‘91 merc 60hp overheating alarm buzzing

[Evinrudej]

Hi everyone so I have a ‘91 merc 60hp 2 stroke (elpto) and I have been running into an issue with the over heat buzzer going off. So at first the basics, alarm only goes off when at idle speed in gear (going through a no wake zone) the tell tale is pumping water well, the block does not get very hot to the touch. Have no idea on the condition of the impeller or thermostat. Sometimes when I would wack the gear shift control module where the buzzer is it would stop it. I seen on other forums this could either be a problem with my cooling system either impeller, thermostat, etc or a faulty oil sensor module. One person suggested unplugging the tan bullet connector that goes to the tan and blue wire and the cooling alarm would still function normal. Should I do this and see if the alarm still comes on and go from there? Thank you!

 

[racerone]

Install a new impeller.

 

[Texasmark]

After you install that new impeller if the problem persists, come back and we can talk about some troubleshooting you can do to isolate the problem. The tell tale comes off the exhaust manifold on my engines and that circuit is separate from the block cooling circuit so the tell tale really doesn't tell you everything you need to know.

 

[Chris1956]

When installing a new impeller, inspect the bottom of the old one. Look for damage there, which has been often known to lead to overheat at idle. I would also inspect/replace the thermostat, as that controls cooling at slow speeds.

High speed cooling is controlled by the poppit valve.

 

[Evinrudej]

After you install that new impeller if the problem persists, come back and we can talk about some troubleshooting you can do to isolate the problem. The tell tale comes off the exhaust manifold on my engines and that circuit is separate from the block cooling circuit so the tell tale really doesn't tell you everything you need to know.

I’m going to replace the impeller and thermostat and start there. Problem is I’ve had this boat out a few times so how can I also check for damage besides a compression test?

 

[Chris1956]

Compression and leakdown tests can tell the condition of the cylinders and pistons.

 

[Evinrudej]

So to update. I replaced impeller and got a new t stat. I tested the t stat to see if it was opening properly and found that it was not opening at all. I never had the alarm go off at high speeds only at idle speed and it continued to pump water. I’ve had it out a few times before replacing the t stat and now I’m worried of warped cylinders. Next steps to check for damage? I haven’t noticed any steam from the engine, decrease in power or trouble starting.

 

[Chris1956]

Gee, a compression test and a leakdown test will tell condition of the piston and rings. Usually, they are the first to be damaged. If they check out, it is likely the rest of the engine is fine.

 

[Evinrudej]

Gee, a compression test and a leakdown test will tell condition of the piston and rings. Usually, they are the first to be damaged. If they check out, it is likely the rest of the engine is fine.

Will be testing tomorrow. Does the poppet valve still allow water to flow through the engine at high speeds even if the thermostat is stuck shut?

 

[Chris1956]

Yes, the poppit and thermostat are in parallel with each other and the water flow. The poppit valve is spring loaded. At about 2000RPM, the water pressure pushes the poppit valve open, allowing a large flow of cooling water out of the engine. The thermostat is also open at high speed, but the water volume thru it is so low, that it does not do much cooling.

 

[Evinrudej]

Yes, the poppit and thermostat are in parallel with each other and the water flow. The poppit valve is spring loaded. At about 2000RPM, the water pressure pushes the poppit valve open, allowing a large flow of cooling water out of the engine. The thermostat is also open at high speed, but the water volume thru it is so low, that it does not do much cooling.

Thank you for the information on how the poppet system works. I compression tested each cylinder at about 110 on each cylinder so that’s good. Now I’m having an issue with the alarm just giving a constant beep at all times. Even after the motor sat cold for days, as soon as I turn the key the alarm goes on and when I turn it full to start the engine it stays on. I tried unplugging temp sender wire, no change from that. If I hit the control box where the buzzer is it sometimes will go off but then come back on.

 

[racerone]

Wiring short or defective buzzer?

 

[Texasmark]

Thank you for the information on how the poppet system works. I compression tested each cylinder at about 110 on each cylinder so that’s good. Now I’m having an issue with the alarm just giving a constant beep at all times. Even after the motor sat cold for days, as soon as I turn the key the alarm goes on and when I turn it full to start the engine it stays on. I tried unplugging temp sender wire, no change from that. If I hit the control box where the buzzer is it sometimes will go off but then come back on.

My service manual for 100 hp range 2 stroke Mercury's says to expect problems if compression is less than 120 PSI. You're close and it may be ok but the manual says what it says!

 

[Evinrudej]

My service manual for 100 hp range 2 stroke Mercury's says to expect problems if compression is less than

Wiring short or defective buzzer?

yeah most likely I’m thinking defective buzzer. Will have to do some testing and report back.

 

[Texasmark]

I’m going to replace the impeller and thermostat and start there. Problem is I’ve had this boat out a few times so how can I also check for damage besides a compression test?

If I were to do an inspection where I may have something clogging the circulation of the cooling water, I'd do the following:
1. Inspect and then replace impeller. While water pump is open, put muffs on the LU and squirt water into the pickups on the LU and see if it freely flows into the open water pump.

Leave the LU disconnected from the mid section for the following tests:
2. Remove the thermostat and with a string (placed in the butterfly valve and stat housing giving you a method of supporting it. Get a pan of water cooking on the stove with a candy thermometer (they measure high heat) inserted in the water. Look on the bottom of the pellet part of the stat for the opening temp stamp....143 (F) is what my engines used.

Drop the stat in the heating water holding it up by the string. Watch the candy thermometer for the water reaching the number stamped on the pellet. Once reached, give it a couple of minutes and +/_ about 5* of that number the stat should open and fall off the string.

Physically inspect the pop-off valve (the large diameter device under the combination it and stat cover}. It shouldn't be corroded and should easily open when you exert mild pressure on the valve.
------- No problem so far? Continue!
3. Remove the water jacket cover on the rear of the engine block....spark plugs protrude through it..... when you removed the LU you exposed the tube/pipe that carries the water output of the water pump up to the engine proper. Connect your hose under low pressure....(10 PSI) to the end of that tube and ensure that you have full flow out the port that feeds the stat and pop off. Find the output of the engine block and shoot your hose into that outlet and ensure that a good flow comes back out of the mid section.
If you find a problem, fix it. If not continue.
4. Put everything back together...a little soap on the impeller and be sure to install the locking key to the drive shaft when you install it. Looking down from the tip of the drive shaft, slowly press the water pump cover down onto the impeller while turning the drive shaft CW. If you are doing it correctly, the cover will deform the tips of the impeller and as you push down on the cover the tips will fold back and easily move into the cover for you to secure it.
5. One more thing: with the LU still off, connect your hose to the "tell tale" outlet on the side of the engine cowl and look for water coming down out of the mid section. If good, you are ready to close everything back up and you shouldn't have any cooling issues thereafter.

 

[Chris1956]

The alarm will sound when the temp sender shorts to ground or when any part of the wire from the sender to the alarm shorts to ground. Since the alarm sounds when the engine is not running and cold, suspect the alarm wire is rubbing somewhere and grounding to the block or other ground wire.

I doubt low compression has anything to do with overheat, unless the head gasket is leaking into the cooling system.

 

[racerone]

I doubt you will find a head gasket on this 1991 model 2 stroke !

 

[Chris1956]

Yes, I was too lazy to look it up. How long did Merc use the blind hole blocks? I presume it was only on il3 and 4's.

 

[racerone]

Most Mercury had ---NO HEAD GASKET----Until the V-6 came out.-----Inline 6 never used a head gasket.

 

[Evinrudej]

If I were to do an inspection where I may have something clogging the circulation of the cooling water, I'd do the following:
1. Inspect and then replace impeller. While water pump is open, put muffs on the LU and squirt water into the pickups on the LU and see if it freely flows into the open water pump.

Leave the LU disconnected from the mid section for the following tests:
2. Remove the thermostat and with a string (placed in the butterfly valve and stat housing giving you a method of supporting it. Get a pan of water cooking on the stove with a candy thermometer (they measure high heat) inserted in the water. Look on the bottom of the pellet part of the stat for the opening temp stamp....143 (F) is what my engines used.

Drop the stat in the heating water holding it up by the string. Watch the candy thermometer for the water reaching the number stamped on the pellet. Once reached, give it a couple of minutes and +/_ about 5* of that number the stat should open and fall off the string.

Physically inspect the pop-off valve (the large diameter device under the combination it and stat cover}. It shouldn't be corroded and should easily open when you exert mild pressure on the valve.
------- No problem so far? Continue!
3. Remove the water jacket cover on the rear of the engine block....spark plugs protrude through it..... when you removed the LU you exposed the tube/pipe that carries the water output of the water pump up to the engine proper. Connect your hose under low pressure....(10 PSI) to the end of that tube and ensure that you have full flow out the port that feeds the stat and pop off. Find the output of the engine block and shoot your hose into that outlet and ensure that a good flow comes back out of the mid section.
If you find a problem, fix it. If not continue.
4. Put everything back together...a little soap on the impeller and be sure to install the locking key to the drive shaft when you install it. Looking down from the tip of the drive shaft, slowly press the water pump cover down onto the impeller while turning the drive shaft CW. If you are doing it correctly, the cover will deform the tips of the impeller and as you push down on the cover the tips will fold back and easily move into the cover for you to secure it.
5. One more thing: with the LU still off, connect your hose to the "tell tale" outlet on the side of the engine cowl and look for water coming down out of the mid section. If good, you are ready to close everything back up and you shouldn't have any cooling issues thereafter.

Thank you this is very useful