I have a 1993 yamaha 115. The overheating alarm goes off when I run full throttle for 4-5 minutes. After the engine drops tp 2000 rpm for a minute the alarm stops and I can resume without any issues. The motor can run all day a 3/4 throttle with no problems. I have changed the impeller, thremostats and still the same issue. I read somewhere that the alarm will sound and the engine drop to 2000 rpm if the voltage drops below 12 volts. I have new batteries in the boat. Anyone have any ideas what I should check next? Thanks.
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Re: yamaha 115 overheating or electrical problem
A few posts down, I wrote the following. I don't know if it's your particular problem, but the symptoms are identical.
I'm betting that you first noticed it at full throttle only and as time goes by, at lower and lower throttle. It will continue to decline with use.
My experience is that such alarms are caused by scale build-up on the outer walls of the cylinders in the block and in the heads. That insulates the aluminum from the cooling water and the heat stays in rather than transferring to the water. I'm afraid that a thermosensor won't detect this condition because the outer cooling surfaces don't get as much build-up and the block will show normal temperatures.
To remove the scale, the heads have to come off. Then lay them flat on their backs and fill the cooling cavities with vinegar or milkstone remover (a farm supply product). The scale on the outside of the cylinder walls can be removed manually with an old toothbrush and milkstone remover. Protect electrical components when you do this, and wear protective goggles and rubber gloves. And definately do it outside where there's plenty of ventilation.
Once done and reassembled, run plenty of fresh water through the motor to clean out the residual acid. Do not use muriatic acid or Zing. Those eat aluminum. Milkstone remover doesn't. A very similar product to milkstone remover is called Acid Wash. They are both phosphoric acids. They come by the gallon and are rather inexpensive.
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I have a 1993 yamaha 115. The overheating alarm goes off when I run full throttle for 4-5 minutes. After the engine drops tp 2000 rpm for a minute the alarm stops and I can resume without any issues. The motor can run all day a 3/4 throttle with no problems. I have changed the impeller, thremostats and still the same issue. I read somewhere that the alarm will sound and the engine drop to 2000 rpm if the voltage drops below 12 volts. I have new batteries in the boat. Anyone have any ideas what I should check next? Thanks.
Is this a salt or fresh water motor? Friend has the same problem. Can you give any more info on that voltage dropping below 12 volts ? He is about to put a 357 slug thru the block. good luck fred
Hey Willy, have you (or anyone) tried Neutra-Salt? It's put out by Volvo, but we've used it on all kinds of things...does wonders for a/c units. I've just tried it on what I suspect is scale buildup on one of a side customers '88 yama 200's but won't know how it worked for a couple of weeks till in the water...just curious.
The motor is used in both salt and freshwater. Most often in fresh. If you search this forum, there were a couple of conversations about how if the voltage drops below 12v then the motor will cut out and drop to 2k rpms and the alarm will signal for a minute or two. Very similar to an overheat symptom. My electrical on the boat has been a little qwerky at times so I plan on checking the poppet valve and look further into the electrical before pulling the head. Any other ideas would be welcome. If those don't work I may need your buddy's 357.
What we did today is worth a shot. We pulled the overheat switches, got a pot of water and used a digital meat thermoter. Hooked up the switch leads to an ohm meter and found out when the switch closed. In our case they both closed at 180 deg F. Took a few minutes but we did eliminate the chance that one switch was closeing prematurely. Had his wife hide his magnum and intend to remove the stats, fill the block with vinigar or acetic acid, fill the head cooling channels with a large syringe while plugging off all the drain holes and see if we cant slowly eat away at what might be in there. Willing to try anything before he goes out and buys a 220 hp. E-tech he has got the hots for. Think he is looking at better than 15K. regards and good luck FRED
yamaha 115 overheating or electrical problem
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