350 mag MPI drain plugs

QBhoy

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Mar 10, 2016
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right guys....the nice chap that I am means that I usually end up taking on maintenance duties on all my friends and family boats.
New to my friend is a maxum 2400 scr with a 2003 350 mag mpi.
Mom going to winterise it this weekend and only had a quick look at it without getting down and dirty with it. Access isn’t great currently with engine hatch still on.
Before I get to it and In about it, can any one with experience in these tell me specifically how many plugs there are.
I’ve winterised literally dozens of different gm V6 and V8 engines, but all with either an alpha one or a VP drive.
The usual is a plug each side of the block, one on each exhaust (either on elbow or at rear) sometimes one on t stat and maybe even power steering cooler.

Looking quickly at this one (only had good clothes on at time so didn’t look too hard), it seems there is one down low stbd side on a bulb shaped fitting, 1 on elbow maybe power steering cooler or cool fuel, it was dark. And another from around the stbd manifold.

Excuse the rubbish description. I don’t have a manual for this engine and it’s new to me. Problem is I couldn’t easily find plugs at the block (without trying too hard with clean clothes on). Is it possible there are pipe hoses from there to a communal drain point (maybe the bulb shaped thing mentioned earlier)

Is this maybe an early half breed version of the single point drain that I have on mine ?

im sure I’ll work it out when at the boat, but might be good to have a starter for 10. Cheers guys.
 

Bt Doctur

Supreme Mariner
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Aug 29, 2004
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19,092
That sounds like the "Quick Crack System" on mercruiser.. Removing the drain plug on the bulbous housing should drain about 4 gallons of water from the engine block, manifolds, fuel cooler, and misc hoses..
The problem arises when the manifold drain port connection internal plug gets jammed and the manifold, or both manifolds dont drain. You need to remove the larger hoses to insure draining.
For the block there are 2 hoses on quick connect fittings. pushing in on the white tab allows the hose to pop off. The block drains always get plugged with scale and rust. Pop off the hose and probe with a suitable object to insure a drain hole is working.
If any of these are plugged up , the engine and associated items will not drain, you will not be able to add A/F and something will likely crack form freezing.
 

QBhoy

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Ah. That’s brilliant BT. Just what I was after. I knew it might be something like that. I’ll take the hoses off to make sure. I do this with my own single point system too. Presuming they will be similar quick connect fittings ?
thanks again.
 

QBhoy

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BT Doctur. Just while you’re here...did you see my post other week also about this engine ? This was the one that the belt perished on and nearly overheated. The belt now replaced but temp creeping higher than I would like at low speed once warmed up. A rev of the engine drops it down again. Classic signs of the belt driven (B3 drive) impeller being worn, but it worked fine before. Totally confised as to why it doing this now. Pulley seems ok. The pump would just have stopped turning and wouldn’t have worn, I’d think. Soon find out when I pull the impeller.
 

Bt Doctur

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Did you think the pumps impeller could have jammed it up and that what shredded the belt?
 

QBhoy

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I’m just not sure. I wasn’t on it when it happened. Just trying to figure out why it’s doing it now. Soon have a look at the impeller to start with.
 

Fun Times

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First try grabbing the impeller pump housing "pulley assembly" and move it all about/in & out to see if the shaft is loose at all...Also sometimes this testing is easier with the belt removed to help know for sure as possibly the impeller shaft internal bearings/Tolerance Ring and E-clips have failed in-turn shredding the belt due to excessive movement/misalignment plus possibly helping to overheat the engine too at certain times/RPM's.

^ If not check the impeller and if rubber blades are missing then the parts could be up as high as the thermostat housing affecting the thermostat operation due to blockage. Check the inner impeller housing, brass cover, wear plates if any for deep score marks too....The grooves in the brass housing cover can sometimes be sanded down/out.

You should (may) also have 2 blue plugs on the impeller housing you'll need to remove for winterizing...Item numbers 8 & 6 are in question, https://www.mercruiserparts.com/bam/...31748/8093/270

Having the engine serial number sometimes helps give you a better visual of where some of the drain plug components are and what style/design they are before digging into a new to you model by way off looking over the parts catalogs easily found online nowadays.....https://www.manualslib.com/manual/1139298/Mercruiser-5-7-Mpi.html?page=84#manual
 

KD4UPL

Senior Chief Petty Officer
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Feb 13, 2010
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653
While changing the belt did you happen to turn the pump pulley backwards at some point? That may have broken some veins on the impeller that didn't like being twisted backward.
 

QBhoy

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Thanks to both who recently replied.
I’ll do just as suggested.
Also, I dodnt change the belt. The owner did it. That’s what’s worrying me !
 

Leardriver

Petty Officer 1st Class
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Oct 7, 2008
Messages
373
If you drain via the one plug, and stick an air compressor blower nozzle into the drain hole, you can hear air circulating throughout the entire engine. It works great for verifying that you have connected flow and no plugs.
 
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