MR-1 CLOSED LOOP FLUSH
(referencing a 2005 Yamaha AR230HO)
I solved an intermittent overheat that resulted in limp mode on one of my engines due to a bad thermosensor, but was still getting overheat warnings on both engines during WOT runs over 4-5 miles. Monitoring with YDS (Yamaha Diagnostic Software), both engines were doing the same thing at about the same rate, so I ruled out electrical issues. I then suspected that the issue was scale build-up inside the water jackets, particularly calcium carbonates, likely due to very poor flush practices from previous owners. I devised this closed loop flush to remove the scale.
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 followed the sulfamic flush 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.
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 an 11/16" drill might've been better. I carefully shaved the threads down on 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: After removing the clean out tray, 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.
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 was too loose and would fall out, so I had to wrap Electrical Tape around the PVC Pipe a few times, just below the Cap edge. I wrapped it until it was just thick enough that it snuggly seated inside the muffler - it doesn't have to be air tight, it just has to stay in place well.
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, using the second pair of Pinch-Off Pliers, I clamped 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 along with the 1/2" OD 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 with the average garden spigot.
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 were 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 tepid 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 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 until sediment became minimal in the bucket. Adding the second hose helps push larger bits of sand out that were broken up during the acid flush or lying along the floor of the muffler.
FLUSH SCHEDULE :
closed loop = pumping, with return hoses feeding back to the bucket for recirculation.
Three gallons of water will be adequate 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 - the acid will not harm the rubber. You can also throw the tail pipes in as well, but be sure to neutralize these parts with soda ash. 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 the holes sit at 12-o'clock to allow air to pass out of the system when the thermostat is closed. Unfortunately, this can allow calcium to settle in the thermostat housing during lower temperature driveway flushing. I 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 during routine flushing.
Trail Tech TTO: For added peace of mind, I later installed sensors (part # 732-EH2) near each thermostat to monitor temps from helm gauges. These are battery-powered gauges that 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. Both engines consistantly showed around 121 degrees Fahrenheit at WOT, which matched readings from another boater with the same sensors.
CrankyGypsy (established 2001)