120 force still over heating HELP

[R A & 3]

I have 1990 Force 120 it over heats after idling about 10 minutes. Here is what happened. I took it out last summer and a wire to the charging system rubbed against the fly wheel and threw off the timing and everything else. I took it out again and it over heated but the alarm never went off. It blew a head gasket and scored the top cylinder but the mechanic that looked at it said the cylinder and wall were ok. The head where the water flows has been cleaned and the head gasket, thermostat, impeller, buzzer and sending unit and the rubber stoppers inside the head have been replaced. Water flows good through the motor and comes out hot but the over heat alarm still goes off when it is trimmed down all the way. When you trim it up a little the alarm turns off. The mechanic cannot figure it out and I am at a loss any help would be much appreciated.

 

[Frank Acampora]

Re: 120 force still over heating HELP

Does the trim have a position indicator? If so, check for a short between wires someplace in the loom or under the dash.

 

[R A & 3]

Re: 120 force still over heating HELP

Don't have a position indicator and i can't find a short anywhere.

 

[john from md]

Re: 120 force still over heating HELP

It sounds to me that the reason your overtemp warning is going off is because the intake ports are getting deprived of water. There are several reasons for this but in order to make a determination, I need to know the following.

Where is your anti cavitation plate with relation to your keel? Ideally, it should be even with the keel.

Do you have a doel fin or something like one on your engine?


Regards,

John

 

[R A & 3]

Re: 120 force still over heating HELP

The anti cavitation plate is even with the keel this is the origenal motor with the boat the lower unit was replaced with a new one 3 years ago. I do not have any added fin or tall on the boat. the boat has not been off the trailer for one year. Every time I got the boat back form the mechanic he told me he ran it in his tank for about 30 mins with no problem but when I would take it to the lake and back it in and just let it run at idle the alarm would go off and when I would tilt the motor up a little it would stop going off. the mechanic could not figure this out and contacted Mercury and they never answered him. I sent them an email and they told me to take it to a certified Mercury mechanic which he was.

 

[john from md]

Re: 120 force still over heating HELP

When the overtemp alarm goes off, is the exhaust plate hot? Run it with the cowl off and when the alarm goes off, stop the boat and put your hand on the exhaust plate. It should be cool enough to keep your hand on it.

This will let us know if we are dealing with a real overheat condition or an indication problem.

John

 

[R A & 3]

Re: 120 force still over heating HELP

I want to think everyone for their input. It will be Tuesday before I can get the lake and try running it. Just so I don't put my hand in the wrong place the exhaust plate where is it? Is it the two holes where the water comes out of the back of the motor?

 

[john from md]

Re: 120 force still over heating HELP

The exhaust box or chest is on the right side of the engine towards the rear when looking at the engine from in the boat. It has a cover plate with many bolts around its perimeter.

John

 

[R A & 3]

Re: 120 force still over heating HELP

Well I don't think it is an electrical problem ran the boat at the lake today. Idled for 3 min 30 sec and the over heat alarm went off. The exhaust plate was hot but not to hot. I could put my hand on it but I did not want to keep it there for long. I tilted the motor up and the alarm did not shut off like the mechanic has told me. Any ideas on what this could be? Anyone out there had a similar problem? Thanks.

 

[john from md]

Re: 120 force still over heating HELP

Pull the thermostat and run it without it. If it runs ok, leave it out. If it does run ok, then it means there is some blockage in the water system. Could be anything including old gasket material stuck in the head passages.

If you get enough flow without the thermostat, you should be ok.

John

 

[R A & 3]

Re: 120 force still over heating HELP

Thanks John that will be the next thing I do.