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How Necessary Is a Thermostat?

C

carpking

Member
After dropping my lower unit several times now trying to figure out why my 6 hp wont pee, I pulled the thermostat and it's fairly corroded and apparently non-functioning. I installed new impeller and get plenty of water discharge at prop but no tell tale. I have cleaned every water line I can find, sprayed water through them and nothing comes from the pee holes. I am considering running motor without thermostat to see if it is the problem. Every dealer and forum I talk to says it should pee. After impeller change, motor never overheats, but no pee. Long story short, if it won't pee without thermostat, it either isn't meant to pee, or something is clogged in block. I have ordered a new thermostat, but I just want to make sure it is safe to run it temporarily without. Any help is greatly appreciated.
 
The thermostat serves to regulate a constant temperature throughout the powerhead. It also provides a needed restrictor to cause the water jacket to fill completely with water, thereby circulating cooling water to the entire powerhead. The top area being most critical because it absorbs the most heat from the cylinder(s) in every motor. Without the thermostat there is NO restriction to water flow through the powerhead and the cooling water of course takes the path of least resistance and just flows unrestricted out the water exits without completely filling the powerhead water jacket. The top of the powerhead receives less cooling water and develops hot spots and early metal fatigue related failures. It doesn't hurt to run the motor for a short time without it just to check if this will cure the lack of a tell-tale stream but I would be very surprised if it does. If you found the old thermostat severely corroded there is a good chance that the interior walls of the cooling jacket are also corroded and the nipple to the tell-tale outlet is blocked with this corrosion or some other object. With the thermostat out you should be able to blow air into the tell-tale outlet and hear or feel it being passed through with the thermostat cover off. If not you're going to need to run some stainless wire or similar up into that tubing till it clears the obstacle out. If you see a lot of corrosion in the water jacket you can spray some CLR into the water jacket and let it clean it out, then flush it thoroughly with water.


-Mike



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Saved my 9.9 by using "saltaway" , I use it with the adapter after every outing, cheap insurance. after completely clogged cooling passages in my 9.9 (previous owener) soaking it through the thermostat housing, disolved the salt and now have a great engine1
 
Found problem. After hours of looking for a diagram of water passages online, I stumbled across a video of an 8 hp 2stroke yamaha with the tell tale shooting from side of motor instead of the two small exhaust holes where I was expecting to find it. Sure enough, small single hole fitting underneath motor with some calcium build up on it. Poked a coat hanger in it, started, and voila, tell tale. Everyone I have asked told me the tell tale should be the two exhaust ports in the back. Could've saved me a lot of trouble if I could've found one person familiar with these smaller Yamahas. One thing I have learned. Yamahas get a lot of praise as good motors everywhere I look, but after pricing the few parts I have for this little motor, this will be the only one I will ever own. With standard shipping, thermostat and small bushing that holds it in was $40....for a thermostat. Ridiculous. Motor really needs a new clamp bracket as one is cracked...price? $125!! In excellent condition, the whole motor has a value of a couple hundred bucks. Now I am resigned to JB Weld and some type of reinforcement. A broken motor mount should not be the end of a good motor for a ridiculously over priced part. Anyway...that's my rant. Not complaining about this forum, mostly the dealers I talked to who assured me the tell tale was the two small holes in back EVEN when I asked if it could be somewhere else.
 
Hamfisted said:
The thermostat serves to regulate a constant temperature throughout the powerhead. It also provides a needed restrictor to cause the water jacket to fill completely with water, thereby circulating cooling water to the entire powerhead. The top area being most critical because it absorbs the most heat from the cylinder(s) in every motor. Without the thermostat there is NO restriction to water flow through the powerhead and the cooling water of course takes the path of least resistance and just flows unrestricted out the water exits without completely filling the powerhead water jacket. The top of the powerhead receives less cooling water and develops hot spots and early metal fatigue related failures. It doesn't hurt to run the motor for a short time without it just to check if this will cure the lack of a tell-tale stream but I would be very surprised if it does. If you found the old thermostat severely corroded there is a good chance that the interior walls of the cooling jacket are also corroded and the nipple to the tell-tale outlet is blocked with this corrosion or some other object. With the thermostat out you should be able to blow air into the tell-tale outlet and hear or feel it being passed through with the thermostat cover off. If not you're going to need to run some stainless wire or similar up into that tubing till it clears the obstacle out. If you see a lot of corrosion in the water jacket you can spray some CLR into the water jacket and let it clean it out, then flush it thoroughly with water.


HI....I see you haven't been on here in a long time but I ran across your reply to the OP and it's of great help. I'm trying to get water out of the bleedhole and something inside that water jacket must be clogged. With the motor running, I have water coming out of the thermostat area when it's removed, so I know the impeller is working. I also know that the bleedhole tube and the tube forming a U on the bottom of the water jacket is free and clear. Something inside that water jacket must be completely blocking the flow as when I try to shoot air through one of the tube ends, it just blows the tube off the nipple. Even shooting air straight into the nipple builds up pressure and essentially blows the air nozzle off. No air comes out of the thermostat area like you suggest. What would you recommend? Can that water jacket be disassembled? And do I shoot that CLR into those nipples on the water jacket? I don't know how it would penetrate into it but perhaps that'll work?

Thanks in advance if you get this message!!!


-Mike



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Hello ! Yes, it's been a long time. What motor are you working on ? Can you get any stainless wire to pass into the outlet nipple? Stainless leader wire is a good tool for this. The water jacket itself can't really be disassembled, but you can remove some plates and covers to gain access to limited areas. Your best bet is to work to get a wire or small drill bit to be able to pass into the outlet nipple and free up whatever is blocking. Running the motor in a tub of fresh water and white vinegar is a good way to do a mild sediment flush on the motor. The CLR is a more aggressive way to clean out the water jacket, but you have to be sure to get a good fresh water flush out after using it.
 
Hamfisted said:
Hello ! Yes, it's been a long time. What motor are you working on ? Can you get any stainless wire to pass into the outlet nipple? Stainless leader wire is a good tool for this. The water jacket itself can't really be disassembled, but you can remove some plates and covers to gain access to limited areas. Your best bet is to work to get a wire or small drill bit to be able to pass into the outlet nipple and free up whatever is blocking. Running the motor in a tub of fresh water and white vinegar is a good way to do a mild sediment flush on the motor. The CLR is a more aggressive way to clean out the water jacket, but you have to be sure to get a good fresh water flush out after using it.
Click to expand...


Awesome! I will try those things and see if I have luck. I've been on TheHullTruth forum as well with bunch of suggestions (some of them repetitive as the responders don't always read the whole thread). I'll see if this has any good results and let you know. Thanks a bunch!! -Mike
 
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