40hp Johnson 1963 Water Pump

[twsnagel]

Hi everyone:
Johnson RDS-25D

OK, I think I’m almost ready to hit the water. One last question remains. I’m uncertain of the condition of the water pump and overheat light.

Since it’s a recirculating system, how do I know if it’s pumping water adequately? The overheat light in the dash looks suspect. How do I (or can I) test the light?

The motor spits a bit of water while idling in a trash can, but I know that because of the recirculating style of the engine, this is not definitive.

I understand that it’s probably a good thing to proactively replace the impeller, but I’d really like to get the boat out on the lake and see how it performs before I do any more work on her.

When I was given the boat, I thought it would be a "clean the carb and hit the water" kinda deal, but this winter, I’ve:
– replaced/rebuilt the entire gear case
– replaced/rebuilt the entire carb/fuel system
– replaced all control cables, refurbished the throttle
– rebuilt the steering
– refibreglassed substantial parts of the hull
– substantially refurbished the trailer
– lots of other things

So I’m pretty psychologically done with this boat, and I’m about 1000% over-budget monetarily, and just want to see it on the water at this point. But I don’t want to blow it up because the overheat light looks so bad. And I’d really prefer not to pull it apart and just replace an impeller proactively.

Thanks for any advice you’d have. You guys are awesome.

[frankr]

Wondering why you didn’t replace the impeller while you were rebuilding the gearcase? Never mind, that’s in the past. You can test the light circuit by sliding back the rubber sleeve that covers the connection to the tan wire that enters the cylinder head, then ground the wire (key turned on). Bulb should light. But this is not much of a test. It does not test the thermal switch in the head. Also, as anybody knows, a bulb can light today but be burned out tomorrow. Besides, you probably won’t even be looking at it when it comes on. That’s why they went to a horn in later years. Nevertheless when all is said and done, the best solution is a known good water pump and don’t be worrying about it.

There should be a light spray of water anytime it is running. When it reaches a certain temperature, the thermostat opens and water discharge increases. Keep in mind, it is not a simple matter of open or closed. The thermostat constantly monitors the temperature a opens or closes as needed to maintain that temperature.

[1946zephyr]

Yea, it would be good assurance to change out the pump, especially if the veins don’t go straight, once the impeller is removed from the housing. An overheated engine is the best way to ruin an outing.

[garry-in-michigan]

While you had the gear case off was the time to worry about the pump impeller. If you ground the wire to the heat sensor, the red heat indicator light should come on. These are often hard to see in the sun shine. I have seen some lights backed up with a buzzer. . . . . . 😀

[twsnagel]

Thank you all for your help. I’m planning to drive it up to the lake next week for a maiden voyage. I’ll test the light before I go.

If she runs well, I will replace the impeller before the second trip.

Thanks again, everyone.

[frankr]

One thing about those lights or horns–they come on after the motor is already overheated. If you happen to be running wide open throttle when it comes on due to total pump failure, you have about ten seconds to shut it down–if that.

[pappy]

quote FrankR:

One thing about those lights or horns–they come on after the motor is already overheated. If you happen to be running wide open throttle when it comes on due to total pump failure, you have about ten seconds to shut it down–if that.

Read Frank’s words again. He is spot on. The light will tell you that you just smoked the powerhead.
Also, what oil ratio are you planning on running?
I have watched an original impeller come apart in a test tank on an FD engine. Watched the water exiting the block slow then stop. The original impeller was in pieces.
Old original impellers are just not worth taking a chance on, period. Or, to put it another way, impellers are currently available and cheap. Powerheads are not.
Same with running additional oil.

[chris-p]

I never run a motor until I have done the waterpump. Had to pick chunks of rubber out of the cooling system once, will never do that again. You never get it all out. New motors to me always get a new impeller. Then every 3 to 5 years after that.

[twsnagel]

Well, you guys make it seem like I’m nuts not to change it.

The light works when I short the wire and it’s super bright. I could easily see it in full daylight.

Does anyone have a part number for the right impeller? Do I just need the impeller or a kit? Will I likely need a gasket when I split the leg?

Is this it? http://www.marineengine.com/newparts/pa … OMC0777213

It kind of sucks because I’m unlikely to get the part before Monday when I was going to haul it up to the cottage.

Changing it is basically unhooking the shift linkage and dropping the gear case off the end of the leg, right? I’m hesitant to split the gear case right away again because the gear case gasket was unobtainable and I used the old gasket and rtv sealant.

[phil-b]

No gearcase splitting involved. Water pump is on the top of the lower unit (above the gearcase).

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