Just wondering about thermostats and flushing!

[andymach23]

If you run your motor hard on the way back to the marina, then turn the motor off and get the hose to flush it using the hose attachment on the engine (80hp Yamaha 4-stroke), will the thermostat still be open as the engine is warm or will it close due to the cold water from the hose?

I'm trying to get my head round this issue of flushing using the hose attachment compared to running the motor on the muffs, which obviously isn't practical at the marina.

I appreciate that the thermostat should be open to get the fresh water round the engine properly. I run in salt water.

Cheers, Andy

 

[Silvertip]

Re: Just wondering about thermostats and flushing!

The thermostat does not control one and only one passage for cooling water. It and the bypass or poppet valve are used in combination. The poppet valve is spring loaded relies on water pressure to open and cool the engine. At slow speeds, the poppet is closed and the thermostat regulates engine temperature. At higher speeds the poppet valve opens by the increased water pressure and cooling water goes around the thermostat to cool the engine. So hooking up the hose to the flusher will still flush the engine via the poppet valve.

 

[Silvertip]

Re: Just wondering about thermostats and flushing!

The thermostat does not control one and only one passage for cooling water. It and the bypass or poppet valve are used in combination. The poppet valve is spring loaded relies on water pressure to open and cool the engine. At slow speeds, the poppet is closed and the thermostat regulates engine temperature. At higher speeds the poppet valve opens by the increased water pressure and cooling water goes around the thermostat to cool the engine. So hooking up the hose to the flusher will still flush the engine via the poppet valve. With the thermostat closed and no poppet valve, you would not be able get water through the engine.

 

[andymach23]

Re: Just wondering about thermostats and flushing!

Ok thanks, that's good to know.

When I flush my Yamaha F80 4-stroke on the marina hose, which has loads of water pressure, using the flushing port, I get a very poor dribble out of the pee hole. Is this a characteristic of larger capacity 4-strokes, or does this indicate a problem maybe?

My F40 Yamaha on my last boat gave a very strong stream from the same hose.

Cheers, Andy

 

[pine island fred]

Re: Just wondering about thermostats and flushing!

Have a YAMAHA F-115. A year ago I realised that the water is not going to circulate thru the block with the thermostat closed. I have since used the hose attachment and run the engine at idle, 700 rpm, for about 10 mins. with no bad effects so far. If I do find that I am destroying the water pump, my next move will be to drill some bleed holes in the stat to let some water circulate thru the block. Some on this site have said that some motors now have bleed holes in the stat disk for this purpose.
Am a fresh water flush fanatic and would have to stand in a muddy canal to use muffs. Same as replacing radiator hoses on your car. refill the radiator, heat up the engine, where did all the water go? Top off radiator. regards FRED

 

[pine island fred]

Re: Just wondering about thermostats and flushing!

Forgot to mention the dribble out the pee hole. Mine dribbles very little and it takes time. The hose attached to the flush port cant be much larger than 1/4 in. if that much. Small hose, lots of cooling jackets. I do stand right there in case the overheat warning goes off. No problems so far. FRED

 

[andymach23]

Re: Just wondering about thermostats and flushing!

Fred

So when you flush using the built in hose attachment with the engine running, is your engine out of the water?

If it's fully down and submerged won't it will still be drawing water in through the leg as normal?

Could you give me some more detail please of what your actually doing here with the motor please? Maybe your boat is on the trailer at this point.

Thanks for the info, much appreciated.

Cheers, Andy

 

[pine island fred]

Re: Just wondering about thermostats and flushing!

When I flush, the boat is on a lift with the leg down but out of the water. This question comes up perodically. Saw a post awhile back where someone said that the YAMAHA reps, I believe in ATLANTA, told him it was OK to do this at idle but YAMAHA does not want to commit to this being OK.
I started considering doing this when I noticed my neighbor flushing his mid 90s, RUDE V-6, thru an attachment where the pee hole is. Did not believe it was right until he showed me his owners manual that stated that this was acceptable. Try doing a search on the subject, a lot has been posted over the years. regards FRED