Overheat buzzer at high RPM's only

[ObiwanKenobi]

1994 Force 120 on a Maxum 1800XR. I can idle it all day and run at low RPM's all day without problems. After having it running for a few minutes, if I open it up a little, the overheat buzzer goes off. Someone already said the buzzer on my model motor is only for an overheating condition and not water in the gas line, so I'm going with that assumption. Here's what I've done so far:
1. Checked the water coming out. It's a powerful stream out of each tell-tale hole. It's a little too hot to hold my hand under for a long time, but not scalding.
2. Checked the engine block's heat level. If I put water on it, it doesn't evaporate quickly. It kind of just sits there. I can touch it, but I can only hold my hand on it for six or seven seconds before it starts to feel uncomfortable.
3. I took off the exhaust plate, and it was clean as a whistle in there.
4. I popped off the head, and it was clean in there, too. There were very-very thin deposits here and there. They were less than half a millimeter in thickness. I scraped them away anyways and reinstalled the head. The problem persisted, however.
5. Changed plugs.
6. Cleaned the thermostat, which had some sand and salt around it. Tested it and reinstalled it.
7. Ran it with and without the thermostat.

Side point: I cleaned the carbs about two months ago.

Google searches often bring up posts saying that it could be an issue with the battery connection, but I haven't been able to wrap my head around the science of that. In Belize so resources are limited. Three Belikins for the solution lol. (But really, I'll mail them or something.)

 

[Nordin]

When I read through your post I feel like your sensor is bad and start to grounding out to make the buzzer sound to early.

As you have good water stream out from the leg and assume you have change the impeller, checked the thermostat, cleaned out the waterjackets etc.
The water out from leg should be hot but not to hot. Also the head should be hot but not to hot after high RPM running.
Water not evaporate from head .... that is also good.

When you touch the head or holding you fingers under the water stream and you feel uncomfortable after some seconds.
That indicate that the temperature is above about 115-120 dgr F (45-50 dgr C).
Our fingertips starts to feel like is is burning and uncomfortable at about 115 F and as water starts to boil at 212 F (100 C) the engine is not overheating.

Operationtemperature when running at WOT should be about 170 F depending on what thermostat you have.

 

[pnwboat]

Sounds like the water pump impeller needs to be replaced if you haven't already done so.

Note: You should run it with the thermostat installed so that the motor reaches the proper temperature for best performance.

Belikins....Belize....I think I'd rather be there in person! LOL!

 

[ObiwanKenobi]

The idea that it's not overheating makes sense, but I have a couple of questions: why would the grounding out of the wire only happen at high rpms? And if water is gushing out of the tell-tale, could there still be a problem with the impeller? Also, the impeller looks good. I checked it a couple weeks ago. Thanks, again

 

[Nordin]

First change impeller if you have not done it. It is a part that should be replaced every 5 year in my opinion.
The impeller that is in now pumps water but a new one may pump more.
I have change many impellers and many of them have looked good BUT it has not pump enough water to cool the engine properly.

The sensor is a bimetal typ and the bimetal bends when the temperature increase and at last it ground out and the buzzer sounds because it get 12VDC from the battery circuit through the wire and down to ground.

When the RPM.s goes up the engine produces more heat and it need more cooling water.
The impeller is mounted on the driveshaft and as the RPM.s increase the impeller pumps more water.

 

[jerryjerry05]

Sounds like you did everything backwards??
The first thing is the pump and then the other stuff!!

IF?? yo can't keep yor fingers on the head then it IS getting hot.

You have access to a heat gun?

The sensors usually doesn't go bad.

Pull the lower unit and check the impeller.
​Possible the impeller cup(stainless steel) is worn out and needs replacement.
​The cup and wear plate should be fairly smooth and no deep grooves.
​The impeller blades shouldn't have any bend.
Pictures??

 

[pnwboat]

Like mentioned above, just because the impeller looks OK doesn't necessarily mean that it is functioning well. The rubber blades should be fairly flexible and pliable not permanently curved.

 

[ObiwanKenobi]

The impeller SEEMS like it's perfect, (it pumps a ton of water) but something JerryJerry said makes me think it may not be ok. Let me describe it: It's rubber and flexible. When it's outside of the cup, its phalanges are straight. It cannot fit into the cup just by slipping it in. You have to bend the fins slightly to get it to fit. I thought this was a purposeful design element because it would make the fins bend in such a way that they would pump water in a specific direction and not just churn it around. But JerryJerry is saying the impeller blades should not have any bend to them. Perhaps the wrong impeller is in there because when the current one is installed, the fins definitely have a slight bend. (The cup looks perfect, btw.)

But that would be confusing because it did the 20 mile run from Belize City to here without any problems and the same impeller.

Also, shouldn't the water be too hot to hold your hand under? If operating t

 

[pnwboat]

Did the motor have this problem in the past or is this something that has recently started to happen?

 

[roscoe]

1994 Force 120 on a Maxum 1800XR. I can idle it all day and run at low RPM's all day without problems. After having it running for a few minutes, if I open it up a little, the overheat buzzer goes off. Someone already said the buzzer on my model motor is only for an overheating condition and not water in the gas line, so I'm going with that assumption. Here's what I've done so far:
1. Checked the water coming out. It's a powerful stream out of each tell-tale hole. It's a little too hot to hold my hand under for a long time, but not scalding.

There is only ONE tell-tale. It is on the starboard side of the motor, at the lower rear corner of the cowling.

What holes are you referring to as tell-tales ?

I suggest you locate the real tell-tale.
Make sure the hose and outlet are not clogged with debris.
Remove lower unit, replace impeller with new.
Remove thermostat cover and use garden hose to force water into block to flush it out.
Replace thermostat with new.
Install lower unit and test run.

 

[Nordin]

What jerryjerry refer to about the impeller blades should not be bend are when it is out of the cup.
When it is in the cup they have to be bend.
The impeller is mounted exentric in the cup, because when the blades flexes it make the water to pump
If they not flex then it will NOT pump.
If the blades are bend when the impeller is out of the cup it can be the cause of your issue.

Change the impeller and see what happens

 

[ObiwanKenobi]

The problem began after I installed a new stator. While trying to diagnose what was a problem with the stator, I tried a bunch of things, but they weren't major and involved the electrical system.

As far as the telltale is concerned, there are two holes out of the back that I believe connect to one hose that concludes the cooling system. Water doesn't "Pee" out of them. It gushes out with force. I'll take a pic and post it.

 

[roscoe]

The holes you are referring to are exhaust relief holes.
Yes, water will exit here, but it is being forced out with exhaust gasses.
Since it is mixed with exhaust gasses, it will be hotter than water that normally exits through the tell-tale.


It is likely your motor doesn't have without a proper tell-tale.
Force did not put one on older models.
But I know the 1995 models did have one.

Here is a video of one.

https://www.youtube.com/watch?v=c4csD_ySrgQ

So, advice remains the same.
Replace impeller and thermostat and water flow will likely increase and keep engine temp down so the alarm does not activate.

 

[jerryjerry05]

Get a heat gun and take it for a ride.
The 2 holes are a pressure relief hole.
Most exhaust and water exits through the prop.

Is the motor original to the boat?
Is it mounted right?
The wrong height can cause the problem.
​The cavitation plate should be even with the bottom.

You can test the sender.
Analog test meter and a pan of cold water on the stove.
​Hook the leads to the sender and then turn the ohms scale on the meter and then turn the stove on.
​Oh yea you'll need a thermometer too to check the temp.

 

[ObiwanKenobi]

OK, just wanna follow up with how things turned out. First of all, thank you to everyone for your replies and help. Let me acknowledge some folks real quick. If anyone else has this problem, they'll benefit from these acknowledgements:
pnwboat boat was right when he asked if the problem had only recently started to happen. It had, and that was my first clue. And the fact that the blades of the impeller shouldn't be curved is also true.
Nordin was right with a lot of stuff, but the following was particularly applicable: "I have change many impellers and many of them have looked good BUT it has not pump enough water to cool the engine properly."
jerryjerry05 was spot on when he said I had gone about doing everything backwards. Water pump first, then everything else.
roscoe was right when he clarified the whole tell-tale misunderstanding. Don't have one lol. And this bit was very accurate as well: "Replace impeller and thermostat and water flow will likely increase and keep engine temp down so the alarm does not activate."

So, here's the solution:
The problem ended up being two-fold.

First problem: Extreme build-up of marine growth on the bottom of the boat. There was a legit REEF under there. I hadn't used it in about a month while I had waited for my new stator to arrive. (True bonehead move to not keep it clean. Now I clean it every Wednesday.) Most of the growth wasn't visible from the surface. So the boat legit had NO CHANCE of getting up on plane. So part of the reason why it only overheated at higher speeds was because there was nothing but thin, churning water around the water intake in the lower unit. That problem was exacerbated by the sheer amount of growth underneath. There was so much, it was as if the motor was--relatively speaking--mounted an inch and a half higher than it actually was, resulting in hole in the water when I tried to accelerate. So I cleaned it off. That took HOURS. After cleaning it, the problem got much, much better, but it wasn't totally fixed. On to the impeller...
Second problem: the impeller. It was nearly perfect. There was only a very, very slight bend in the blades when I took it out for inspection. I'm talkin about a bend so slight that you have to have the impeller at *just* the right angle to even see it. There was also an extremely small crack at the base of one of the blades, maybe about 2 mm long. Every boater, mechanic, etc. I showed it to swore it was absolutely fine. They had seen impellers that were missing a blade work fine, and mine was 100 times better than most they saw, etc. etc. But I heeded everyone's advice here on the forum and got a new one. They are impossible to come by in Belize, so I ended up using one that's made for a Yamaha motor that was pretty much exactly the same size. The hole for the shaft was about a millimeter too small. (Gonna order another one and just wait the month and a half it's gonna take to get here.) Got it on there, and, BOOM, problem fixed. It's been running perfectly ever since.

Lessons learned:
1. Keep the bottom of your boat clean.
2. Start with the pump then work your way up when diagnosing over heating issues.
3. The sensor indeed does not usually go bad. Trust it.

Thanks a lot, everyone. Maybe I'm sick in the head, but I actually enjoyed doing all of the investigating and work, etc. Now on to the next issue...

 

[pnwboat]

Well..... glad you were able to get to the "bottom" of this and figure out the problem LOL!

Next problem......where and how many Belikins should I have????

Happy boating!