Don’t change your thermostat

[Noble Savage]

A guy told me not to change the thermostats on my 1996 OX66 Yamaha outboard because I risk breaking the bolts off. My outboard has super low hours (like 200) and virtually no signs of corrosion under the cowling. But the outboard is 27 years old. Has anyone else broken these bolts?

 

[seasick]

How long have you owned it? Do you know when t-stats were last serviced.

If not a long time, it is possible that the previous owner changed t-stats regularly. Not changing the t-state is one reason why the bolts may break
Does you 'guy' also suggest that you don't remove any other bolts like the LU, water pump, zinc anodes, etc
I have a 1999 OX motor and I have not had issues servicing the t-stats. Then again, I often dab a little anti-seize on bolts.

 

[oldrusty]

Seasick is correct, worst thing to do is to not service the motor regulary including the t -stats. Think its better to break a bolt onshore during maintenance, than a overheating problem at sea. i have a 1994 Yamaha 150 2 stroke and not afraid to pull t-stats when needed. Age makes no difference, regular maintenance does. You might give the bolts a couple days of soaking with a good penetrating oil first.

 

[family affair]

While it's a long time to potentially not take something apart, I wouldn't let it stop you from trying.
For that application I'm not a fan of penetrating oils. I think their use is over rated unless you can back the bolt out enough to get oil under it. I've had far better luck with a hammer and/or hammer and punch to tap/pound on corroded bolt heads to break loose corrosion. Heat from a heat gun can help too depending on the bolt location to an edge. There are a number of other tricks to consider. I won't add to the list, but the above is my go to. If it isn't budging, stop before you do break it. At least at that point you can determine if you want to risk doing nothing, or budget time for a broken bolt.

 

[DennisG01]

I would agree with the others that it's way too cautious of advice that you got. I would never NOT change a t-stat for that reason... besides, the bolts are at least in a good area to extract if needed.

Whether penetrating oil will sneak in there or not is debatable - but it also can't hurt to use it. Impact is one of the keys - even using an impact gun - one hit forward, one hit reverse, repeat.

 

[Fishtales]

Could try a product called Superzilla. Check it out on the web. I've never used it but if anything like it is advertised, I just may.

 

[Noble Savage]

Wow. I really appreciate the advice. I had already ordered and received genuine yamaha thermostats and planned on changing. I’ll give it a go and let you guys know how it works out. Should be fine. Btw, I bought the $100 ac delco torque wrench and it is amazing. Tested in next to my friends $400 snap on and it was dead on. Takes out the guess work. Thanks again for the advice

 

[Chessie246G]

Wow. I really appreciate the advice. I had already ordered and received genuine yamaha thermostats and planned on changing. I’ll give it a go and let you guys know how it works out. Should be fine. Btw, I bought the $100 ac delco torque wrench and it is amazing. Tested in next to my friends $400 snap on and it was dead on. Takes out the guess work. Thanks again for the advice

Hopefully you ordered the gaskets as well. The thermostats do not come with them.

 

[seasick]

Overheating at idle speeds can be a weak pump or a stuck open poppet valve. Overheating at speed is not a symptom of a stuck open poppet valve but a weak pump is ( along with some other ugly causes).
My guess would be tha the water pump needs to be rebuilt