120 Force Cooling

[imported_bowfisher]

Late 90's 120hp Force.

Runs great, but will not cool consistantly. I have replaced complete w/pump assembly, head gasket and removed thermostat thinking it was not opening. Motor will stay cool at idle, get on the throttle and it will run about 200 yards and overheat? Seems like the water pump slows down and only shows a trickle coming out of the water indicator hose. Thought it was plugged with sand so I removed lower unit, flushed the system and replaced head gasket. I have not removed the side jacket (exhaust cover) to inspect as of yet.

Thoughts?

Thanks!

 

[pnwboat]

Re: HELP!!!!!!!! 120 Force Cooling

Re: HELP!!!!!!!! 120 Force Cooling

I would look at the exhaust cover next. There is a water passage in the head too, but it's larger and not as easily plugged as the exhaust cover. Just be careful when removing the bolts in the exhaust cover. If they're corroded, you may end up breaking them off.

 

[imported_bowfisher]

Re: HELP!!!!!!!! 120 Force Cooling

Re: HELP!!!!!!!! 120 Force Cooling

Whats next? Removed exhaust covers, a little sand in there but not much. Replaced the two gaskets I thought may be leaking exhaust into the water jacket. Fired it up and same thing, low water pressure. Started getting hot quickly. Removed thermostat again and restarted to have it not over heat as fast, but still water was HOT coming out of the tell tale and exhaust ports on the mid section. Just acts like low water pressure. I flushed motor backwards with garden hose, nothing came out as if it was plugged. THOUGHTS? ANYONE?

 

[j_k_bisson]

Re: HELP!!!!!!!! 120 Force Cooling

Re: HELP!!!!!!!! 120 Force Cooling

Don't mean to be a smart *****, but did you impeller have a flat or key to locate it to the drive shaft? I have left a ke out once myself. The imeller will spin but the pressure will be low. Also how about the metal cup in the housing for the impeller. Was that lined up properly to the housing. Is the exit hole lined up correctly. Or is the rubber bushing for the water tube inserted correctly. Double chack the water pump and installation. Something must not be right is you checked everything else.

Worst case leave the lower unit off and hook up the garden hose to the water tube and run it. If the temps stay down, put the thermostat back in. Re check with hose, if still ok then its you pump. Eliminate each component in the water system by bypassing them.

Do not run too long without the thermostat. You could get a cold seizure of the block.

Also seeing you have over heated it, check compression. Might have thrown a ring or a scored a piston wall. Did it with my 1991 120 force.

 

[imported_bowfisher]

Re: HELP!!!!!!!! 120 Force Cooling

Re: HELP!!!!!!!! 120 Force Cooling

OK, hooking it up without the l. unit on..... how does one do this? I have seen where it has been done before in other posts. Also to answer the question, yes the drive key is in place. I even checked the hub in the impeller to make sure it isnt spinning in the rubber.
One thing I failed to mention, it seems that the cylinder head itself is getting the hottest. The water jacket on the block seems to stay lukewarm, but the head gets hot.
Im still stumped as to why when the RPMS go up the stream does not get stronger.


THANKS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[pnwboat]

Re: HELP!!!!!!!! 120 Force Cooling

Re: HELP!!!!!!!! 120 Force Cooling

Keep in mind that sometimes the hose does not supply enough water for the cooling system to operate like it should. If you can get a tub that is at least 2 feet deep, you might want to try that. Of course you could always drop the boat in the water. Depends on what best suits your situation.

If it continues to get hot, I'm assuming that the over-heat buzzer is going off? Here are some pictures of how the water flows through the head. After you remove the head, there is a "head cover" that is held on with four bolts right next to each spark plug. Remove these and it will expose the water passage in the head.

Postion of the 4 bolts.


Head with head cover removed.


Water enters the water passage in the head past the thermostat here.


Water exits the head here and gets dumped into the lower unit.


Check for any blockage here, but before you take the head off, make sure you are getting enough water to the motor. Depending on your house water pressure, it may not be enough.

 

[imported_bowfisher]

Re: HELP!!!!!!!! 120 Force Cooling

Re: HELP!!!!!!!! 120 Force Cooling

Ok thanks - thats another angle I have not taken (removing the head cover from the head) When I replaced the head gasket I did not notice any major blockage around any of the ports, but possibly its blocked internally under the cover. Just as an FYI I have actually been running the motor in a tank, not on the hose. I think I commented earlier, when I backflushed the system I put the garden hose tightly into the thermostat housing, there was a SOLID stream coming out of the water pump tube with the l.unit removed. Yes the hot horn is sounding when it gets hot.

I failed to mention this motor was brought tome last year packed full of sand, the impeller housing was jammed full of sand. Worse than i have ever seen in 15 years.

Thanks a million for the advice!

 

[pnwboat]

Re: HELP!!!!!!!! 120 Force Cooling

Re: HELP!!!!!!!! 120 Force Cooling

Sounds like the water passage from the thermostat to the water pump is OK. Next would be to check the water passage from the thermostat through the head and out the lower leg. This is kind of strange because most of the times the blockage is before the thermostat. I haven't seen any after the thermostat. Maybe part of the rubber thermostat "O" ring came off or part of the gasket??? Who knows, but I think it's worth a check.

 

[imported_bowfisher]

Re: HELP!!!!!!!! 120 Force Cooling

Re: HELP!!!!!!!! 120 Force Cooling

Is there anything where the powerhead is mated to the exhaust housing that may be creating the seemingly weak flow of water? Like I said it appears to have good flow with hose pressure from the thermostat down.

Im definately going to check the head cover. Just odd too me that the head is about the only place thats getting too hot.

 

[pnwboat]

Re: HELP!!!!!!!! 120 Force Cooling

Re: HELP!!!!!!!! 120 Force Cooling

Nothing that I can think of. The water flow from the pump goes up the tube to the bottom of the block and into the exhaust cover. From there it goes to the water jacket down the left side of the cylinders then up the water jacket on the right side of the cylinders to the thermostat. From there is goes down the water passage in the head and out through the lower end.

Make sure the little rubber tubes in the water jacket are in place when you take the head off. It's circled in yellow. There should be 3 of these all together between each cylinder. These divert the flow of water down the left side of the water jacket around the cylinders and up the right side to the thermostat.

 

[imported_bowfisher]

Re: HELP!!!!!!!! 120 Force Cooling

Re: HELP!!!!!!!! 120 Force Cooling

Thanks guys, will be working on it tonight, will check back in the AM with hopefully good results!

 

[Justinde]

Re: HELP!!!!!!!! 120 Force Cooling

Re: HELP!!!!!!!! 120 Force Cooling

Hi

My 1988 125 was doing the same. I replaced the exhaust plate out of necessity- mine was corroded- and replaced gaskets etc. My exhaust plate water passages were completely corroded and blocked. I replaced the water pump, and now she overheats on the hose. It ran very well for about 1/2 an hour, then now the overheat buzzer comes on after a couple of minutes, with the head getting the hottest. My compression is still great ( unchanged). Next is to test her on the actual water- I just have a feeling that the hose is not supplying enough water to the engine. Whenever I am on the water- even at idle- water pressure and flow is noticebly higher than when stationary on the hose. I am going to fill her up, and take her for a spin. If there is a blockage, I am going to do my best to blow it out with sheer grunt The weather hasn't been great in Sydney the last couple of weeks, but this weekend is looking great for a test. I'll let you know how it goes.

 

[imported_bowfisher]

Re: HELP!!!!!!!! 120 Force Cooling

Re: HELP!!!!!!!! 120 Force Cooling

First and foremost thank you to all who helped with the problem I was having. I finally found the problem yesterday evening. About 20 pebbles of sand had become lodged on the opposite side of the water diversion tube on the second cylinder, essentially slowing flow enough the motor was over heating. I removed the head thinking there would be a bunch of sand behind the head cover. I ensured it was clear by running water through the head. I then did some further water flow testing while the head was off on the engine to find flow to be clear and no restrictions. Upon performing this I noticed a grain of sand between the cylinder and water jacket. I plucked it our to find another, and then a complete line of pebbles parallel with the cylinder in side the water jacket. The pebbles were acting just like the rubber deversion tube on the opposite side of the cylinder. I knew right then I had found the problem. Success!!

Thanks again for all the ideas and advice. I hope I may be able to return the favor!

Pat

 

[pnwboat]

Re: HELP!!!!!!!! 120 Force Cooling

Re: HELP!!!!!!!! 120 Force Cooling

Those pesky pebbles! Glad you were able to get it straightened out.