Fittings for 8.1 hot water heater connections

skibum

Well-Known Member
Jul 30, 2007
2,726
Perry Hall, MD
Boat Info
2005 Sundancer 260
Engines
496 Magnum HO
Hello everyone. I'll be installing my new Kuuma 11811 water heater in a couple of weeks.

I have the instructions showing where to make the connections to the cooling system, but they do not show any information about which fittings to use. Does Merc sell the proper fittings, or should I just go to the auto parts store and pick up some 5/8" water line fittings like these?

Thank you
 
For the engine coolant connections.....I would use brass fittings easily available at HD or Lowes. For the potable water line connections it comes back to what you have now and whether you want to install a bypass for easy winterization.

1707161204959.png
 
You shouldn’t use brass if it is a salt water cooled block.

The iron automotive are fine, the block is iron.
 
You shouldn’t use brass if it is a salt water cooled block.

The iron automotive are fine, the block is iron.
I took a guess that he has a fresh water cooled boat since it is a 2006. I don't know of too many inboard boats built after the 1990s that weren't. That said.....even if it wasn't.....I would use brass over steel pipe. Just not a fan of it rusting.
 
For what is worth (usually nothing) here is a picture (bottom left of photo) of where my hot water connects to the motor. I’m not sure if you were referring to the hot water heater side or engine side, but none the less, the fitting on my motor is brass.

1707187134437.jpeg
 
Thanks, guys. I was surprised when I pulled the parts list for my engine and didn't see the fittings listed. Merc usually shows the small, optional stuff like this like this in there. I'm glad they didn't since the price would likely be close to $100 each. Like the 2 screws I ordered to replace the 2 that I snapped off removing my Cool Fuel module lid. $24 for 2 #6 x 1 mm screws. Unreal.

Where I boat, we have brackish water. Near my marina, very low salt content. Almost none. 15-20 miles south, and the spray starts leaving salt deposits on the boat. As John suspected, I do have fresh water cooling. I bought this boat when it was two years old and the previous owner had already managed to crush and split one of the connections for the heat exchanger on the water heater. It was not connected to the engine when I got her. Now that the engine is removed and I have easy access, I'm replacing the HWH. I almost did it a few years back, but I didn't think $650 was a reasonable price for a HWH so I put it off. I just plugged the boat into shore power for 20-30 minutes at the beginning of the day and it would heat up the water enough to last most of the day. I'm glad the Kuumas have arrived on the scene since I last looked. Their prices are (and I can't believe I'm saying this about a marine product) very reasonable. I'm going to have my mechanic drain all of the coolant and flush the block with water before putting the engine back in, so I'm feeling a little more comfortable about running the HWH off of the engine knowing that there will be fresh coolant flowing through it. I'm not sure that it matters, but it does make me feel better. I'm really looking forward to having hot water all the time. I hate shaving with cold water.

Ironically enough I have that exact bypass kit in my shopping cart. I also have the "Camco 35953 8" Supreme Permanent By-Pass Kit" in my cart. I'm trying to decide between the two. The one you show has a one way valve fitting and a plastic tee (that I'm not crazy about) and the other just has two of the 3 way brass valves. I like mechanical simplicity, so I'm leaning towards the 35953 kit. I can handle turning 2 valves twice a year. I measured across the inlet and outlet of the HWH, and it looks to be slightly more than 8". Is it safe to assume that the 8" version of either kit will work on the 11811?

I appreciate the info on the fittings. I just wanted to make sure that Merc didn't throw me a curve ball with an obscure thread pitch or something before I bought them. I'll procure a couple of brass ones locally.
 
For what is worth (usually nothing) here is a picture (bottom left of photo) of where my hot water connects to the motor. I’m not sure if you were referring to the hot water heater side or engine side, but none the less, the fitting on my motor is brass.

View attachment 158528
You just reminded me that I need to order 2 of those rubber seals that they heat exchanger plugs into. Mine leaked about 10 years ago and I've already replaced them once. Thanks!
 
The Supreme kit is the way to go. Camco 35953 8" Supreme Permanent By-Pass Kit"

Just make sure to measure between the in and out fittings to make sure the 8" hose will work. If it doesn't .....order this one:

By-Pass Kit - 12" Supreme Permanent for 10 gallon tanks - 35963​

 
I personally used the Supreme kit. Get that one.

If I remember correctly, the plugs in your engine (where you hook up the coolant supply to the heater) are the same as your garboard drain plug. I would go with brass, as well. Lot's of fittings in blocks (even raw water cooled engines) are brass. If you can find bronze, even better.
 
I installed a Kuuma 11811 in my boat in 2018 and it has worked perfectly. I think I went with the 35963 12" Supreme Permanent By-Pass Kit due to the distance between the fittings. I just would rather have too much hose than not enough. :)
 
If you have a freshwater cooled system, make sure you also install an anti-scald valve. The engine coolant temperature gets high enough to heat the water in the tank to dangerous levels. 160° can produce serious burns almost instantaneously. The anti-scald valve is also required by ABYC standards.
 
I installed a Kuuma 11811 in my boat in 2018 and it has worked perfectly. I think I went with the 35963 12" Supreme Permanent By-Pass Kit due to the distance between the fittings. I just would rather have too much hose than not enough. :)
Yep. I measured the distance between the fittings, and it was exactly 8" between the perimeters of the two. Not to mention that using the 8" one would require passing directly over the access cover with very little extra room. I'm not fond of the idea of not being able to open the cover easily so I went with the 12" version as suggested. Thanks for the tip. I almost ordered the shorter one.
 
The bypass kit has arrived and I have installed it. The 8" kit absolutely would not have worked for me. It would have required going straight across the access cover. That wouldn't be possible without using a close nipple and a coupler to raise each valve up at least 1/2" so I would be able to tighten the hose connections. I almost couldn't turn the valve enough on the cold side to get the inlet facing the valve on the hot side. Another couple more degrees clockwise would have been better, but I didn't want to risk breaking something. After connecting the hose finger tight on both sides, a little twist was all it took to get a nice loop that does not touch anything or cause any kinks. I still have full access to remove the cover if I need to.

On a side note, the 2 screws "holding" the power cord strain relief bracket in place did not appear to be screwed into anything. The 2 holes under the bracket are so large that the screws drop into them right up to the heads. There is insulation under them. I didn't find any nuts, or anything that looked like a backing plate in there. Nothing is rattling around in it. Has anyone else seen this? I'll put a couple of nuts on it as soon as I can find some in my workshop that will fit.

hwhbyp.jpg


Thanks again for the help.
 
As all Merc 496 or 8.1 engines (both the same engine - 496 for IO's & 8.1 for inboard applications) are fresh water cooled (antifreeze) so no issues with having to winterize the lines from the engine to the water heater and back to the engine - they are full of antifreeze nominally.
 

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