View Full Version : Raw Water Flush Kit for 81L Mercruiser MIE

12-28-2008, 01:39 AM
"Has anyone installed or have the option on thier engine (early model 8.1L inboard) for the FLUSH KIT assembly? The hose connect is mounted on the riser. I have contacted Merc and they refer me to ask a dealer, neither wil give the info without purchase of the kit. My queesitn is where does the kit attach to th raw water system? Prior to or after the raw rwater impeller housing?"

01-05-2009, 10:47 PM
"Attachment point would depend on whether you will be running the engine while flushing. Attach before the raw water pump and close seacock while flushing. Let the water run for a minute or two to flush saltwater back out seacock, close seacock, then start engine. Make sure you don't have too much water pressure in hose. Attach after raw water pump if you want to flush with engine off. I have found most water hose can't keep up with raw water pump much above idle. My 350 will suck the hose flat at 2000 rpm. I bought a used heat exchanger and plumbed all my own cooling and flushing systems."

01-12-2009, 03:01 PM
"Thankx Jim. I did find out this much from another owner and this is what I did to keep costs down. I had the top of my strainers drilled for 1" NPT fitting (1-1/4"O.D.) and then have a reducer adapter for garden hose full flow of 3/4". This works good two ways. Without the adapter, I can connect a 1-1/4" hose directly attached to 6 gallon bucket with antifreeze and wineterise my engine. Plenty of water and flow. With the adapter for 3/4" then engines will flush without collapsing the hose (use 3/4" garden hose) provided you use 3/4" hole for good volume (pressure is not the issue here) and limit the RPM to not greater than 1100; which is a sufficient RPM and run engines for 10 minutes or until water is clear from exhaust. To do the entire set up cost me $58.00. $28 in parts and $30 (cash) to the machine shop to drill and thread the holes in both strainer caps. I can also do a set up for emergency bilge pump by tapping into the same fittings and use the engine pump. All other options I priced ont he internet would have run me easily over $225.00. You may want to comment further but I was told by my mechanic that you can risk water entering the engine by flushing the raw water section (aft the impeller) without the engine running; since the exhaust pressure keeps water from back-tracking in the manifold riser."

01-27-2009, 04:58 PM
"cholly: make sure you have a positive method for sealing off the 3/4' hose, preferable close to the seacock, if you keep your adapter installed. A marine grade ball valve would probably be the most economical.

The concern is for an air leak; the impellers don't like them."

01-27-2009, 05:50 PM
"Yes Mako. I completed the taps into the strainers. I shut the seacocks off and then the antifreeze is drawn from the bucket. it worked sweet. It took all of 30 seconds for that 8.1L impeller to swallow up 6 gallons of antifreeze to the raw water sytem all the way to the mufflers. The same will go for the 3/4" hose. Volume is important and yes, you don't want to have an air pocket; its hard for the impeller to prime. BTW my strainers bottoms are above waterline. Thats a good thing cause I can easily prime my strainers and not have a dry impeller as well as if my seacock is open adn I uncover the strainer, no water enters my bildge."

01-27-2009, 07:04 PM
"I was thinking more of 'normal use' and the 'winterizing port' being a source of air leaks for that thirsty pump. the ball valve, if closed, fixes that scenario.

I just pull the hoses off thte seacocks and connect them to the flush bucket - a drywall bucket with a hose barb sunk into the bottom - with an extra length of hose. 4 gal in about the same time and the raw water system is good for a few months."

01-27-2009, 07:32 PM
Oh yeah. What I did was have a 1" NPT nipple threaded into the top of the strainer. Then I have a reducer to a hose fitting. I can leave the fitting on for hose and flush my engines each timwe after saltwater use and not have to disconnect any hoses at seacocks. My seacocks are 18" down from deck. If I remove the reducer fitting then I hook my 1-1/4" ID hose from the bucket direct to the NPT fitting. its that simple. I pointed out to Jim Norvell that it cost me under $100 for the setup for both strainers compared to T'ing into the raw water inlet hose and having more s.s. clamp connections. at a cost of approx. $225.00. My connect now are just 8" down when i open my engine hatch. Sooooo convenient

02-15-2009, 10:28 PM
"A Picture is worth a thousand words"....here is what I was describing in the Post Message Above.http://www.marineengine.com/discus/messages/8/249222.jpgRaw Water Strainer Flush