Temp warning alarm buzzer sounding- requesting info on how to troubleshoot.

[JCStorey]

Hello all, thanks for taking the time to read...

I have a 1994 70hp Mercury Force 2-stroke outboard on a Bayline 1600 Capri. Just bought the boat a couple months ago, and it's my first boat.

Three times, all when running a WOT or close to WOT the temperature alarm has gone off(at least, I'm assuming it's the temp alarm from reading other threads. It's a continuous high-pitched beep coming from under the dash.). The alarm ceases to sound only when I turn the key off(idle and neutral do not affect it). After I leave the boat off for about a minute the alarm dies down and stops. Immediately after the boat starts up just fine and will run again without a problem.

From perusing the threads I suspect that this is the temperature alarm.

I also suspect that this is noy simply a short or electrical malfunction, as the alarm is sounding in similar scenarious each time.

I had the marine mechanic check the impellar(twice), and they said that it was fine. The boat also had a full tune-up($1000 worth) right after we bought it.

So my question, coming from a mechanically naive land-lubber, is this:

What are some ways that I can troubleshoot this at home and determine if in fact the engine is overheating? Am I stupid to try? Please help this proud soul out!

Thanks!
josh

 

[Robert D]

Re: Temp warning alarm buzzer sounding- requesting info on how to troubleshoot.

Go to Harbor Freight and buy one of their laser temperature guns. Usually on sale for around $29.99

Point it at various locations on the engine to see what the real temps are when the alarm goes off. Have you replaced the thermostat yet? Might be as simple as that. Top of the engine in the back, a couple screws to take out......drop it in a pan of water with a thermometer and see what temp it opens at. While you're at the back of the engine, look for a single wire going to a round object on the head. Follow that wire to the buss connection, make sure it's not grounding out. If thermostat tests okay, check the sending unit wire to see if it is grounding out somewhere. If all is okay, then replace overheat sending unit. If it still goes off and you've verified with the laser temp gun that it is in fact overheating.....it's almost time to take things apart and look for a piece of the old water pump impeller lodged/blocking the cooling system. Only other things I can think of:
1. Running to lean a setting on the carbs? Maybe a partially plugged jet, causing it to be too lean?
2. Correct fuel/oil mix? (50:1)
3. Might want to do a compression check as well.

 

[fucawi]

Re: Temp warning alarm buzzer sounding- requesting info on how to troubleshoot.

Dont go to Harbour Freight and buy anything ...take out temp overheat switch and wire up to a small bulb and battery or an ohm meter ....put in a kettle with a thermometer and turn on kettle ..see what temp it switches on at ......that will eliminate the swich and you will know if its overheating or not .

 

[john from md]

Re: Temp warning alarm buzzer sounding- requesting info on how to troubleshoot.

This can be caused by several scenarios. 1) if you have one of the black thermoswitches, it could be going off at too low a temp. The red thermoswitches were more reliable. Good luck in finding one, maybe on fleabay. 2) there could be something floating around in the cooling jackets. I have seen scale floating around the cylinder jackets intermittantly blocking the water usually at high rpm. You need to take the head off to check for this. I have also seen a 'lost' rubber gasket from the thermostat do the same thing.

The suggestion about the thermo gun is a good one. I am a professional mechanic and I keep two in my tool boxed and one in my boat tool kit. If you compare your cylinder heat readings when the engine is running good, you can find the hot (or cold) running cylinder when you have a problem. This is great for finding intermittant CD switch boxes.

In any case, if you are running hot, you will start transferring aluminum from your pistons, starting on the top down, which will eventually cause the engine to quit. That means boring cylinders and replacing pistons. Don't wait, find the problem now.

 

[JCStorey]

Re: Temp warning alarm buzzer sounding- requesting info on how to troubleshoot.

Thanks for all the replies- you've given me a starting place, to be sure!

josh

 

[surfsalterpath]

Re: Temp warning alarm buzzer sounding- requesting info on how to troubleshoot.

......

...similar issue. 1995 70HP force. New plugs, new impeller.
Is the thermo switch(get the red, not black) and the thermostat the same thing?
Is the thermo switch inside the engine or on the alarm?

Our issue is the alarm sounds when we are going slow and the RPM's are very low.
The pee stream is weak. When we rev up and start moving the pee stream gets
much stronger and the alarm will cut off.
I am assuming the water flow through the cooling part of the engine is strong enough
to do its job. Are your tips from above the same in this scenario?


When I asked our marina to replace the water pump all they do is replace the impeller.
Is there an actual pump that needs replacing also?

Thanks! I really enjoy reading these threads. You guys are wonderful @ assisting us
newbees in figuring this stuff out!

 

[Robert D]

Re: Temp warning alarm buzzer sounding- requesting info on how to troubleshoot.

Normally the impeller is an adequate repair for the pump. Sometimes the plastic housing is cracked, scored, or not useable. You may have an issue with blockage in the cooling system; Perhaps the water tube didn't seat correctly when installing the lower unit; The key that holds the impeller may be excessively worn, allowing it to slip; or it could simply be a bad temperature switch or thermostat. Using the above referenced laser temp gun, you can start the engine and let it idle. If should stay well under 180 degree's. You can watch it as it warms up, pointing the laser at the side of the cylinders and head. If the alarm goes off and you're not even close to being hot, there's your answer. It it warms up to 180 degree's and higher, shut it down and start looking for another problem. My Force 150 never gets over 170 degree's with prolonged idle speed, and it does have a reduced water flow at idle. Anything over idle it really spits the water and stays about 165 degree's. I installed a sending unit and dash gauge to watch it.....I'd never want to rely on the warning buzzer.

 

[fucawi]

Re: Temp warning alarm buzzer sounding- requesting info on how to troubleshoot.

temp switch that operates the alarm is screwed into the head with wire attached..the thermostat is inside the head under a cover...