78 2hp Johnson Running Hot????

[silverado636]

How do you know if this little engine is running hot? I have it running in a barrel and the engine gets a hot smell. The block is almost too hot to touch. I inspected the water pump and it looks OK. The tube seems to be attached to the pumo and up the the leg. What else do you look for?

 

[OBJ]

Re: 78 2hp Johnson Running Hot????

Well since there's no t-stat to change out, it's either a bad impeller or you got pluggage in the water circuit.<br /><br />Drop the lower unit and connect a hose to the water tube going to the block and put a little water on and see if it comes back out. <br /><br />Pull the impeller out and look at it...do the impeller blades spring back out straight? Or do they stay curved in the form of the cup? If they stay curved....put a new impeller in it.

 

[Xcusme]

Re: 78 2hp Johnson Running Hot????

If this is a new to you motor,replace the water pump impeller. Visually inspecting the impeller is not a reliable test. When you replace the pump,you know it's age, you have a baseline for future reference. Removing the head and inspecting/cleaning the cooling passages is another option, especially if the motor has been operated in saltwater. Marine dealers sell a temperature melt stick,designed to melt at a certain temperature. If the powerhead melts the stick, it's running too hot. Infrared temperature test guns work well too. The rule of thumb is,if you can touch the head for a few seconds without burning your fingers, you're OK. Sometimes the smaller motors will run a bit warmer due to head gasket/cooling passage configurations.

 

[Chinewalker]

Re: 78 2hp Johnson Running Hot????

FYI - those motors will run a little hotter than others, at least in the area where you can touch it. The exhaust cover is not cooled, for one, and for two - the cylinder head has minimal water flow through it, so both parts will get quite hot to the touch, even under the best of circumstances.<br /><br />That said, Xcusme's advice about replacing the impeller as a matter of course is VERY good advice, regardless of how "good" it looks...<br /><br />- Scott

 

[BF]

Re: 78 2hp Johnson Running Hot????

ditto on the impeller. When I changed it on my 2 hp (looked fine), and the water flow noticably increased.<br /><br />Should spit a mist out the 4 relief holes at low rpm's and more are higher rpm's<br /><br />Brent

 

[gcglastron]

Re: 78 2hp Johnson Running Hot????

I also have a Johnson 2 HP (1974) that I am wanting to replace the impeller. I have not been able to find the correct kit/impeller on-line. I checked the iboats parts link, and could not find an impeller for my year. Is there an OMC number/Sierra parts number for an impeller that will work? Also, as an aside (since this is a Johnson/Evinrude message board), I need to replace the impeller on a 1972 50 HP Merc (4 cyl) that I recently purchased - should I buy the entire kit containing the upper and lower housing, the impeller kit with the lower housing, or just the impeller? What has been the experience of those of you who have done alot of these? I have in the past just had the marina do the maintenance, but with these older motors, I figured I would start doing it myself. Thanks very much. -Jay

 

[gcglastron]

Re: 78 2hp Johnson Running Hot????

oops, on the choice of parts to buy, it should read the impeller kit with just the UPPER housing (instead of lower housing). I guess the choices were: (1) impeller kit with gaskets itself, (2) impeller/gaskets/upper housing, or (3) impeller/gaskets and upper+lower housing? I was going to take the lower unit off and look first, but with my habit of not putting things together after taking them apart, I figured I should try to do it all at the same time (fewer leftover parts that way!)!