Constant overheating alarm

I have a 2000 honda 40 and the overheat alarm comes on within 10 min anything over 3000rpm ??
We have changed the impeller ,changed the thermostat and the pee hole shoots water out but it is very hot water also engine to hot to touch .engine compression is 85-90 all 3 cylinders .the engine runs great until alarm goes off. I've poured CLR down the thermostat hole and then taken the lower unit off and flushed it both ways from thermostat down and from lower unit up
So what are my choices ? flush again with salt away ?

How do you flush with muriatic acid ? How about putting engine in barrel and using CLR, vinegar , or muriatic acid ?? whats the consences out there ? need help
 
Your compression looks really low -- about 50 percent of what it should be for a 4 stroke motor. Hopefully the test was done without opening the throttles wide open -- that could account for the numbers. Your readings are marginal for a 2-stroke. Ron
 
Ron how do you do a compression test with throttles wide open????
I tried to run engine today for a few min no pee so shut down motor did some laser gun engine was over 280 degrees so I think there is definatley some sort of blockage so I think disassemble motor is in order any other thoughts ?
 
For wide open compression test, find out where throttle cable attaches to carbs, or if fuel injection, to throttle body. Disconnect the throttle cable (if needed) and manually hold the motor throttle lever wide open. Have all the spark plugs out, and pull the coil wires loose so that you don't get shocked by touching or being near the spark plug wires while you are turning the motor over. Screw the tester into the plug hole and turn it over with the key. Also, some of the testers do not read well either because of poor design, dirt in the check valves, or too much flex in the line running to the gage from the adapter.

With the engine overheating like you say, it sounds like your water flow pipe from the outdrive might not be sealing well into the upper unit, unless the pump is not performing. Primary things to check is the water intake on the lower unit, the pump (making sure the impeller key is in place and the impeller is good), the tube running from power head to lower unit is good and inline properly, and the thermostat.
 
Well we think we found the culprit there were no blockage in passageways but the head gasket looked a little suspect also num. 2 cylinder has minor scoring I will replace piston and rings and have cylinder rehoned and all new gaskets and start again .

We have new water pump kit and new thermostat installed so once engine is back together we should be good to go .

The boat runs great except for overheat now to redo gelcoat and clean up, then see which boat my wife wants to keep ??
 
First my apology to Tad, I missed your questions, and then lost this thread as we traveled somehow.

Using Muriatic acid is not something that should be done without a lot of thought and with professional advice. If you use it--dilute 2 cups in 5 gallons of water, pump it into the passages, and then let only sit 5 minutes, remove, flush with water and then baking soda.....

CLR or phosphoric acid is safer--as is white Vinegar.

We have a 5 gallon insecticide sprayer, with a 1/2" hose connected, so we can put fittings on the end of the hose, and fill passages with it.

There are other issues in engine overheating--scale production which has lodges in some small passages, debris which was picked up into the passages, as well as pieces of impeller.

I have always thought that the Hondas seem more susceptible to corrosion in salt water than some of the other motors--yet have owned them without problems. The idea of taking them apart every few years is good, and preventing problems with salt away and good flushing is also something which will pay off down the line.

Having the thermostat in place is another obstruction--normally it is not an issue, but if there is some corrosion or narrowing of passages, it may be enough to just tip the scales. I agree that in our Florida Waters, that we can usually run without the thermostat, if the engine warms up slowly. (in our case we have 10 minutes at no wake speeds before we go into the bay).

Either running the engine in fresh water, or running on muffs is better than the block rinse. The former allows good flow into all of the passages. Also there is that rare occasion where the water tube is not properly gasketed or aligned.

Now that I have a carbonated Honda 90, I'll have to be watching for these problems--but I believe that the engine was operated in mostly brackish to fresh water. That will make it less likely to have problems. Also that the skeg is not scrapped up is good-- it suggests that the engine has not been run in sand or mud.
 
Having the same problem with my 2008 150. Alarm has come on when decelerating quickly from about 4500 rpm. Engine shuts itself down after about 20 seconds. I've been able to restart in a minute or two, and limp back to my slip at about 14kts. with no recurrrence. Water coming out of peehole isn't hot to touch.
I've flushed with fresh water after every use, per owner's manual. Think Salt Away, muriatic acid, vinegar, etc, are necessary, too?

I did run seriously into the mud once, but that was a year or two before the problem came up.

Dealer has not been able to figure it out in three tries; says he'll call Honda Monday morning.

Very frustrating!
 
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