Thermostat

[Kostamayakid]

I live in Southern Mexico and I have an 85 HP two-stroke that started an overheat alarm after running for a short period. The tell-tale has a strong stream but the water is hot enough that I cannot put my hand under it for very long. I'm thinking it might be the thermostat. My question is can I just remove the thermostat and leave it out? Would this affect anything? The water temp down here runs around 80° year-round. Thanks for your help.

[boscoe99]

You need a thermostat in the motor. Not overly expensive and easy to change.

By the way, water out of the tell tale has nothing whatsoever to do with the thermostat. Water out of the Yamaha tell tale should not be hot. But, it has nothing to do with the thermostat.

[Kostamayakid]

Yeah, I know that the thermostat has nothing to do with the water coming out of the tell-tale Bosco. I only said that so that you would know that it wasn't the water pump or the impeller that was the problem. Another one of my problems is that I live about two hours away from the closest city. We have no Postal Service here, nor any kind of delivery like DHL or FedEx or even a grocery store. We have what they call tiendas which are like little mom-and-pop corner stores. In other words, just to even pick up a gasket is a four hour trip for me. After your reply I did some more extensive reading concerning the thermostat and the consensus is that it will run without it but it's better to have it so that your engine will operate more efficiently at the temp that it was intended to. What I have decided to do is go ahead and remove the thermostat and run the engine until I either get a heat alarm or I don't. I can also go ahead and check the thermostat to see if it is operating correctly while I have it out. If it's not a stuck shut thermostat that is the problem then I don't know where to go after that. Thanks for your input and hopefully I'll never have to use this forum again. LOL.

[robert graham]

When you remove the thermostat cover check there also for a black plastic spring loaded Pressure Control Valve which can get sticky like the thermostat. The thermostat and Pressure Control Valve can both be cleaned with a mild acid and an old toothbrush....often mineral/calcium deposits get on these items and cause sticking....good luck!

[99yam40]

the stat not only opens and closes to keep motor at a preferred temperature,
It also acts as a restriction even when open, which helps force water to flow properly to all parts of the motor as long as the passages are clean.
Without the stats in place there will be hot spots and cold spots in different parts of the motor.

Best to test the stat and put it back in if it functions as it should.

being that the tell tail come off before water flows through the motor on the Yamahas I have seen , I have never had the water from tell tail get hot before,so not sure what would cause it. sounds like not enough water flow or plugged passages maybe if stat is good.

[Mdelgado]

My question is can I just remove the thermostat and leave it out? Would this affect anything? .

If your engine isn't running at operating temp, you run the risk of excessive carbon build-up since it won't burn off completely. Build-up leads to fouled plugs and stuck rings. It won't happen over night, but will shorten the engines life and reduce performance. So i would say short term so you can use the boat, fine. Long term, no

If your engine is fuel injected, there are more reasons

[Kostamayakid]

Well, I can definitely say that the problem is not that my thermostat is stuck shut. When I took the thermostat cover off, guess what? No thermostat! No pressure control valve either. I'm going to do a quick start up and see if water is even getting up to where the thermostat should be. If not, then I know I have a blocked passage somewhere in the cooling system.

[99yam40]

Are you saying this motor does not have a PCV built into it or that someone removed it?

Removing it is just as bad or worse then it sticking open, it dumps too much water and the block will not fill up

[boscoe99]

What is the complete model of the motor?

It will not hurt your fingers to press a few more keys on the key board.

[Kostamayakid]

Yes 99yam40 someone has removed the thermostat and the pressure control valve. The complete model number is 85AET 688L1016966. Would anyone happen to know the year of my motor from the serial number?

[boscoe99]

Best guess is that it is circa 2003.

Is their a sticker on the side of the clamp bracket that provides the month and year of production? There should be.

[99yam40]

Yes 99yam40 someone has removed the thermostat and the pressure control valve. The complete model number is 85AET 688L1016966. Would anyone happen to know the year of my motor from the serial number?

You did understand what I wrote about the block not filling up at low RPMs,
It will cook the motor is there is no water in all places to cool

[Kostamayakid]

Yes understood 99yam40. The next time I make it to the big city I'm going to buy a new impeller, new gear oil, a thermostat, and PCV. The Yamaha 85 is the most popular engine in Mexico so hopefully the dealer will have everything I need and if not, I'll order it. By the way Bosco I was thumbing through the manual for the motor and noticed that the first printing of this manual was in 2007. I looked for a date sticker on the transom and couldn't find one. All there was was the model and serial number sticker. I'll post once everything is replaced let y'all know how it worked out. Thanks for your help.

[99yam40]

has this motor run ok without the stats and pcv in the past?
I do not see how it would, but I thought I would ask

May be you can contact the nearest shop and see if they have the parts or make sure they get them for you for when you make it to the area

[JohnOrrett]

That serial number seems to put it in the 2008 category. Seems to match the manual?