This is just a followup to my
earlier posting in this thread about my own 2001 Honda BF50A "making oil," and how it is commonly held that the most likely mechanical cause for this is a sticky goobed-up thermostat not allowing the engine to get up to proper operating temperature, which in turn allows unburnt fuel to mix in with the engine oil.
I ordered a new thermostat from the great folks at Boats.net (
part 19300-ZV5-043 THERMOSTAT ASSY. [Honda Code 5592167]) for just $19.25, and it arrived in just a couple of days. Swapping it for the old one is a snap and takes only a few minutes.
Nobody should fear this little job, no matter how otherwise mechanically
uninclined he or she may be. All you need is a 10mm wrench or, quicker still, a socket and ratchet. Just unclick the front and back engine hood clips and remove the hood. Next, remove the four bolts holding down the big black plastic cover over the top of the engine itself. One of these bolts, also holding down a little hose bracket on the right (starboard), may be longer than the others, so just remember that for later. The thermostat is inside a little gray metal cover located above and to the rear (aft) of the oil filter atop the engine, and is just held down by two 10mm bolts. Remove these two bolts and give the gray cover a gentle tap or two, and it should pop right off. Try to remove it without ripping the little papery gasket below (mine was green). You should be able to pull out the old thermostat, or, if it was as encrusted and corroded as mine was, just give it a gentle tap or two and it'll slide right out. At this point you might examine the housing in which it sits and clean it out a bit if needed. Mine was pretty gritty, so I just cleaned it up a bit with little pieces of fine sandpaper, some silicone spray and a rag, being careful not to tear the gasket. Next, drop in the new thermostat and replace and bolt down the grey metal thermostat housing cover. Before replacing the large black plastic engine cover, now would be a good time to give everything a good shot of silicone spray or WD-40 or similar, and wipe it all down a bit. It couldn't hurt to clean up the underside of the black cover a bit too. (By the way, you should know that this black cover would have to be removed if you ever needed to emergency "rope start" the engine if, say, if your battery was dead, as described on pages 40 through 42 of the
Service Manual.) Next, replace the black cover with the four bolts, click back on the big engine hood, and that's that.
Although I am not likely to test mine for a month or more, from what others have said about this being the likeliest cause for outboards "making oil", and given the non-functional state of the thermostat I pulled out, I am fairly confident that I may have solved the issue.
Some additional observations:
[*] My old thermostat was pretty well encrusted with salt and calcium and whateverallelse Neptune chose to spew at it before I got a hold of her. Once I got it home, I tested it by tossing it into a saucepan of water and gradually heating it with a meat thermometer hanging over the edge. Sure enough, the thermostat didn't even budge all the way up to a boil. So, I pulled it out, gave the unit a bit of a brush scrub, dumped a cup or so of white vinegar into the water and tried heating it up again. At about 180 degrees Fahrenheit it eventually popped open with an audible "
Pop!" After a few more coolings and scrubbings and heatings in the water-vinegar mix it started consistently opening smoothly at about 160 degrees, which is just what it should be doing (for Honda BF50s the operating/opening temperature depends its year of manufacture: through 2003 the thermostat opens fully at 162°F., while After 2003 it fully opens at 144°F.). So, it seems I now have a nice little working spare for swapping and cleaning out the one in place every now and then. It bears mentioning that folks who may be underway and away from regular mail service and experiencing overheating or "making oil" issues or discover that their "pee stream" is a bit too cool (and that this is not due to
far too many icey Margaritas) might do well to swing by the nearest waterfront restaurant, get a cup of vinegar, pull the thermostat, and just soak and scrub it while you have dinner. Any vinegar would do, and you don't really
need to heat it (though that
would speed the cleaning process), and a toothbrush would do the trick for scrubbing. This might just get you and your engine home in one piece without some big service bill from Cap'n Shifty's Marine Repairs.
[*] Once again, for Mac 26X owners, I cannot praise enough Harbor Freight's little
105 Pc Tool Kit with 4-Drawer Chest that I
first mentioned back in August. For less than $40 on sale or with a 20% off coupon, you'll have most every tool you're ever likely to need for thermostat swapping or almost anything else, all neatly laid out ship-shape and Bristol fashion in a handy box that's an absolutely perfect fit for the storage area under the settee forward of the galley. It's like it was
designed for the spot. I cannot say how it may fit in on a 26M, but on an X, as my British friends might say, "It's the dog's balls"...just
perfect. Get one.
