Overhearing again

[Michael Lang]

1991 70 hp force
I have gone full cycle on overheating causes and still have overheat buzzer warning after Two to Five minutes of operation.

Replaced lower unit driveshaft seal, water pump bottom plate, gaskets and impeller ( stainless housing looks good).

Pulled power head off, removed exhaust plate replaced gaskets and cleaned complete exhaust chest, removed head,
and checked water jackets and cylinder walls and pistons (looked good) replaced head gasket and torqued per service
manual.
Removed bottom spacer plate copper pipe (no blockage) replaced gaskets and exhaust tube seal.
reassembled power head on motor leg.
replaced thermostat, thermo overheat indicator, new carb. (TC111A), new plugs and starter.

Bottom line motor starts right up runs really great, overheated in Two minutes yes the head and exhaust plates were
Hot could not touch.

Went to lake anyway and every thing set to factory specs, perfect hole shot, hit 35 MPH, then overheat buzzer again.

What can I do to find the problem? I need help.

 

[Jiggz]

Re: Overhearing again

First thing to check is the exhaust cover to make sure there is no blockage and then the t-stat to make sure it is opening. Better yet, remove the t-stat and test again. Attached is the water flow diagram for a 4 cylinder engine although most cooling water flow is the same for either 2 or 3 cylinder motors. Hope this helps.

 

[pnwboat]

Re: Overhearing again

At this point it's hard to tell if you have some type of blockage in the power head or the water pump isn't working properly.

First thing is to make sure that the thermostat is opening. Heat it up in a pan of hot water. They normally open up at either 130? or 143? depending on the rating of the thermostat.

The water pump is pretty basic. Make sure the key on the impeller is in place. Make sure it's the correct impeller. There are several impellers and they look identical with subtle changes. One of the differences is the keyway slot. Some have slightly different dimensions and it's easy to overlook. If you can, compare the old impeller to the new one. If you have an impeller with the wrong keyway slot, it may not be turning.

Remove the thermostat, and re-install the thermostat cover. Remove the lower unit so that you can get access to the water tube that goes to the power head. Take your garden hose and attach it to the water tube. You should get a good flow of water coming out of the exhaust tube. If you do, then this might be an indication that the problem is in the lower unit, not the power head.

If you do not get a good flow of water out of the exhaust tube then that might be an indication of blockage in the power head. The only water passage that I didn't see you mention checking was the water passage in the head itself. You have to remove the head. Once you remove the head, there is a head cover that is held on with 3 bolts located by each spark plug. There is no gasket for the cover. They just use sealant, so it may be difficult to see. Attached below is a head with the cover removed. NOTE: Pics below are for a 4 cylinder, but it's the same as a 3 cylinder.


The water exits the block by the thermostat (left side of pic.) and flows downwards to the outlet (see pic. below). It then gets dumped into the exhaust tube and lower leg housing.




There is a slotted passage in the power head for the water flow flow into the exhaust tube for the water to get dumped into the exhaust tube. See Pic. below.



Also check to make sure the water diverter tubes are in place if you have them. You should either have the tubes, or the power head itself is cast so that there is no passage "between" the cylinders. The pic below points out the tubes, or if no tubes, the casting should be filled in here. Here is a picture that illustrates the water flow through the block



Better picture of the diverter tube. It's just a piece of rubber hose inserted vertically in a slot to block the flow of water. Make sure there is no other blockage. Had one block where there was a row of small pebbles lined up perfectly almost like one of the diverter tubes restricting the flow of water.

 

[Big Fish Billy]

Re: Overhearing again

Ditto on giving the thermostat a boil to see if it opens at the right temp, I do it every time I change one in anything, especially automotive. Usually they fail open, but not every time. Ditto on running it without it in, sometimes you can get an airlock, if you have a brass plug on top loosen it up and see if you're getting water to the top.

 

[Michael Lang]

Re: Overhearing again

Thanks to all for reply and pic's.

 

[Michael Lang]

Re: Overhearing again

This web site is a bit fussy, never the less here is my follow on to my overheat problem, tested the thermostat twice, have good water flow coming out of pressure relief holes in back of motor leg which means the leg is filling up with water?
It seems like I am not getting water to number one cylinder, so if I push water through the bottom copper water pipe and remove the thermostat and cover should I see water coming out of the top thermostat opening?
Second question: Is it possible to remove the brass plug on top of number one cylinder and use a hose to prime while the motor is idling ( of course I would make some sort fittings to do this).

Any thoughts would be appreciated.

 

[Jiggz]

Re: Overhearing again

Answer to your first question is Yes, if you remove the t-stat and its cover and you feed the garden hose through the copper pipe at the midleg, water will exit at the t-stat opening and will probably wet all your electronics nearby. If no water exits, then it tells you there is blockage either at the head or the exhaust plate.

The brass plug you are referring to is that the one on top of the t-stat cover? If it is, yes you can remove this but I do not believe priming is the problem instead if there is no water getting into the head, it is some blockage in the system. As mentioned try the easy troubleshooting steps first by removing the t-stat and test again. If problem persists, remove the head and inspect the water ports. Better yet connect a garden hose and make sure the water makes it past the exhaust plate and should be coming out of the top cylinder as mentioned by PNW. If water does come out of this port, dismount the head cover and inspect for blockage and also the tube or casting barriers in the block ports.

For this troubleshooting, try running the motor on muffs and make sure you regulate the faucet pressure just enough not to lift muffs off the water intake. As soon as the engine starts, with properly working cooling system, cooling water will exit with the exhaust in the exhaust snout. If no water is coming out, try holding the muffs against the water inlet even for a few seconds, you should see water coming out of the snout. If no water still comes out of the snout after holding the muffs against the water inlet, shut down motor. This means the impeller is not pumping water or there is serious blockage in the system.

If water is coming out of the exhaust snout, there will be very little (if any) water coming out of the two exhaust holes (nostrils) at the midleg until the engine warms up and opens the t-stat. Then there will be more water coming out of the nostrils (although not as much as the one coming out of the snout) indicating the t-stat has opened.

 

[Michael Lang]

Re: Overhearing again

Thank you Jiggz for the complete instructions, One more silly question when you refer to exhaust snout, that must be the exhaust openings on both sides of motor leg just above the cavitation plate, I also have exhaust coming out prop hub. When I do the test should I see water flow both out snout and prop hub.
Thank you again Jiggz you have been a big help.

 

[Jiggz]

Re: Overhearing again

With your motor there is actually no snout since the exhaust is at the hub. So water should initially come out of the hub with the gas exhaust.

 

[Frank Acampora]

Re: Overhearing again

Even at normal operating temperature, the block and head will be hot to touch. It may be too hot to touch. Run the engine until it "overheats" Then dribble water on the block and head on top of #1 cylinder. If is does not boil off quickly but simply evaporates due to heat, then the engine is not overheating--replace the defective indicator.

 

[Big Fish Billy]

Re: Overhearing again

I could never get my Force 40 to run properly/consistently on the muffs, thought it wasn't pumping, so I cut a trash barrel to fit and it pumped like crazy. Also mine didn't have a telltale stream so I got a 90 degree fitting and hose and took out the brass plug. Through my experiments, and not paying attention, in a matter of seconds after starting, water poured out of that plug...so as was said if water isn't quickly getting to that plug, it isn't pumping.

 

[Michael Lang]

Re: Overhearing again

Frank, I read in one of your old replies regarding installing a thermostat and making sure that the small hole or notch was pointing up and I removed the thermostat cover and found good evidence of moisture then checked thermostat again and no indication of a hole or notch, do you recommend drilling a small hole i.e. 3/32 in the flange of the thermostat, have heard the hole referred to as "weep" or "bleed" hole.
Any ideas?