waterflow through an FD model Johnson 18-20 hp

kfa4303

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Hi all. Just wonder which of the two pics below shows the correct flow of water through the power head, in and around the thermostat, for a typical FD model Johnson (18-20 hp). Thanks.

waterflow 1.jpgwaterflow 2.jpg
 

1946Zephyr

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Re: waterflow throuh an FD model Johnson 18-20 hp

Re: waterflow throuh an FD model Johnson 18-20 hp

I believe it's the pic on the right. The best way to comfirm it, is to pull the t stat housing and fire the motor up. You will then see exactly where the water is coming from.
 

kfa4303

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Re: waterflow throuh an FD model Johnson 18-20 hp

Re: waterflow throuh an FD model Johnson 18-20 hp

I think you're right Zeph. Here's a diagram I found, and it looks like the water does come up trough the small, square-shaped opening (as well as through several other small holes in the cylinder the t-stat drops into), then over the T-stat and down the larger hole on the right side of the T-stat housing. If so, that's where I'll tap my ell for the tell-tale I plan on installing. I just want to be triple sure I'm in the right spot before start drilling holes everywhere. Thanks again.

6hp water passage.jpg
 

1946Zephyr

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Re: waterflow throuh an FD model Johnson 18-20 hp

Re: waterflow throuh an FD model Johnson 18-20 hp

You betcha. Good luck on everything. I hope it works out. ;)
 

Haffiman

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Re: waterflow throuh an FD model Johnson 18-20 hp

Re: waterflow throuh an FD model Johnson 18-20 hp

The diagram you have put up, just says what I mentioned in your other post:
The tell-tale/pee on newer models replaces the by-pass from exhaust chamber to the out-side of your thermostat. This to ensure proper cooling of the exhaust cover even if thermostat is closed. The Pee as indicator is just an add-on effect from its original purpose.
 

kfa4303

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Re: waterflow throuh an FD model Johnson 18-20 hp

Re: waterflow throuh an FD model Johnson 18-20 hp

Thanks haffiman. I'll be tracking down a smaller ell today, or tomorrow. The one I have is 1/4" and need 1/8", or so. I also have to add some JB weld to the t-stat housing cover and let it fully cure. Thanks again for all the help. I'll be sure to take pics and do a how-to thread for any folks hat may want to do it in the future.
 

F_R

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Re: waterflow throuh an FD model Johnson 18-20 hp

Re: waterflow throuh an FD model Johnson 18-20 hp

Neither picture is correct. Water follows two paths through the powerhead. Only one path is thermostat controlled.

First path is up through the hole next to the thermostat, across the cavity and down thorough the hole on the right. That path is always open.

Second path is up through the hole the thermostat sits in and down through the hole on the right. That path is cut off when the 'stat is closed, except for a small bypass notch in the 'stat. The 'stat element is thus bathed in the water to sense it's temp, and opens when it is warm enough.

First path cools the exhaust cover, and part of the cylinder head, and is discharged into the exhaust housing to cool it. Those are the hot spots that require constant cooling.

Second path cools around the cylinders and the rest of the head.
 

kfa4303

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Re: waterflow throuh an FD model Johnson 18-20 hp

Re: waterflow throuh an FD model Johnson 18-20 hp

Thanks for the clarification F_R. I think I got it now. Is this pic/diagram correct? Thanks again.

waterflow 3.jpg
 
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