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2007 Yamaha F200 Thermostat Problem

G

glentre

New member
After repairing a leaking port side thermostat housing on my 2007 Yamaha F200, I installed a new thermostat. On starting the engine after this work, there was no water coming out of the telltale. As soon as the overheat beeper sounded, I shut it down. The motor was on the boat and sufficiently deep in the water to get the water pump working. Thinking I had a defective thermostat, I removed and tested it in hot water and it appeared to open at about 150 degrees or so. I then assembled the parts but without the thermostat installed and cooling water came out of the telltale with a strong stream and the motor ran fine without overheating.

Are there any electric wires or tubes I may have dislodged or disconnected that would prevent the thermostat from working? What could I have done wrong that would prevent a new and seemingly good thermostat from working? Any help or comments would be appreciated.

Glen
 
Purchased on the net......not sure if they are OEM or not. Both new thermostats as well as the olf one taken out of the engine tested as properly functioning.
 
Water flows upwards from the water pump through the oil pan.

First stop is the exhaust guide. From there water goes in two directions.

1. To the rectifier/regulator, then on to the fuel cooler, then on to the tell tale.

2. To the motor itself.
 
Boscoe,
Thanks for your input and what happens to the water flow inside the engine. Please remain patient and stay with me on this. I'm still confused, though. I had no water out of the tell tale after replacing the thermostat but had water out of the tell tale when the thermostat was taken out. Assumption being the thermostat was the problem but the two new ones and the old one tested ok in water on the stove.

The reason for all this is that I had a small hole in the thermostat housing in the block that leaked coolant water. I took off the thermostat cover and using a Dremel, thoroughly cleaned the hollow bowl shaped recess inside the engine down to bare aluminum all around the hole. Same with the outer surface of the block housing. I then used quick-set JB Weld inside the casting, allowing it to squeeze out the hole and also built up a layer on the outside surface. If I overfilled the internal thermostat housing bowl with the Weld in my effort to ensure there was sufficient patch material to plug the hole, could that interfere with the flow of water around the thermostat, preventing it from opening?

The JB Weld resolved the leaking problem but now the engine overheats with the thermostat in place. Am I thinking this through correctly or could I have done something else in the process of taking things apart that is causing the overheating problem? Your input is much appreciated.

Glen
 
Boscoe,
Your informative diagram helps to understand the flow of cooling water in the motor. Thanks for sending it.

You mention the thermostat has nothing to do with water flow out of the tell-tale and your diagram seems to show that. But I thought that with the thermostat closed, there would be no flow of coolant in the system and thus no water coming out of the tell-tale until the thermostat opens and flow starts. What am I not understanding? After my repair, there was no water out of the tell-tale and the motor overheated. After running with the port side thermostat removed, there was an immediate flow out of the tell-tale and the motor did not overheat. Then there is the starboard thermostat that has not been touched. I guess I'm not understanding how the two thermostats function and what action I should take at this time.
 
In some Mercury Marine motors the tell tale water comes after the thermostat. Known as a hot pisser. Yams are cold pissers. Water is generally luke warm at best.

With the boat in the water Yams should start peeing shortly have the motor starts. On a cold day, long before the thermostat opens.
 
boscoe said:
In some Mercury Marine motors the tell tale water comes after the thermostat. Known as a hot pisser. Yams are cold pissers. Water is generally luke warm at best.

With the boat in the water Yams should start peeing shortly have the motor starts. On a cold day, long before the thermostat opens.
Click to expand...
My motor tell-tale peed nicely before I started repairing the leak. After patching the hole and installing a new thermostat, no water came out of the tell-tale and the helm beeper went off because, I assume, the motor was overheating. I then removed the thermostat and reassembled all that I had taken apart. On starting, the tell-tale began peeing immediately. Can I correctly assume the water pump is functioning ok? My unresolved question is why did no water come out of the tell-tale and the motor overheated after the repair? And, why did water come out of the tell-tale after the thermostat was removed and the motor did not overheat. Knowing why that happened should guide me on what to do next to get my motor running properly again. I really appreciate your patience on this and look forward for some advice from you.
 
Failure analysis is tough. Millions of dollars spent in aviation trying to determine why stuff went wrong and many times they never find a smoking gun.

If water is now coming from the tell tale and the motor is not over heating then all I know to do is to drive on. Just one of those days.
 
boscoe said:
Failure analysis is tough. Millions of dollars spent in aviation trying to determine why stuff went wrong and many times they never find a smoking gun.

If water is now coming from the tell tale and the motor is not over heating then all I know to do is to drive on. Just one of those days.
Click to expand...
Thanks for your quick reply. Yes, water is now coming from the tell-tale and the motor is not overheating but, importantly, it does not have a thermostat on the port side. Would it be ok in your opinion to run the motor under full throttle conditions for extended periods of time without one of the two thermostats in place?
 
For what purpose would you not want a thermostat installed? Motor would run far too cold I would imagine.

More on the path of water flow out of the thermostat.

 
Sorry if I confused you. No, I do not want to run the motor without a thermostat. Just asking your input whether my f200 Yamaha would be OK to use without one.

My problem is that the motor overheats with both thermostats installed but with the port thermostat removed, it does not overheat. It seems to run fine on the river at least at low throttle but because one thermostat is removed from the motor, I have not taken the boat up on plane or at full throttle for fear I might damage the motor with one thermostat removed. At this point, I guess it would be best if I tested the motor again by re-installing the port thermostat and see if it again overheats. I do not understand why this is happening.

I'll be away most of the coming week but will reinstall the port thermostat when I get back and see if it again overheats. I'll keep you posted.

Glen
 
Sounds to me like something is preventing the port side thermostat from opening up or allowing water to flow freely.

Many have run Yams without thermostats installed. Bandaid approach to fixing whatever the problem is.
 
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