Flushing Yamaha F250s

[grady33]

My 330 Express is on the hard for the winter and goes back in the water in 2 weeks. We got her ready this past weekend and replaced the thermostats and anodes and I wanted to run her for a few minutes to make sure all is ok prior to launch. In the past, I’ve used a large tub which is a pain. I’ve heard you can tape up bottom pick up and use double sided muffs with good water pressure.

I’m a little bit worried about trying it that way and was wondering how my fellow Grady F250 owners are doing this. Have seen some flush bags out there but not sure they are big enough.

 

[seasick]

Yes, you can tape the high speed water pickups and use muffs. Dual muffs are OK but dual cup/single feed will also work. As long as you see water coming out of the drain holes and prop before and after starting and see the telltale stream within about 30 seconds or so after starting the motor, you should be fine. Don't rev too high.

 

[DennisG01]

Ditto the above. You don't need to spend the extra money on a dual-sided muff - the $6 one is just fine. It's still the same amount of water going to the same place.

 

[Doc Stressor]

You need to tape the low water pickup as others have said. But I've found that my F250 would send an overheat signal if I at anything over the 700-800 rpm dead idle speed using only the muffs (the large double-sided ones). My Yamaha tech neighbor turned me on to using 2 hoses, one to the muffs and the other to the hose flush connection. I've done diagnostics at high rpm without overheating with that setup.

 

[DennisG01]

One thing to add - just sort of a side note... results will vary based on conditions... specifically, length of hose, GPM and PSI of your water source. At my house, I have about 9gpm and 75psi and plumbed a new faucet with a 3/4" supply line (from the main, 3/4" house supply), highflow faucet and 3/4" hose. I've run all kid of engines - including large sterndrives that require a much higher flowrate impeller - never an issue with a normal muff. But again, results will vary based on conditions.

Also... NO hose will equal actually being in the water.

 

[wrxhoon]

I always flushed engines with muffs, single sided and double, never had a problem with overheating or salt deposits in the jackets. I flush for about 10 minutes always at idle speed . When I had two stroke engines I would pump the throttle at the end of flashing time to dump extra oil in the crankcase then turn off. No advantage doing this with a 4 stroke. It is not high pressure you need, it's volume and the hose usually has more than enough volume ( in our part of the world) to adequately cool the engine at low RPM. The factory flashing port is there for boats kept in the water, it's not as good as flashing with muffs and engine running, hot water will dilute salt much better.
By the way modern engines will have overheat alarms, always stay with the boat whilst flashing just in case something happens to the water supply. You will damage the water pump running it dry, turn water on wait a few seconds then start.

 

[SkunkBoat]

My ox66s will not run on muffs. Have to fill up the Yamaha hot tub...

 

[Fishtales]

When I do it, I use a tub as well. I just don't trust the muffs.

 

[DennisG01]

Skunk... what happens with your OX66's? Although most 2-strokes tend not to run as nicely on a hose (need to be in the water for some backpressure on the exhaust), I've never had an issue running mine. Slightly erratic, at first, but runs fine.

 

[seasick]

Skunk... what happens with your OX66's? Although most 2-strokes tend not to run as nicely on a hose (need to be in the water for some backpressure on the exhaust), I've never had an issue running mine. Slightly erratic, at first, but runs fine.

My OX66 runs on muffs OK as well. I have also run it once or twice on the flush port (Yamaha is iffy on that practice),
Regardless, if you see a decent telltale within about 30 seconds of starting, sufficient water is circulating. Whether or not you will get enough water may depend not so much on water pressure but on water volume. If you use a too small diameter or a too long hose or one of those shrinkable crinkly hoses, you may not get sufficient flow.
Many motors , especially 2 strokes, may run rough on muffs and it has nothing to do with cooling. The exhaust systems are tuned to optimally operate with some back pressure which ig there when the lower unit is under water and the exhaust has to push against the water. When on muffs, the back pressure is reduced and the motor may run rough.

 

[Ky Grady]

My F225 doesn't like the muffs, throws a overheat alarm. Have a old water trough left from my horse riding days, Rubbermaid Yamaha hot tub.

 

[SkunkBoat]

It might be that I'm 3 hoses from the house...They just don't ever pee in a decent amount of time unless they are in a tub...then its immediate...

My old boat had a DF140 that ran fine out there and my father in law has Volvo I/O that he runs out there too.

 

[Fishtales]

My F225 doesn't like the muffs, throws a overheat alarm. Have a old water trough left from my horse riding days, Rubbermaid Yamaha hot tub.
View attachment 7334

 

[Fishtales]

My F225 doesn't like the muffs, throws a overheat alarm. Have a old water trough left from my horse riding days, Rubbermaid Yamaha hot tub.
View attachment 7334

Can you provide details on that trolling motor. That looks interesting.

 

[Ky Grady]

Can you provide details on that trolling motor. That looks interesting.

Minn-Kota EM 80, 24 volt. I use it while drift fishing if/when the wind dies. Need to be moving to catch fish. Works well for what I want it for. No deployment needed, just turn knob for desired speed and away you go. Steer with the helm. When up on plane, it's out of the water for the most part.

 

[SmokyMtnGrady]

Minn-Kota EM 80, 24 volt. I use it while drift fishing if/when the wind dies. Need to be moving to catch fish. Works well for what I want it for. No deployment needed, just turn knob for desired speed and away you go. Steer with the helm. When up on plane, it's out of the water for the most part.

View attachment 7355

Does it have a turbo boost when on the plane? I bet it could get you an extra mile per hour on it. Lol. If your motor died for whatever reason on the lake, I bet it would get you home. That's pretty cool.

 

[seasick]

My OX66 runs on muffs OK as well. I have also run it once or twice on the flush port (Yamaha is iffy on that practice),
Regardless, if you see a decent telltale within about 30 seconds of starting, sufficient water is circulating. Whether or not you will get enough water may depend not so much on water pressure but on water volume. If you use a too small diameter or a too long hose or one of those shrinkable crinkly hoses, you may not get sufficient flow.
Many motors , especially 2 strokes, may run rough on muffs and it has nothing to do with cooling. The exhaust systems are tuned to optimally operate with some back pressure which ig there when the lower unit is under water and the exhaust has to push against the water. When on muffs, the back pressure is reduced and the motor may run rough.

A funny thing happened two weeks ago. Although I previously stated that I run my motor on muffs with no issues and have for years, this season while getting things ready for launch, I did get an overheat alarm on land on muffs. Of course I first though that the pump or t-stats were bad after the winter. It felt that one head was hotter then the other so I pulled the t-stat and it was open (and hot) and as it cooled it closed as it should. The telltale was streaming but there was an odd pattern to the flow of water out of one of the LU's weep holes.
To make a long story a bit shorted, I had extended my hose by adding one of those crinkly shrinking hoses. Although the pressure was fine, apparently the volume wasn't. I swapped out that hose for a regular one and the motor ran without overheating. Once in the water all was well.
So once again, you learn something new every day.

 

[Fishtales]

Thanks for the explanation. That is a nice little add....

 

[DennisG01]

Yes, it's definitely all about flow. Too often pressure is all we look at and think everything is fine. A 1/8" tube attached to the end of a garden hose can supply A LOT of pressure... but imagine how long it would take to fill a bucket!

You can get inexpensive PSI testers ($10) at just about any home center and screw it onto your fitting. To check flow (GPM), use a 5-gallon bucket and time it, then do the math. For comparison, I have 72PSI and approximately 9GPM - more than enough to satisfy the Merc specs for a Bravo III sterndrive, which pumps a lot more water than an Alpha or an outboard. I have run the Yami and many, many sterndrives on that - sometimes for 30 minutes.