67 20 HP Johnson very hot, but moving water

Hi all. I have a FD-22 outboard that I have tried to bring back from the brink of death. I took it out to the lake today to test it out and to see how it pushes my boat. I ran into an issue and was hoping for some guidance with troubleshooting, as neither the OEM service manual, nor the Seloc outboard repair manual are very good at troubleshooting.

The primary issue is that the motor is not cooling at all. I ran it for less than three minutes (at close to WOT to be sure), and in that time the heads were too hot to touch, and would sizzle a drop of water on it. There is water coming out of the back (no pee hole in this old girl), so I would assume the impeller is working well enough to pump water. I can't attest to the specific condition of the impeller, as I haven't replaced it. I was told by the person I got the motor from that the impeller had been replaced two months ago. When working on the motor (I did replace the ignition components, among other things) I could hear the impeller blades squeaking against the pump housing when I turned the drive shaft, so I assumed it was good.

So, this is the troubleshooting path I am going to follow, please tell me if I have missed something, or if I have things out of order. My basic goal is to start at the least complicated/least expensive components and go from there.

1. Check impeller for wear or damage.

2. Check the usual components for water pump rebuild; o-rings (driveshaft and the two that go on either end of the exhaust housing spacer) and the grommet.

3. Check thermostat for proper operation.

4. Pull the head and inspect the water passages to look for blockages or build-up.


Again, if there is anything I can do short of pulling the head, please let me know. The powerhead has great compression, and I would really hate to mess with that if I didn't have to.

Also, if I have to pull the thermostat, do I need to replace the gasket? I would assume yes.

Thanks in advance for your help.

Rgds

Eric

Re: 67 20 HP Johnson very hot, but moving water

Possibly could be the thermostat so definitely check that. If that is closed/stuck shut then your motor will overheat quite easily. You can check its function in a pot of water on the boil, alternatively, just replace with a new one while you have the water jacket off to make sure, and yes, use a new gaskets wherever you touch the old ones.

otherwise your troubleshooting path seems logical.

Re: 67 20 HP Johnson very hot, but moving water

Thanks for that first reply. Back a few months when I was fixing up another outboard, someone suggested backflushing the cooling passages. this also seems like a useful procedure to verify that water is in fact moving around the cylinders. Can somebody elaborate on how you backflush they water passages? Where do you try to get water through? From the thermostat, or from the copper tube that slides into the grommet on the pump housing? I would think that if I remove the thermostat I should be able to verify if water is getting to the jackets around the cylinders?

-Eric

Re: 67 20 HP Johnson very hot, but moving water

HA! It seems to be the thermostat. I opened up the housing for the t-stat, and didn't find any weird build-up or residue. I connected a water hose to the copper tube, and it came shooting out of a passage at the top of the motor. When I adjusted the flow somewhat, I saw that the water moved from this passage across the top of the thermostat (the top of the thermostat sealed off the space below it), and then down another passage which eventually went out the exhaust port. I removed the thermostat, and saw in the space it occupies two water passages; one at the bottom and one near the top. I slowly allowed that space to fill, and I could hear it drain somewhere into the power head, and eventually back down the copper tube. If I blocked the copper tube with my finger, whatever was filling up from the top (I would presume it was the water jackets) would fill completely, and then begin to spill out the top hole and would channel to the passage that went to the exhaust. On a hunch, I collected the water as it drained back down the copper tube, and checked its volume against the capacity of the water jackets in a parts motor that I have on which I have removed the head. It was about the same, so I concluded that the water jackets are in good enough shape to justify not opening the head to inspect further. I then put the thermostat to the temperature test; I suspended it in a pot of water that I slowly heated. I had a thermometer on the pot, since the magic was supposed to happen at 140-ish degrees. I let the temp get to over 200 degrees, and no change in the thermostat. I would assume that at some point its supposed to get longer such that it unseals the space it sits in and allows water to flow in and out.

I do have one question, if anyone can answer; Would it hurt the engine any if I ran it without the thermostat? It occurs to me that just for testing purposes to verify that the motor won't overheat and is moving water correctly, It wouldn't really make a difference if the thermostat were present, since the default behavior would be to open the water passages and thus cool the motor.

-Eric

Re: 67 20 HP Johnson very hot, but moving water

As a test, that won't hurt a thing. Just put the thermostat cover back on, and start it in a tub of water. The engine will only get warm to the touch if the pump is OK.

Re: 67 20 HP Johnson very hot, but moving water

I always test em with no thermostat if I have cooling problems. Wont hurt it at all, it'll just run cool.