Overheat alarm

[JoeCrow]

I have a 1986 Force 125 on a 19' Bayliner, 13 x 19 prop
The engine runs great all through the RPM range
The compression is 125 to 130 on all cylinders and it starts right up
But at WOT the alarm goes of after 2 or 3 minutes
I've replaced the waterpump impeller, the housing and the thermostat
It seems to be pumping water well, but after a few minutes at WOT,
the overheat alarm goes off
If I bring it down to half throttle, the alarm silences and it runs fine
I can run it as long as I want at 1/2 throttle, but as soon as I take it up to 3/4 or full throttle
The alarm goes off
Any suggestions?
Thanks

 

[john from md]

Re: Overheat alarm

Joe,

Do you have tabs or a hydrofoil on the boat? If so, what kind?
Is it manual or hydraulic trim?
If manual, what hole is the pin in?
Does the boat plane? At what speed?
What RPM and speed does the alarm go off at?
Do you have a tell tale on the engine?
When was the water pump rebuilt?
Are you mechanically inclined?
Do you have an engine manual? Which one?
Does the boat now or before ever had damage below the water line?

Hang tight and well work this out as these are simple engines.

John

 

[pnwboat]

Re: Overheat alarm

You may have some type of blockage in the water passage. I had a similar problem. Apparently a piece of the impeller broke off and lodged in the water tube or in the block. To get it out, I had to drop the lower unit, remove the thermostat and backflush the system with a garden hose. You may have to use a rag to get good seal around the end of the hose when you insert it into the opening where the thermostat was. As soon as I did that, a piece of rubber popped out of the water tube. Problem solved.

 

[JoeCrow]

Re: Overheat alarm

Thanks for the help guys,
I'll add the needed data as best as I can
There's no hydrofoil, everything is factory
It does have power trim, I just power the trim to the lowest setting to get on plane and leave it there
The boat planes fine at about 15 to 20 (the speedo is questionable)
The speedo reads about 30mph when the alarm goes off
I ordered a mini tach for it last week as of today it still hasn't arrived
By telltale, do you mean the 2 peeholes just below the powerhead?
If so, yes and a good flow of water comes out of both of them
The water pump was rebuilt about 2 weeks ago
I thought I was mechanically inclined until I did the pump
The pump job was easy.....
Then I couldn't get the lower unit back on and took it to a mechanic
He checked the pump, changed the thermostat and reinstalled the L/U
I have a Seloc manual
As for damage, there was a chip on one of the fins of the prop,
but everything else looked good below water
I'm starting to wonder if the temp sender or alarm could be bad?
Could it be going off at a temp below where it should?
I also went from a 17p to a 19p prop to try and lower the rpm's
But that didn't help
I appreciate the replies and help,
Thanks,
Joe

 

[gregmsr]

Re: Overheat alarm

Yes, although not likely, the sending unit could be giving false over-heat alarms. There is a way to test the sending unit. Directions to test it should be in your repair manual. Or, aim a temp gun at the engine while the alarm is sounding. See if it is actually hot.

 

[GrindKore]

Re: Overheat alarm

You can always use the "hand test". Basically under normal operating conditions and properly operating cooling system engine surface temperature should feel warm to mildly hot, defiantly not hot enough to to burn your hand. After running at WOT and getting a buzzer, shut down the engine and carefully tough the head area around the spark plugs. If it's too hot to hold your hand more than 1 second, it is likely the cooling watter circulation issue and it has to be fixed ASAP. If the motor is warm, but you have no problem keeping your hand on it, than it's the buzzer sensor.

Just be carefull, and make sure you shut off the motor.

 

[JoeCrow]

Re: Overheat alarm

I'll take it out this weekend and try the physical heat test
Fortunately I have an infrared gun and won't have to sacrifice any digits during testing
My tach also arrived this afternoon and that may shed some light on my problem
I also ordered a sending unit for the alarm, just in case
Thanks to all,
Joe

 

[dorelse]

Re: Overheat alarm

Well, in my case, my thermostat wasn't operating properly. I could do the 1/2 throttle thing too, and it would be ok...but I also boat in fairly cold water so that can mask cooling issues a bit. (Usually 68-75 degrees.)

Anyway, I 'cooked' the thermostat in hot water to make sure it was opening correctly, which it wasn't, but the hot water seemed to unfreeze it. It looked like a bunch of mineral deposits weren't allowing it to operate properly.

Once I did that and cleaned off all the gunk that was on it, problem solved.

 

[JoeCrow]

Re: Overheat alarm

After reading every available manual on these motors, I found this in an old Force repair manual #1100
I posted a scan from page 6-10 but if it's not clear, what it says is there were 3 different sending units made for these motors
All three were replaced with a new higher temperature sending unit that should be used in all these motors
I ordered a new "red" sender to replace the "white" sender I now have
Hopefully this will solve my problem and maybe save someone the aggravation I've gone through
Thanks for all the help
Here's hoping it solves the problem
If not look on e-Bay as this motor is going away if this doesn't solve the problem
Thanks again,
Joe

 

[john from md]

Re: Overheat alarm

Joe,

Who did you order your temperature sensor from? I need a new one also.

John

 

[JoeCrow]

Re: Overheat alarm

I'm getting it from a place that's local to me here in Jersey

Pennsauken Marine
5910 Rt 130 S
Pennsauken, NJ
08105
856-662-1002

I haven't received it yet,
but he says it's ordered
I'm still leaning very hard towards buying a new Merc Optimax 115hp

 

[john from md]

Re: Overheat alarm

I know exactly where that is as I was raised in South Jersey. How much do they go for?

John

 

[JoeCrow]

Re: Overheat alarm

He said it shouldn't be too much......?
Not sure if that's by Bill Gates or Poor Willy's standards though
If you want, I can ask him to get 2
Rather than clog the board, you can e-me at
joecrow@joecrow.com
If you prefer
Joe