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Author Topic:   Silently Flush Your Outboard Engine
rmart posted 07-23-2003 11:23 PM ET (US)   Profile for rmart   Send Email to rmart  
[Seeks] any experience with back-flushing engines, that is, running fresh water through the tell-tale or water pump indicator backwards through the engine? I saw a back-flusher kit on Ebay recently (for $20) and it is advertised as a way to flush your outboard engine without running the engine. Even suggests that it can be used while in water.

While my neighbors would love if I silently flushed like this, I am not sure if it is as thorough as with earmuffs or whether it could even damage the water pump, thermostat, or any other component. Your thoughts and input is appreciated.

whalerron posted 07-23-2003 11:47 PM ET (US)     Profile for whalerron  Send Email to whalerron     
I am not sure what year or make motor you have but the newer Johnson motors are setup so that a hose can be connected where the telltale stream comes out of the motor. The stream fitting can be removed and the garden hose can be connected in its place. Then, if you turn on the house water to the hose, the motor can be run. The Johnson manual says this can be done with the boat in or out of the water and with or without the motor running. The neat part is that you don't need to buy any flushing device other that a garden hose.
Jarhead posted 07-24-2003 08:42 AM ET (US)     Profile for Jarhead  Send Email to Jarhead     
rmart--You still have to run the engine using the back flush in order to open the thermostat and circulate water through the water passages, so the kit wouldn't help with the noise.
BW23 posted 07-24-2003 09:38 AM ET (US)     Profile for BW23  Send Email to BW23     
I keep my 23 [unclear], Mercury 225 EFI in the water. I learned from another site not to run the motor when using the [tell tale] cowling connection.

I now flush with muffs after every weekend.

I agree with JARHEAD, you need to run the engine to open the thermostats for the "best" flush.

triblet posted 07-24-2003 10:37 AM ET (US)     Profile for triblet  Send Email to triblet     
The owners manual for my c.1996 Evinrude 90 2-stroke says you
don't have to run it if you flush it through the tell-tale
plug. I've been doing this for five and half years of
saltwater every weekend.

But don't turn the hose on full blast. The manual says 50
PSI max. My house gets about 60 PSI static pressure, the
Pt. Lobos ramp gets 125 PSI static pressure. I rigged up
a pressure gauge -- 1/4 turn on the hose bib gives about
30 PSI at the motor.


bsmotril posted 07-24-2003 10:41 AM ET (US)     Profile for bsmotril  Send Email to bsmotril     
You do not have to run late model Mercury motors to get a good flush. The thermostats are on the water feed sides to the block and heads. The flusher port is on the output side of the heads. You are back-flushing and the water pressure is enough to open the spring loaded thermostats and pop valves to back-flush the exhaust. The flush water coming in the port goes through the heads before even hitting the t-stats. After passing the t-stats, it then backs down to the water pump housing.
Bigshot posted 07-24-2003 10:49 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
If engine is warm t-stats are already open now aren't they?

Back-flushers RULE!

ShrimpBurrito posted 07-24-2003 03:47 PM ET (US)     Profile for ShrimpBurrito  Send Email to ShrimpBurrito     
Of course, you could also always by a $10 30-50 gallon plastic tub at Wal-Mart and use it as a tank to flush your motor. Obviously, it's just as quiet as idling while the boat is in the water.
Bigshot posted 07-24-2003 04:16 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Heck, throw it in the pool!
rmart posted 07-24-2003 10:57 PM ET (US)     Profile for rmart  Send Email to rmart     
Whalerron, my engine is a 1987 Yamaha 115hp and does not have any such setup for a back-flusher, however, the installation of this kit seems pretty darn simple. My only concern was would damage be done by reversing the water flow through the telltale hole. From the comments here, I assume no such damage would occur.

With respect to running the engine, with the water running in reverse would it still be safe to run the engine? Does the direction of water flow matter?

Thanks again.

hookinfinger posted 07-25-2003 07:15 AM ET (US)     Profile for hookinfinger  Send Email to hookinfinger     
Hi everyone !
I would like to flush my engine after every use. I just rented a wet slip and would like to be a good neighbor.

Is there any reason why I can not flush ny 1990 70 Johnson motor in the fully tilted down position using muffs?

If the muffs are making a tight seal I see no problem and the noise factor has been eliminated.

Am I wrong ?
Regards, Dennis

5 mi E of Milwaukee posted 07-25-2003 07:38 PM ET (US)     Profile for 5 mi E of Milwaukee  Send Email to 5 mi E of Milwaukee     
Overtons sells something called a “Flush Muffler.”

It works swell. My 90hp 2 stroke Mercury can be run on earmuffs without my having to wear earmuffs as well. In fact, you can actually talk to someone while standing near the rear of the boat while the motor is running.

Besides significantly reducing the racket, it’s my guess that it adds a little back pressure to the through prop exhaust, more nearly simulating in-water running. It’s my guess, as well, that the motor “likes” this.

(Interestingly, when I first heard of such a thing I went to the local Boat/US store where they had yet to hear about it. They called a Boat/US buyer who said they wouldn’t be stocking it because such a thing couldn’t possibly work. Once again, the empirical method trumps theory.)


Bigshot posted 07-26-2003 03:35 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
No you can not flush an engine with earmuffs in salt water. The seal is not tight enough and you would be "peeing in the wind" Back flushers DO NOT hurt the engine but you should NOT run the engine while doing so. You can run an engine on muffs tilted out of the water but there is a 10,000:1 chance you may ingest water or leak gas, etc and do some harm. I would do it and have if I had no OTHER choice. With Steve's backflusher or flush muffler you have a choice.
triblet posted 07-26-2003 10:19 PM ET (US)     Profile for triblet  Send Email to triblet     
The owners manual for may 96ish 90HP Evinrude 2-stroke says
you can run it on the backflusher, but you don't have to to
flush it.


rmart posted 07-26-2003 10:37 PM ET (US)     Profile for rmart  Send Email to rmart     
Thanks Bigshot, I had a feeling that running the engine would not be recommended but also wanted to confirm first that the whole notion of running water in reverse was not itself damaging. Thank you.

As far as the backflusher goes, I did order from Ebay and the item was delivered immediately upon payment. Now just has to be installed.

where2 posted 07-28-2003 12:03 AM ET (US)     Profile for where2  Send Email to where2     
I'll have to stand on the opposite side of the fence this time Bigshot. I think you can actually flush an engine on earmuffs in salt water. My earmuffs are notoriously leaky when flushing in my driveway, so if I use them in salt water, I will likely be leaking some fresh water around the muffs into the salt water, but not likely be leaking salt water into the muffs to be drawn through the engine. Since Air is much less viscous than water, and they don't leak air while flushing in my driveway, salt water should not be drawn in while the earmuffs are running.

The thought you probably had was that the user would turn off the fresh water flush before tilting the engine clear of the water, ingesting salt water back into the lower unit, negating some of the flushing action. I believe this could be avoided by continuing to run the earmuffs until the engine is tilted clear of the water. At which point, the engine should still be hosed down to rinse any remaining salt off the exterior of the engine. The rinse job would be slightly less effective than a true back flusher, since the water in the nose of the lower unit would still be salty. However, it's probably way better than no flush at all...

For Triblet: They actually sell hose pressure regulators at RV shops. $9 for one factory set at 45psi... $18 if you want the one with the built in gauge... You could install it at the flusher connection and go anywhere.

rkong posted 07-28-2003 04:52 AM ET (US)     Profile for rkong  Send Email to rkong     
FYI, the guy who actually makes the "Backflusher" is a member of this forum. Steve Leone, the OMC mechanic you hear from time to time. I bought on from him and it works quite well.
Bigshot posted 07-28-2003 12:12 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
My manual states do not run on backflusher unless engine is in DOWN position. This would defeat the purpose if you are in a slip, which he is.

If you believe that the water pump on an outboard is not strong enough to suck in salt water....Ok. If you think the seal is tight enough then why does it leak water when used on a hose? To really know for sure, do it and take a water sample and have it checked for salinity. What does it taste like?

BW23 posted 07-29-2003 10:35 AM ET (US)     Profile for BW23  Send Email to BW23     
Oh no .....Not the taste test!!!

I agree with WHERE 2 and will continue to flush with muffs in salt tilted down of course.
When I rebuilt my waterpump it was apparent that this procedure works quite well.

FISHNFF posted 07-30-2003 01:50 AM ET (US)     Profile for FISHNFF  Send Email to FISHNFF     
Have had a slip berthed boat for many years. Always flushed with muffs, engine down.
Always started and stopped flow when motor was intilted position, just to check for flow (I also put a SS screw in through the rubber and hose barb onthose Tempo flushers to keep it from blowing off). Water tastes fresh from pee hole. Also use SaltX/SaltAway periodically. Had Yamaha 175 rebuilt some years ago with 1500 hours, and water passages were clear of salt build-up. Mechanic showed me a set from a Yamaha which was never flushed. Restricted over 50%!
My 2000 Merc 90 4S is berthed for the Summer monthes, and has always been run in the tilted position using the flush port. Only 350 hours, but OK. Can't remember if in manual of from mechanic, but this method is acceptable. Oh wait! Mechanic gets paid for broken motors!! I'll check my manual tonight!!!

Tsunami 17

Steve Leone posted 07-31-2003 02:45 AM ET (US)     Profile for Steve Leone  Send Email to Steve Leone     
I am the inventor of the Backflusher. It was originally produced for sailboats, being quite difficult to attach conventional muff style flushers to extra-longshaft outboards. I have been marketing this product for approx 9 months now. I have sold over 2800 units, not entirely on Ebay. I have extensivly tested it on just about every outboard ever produced that are equiped with a tell-tale or waterpump indicator (pisser). Water pressure is the key. Common city water pressure will push open the thermostat(s) of most outboards allowing fresh water to reverse circulate through the thermostat(s) AND the bypass (most outboards have a bypass). This will completely flush the cooling system and water will come out the water pick-up on the lower unit. It will even work on models with "cold water" or waterpump side tell-tales as the flushing water "fills up" the watertube and backs up through the powerhead. Allthough I have run many outboards using my device I do not recomend it. For one thing the waterpump will be working against it, defeating the purpose. The other being that even with conventional flushers it is not redcomended to go more than 1500 RPM`s whilst flushing. I have 10 different designs for just about any outboard. They are jetted as not to exceed specific water pressures (don`t want to blow out the oil/water seal under the waterpump). Earmuff styles do leak when in the water. They also fall off sometimes, this being detrimental to the pistons, rings and cylinder walls. Happy Happy, Joy Joy, Steve
Steve Leone posted 07-31-2003 04:11 PM ET (US)     Profile for Steve Leone  Send Email to Steve Leone     
Ebay item # 2426196961.
captbone posted 07-31-2003 04:26 PM ET (US)     Profile for captbone  Send Email to captbone     
I say put the muffs on the motor and then trim it down and flush it while it is in the water. It may be like peeing in the wind, but it will be better than nothing and can not hurt.
Steve Leone posted 08-01-2003 01:38 AM ET (US)     Profile for Steve Leone  Send Email to Steve Leone     
"Peeing in the wind". Now there is a technical term...
Whalerdan posted 08-01-2003 04:03 AM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
I agree with the capt. The pressure from the hose has to be greater than the pressure in a foot or two of water. So the pressure under the ear muff must be greater than the pressure outside of it. There's no way saltwater can get in there.
Steve Leone posted 08-01-2003 12:43 PM ET (US)     Profile for Steve Leone  Send Email to Steve Leone     
I will measure the volumetric pressure in 20in. of water. A large body of water such as the Ocean. It must be substantial because outboards are exhaust tuned. This means that the manufacturer of the outboard must take into consideration the back pressure produced by a large volume of water. In order for the exhaust to flow through the prop hub and not "stall" the engine at idle there has to be greater pressure coming from the exhaust than the surrounding liquid. Another concern would be the seal around the muffs. With the outboard running at idle will it draw only the water from the hose or also draw in some salt water? I guess it also will depend on the painted surface of the lower unit by the pick-up being uniform or rough. Even so it is easier to couple a hose onto the pan rather than bend over to install earmuffs risking a dunk and fighting the muffs. Steve
frostbite posted 08-01-2003 01:44 PM ET (US)     Profile for frostbite  Send Email to frostbite     
Water pressure increases .434 pounds per foot of depth, so at 20" depth the pressure is still less than 1 psi. I believe the earmuff type will work, but the Backflusher sounds easier,more reliable and compact, in or out of the water.
Whalerdan posted 08-02-2003 06:49 AM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
Pressure in 20in of water is the same in a 5 gallon bucket as it is in the ocean.

With the hose pressure under the muff being higher than the water pressure on the outside (even with the engine bleeding off the pressure under the muff) there is no way the engine can suck saltwater. I know there is some pretty good positive pressure under there because when I run it in the driveway, even with the engine running, water squirts out hard around the muff edge to lower unit join. Fresh water will be force out into the salt if the fit is not tight. Pressures move from high to low, not low to high.

I agree the muffs are a pain and your system is a lot easier to use though :).

No offense just my thoughts.


repton posted 11-03-2009 01:32 PM ET (US)     Profile for repton  Send Email to repton     
[Six years later;]

Steve--Where can I get one of your back-flushers?


deepwater posted 11-04-2009 04:10 AM ET (US)     Profile for deepwater  Send Email to deepwater     
Im not sure if Steve still posts in here. This post is 6 years cold but there ways to find the back-flusher kit if its still made.

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