Audible Alarm On My '86 Merc 135 Hp Black Max

[the reel ess]

Yesterday I got this alarm after trolling at idle for maybe 15 minutes. I switched off for a few minutes, cranked it and it was still alarming. I sped up and it went away. Is this overheating? When I got the boat, there were no thermostats in it (If I remember correctly, there should be two). I had a mechanic put them in. 

[the reel ess]

I should mention that the oil injection system was professionally disabled by a Merc mechanic and I premix 50:1 fuel, so I don't think the alarm should have anything to do with oil injection operation. And the water pump impeller was also replaced at the same time. There has been very little time put on the motor since then.

[Rivers Edge]

I believe if its a continues beep it could be overheating. Was it weedy where you were fifing?

[the reel ess]

No it was pretty much weed-free. I was slow trolling at idle though-not much water circulating thru the motor.

 

Like I said, when I got the boat the thermostats were missing. Now I must assume that's why. When I took it to a mechanic he asked me if the motor was cold-natured. I said it was, extremely. It can sometimes run the battery down cranking for the first time. He wanted to return it back to stock at the same time the oil injection was disabled. I guess I need to remove them.

 

I guess I should have known better because I bought the boat from a car mechanic who had been the only owner. But I figured a Mercury mechanic's opinion  was better than a car mechanic's.

[WIGuide]

If I had to guess I'd be guessing your impeller is on it's last leg. They should be changed every few years as it's more a wear and replace part. The fact that when you gave it a little more gas makes me think it's that since at a higher rpm your motor starts to move a higher volume of water through it. Even if it's not working efficiently, a worn impeller will still move more water at a higher rpm. Leave the thermostats alone for now unless you're going to try flushing the cooling system with the lower unit off to get anything out of there. If you don't know when the last impeller was put in, that would be my first move. 

[Skeeter Dan]

Is you motor putting out a steady stream of water when Idle? If not change the impeller. It should be putting out the same amount as running at higher RPMs.

[the reel ess]

Is you motor putting out a steady stream of water when Idle? If not change the impeller. It should be putting out the same amount as running at higher RPMs.

Thanks, Yeah, it seems to be "peeing" with a sufficient stream. The impeller has very few hours on it as well. I had it changed by the same Merc mechanic that did the rest of the work a few years ago and haven't used the boat 5 times since.

 

I'm not certain I agree that it should pump the same volume at idle though. The impeller speed is directly tied to engine RPM, correct?

[the reel ess]

If I had to guess I'd be guessing your impeller is on it's last leg. They should be changed every few years as it's more a wear and replace part. The fact that when you gave it a little more gas makes me think it's that since at a higher rpm your motor starts to move a higher volume of water through it. Even if it's not working efficiently, a worn impeller will still move more water at a higher rpm. Leave the thermostats alone for now unless you're going to try flushing the cooling system with the lower unit off to get anything out of there. If you don't know when the last impeller was put in, that would be my first move. 

The impeller has been replaced and barely used since.

[WIGuide]

The impeller has been replaced and barely used since.

You aren't one of those people who starts their motor out of the water are you? I've seen too many who have done that to not ask. 

 

If it's not the impeller, then it could be the thermostats. You might have got one that isn't calibrated correctly. Also if the motor has been run in any salt or brackish water, that can sometimes cause the t-stats to corrode slightly and not operate as smoothly. Also worth noting, they can get crap in them. My friend had a Merc that wouldn't pump water and when he took the t-stat out, it had a small piece of gunk stuck in the spring.

 

Another possible cause is the water temp sensor that turns on just a little early.  

[the reel ess]

You aren't one of those people who starts their motor out of the water are you? I've seen too many who have done that to not ask. 

 

If it's not the impeller, then it could be the thermostats. You might have got one that isn't calibrated correctly. Also if the motor has been run in any salt or brackish water, that can sometimes cause the t-stats to corrode slightly and not operate as smoothly. Also worth noting, they can get crap in them. My friend had a Merc that wouldn't pump water and when he took the t-stat out, it had a small piece of gunk stuck in the spring.

 

Another possible cause is the water temp sensor that turns on just a little early.  

Thanks for the reply. No. In fact, I have the ear muffs for running it on land. I'm thinking it's just too big a coincidence that the thermostats were out when I got it. During lunch I went digging thru a bucket of things the guy gave me with the boat and there are two old ones in it. I must reasonably assume there's my sign.

 

I'm not immune to doing something stupid though. I was ready to take it to a mechanic once because it wouldn't crank. My dad suggested I check the kill switch. Bingo!

[RAMBLER]

Thanks, Yeah, it seems to be "peeing" with a sufficient stream. The impeller has very few hours on it as well. I had it changed by the same Merc mechanic that did the rest of the work a few years ago and haven't used the boat 5 times since.

 

I'm not certain I agree that it should pump the same volume at idle though. The impeller speed is directly tied to engine RPM, correct?

A few years ago..........  Your impeller needs replacing.  You leave something like that sit, that long, here in Florida and it will dry rot.  Also, mud dabbers will put mud nests in any hole they can get into.  That whole system may need flushing out by a mechanic.

[Bluebasser86]

A few years ago..........  Your impeller needs replacing.  You leave something like that sit, that long, here in Florida and it will dry rot.  Also, mud dabbers will put mud nests in any hole they can get into.  That whole system may need flushing out by a mechanic.

I agree that your impeller probably needs replacing. It's just rubber, it'll dry rot and need replaced regardless of use after a few years. I had something very similar happen with my last boat and it turned out to be the impeller. It wasn't in the best shape so it wasn't pulling enough water at idle speeds. 

[the reel ess]

Thanks for the responses. Just using the boat once I'm reminded why I like the kayak so much better. Such a hassle to haul it to the big lake and catch one dink bass and lose a small striper at the boat, then haul it back home.

 

I also had to gas (and oil) it up and rig up a drain plug because mine broke the night before on a Sunday night.