressure to see results and give it time, and the penetrating oil time to work.

If I can't get an impact on the bolt, like where the cowling is in the way, I use a ⅜" breaker bar (rather than ratchet since it is a fixed prying device) and a 12 oz. ball peen hammer. Whack CCW, whack, CW, etc. etc. I like Kroil penetrating oil and pre soaking continuously. An electric heat gun, 1500 W, like sold at Harbor Freight can apply the heat for you without the flame and resultant fire (of the penetrating oil) experienced with a torch. Course once it's moving then bring it on out.
 
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faztbullet said:
Exhaust side cover restricted............
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Got it off. No issues with stuck bolts. I also removed the end cover and fished/flushed every port I saw. I didn't see anything that looked like an obstruction, but after flushing blew everything out with an air nozzle. I'm waiting for new exhaust and end cover gaskets to arrive and hope to report success after reassembly. The cooling flow on these engines is really quite simple and I feel like things should cool nicely now. Thanks for the suggestions and cross your fingers.

SLW
 
While you were there, did you remove and check the thermostat, or better yet, check the temp stamped on the bottom of the large pellet component of the TS for the correct temp, and get a new one. I realize that a lot of engines plumb pee off the exhaust manifold cover, but when you said the top cyl was very hot, unlike the others, that's where the stat is and if it isn't opening properly, that is where you experience your hottest block internal temp.
 
Texasmark said:
While you were there, did you remove and check the thermostat, or better yet, check the temp stamped on the bottom of the large pellet component of the TS for the correct temp, and get a new one. I realize that a lot of engines plumb pee off the exhaust manifold cover, but when you said the top cyl was very hot, unlike the others, that's where the stat is and if it isn't opening properly, that is where you experience your hottest block internal temp.
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This engine has no thermostat. 1997 was the last year of the four cylinder 44 cu.in design.
 
Texasmark said:
While you were there, did you remove and check the thermostat, or better yet, check the temp stamped on the bottom of the large pellet component of the TS for the correct temp, and get a new one. I realize that a lot of engines plumb pee off the exhaust manifold cover, but when you said the top cyl was very hot, unlike the others, that's where the stat is and if it isn't opening properly, that is where you experience your hottest block internal temp.
Click to expand...


Thanks, thermostat was my first thought, but my engine design does not use one. It looks like a blockage in the return holes to the exhaust cover. I'm waiting for new gaskets to arrive and will give an update when it is reassembled.

SLW
 
swill936 said:
Thanks, thermostat was my first thought, but my engine design does not use one. It looks like a blockage in the return holes to the exhaust cover. I'm waiting for new gaskets to arrive and will give an update when it is reassembled.<br>
<br>
SLW
Click to expand...
<br>

Got new gaskets yesterday!!! Made sure all gasket surfaces were clean and reassembled the engine. Somehow managed to lose a spark plug and had to buy a new one...is any repair complete without losing at least one small bit??!! Either way, after reassembly, the engine started without incident and pees like a horse on Flomax. Water temp is normal and all cylinders are cool to the touch after 15 minutes run time. Thanks for all of the suggestions!! I'll be fishing in the morning.

Sonny
 
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