Force 120 overheating.

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Brooksyde

Cadet
Joined
Sep 13, 2003
Messages
15
I have a 1991 120hp Force on a Bayliner 2002. The engine runs very sweet up to about 28mph. Above that speed the overheat siren comes on within a few minutes. Kept below 28mph no problem. The impeller has been replaced although it seemed ok.The thermo was damaged but the problem was exactly the same when run without a thermo.Water coming from the two top ports appears to reduce as speed is increased over 28mph. Anyone suffered the same problem/ any ideas please?
 
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Fouled Plug

Ensign
Joined
Jun 29, 2001
Messages
935
Re: Force 120 overheating.

I wonder if the water pickup on the lower unit is coming out of the water a bit at high speed. Has this engine/hull combo gone faster in the past without overheating?
 
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Brooksyde

Cadet
Joined
Sep 13, 2003
Messages
15
Re: Force 120 overheating.

Thanks Fouled Plug. The engine/boat combo has previously worked well at max speed.
 
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The Marine Doctor

Commander
Joined
Jul 25, 2003
Messages
2,177
Re: Force 120 overheating.

Check the compression of the engine...we could have the start of a blown head gasket.<br /><br />TMD
 
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Brooksyde

Cadet
Joined
Sep 13, 2003
Messages
15
Re: Force 120 overheating.

Thanks Marine Doctor, I will have the compression cheched next week.<br /><br />Peter
 
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Brooksyde

Cadet
Joined
Sep 13, 2003
Messages
15
Re: Force 120 overheating.

Thanks Marine Doctor, I will have the compression cheched next week.<br /><br />Peter
 
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force01

Petty Officer 2nd Class
Joined
Aug 12, 2003
Messages
152
Re: Force 120 overheating.

I read your post, do a compression test like the Dr. ordered. one of the possibilities other than head gasket would be exhaust plate gasket under high rpm's this could be leaking enough water to cause the motor to over heat this could also cause steaming of the exhaust and cause poor performance. good luck, Bret forceparts@yahoo.com
 
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TopKick

Cadet
Joined
Sep 1, 2003
Messages
9
Re: Force 120 overheating.

I also have a 120hp Force (1999 year). Mine does the same thing at 38mph. I finally realized that the rpms were at or above 5000. Seems like everytime I run at 5000 rpms for 30 secs or more the buzzer goes off. I stop the boat and let the engine idle for about 30 secs and the buzzer will quit. I think the max rpms are 5250. I just keep mine under 5000 and it doesn't overheat. There is also water coming out of the pee tube the whole time.<br /><br />What is your prop pitch? Mine is 19 and I guess my top speed with that is 38mph without overheating.
 
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Brooksyde

Cadet
Joined
Sep 13, 2003
Messages
15
Re: Force 120 overheating.

Thanks TopKick. My outboard is not fitted with a rev.counter so I cannot tell at what r.p.m. the overheat starts.This problem has only started to occur recently, previously it ran flat out with no problem. I will check the prop pitch when I next go to the boat and let you know. It could be some time before I am able to do this, at least 3 weeks.<br />Regards.
 
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pasprintfan

Cadet
Joined
Sep 23, 2003
Messages
6
Re: Force 120 overheating.

You did put a new thermostat back in,, right? <br />without it the water can't stay in the engine long enough to cool properly, especially at high speeds, this is what I have learned from cars, someone correct me if I am wrong
 
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scotiany

Senior Chief Petty Officer
Joined
Aug 3, 2002
Messages
749
Re: Force 120 overheating.

LocalBoater, actually it's the opposite. Without the thermostat restricting water flow, the engine won't warm up ehough to properly atomize the fuel charge. Rough running and fouled plugs will be the result.
 
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Brooksyde

Cadet
Joined
Sep 13, 2003
Messages
15
Re: Force 120 overheating.

I have had the boat out of the water over the winter and am now trying to again address the problem of overheating. I have removed the censor and tested it in hot water. It activates at 68 degrees C and shuts down at 64 degrees C. Since the thermostate opens at about 60 C it seems to me that the censor might be faulty. Does anyone know at what temperature the censor is supposed to set off the horn, please?
 
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doggies3

Cadet
Joined
Feb 24, 2002
Messages
12
Re: Force 120 overheating.

Brooksyde, I have an '89 Force 125 with a similar problem, but I was getting the overheat buzzer if I idled too long. I changed the impeller even though it looked good, checked the compression and thermostat, blew out all the passages I could with air, and seemed to get the temp. down just enough to stop the buzzer. I am still putting our a cloud of steam (especially on a cold morning, you know - 60 degrees in CA)at idle speed and don't know what else I can do. I do know that these Force motors can't take excessive heat, so I would like to get it running cooler again before I blow it up. Anyone got any other idea's? It has been a great motor other than this problem.
 
OBJ

OBJ

Supreme Mariner
Joined
Dec 27, 2002
Messages
10,161
Re: Force 120 overheating.

Guys....not knowing how long either of you have owned your rigs or if the problems are new since you've owned them, I'll ask a couple questions.<br /><br />How high on the transoms are your engines mounted? It is possible to mount an engine so high that when you come up on plane, you lose water to the pump.<br /><br />Either of you run in salt water? If you do, there is always the possibility of salt build up in the cooling water passages.<br /><br />Keep posting, the guys here will try and help.
 
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Brooksyde

Cadet
Joined
Sep 13, 2003
Messages
15
Re: Force 120 overheating.

Fror those who have kindly treid to help me with the overheating problem you might be interested to knoe that I think I have solved it. I ordered a new sensor a tested it. The new one opens at 78 degrees C (10c higher) and closes at 64c. I will not be able to try it on the water for a couple of months (British weather) but it looks like the problem was quite simple in the end. Thank you all for your help.
 
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Brooksyde

Cadet
Joined
Sep 13, 2003
Messages
15
Re: Force 120 overheating.

For those who have kindly tried to help me with the overheating problem you might be interested to know that I think I have solved it. I ordered a new sensor and tested it. The new one opens at 78 degrees C (10c higher) and closes at 64c. I will not be able to try it on the water for a couple of months (British weather) but it looks like the problem was quite simple in the end. Thank you all for your help. (reposted with typing errors corrected, sorry)
 
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moff1959

Cadet
Joined
Nov 23, 2003
Messages
9
Re: Force 120 overheating.

Hi Brooksyde what part of Cheshire are you from ? I moved from Manchester UK to Richmond Virginia 2 years ago and I wouldent go back there for a gold clock by the way this is a great site keep it going<br /><br />cheers mate<br /><br />Paul
 
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Brooksyde

Cadet
Joined
Sep 13, 2003
Messages
15
Re: Force 120 overheating.

Hi Moff 1959. Thanks for your message. I live at Whitegate near Northwich and keep the boat near Pwllheli during the summer, we have a place down there. Unfotunately the weather is not always as kind as it might be but it was good last year and we spent plenty of time on the water. Let me know what life is like where you are.
 
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moff1959

Cadet
Joined
Nov 23, 2003
Messages
9
Re: Force 120 overheating.

Life is great here, I always fancied owning a boat but its to expensive in the UK and very affordable in the USA, I live about 4 miles from a boat launch on the river James we spend most of our time on the James or at Chesapeake bay. We are going to try a few of the large lakes in Virginia this summer, anyway bye for now and happy boating<br /><br />cheers<br /><br />Paul
 
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