1972 Johnson 4hp Outboard Water Pump Test

Testing a 1972 4hp Johnson engine to find out if the water pump is working to cool the engine. Outboard engines are cold by water sucked up from the river and pushed through the engine in order to cool the head and keep the engine running correctly.

[@downintheparkfishing]

Thank you for this, I just got one of these motors and was concerned when I didnt see any water coming out of any holes like every outboard I have ever seen.

[@PatriotContraptions]

It worried me allot too ... The motor has been super reliable overall for me now I know that it has cooling and am not worrying 😃

[@davidgimellihemme5992]

Thank you for this. It's been something I have wondered about for quite a while.

[@donk499]

OK, well it is important to have you tank water level high enough to make sure the water inlets are covered by water. The water level should be above the gearcase/exhaust housing joint. Pulling the gearcase off is easy, trying to realign that water tube during assembly is the tough part for sure! Always remember to make sure the upper driveshaft oring is in good condition and lube the splines properly or else the crank/driveshaft splines will get wiped out and the poor little motor will be ruined.

[@Officerwilliam2015]

Do you have any tips on removing and cleaning the carb on the exact engine? Picked one up the other day!

[@PatriotContraptions]

I have never needed to clean the carb on this engine as I bought it running...

[@reidliimatainen5153]

I took the lower housing off to do the same test, I then hooked a squeeze bottle and hose up to the pickup tube but very hard to get water through. How much preasure should it take? I feel as though it may have a restriction. Idk if these small motors have a thermostate?

[@PatriotContraptions]

I don't remember it being super hard...it just seemed to flow right through...

[@anthonybosnic5801]

You need a bigger test tank and the leg of the motor should be deeper in the water.

[@evinrudej]

There are small holes above the water line that you can tell if water is coming out of them

[@PatriotContraptions]

Is that the four on the back of the unit? Because I was thinking it would come out there too but it doesn't when I have been testing it...I think it's just falling all the way to the bottom and going out the exhaust do to lack of pressure to go out the holes in back...

[@evinrudej]

@@PatriotContraptions yes those are the holes water should be coming out of them. Sometimes it may take a while for the water to start shooting out but it should. On these 4hps it doesn’t pump water to the head it’s only to cool the exhaust tube. I’d just replace the impeller and the gaskets below the impeller plate. to be safe not sorry very cheap and easy. I had one of these 4hps that I forgot to check if it was pumping water when I bought it and next thing you know I burned up my exhaust housing. Very nice one you got there they are tanks!

[@jimmysparks315]

@@evinrudej Water doesn't cool the head ??? What stops the engine overheating & seizing ?.....

[@beerggls]

@@jimmysparks315 Good point, seeing as the motor is snug as a bug in a clam shell under the dog house cover, where no fresh air gets in there to cool anything. I have an old McCulloch that’s the same way, from what I read about it on the subject, but I still don’t understand. Heck, I still don’t understand why there’s no air filter on outboard motors. Even though there’s no dust on the lake and the carburetor is sheltered inside the clamshell, there’s always all kinds of spider eggs and earwig crud and mouse crap and cat food at the mouse drug in.. all waiting to get inhaled into the cylinder.

[@robertcovemaker9440]

@@evinrudej Has anyone checked the actual temperature of the head while running . I have a little water coming out those weep holes ,but not much. I checked the temp with an infra red meter at the head where the plugs screw in and got around 400 degrees F will probably just do the pump

[@jimmysparks315]

We have a Mercury 4hp... no water tell-tail... Do these engines have one ?

[@PatriotContraptions]

My understanding is that most outboard engines do... normally in lower unit like this... Sometimes you can find a manual at a library or look for a boating forum online...

[@jimmysparks315]

@@PatriotContraptions Yes I would have thought so... we took the bottom of the leg off & spun the water pump shaft & water flows... however no tell tail when engine running... can't find any youtube video's of this motor with tell tail

[@outboardfixer]

Not in ANYWHERE NEAR enough water. The pump does NOT draw water, it needs to be under water. There is tiny holes on the BACK of the leg that blows out water or a MIST when it is ACTUALLY working. That impeller is NOT good, it has lost its flexibility. This guys needs to go back to school on outboards.....or at least STOP giving tutorials he doesn't know much about.

[@JBOutboards]

Your waterpump needs to be submerged for it to pump water. Get a deeper test tank.