How much water?

[7325johnsonhelp[]

I'm putting a 1973 Johnson 25hp outboard back into service after many years. I have replaced or rebuilt just about everything, and it runs great in a tank. There is a good bit of water coming out of the top snout with the exhaust, but I only run it for short periods because I'm not sure my water pump is working properly. I'm basing this on the fact that I took the cover off the thermostat slot and removed the thermostat. When I run it like that NO water is coming out of the thermostat hole, either one. When I changed the impeller, I flushed the connection from the water pump discharge in the leg, just to make sure it was clear, and water shot out of the thermostat hole, thermostat removed. I initially installed the new impeller backwards. I pulled it apart and re-did it right but still no water flow through the thermostat. Is it possible the pin in the driveshaft reamed out the impeller or broke and now the impeller is just not turning even though it's installed right? I don't see how it could be working but not be pumping water at a high enough pressure to be blowing out of that open thermostat hole. Anyone with experience with these little motors, HELP. I don't want to burn it up and I'd like to avoid pulling the leg again.

 

[saltchuckmatt]

I'm putting a 1973 Johnson 25hp outboard back into service after many years. I have replaced or rebuilt just about everything, and it runs great in a tank. There is a good bit of water coming out of the top snout with the exhaust, but I only run it for short periods because I'm not sure my water pump is working properly. I'm basing this on the fact that I took the cover off the thermostat slot and removed the thermostat. When I run it like that NO water is coming out of the thermostat hole, either one. When I changed the impeller, I flushed the connection from the water pump discharge in the leg, just to make sure it was clear, and water shot out of the thermostat hole, thermostat removed. I initially installed the new impeller backwards. I pulled it apart and re-did it right but still no water flow through the thermostat. Is it possible the pin in the driveshaft reamed out the impeller or broke and now the impeller is just not turning even though it's installed right? I don't see how it could be working but not be pumping water at a high enough pressure to be blowing out of that open thermostat hole. Anyone with experience with these little motors, HELP. I don't want to burn it up and I'd like to avoid pulling the leg again.

You say you flushed it out through the water pump discharge. Do you mean the pickup tube?

If you did flush through the pickup tube and water came out and it won't with the pump than you must have done something wrong. Keeper seems the most likely.

 

[racerone]

Water must be 6" above the impeller in the test bucket.

 

[7325johnsonhelp[]

Keeper seems the most likely?
Six inches above the impeller? My test tub has the water level right where the foot separates from the leg, approximately 4 1/2" above the pick up but below the impeller. How would the motor keep itself cool running at full speed on a boat when the water would be only an inch or so above the pick up?

 

[saltchuckmatt]

Keeper seems the most likely?
Six inches above the impeller? My test tub has the water level right where the foot separates from the leg, approximately 4 1/2" above the pick up but below the impeller. How would the motor keep itself cool running at full speed on a boat when the water would be only an inch or so above the pick up?

Because it's being forced up there. Pump is not self priming so must be higher than the pump at least when running in a tank. Clip some muffs on it or raise your water level.

 

[racerone]

Put the water 6" above the impeller and test run !!

 

[7325johnsonhelp[]

I agree something is wrong. If a properly functioning impeller would pump hard enough to blow water out of an open thermostat cover, no thermostat, and there a no clogging between the pump and thermostat, it would have to be a problem with the pump, impeller. Since the motor runs smooth and the impeller housing looked good, checked well last time, it must be the impeller is not turning. Of course all that depends on whether or not water should be getting blown out of that open thermostat cover. Jeeze!

 

[7325johnsonhelp[]

Tried muffs at full hose pressure, 60psi. Same thing. Nothing making it to the thermostat.

 

[7325johnsonhelp[]

Don't have a tank that deep/tall. Not sure it even sits that low when the boat is sitting in the water.

 

[F_R]

How are you putting muffs on it???? The water intake is the screen on the forward edge of the underwater exhaust outlet. Even so, you cannot test a water pump by running on muffs. It isn't "pumping" as you are doing that--only allowing hose water to pass through.

Get that thing in a suitable container, or better yet get it on a boat on the lake where it was designed to run.

 

[racerone]

There are lots of posts on here where a novice added more water to the test bucket.-----Reported that all was then good.-----Not the same as a boat getting on plane with the pump primed !!

 

[saltchuckmatt]

I agree something is wrong. If a properly functioning impeller would pump hard enough to blow water out of an open thermostat cover, no thermostat, and there a no clogging between the pump and thermostat, it would have to be a problem with the pump, impeller. Since the motor runs smooth and the impeller housing looked good, checked well last time, it must be the impeller is not turning. Of course all that depends on whether or not water should be getting blown out of that open thermostat cover. Jeeze!

You might have burned up the impeller running it without enough water.

Either way, pull the gearcase and be done with it.

 

[OldOMC31]

I rebuilt a johnson 25r73a a few years ago. I had this same issue as you were having. I had to use a deeper tank to test it as muffs didn't fit anywhere on this engine. Originally had water in tank to this hole (see picture). Burned up head gasket while chasing my tail adjusting low speed needle. Didn't check if pumping water before adjusting.

 

[OldOMC31]

Then got deeper tank after replacing head gasket and filled water past here (see picture). A few air bubbles bubbles came out to started pumping water. Definitely listen when everyone tells you you need to get the pump primed by having water above the level of the impeller to get the system primed yo get water to pump.

 

[7325johnsonhelp[]

That looks very familiar OldOMC31. I will take everyone's advice and take it to the river mounted on a 14' Jon Boat, since I don't have a deep enough tank. I'm a retired science teacher and very suspicious but I know enough to know "it don't have to make sense to me." Maybe the pump does need to be a certain depth to prime properly. It will sure have to maintain pressure/cooling when at full throttle and the water level is much lower. I don't want to burn this motor. Is there any way to be certain it's not overheating? I've watched the spray out the back of the top snout on motors restored in you tube videos. Mine looked about the same. Still not comfortable with if it don't burn up the water pump must be working right.

 

[7325johnsonhelp[]

Thanks all for your help. I'll report back.

 

[saltchuckmatt]

That looks very familiar OldOMC31. I will take everyone's advice and take it to the river mounted on a 14' Jon Boat, since I don't have a deep enough tank. I'm a retired science teacher and very suspicious but I know enough to know "it don't have to make sense to me." Maybe the pump does need to be a certain depth to prime properly. It will sure have to maintain pressure/cooling when at full throttle and the water level is much lower. I don't want to burn this motor. Is there any way to be certain it's not overheating? I've watched the spray out the back of the top snout on motors restored in you tube videos. Mine looked about the same. Still not comfortable with if it don't burn up the water pump must be working right.

I would pull the foot and inspect/double check pump.

After installing you can put a cordless drill on the driveshaft and test in a barrel of some kind.

I would want to know before I went to the river.

 

[F_R]

Fallacy---a deceptive, misleading, or false notion, belief, etc.:
Fallacy---running a drill on the drive shaft will tell if the pump is working. Not really. A running motor blows the water out of the area where the pump is located, leaving the pump surrounded by air (exhaust) rather than water. Not the same thing.

 

[racerone]

Well , pumps are so simple , I have tested one with a drill !

 

[7325johnsonhelp[]

Ok. This morning it occurred to me I could use the kitchen trash can as a tank that would completely immerse the impeller, see image.

I removed the thermostat cover and thermostat, filled the can, cranked her up,, and.... WATER ERUPTED OUT OF THE THERMOSTAT HOLE! Granted it sprayed out of the small hole, right side of image, not the one the thermostat goes in, but I'll assume that's correct. I screwed up and put it back together before taking an image with it running. It's a whole lot more than ever before and the spray was coming out of the top exhaust snout as well.

Racerone, you called it first. Six inches above the impeller seems a little arbitrary to me but I'll definitely concede the impeller must be completely immersed.
Oldomc, you brought back memories I had of me doing something similar to a similar motor and learning the same lesson, about 35 years ago!
Thanks to all for your ideas. They all made me think. Now wish me luck. I got a gator tag this year and me and the S.S. Gatorbait are headed to Lake Eufaula to fill it tomorrow, I hope!