running on muffs

All this waterinversion/reversion talk gets me nervous.<br /><br />When running the boat on the muffs with water from the hose, is the typical water hose pressure okay to flow into the system at full ON?<br /><br />Also, I heard Merc says not to let the motor run below about 1200 RPM when on the muffs---is it okay to run at idle while on the hose and muffs?<br /><br />My old boat was a straight 6 and it pushed the water through and out the exhaust a lot faster than this V8 I am currently running.

Re: running on muffs

Hi<br /><br />Just keep an eye on the engine temperature. The water pressure should be enough to force the water high into the outleg so that the pump doesn't run out. It will be noisy as well as you have the exaust exposed so I doubt if your neigbhours would be happy with you running full on.<br /><br />Just use common sense and keep an eye on the temp.<br /><br />Best of luck withg it.<br />Donie

Re: running on muffs

I should have been a bit more specific.<br /><br />We've been doing this for years----several different boats---running at idle to warm the oil before changing, etc.<br /><br />I always watch the guages to know when thermostat has opened and everything is flowing.<br /><br />But I thought Merc came out this summer with a tech bulletin that said not to run to much water pressure through the hose and to keep engine above 1200 RPM to avoid water reversion.<br /><br />Does anyone have this bulletin?

Re: running on muffs

I run many many boats on muffs at idle and have never had a problem.

Re: running on muffs

I've always thought that only about 1/4 of hose water pressure was desirable, due to excessive pressure damaging the impeller.<br /><br />Have heard this rationale stated many times. Anyone else agree?

Re: running on muffs

I think revin the engine would cause more of a prob then idling. I saw the bulletin but I forget most of it, maybe walt can post it. I know I woldnt worry.

Re: running on muffs

I'm sure my manual said not to run ABOVE 1500rpm or so due to the risk of collapsing the garden hose. I've never had (or heard of) a problem caused by idling with muffs on. I always use full pressure and the excess just squirts out the side of the muffs. If anyone out there has had problems I'd be interested to hear them.

Re: running on muffs

The service bulletin is specific to flushing. My guess is that many engines (like mine) never open the thermostat if you run them at idle in cold ambient temps, so maybe that's why Merc says to use 1300 rpm instead of idle--to make sure the t-stat opens and the block gets flushed. I don't know, I suppose you could ask Merc. I use the hose to avoid trashing the impeller and to provide cooling if it becomes needed. I've always ran my hose half-open, but water pressure varies so much from place to place, that doesn't mean much.<br /><br /> http://www.boatfix.com/merc/Bullet/99/99_09.pdf <br />New Flushing Procedure for Alpha and Bravo Engines When<br />Using a Flush Attachment on the Sterndrive<br />Models<br />MCM 3.0L, V6 Gen+, V8 Gen+ 305/350 cid and<br />V8 454/502 cid Sterndrive Engines: S/N 0F803000 and above.<br />Situation<br />A new flushing procedure has been developed for use when using a Flush Attachment over<br />the water pickup holes in the sterndrive. This new procedure was developed to reduce the<br />possibility of water ingestion that may occur while running the engine at idle rpm on a Flush<br />Attachment.<br />This new flushing procedure should be used by all dealers and boat owners on all engines<br />above the serial number listed above. It will be added to the owner’s manuals and service<br />manual when they are revised.<br />New Flushing Procedure<br />1. Install Flush Attachment and water hose over the water pickup holes in gear housing.<br />2. Open water tap enough to cool the engine, about ½ of its maximum capacity. Adjust as<br />required so that the engine does not overheat.<br />3. With drive in neutral gear, start engine and advance the throttle until the engine reaches<br />1300 rpm.<br />IMPORTANT: DO NOT run the engine at idle rpm. Watch engine temperature gauge<br />on dash. Do not run the engine above 1500 rpm or engine overheating may occur.<br />4. Run engine for 10 minutes or until the discharge water is clear.<br />5. Slowly return the throttle to the idle position and turn engine off.<br />IMPORTANT: DO NOT do ‘Throttle Chops’ anytime or water ingestion may occur.<br />6. Shut off water supply and remove flush attachment from the drive unit.

Re: running on muffs

Interesting, I hadn't heard that. My engine is an '81 470 with FWC so the t'stat doesn't need to open to flush all the bad stuff out. After this many years, if idling on the muffs was going to hurt my motor it would have done it by now. Good words on the "throttle chop" though. Thanks.

Re: running on muffs

The service bulletin is correct. It has to do with long term idling. It has nothing to do with the thermostat. The new style engine is where the problem lies. The new style engine has a pulse at idle in the exhaust that will pull water in thru the exhaust. The manufactures have been raising the idle to cure the problem. Many ecms have been updated to increase idle speed. Above 1000rpms the problem seems to go away. The bulletin has to do with idling for a long time. There have been updates to increase idle on some engines. Mercruiser number 1 warranty issue of 2002 water injestion issues. I would bet 2003 is the same. The problem is from the new style engine design. We make alot more power with the new style engines. A mercruiser 350 cid. made 260 hp. Now 350 cid. makes 310 hp.

Re: running on muffs

Once again, thanks for all the good info. I had missed the reference to engine serial numbers on the bulletin when it came out---I don't think it applies to my 350, but I will check the numbers.

Re: running on muffs

hello<br /> we dont see so much reversion on the muffs as gravity takes the water down. there is a bulliten out also about how to properly shut down the engine after idleing more than 10 min or so. ie docking or no wake zones. the problem comes from both a valve overlap and the new engines have eliminated the exhaust crossover passges in some heads.the reason for the extra rpm is to make sure enough exhaust gas and heat can vaporize any moisture and keep the water pushed downstream of the riser. volvo bought a lot of 8.1's before the exhaust balance promlem was found.which is why I recommend fogging the engine lightly after each use . keeps the valves from sticking.<br /> good luck and keep posting