(referencing a 2005 Yamaha AR230HO)

I solved an intermittent overheat on one of my engines due to a bad thermosensor, but was still getting overheats on both engines during WOT runs over 4-5 miles. I suspected that the issue was scale build-up inside the water jackets, particularly calcium carbonates. Monitoring with YDS (Yamaha Diagnostic Software), both engines were doing the same thing at about the same rate, so I ruled out electrical issues. Using an infrared temp sensor, I also found a particularly hot area of the starboard motor around piston #1, leading me to believe there was a mass of calcium/sand/salt there. Checking the PWC forums, I ran across this issue a few times and is likely due to being far from the flush inlet. Though my flush system here solved my overheats and reduced this hot spot, I was never able to fully flush the crud I assumed was built up here.

I always flushed the engines thoroughly post-salt with Salt-Away during wash down at the house and I would "pre-flush" with fresh water from a spigot before I left the dock area, when available. I am convinced that there is just no way to prevent the accumulation of build up, especially from salt water. I've also concluded that the small-diameter factory flush inlet is inadequate to fully fill the waterway components. I experimented with solutions and tried a few different approaches to closed-loop flushing over two years and it improved my temperature readings each time. This write-up only explains what I found did the best to remove the crud while minimizing the risk of damaging the engine. Check here for the full experiment, including results of different acid solutions and my thoughts on the shortcomings of the Yamaha flush system.

SULFAMIC SOLUTION: This is what I used to flush the system and is not to be confused with sulfuric acid. I did a few impressive experiments with it on parts prior to coming up with this flushing technique. It works very well on calcium that builds up from salt water. I tried different concentrations and found 4% to be adequate without being too harsh. You can buy Sulfamic Acid crystals at Home Depot in the tile cleaning section. To prevent damage to the aluminum parts, I mixed in some Thiourea which can be found on eBay. The formula is explained below. I would follow this up with a solution of Soda Ash to neutralize the acid - this was purchased on Amazon as it is commonly used for making tie-dye shirts. Each engine got a fresh batch of each solution.

- Submersible Water Pump (Northern Tool #42358).
- Garden Hose Remnant (Northern Tool #500011).
- 2" PVC Pipe cut to a length of 6" (1).
- 2" PVC Cap (2).
- 3" PVC Pipe cut to a length of 2" (3).
- 0.50" x 2" PVC Riser (in the grass sprinkler section) (4).
- 3" to 1.50" PVC Reducer (5).
- 1.50"-to-1" PVC Reducer Bushing (6).
- 0.75" Slip x FHT PVC Hose Fitting (in the grass sprinkler section) (7).
- Male end of a Garden Hose with about 48" of hose attached (8).
- All Purpose PVC Cement.
- 3/8" ID Tubing about 10' in length.
- 3/4" ID Tubing about 2' to 2.5' needed.
- 1/2" OD Tubing about 2' in length.
- Garden Hose Repair End (Female 5/8" to 3/4"; see pic further down ).
- 5 gallon bucket.
- Roll of Electrical Tape.
- (2x) Radiator Hose Clamp Pinch-Off Pliers.

BUILD THE FLUSH ASSEMBLY: Assembled parts 3 to 7 in the above pic just as they are laid out with the PVC cement. I was careful not to allow the FHT Fitting (7) to seat completely into the back of the 1" Reducer Bushing's (6) recess so it didn't glue the spinning collar in-place. Then drilled a hole in the large 3" Reducer (5) with the short section of 3" Pipe (3) already glued in.  The largest regular bit I had at the time was 5/8" but I think at least a 7/16" drill would've been better. I carefully shaved the threads off one side of the 0.50" Riser (4) with a bench grinder - for it to fit into the 5/8" hole I drilled, I had to get the wall fairly thin. Applied cement and tapped it into the 3" Reducer (5) with a mallet.

DISASSEMBLE THE EXHAUST:  I flushed one engine at a time and started by removing the clean-out plug tray to gain access to each water box and removed their straps. Loosened the four hose clamps that secure the aluminum joint with "UP" on it (fiche part #45; referred here after as the "UP Pipe") between the muffler (fiche #36) and the water box. Removed the UP Pipe and both rubber collars (fiche #46 & 47) that are attached to either side. Finally, unbolt and remove the tail pipe and gasket (fiche #43 & 42) to allow for larger debris to flow out of the system quicker.

MOVE THE WATER BOXES: Back under the clean out tray area, I unclamped and popped off the large hoses coming off the top of both water boxes. I removed the starboard water box up & out through the tray hole and then slid the port water box aftward a few inches. I finally unclamped and removed the long, white drain tube that runs from the interior deck to the scupper.

MAKE THE LOOP: With the UP Pipe (fiche #45) removed from the engine, I slipped the Flush Assembly (3-7) over the smaller end of the UP Pipe - I had to use very course grit sandpaper (40grit) to open the inner diameter of the PVC (3) enough to get it to slide over it snugly (someone told me that I could have heated the PVC up to get it to stretch over the pipe). With the embossed letters "UP" considered 12 o'clock, I affixed it so the Riser (4) pointed between 9 and 10 o'clock. I used Electrical Tape to secure the Flush Assembly (3-7) to the UP Pipe and make it all water tight. I then added the 3/4" ID Tubing to the Riser (4). The Garden Hose (8) should now be attached.

Placed the 2" PVC Cap (2) onto the short length of 2" PVC Pipe (1) and inserted this into the end of the muffler (fiche #36) - this plug helps prevent the solution from making its way up the exhaust and to the pistons. The pipe portion will be too loose, so I had to wrap Electrical Tape around the PVC Pipe a few times, just below the Cap edge. Wrap it until it is just thick enough that it snuggly seats itself fully into the muffler - it doesn't have to be air tight, it just has to stay in place well.

I slipped the larger rubber exhaust collar (fiche #46) back onto the end of the muffler (fiche #36). I took the entire Flush Assembly (now consisting of parts 3-8, the UP Pipe, and the 3/4" Tubing) and inserted the Garden Hose (8) through the exhaust hole in the stern, ran it over the first water box support bracket, through the hole in the second support bracket, and then outside through the scupper. I plugged the entire Flush Assembly back into the rubber muffler collar (fiche #46). While supporting the assembly level, I tightened the two hose clamps (fiche #48 & 49).

I removed the two hoses coming from the top and bottom of the thermostat housing. I cut the 3/4" ID Tubing coming off the Flush Assembly's Riser (4) so it was long enough to reach the larger/lower nipple of the thermostat housing. With the correct length measured/cut, I unbolted the housing to remove the thermostat and attached the Tubing to the lower nipple. I remounted the thermostat housing. I attached the 3/8" ID Tubing to the upper nipple on the thermostat housing and ran it up and out to the 5 gallon bucket sitting below the scupper. The purpose for this 3/8" Tubing is to give any excess pressure and solution a route to escape back to the bucket - not including this will likely cause/worsen back flow into the exhaust and up to the pistons.

I attached the Female Garden Hose Repair End to the end of the Hose Remnant coming off the Submersible Pump. I disconnected the hose that delivers raw cooling water from the impeller duct to the starboard side of the engine - this will be plugged into the back of the pump plate on the port side. I plugged the Repair End/Hose Remnant into this hose - this will feed the flush solution to the engine from the Submersible Pump. Using Hose Clamp Pinch-Off Pliers, I clamped off the red Yamaha flush inlet hose above where it and the raw water inlet meet at the y-coupler just inside the engine bay.

At the impeller housing, above the bucket of flush solution, I inserted the 1/2" OD Hose into the upper starboard outlet located on the outer-side of the pump plate (the red hose in the next pic) - this connects to the hose (fiche #5) coming off the muffler. Finally, I clamped off the hose (fiche #4) that runs out from the huge 90* rubber elbow (fiche #33) out to the starboard peehole. The system is now closed-loop and ready for pumping.

HOW IT WORKS : The engine is not running during this procedure. The Pump delivers solution up the Remnant Hose and into the raw water inlet hose that the boat's jet pump utilizes. This flushes throughout the engine and is returned via the Flush Assembly and the hose plugged into the outside of the jet pump plate. Some excess solution should make its way up to the thermostat housing. I originally tried using the factory flush inlet but found I did not get nearly as much pressure or solution through the system due to that hose's much smaller inner diameter. This was probably also not allowing me to fill the entirety of the exhaust jackets during my routine post-outing flushes. To me, this small diameter hose is a flaw in Yamaha's design which prevents a thorough flush. The increased pressure through the raw water inlet helps break up and push out any sand.

MIXING SOLUTIONS: I opted to use a 4% acid solution with about 1% inhibitor (that's 1lb of sulfamic crystals and 1.5oz of thiourea in 3 gallons of water). I mixed up the sulfamic solution with boiling water and mixed the solution in a 5 gallon bucket after the flush system was installed. The hot water is required to fully dissolve the crystals and also allowed me to feel that different areas of the engine where getting the solution. I would flush for 15 minutes and allowed it to drain. I then removed the Flush Assembly (including the UP Pipe) and fired the engine for two seconds. I immediately reattached the Flush Assembly and flushed the system with a 2% neutralizing solution (0.5lb soda ash in 3 gallons of water) to prevent any chance of the acid doing damage. I again drained the loop and the exhaust, pulled the Flush Assembly, then fired the engine up for a second or two (I did this between following every drainage phase).  I followed this with a flush of some soapy water then several clean flushes of fresh water with an additional garden hose feeding the Yamaha flush inlet (red hose) until sediment became minimal in the bucket.

1. Sulfamic solution (closed loop) - 15mins
2. Clear system
3. Soda Ash solution (closed loop) - 10mins
4. Clear system
5. Soapy rinse (closed loop) - 1min
6. Clean rinse w/ additional hose at Yamaha flush adapter (open system) - 3mins
7. Clear System. Reassemble.

closed loop = pumping with return hoses fed back to the bucket.
clear system = remove "UP" pipe and PVC Plug, then fire engine for a few seconds.

open system = pumping, but return water spilling out of bucket or onto driveway (no loop).

Three gallons of water will be enough to fill the system and leave enough in the bucket so that the pump doesn't cavitate. The thermostats can be placed into the bucket of sulfamic acid to clean them while the flush is being done. It will not harm the rubber. You can also throw the tail pipes in as well. Be sure to also neutralize them. I always replaced my tail pipe gaskets, but this probably isn't necessary. I advise flushing for 15mins because this should allow enough time to dissolve a decent amount of calcium without the solution backing up into the cylinders. I would recommend repeating Steps 1 and 2 before moving to Step 3 if you are having overheat issues. I did three flushes, one with a retail descaler followed by one with the acid in the spring of 2016 then another acid flush Spring 2017, and was still getting plenty of junk out.

RESULTS: During the fresh water rinses, I eventually added another garden hose hooked to a spigot with the Yamaha flush adapter to the standard flush inlet under the hatch. Feeding both inlets simultaneously, the greater volume helped to push additional bits of larger debris along. I did a few cycles with clean water, catching the water in the bucket and letting the sediment settle. I then skimmed the water off and collected the sediment in a jar from all phases. Unbelievably, the jars shown here contain only a portion of what I flushed out of each engine on the third flush! There is a bottom layer of sand, a middle layer of very fine silt (dissolved calcium?), and the top layer of solution. I am also showing how well the thermostat housing was cleaned. Following my flushes, I had zero issues with overheating in the remaining years I owned the boat.

FUTURE CONSIDERATIONS: This is something that should probably be done every one or two years, depending on the type of water frequented and the number of outings. I would have liked to modify the flush assembly for a larger output hose diameter and connect directly to the barb on the back of the scupper (rather than run the short garden hose through it), allowing increased system flow. My hopes for this would be to increase the current to move debris along and to reduce solution backing-up into the exhaust. The downside to this could be that the system empties faster than it can be filled, preventing the sulfamic solution from cleaning the upper surfaces. However, a plastic ball valve could be installed on the return hose to restrict flow during acid flushes (calcium) and open it fully during clean water flushes (debris). In either case, I have proven that this system does what it was intended to do.

THERMOSTAT MOD: I decided to drill an additional hole in my thermostats. I am not the original owner and the manual does not state how to orient the hole in the thermostats - my guess is they sit at 12-o'clock to allow air to pass out of the system when closed. Unfortunately, this causes calcium to settle in the thermostat housing during flushing as the thermostat stays closed with spigot water. I still believe these boats were designed/intended for freshwater use (due to the make-up of the factory anodes and the inadequate flush system), so calcium may never have been a big R&D issue. The new hole is 1/16" and I opted to place the larger, original hole at 6-o'clock to help evacuate any minerals.

Calcium content of waters (PPM = mg/L):
Seawater: 400 PPM
Freshwater: ~40 PPM*
* A very rough average as waters vary greatly across the US . The range seems to be as low as 0.50 PPM and can be as high as 90 PPM.

Trail Tech TTO: For added peace of mind and to view something tangible for how well it worked, I installed sensors (part # 732-EH2) near each thermostat to monitor temps from helm gauges. These are a version which can be hooked up to an outside power source, are programmable, have clocks, and are backlit. The 22mm adapter is a very tight fit - I could probably get away without the clamps! There is a 19mm option, but that could be too much of an exact fit to be water tight.

CrankyGypsy (established 2001)