1990 120 hp force overheat

[bozgolf]

I have a 120 hp force and have had problems with the overheat buzzer going off. The first time was about 2 yrs ago and I replaced the impeller and the old one looked good though it was the original. Then last year it went off again so I changed out the thermostat. Then a couple of weeks ago it did it again. Each time the buzzer sounded the boat was moving but at idle in a no wake zone and it does not do it all the time. I went out last weekend and there was no problem. I have done some reading here on iboats and was considerring looking at the water tube for cracks. My questions are: 1. How do I reomve the tube, I have removed the lower unit? 2. Is this the right direction? 3. Does anyone have any other suggestions?

 

[pnwboat]

Re: 1990 120 hp force overheat

I wouldn't go through the trouble just yet of removing the water tube. If my memory serves me right, I think you have to remove the power head to get the tube out. Can't remember 100% for sure though.

Anyways, there are several other things that you can check before going that route.
1. Bad head gasket. Perform a compression test.
2. Clogged water passage. One spot where debris may collect is the water jacket in the exhaust cover (held on with 27 bolts) #27. Also check #26, the stainless steel exhaust plate for cracks. The exhaust plate is exposed to the hot exhaust gas exiting the cylinders. It's often pretty warped. Don't let this alarm you. As long as it's not cracked, it should be OK.



http://www.boats.net/parts/search/Merc2/Force/120%20H.P.%20%281990-1994%29/0E000001%20THRU%200E093699/CYLINDER%20BLOCK/parts.html

 

[N Wolf]

Re: 1990 120 hp force overheat

I had the same thing happen to me and it was a supper easy fix. The low speed mixture screws were set to lean. Open them up a bit and Ill bet the problem goes away. Since it doesnt happen all the time they are probably close so it wont take but mabee a quarter turn.

 

[bozgolf]

Re: 1990 120 hp force overheat

I did a compression test.
#1-90
#2-100
#3-95
#4-85

Another question I have is the 2 water outlets how much water should come out those whith muffs or in the water at the boat launch or on plane? Are there any ways to check for a clogg with out pulling the exhaust cover?

 

[daffidad]

Re: 1990 120 hp force overheat

I have the same question on a Force 1992 150. even on water at idle it is a very slow output but when I hit the throttle she shoots out fine. I am replacing a piston on it now so I want to check all causes of a melted number 2 cylinder.

 

[jerryjerry05]

Re: 1990 120 hp force overheat

Daffidad,They don't like it when you ask questions on anothers thread.You should start your own.
Bozgolf,You can't remove the tube from the lower.Since you have the lower off check the pump housing and wear plate.If it's got lot's of grooves it might not be pumping enough water.The tube could be pluged with debris or pieces of an old impeller.If the overheat goes off and it seems to be pumping fine(most of the water exits through the prop area)The holes on the back of the housing are for the pressure relief/bypass.Some water will come out there.
Under the sensor could be getting a bad ground.You run in fresh water and there shouldn't be a problem with corrosion in the water jacket.
DAFIDAD:1 piston going bad could be a water circulation problem.Or cheap oil.Excessive carbon,too much oil.The carb air screw not set right.A bad head gasket.Timing set wrong.J

 

[pnwboat]

Re: 1990 120 hp force overheat

Those compression numbers are not very good. It will run, but you will not get optimal performance. I would be inclined to perform a de-carb to see if this has any affect. Possibly changed the head gasket too.

Only time you should see water coming out of the two holes on the back is at idle or slightly above idle. These are the "idle relief exhaust" holes. Just relieves exhaust back-pressure when the lower unit is deep in the water at idle speed. Once you get up on plane, the lower leg sits up higher in the water. The water should be at or just below the cavitation plate. This reduces the exhaust back pressure so all of the exhaust and cooling water exits the snout just above the propeller.

You can try back flushing the block through the thermostat opening, but you have to take the lower unit off. Not much will pass by the impeller so you have to remove the lower unit to allow any debris to come out of the water tube that feeds the block.

 

[jerryjerry05]

Re: 1990 120 hp force overheat

Yea get a good compression tester.Remove all the plugs and open the throttle all the way.Then post the readings.J

 

[OldNBold51]

Re: 1990 120 hp force overheat

I did a compression test.
#1-90
#2-100
#3-95
#4-85

Another question I have is the 2 water outlets how much water should come out those whith muffs or in the water at the boat launch or on plane? Are there any ways to check for a clogg with out pulling the exhaust cover?

those #'s are way low. You might want to verify those again with a different tester and see what you get.

 

[bozgolf]

Re: 1990 120 hp force overheat

Removed the lower unit and thermostat and back flushed through the block and saw some ddebris come out. When I did the compresion test I did not have throttle open it was closed. I am going to try it again this weekend. I am going to also going to try to the low speed adjustment also. Thank you everyone for all the input suggestions it is much appreciated

 

[92rslt1]

Re: 1990 120 hp force overheat

yep, throttle must be open to comp test.

 

[pnwboat]

Re: 1990 120 hp force overheat

If those compression numbers don't come up, I would be tempted to do a de-carb and hopefully free up stuck rings.

 

[92rslt1]

Re: 1990 120 hp force overheat

my guess is at least 140 or more when he opens the blades and test it. Im surprised he got 80 with his blades shut