UPDATE Removed the lower unit this a.m. There are no screens in the lower unit. You can see the entire passageway down to the inlets, and there is nothing blocking anything. There are also inlets on the front of the gearcase, and I used compressed air to verify that there are no blockages there, either. I put the fitting on the back of the motor and flushed. Nothing but water came out. I then squirted a hose up into the water pipe in the shaft, and the water will not go in that direction... Presumably because of the thermostat(s). I can see no evidence of blockage anywhere, although I don't know if there is some and it is slowing the water down. If there is, it would have to be up in the engine where I can't see. I would not think this is a thermostat issue, because it is fine at higher speeds, so the thermostat must be opening, right? Or could it be opening too much, too early? I need to figure out where to look next. I'm not sure where the poppets and thermostats are but I guess my next step is to see if I can find them.
Water should flow freely up through the supply pipe which is the output from the pump. It should come out the telltale and down through the exhaust regardless of the thermostats. You may have sand in the midsection or the block. Remove the thermostats and flush through there with a rag wrapped around the end of the hose. Then up through the supply pipe, and repeat. I think you are saying that one of your pickups is low on the lower unit. Those will vacuum up sand big time. jim
Jim There appears to be a belt driven waterpump too [ok - it is an air pump - not a water pump, just to clarify] It stops waterflow from coming out the tell [I'm told now that the thermostats are what stops the water from flowing up through the water tube in the shaft but I'm still not sure...; corrections added to this post by Markbano on 7/13/11]
Got the news from the repair shop. It was a bad starboard side thermostat. I had already figured out that it was a thermostat through online research. If it is cool at WOT, which it was, but overheating at low to mid range, and you have a good Impeller then that usually rules out blockage, Impeller, and poppets (which open at higher rpm/pressure and essentially bypass the thermostat), which leaves the thermostat(s) as the leading suspect. Good info to have.
Just to finish off this topic.... Post thermostat replacement, I was seeing temps no higher than about 137 degrees last weekend, no matter what I did with the boat. So.... If you are seeing temps up in the 150s or 160s or even low 170s with an optimax, perhaps you should investigate - either impeller, thermostat, or poppetsm, or a clogged intake. Once you hit the mid 170s - you should get a warning horn. I know Jim is going to ask me what water pressure numbers I was seeing, and I have to apologize because I never really paid attention. I was too busy pulling skier after skier all weekend but I know that the temps were usually in the 120's.
I check my water pressure before putting the engine in gear to make sure that I have some and to note any trend in idle pressure. This usually the first indication of a weak impeller.--loss of some idle water pressure. jim
Mark; glad your problem is finally resolved, and thanks for posting. It's a very informative thread with a resolution! I'll be saving this one in my trouble shooting file.
Mark glad you got it fixed. I would have answered earlier but have been kinda busy lately myself. Your OPTI should always run around 137 degrees earlier this year I had an OPTI running at 98 degrees and had sand stuck in the thermostats. The pee hole water comes directly from the air pump so if that plugs up your air pump will not stay cool enough and will wreck the air pump. I also had some coils that went bad but there is a recall on them. Your tech should be able to help on this.
I have been installing water pressure gauges on all engine, after new impeller test drive and see what pressure you have at different RPM, now when your driving you will know if you lost one of your impeller blade or if intake is getting plugged on in one case the boat pickup was not in water, lift to high.
