18 HP Johnson overheating

[mike6669]

I recently purchase a 16 al v bottom with 18 hp johnson. When I purchased the boat the seller said he had just installed a new impeller. When we tried the boat out it overheated. At that piont he realized it wasn't pumping water. I then purchased the boat at a reduced price as we thought the mmotor was toast. Aftrer i got the boat home I was going to take the motor off and tried to start it one more time and it started and run like a charm however it still wasn't pumping water. I took the lower unit off and inspected the impeller it looked ok but the bottom plate wasn't sealed good. I then sealed the bottom plate to the lower unit housing and sealed the pump housing to the plate. I then use my air compressor to blow through the copper tube going up to the motor to check for blockage and it seamed ok. I the put the lower unit back on and tried it and it is pumping water now but still gets hot. After i run full throttle for about 4 to 7 min it starts getting hot and if i try to come down to idle it will die and not restart untill it cools. <br />Any help would be greatly appreciated.

 

[Joe Reeves]

Re: 18 HP Johnson overheating

Mike..... Many times, installing just the impeller isn't good enough, and the engine would require the complete water pump kit. HOwever, check the spark plugs for traces of water, and check the compression, as you could possibly have a leaking head gasket that is expelling exhaust gases into the cooling system at a high rpm.

 

[mike6669]

Re: 18 HP Johnson overheating

where can i order a pump assembly for that motor. I don't have a clue as to what year it is. or model numbers.<br /> also how much contact shouls the nipple of the water pump make with the copper line coming from the engine as I put the lower unit back on? Now it just starts to touch as the lower unit begins to make contact with the shaft housing. I think it should slide into that nipple but now it doesn't. could the tube coming from the engine have gotten pushed up into the shaft housing too far if someone tried to install the lower unit whithout have it properly aligned?

 

[Joe Reeves]

Re: 18 HP Johnson overheating

Mike.... The water tube should insert into the water pump housing grommet completely. It sounds like someone didn't have the tube aligned at one time and bent the tube upwards. Many of those tubes simply slide into another grommet that's up inside the exhaust housing. Look up in there, and if that's the case, pull it out, straighten it up somewhat, and then reinsert it. That is no doubt your present problem. Pertaining to the model number... look on the port (left) transom bracket. There should be a plate there with the model and serial number. There should also be a core plug (looks like a quarter size freeze out plug) on the powerhead with those same numbers. Get the "Model" number to us and someone here will pinpoint exactly what engine you have. When we have that model number, we can also give you the part number of the complete water pump kit.