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Water drain plugs locations on Mercruiser V8. (pics)

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  • Water drain plugs locations on Mercruiser V8. (pics)

    I read the sticky on winterizing, and decided it was simple enough to do my own winterizing. What I couldn't find, was a decent diagram of where the drain plugs are located. Even in my shop-manual, it's kinda hard to tell from a B&W cartoon. They are pretty easy to spot once you know what you're looking for, but I'll save some of you the hassle of searching by posting some pics

    This thread is just to cover the drain plug locations on a 1996 Mercruiser 5.7L (raw water cooled), but I assume that other year 5.7L, and most 5.0L Mercruisers have pretty much the same thing.





    As you can see, not all boats have a conveniently visible blue plastic plug. Mine has brass bushings with smaller brass plugs in the block, and a black plastic plug in the exhaust riser. Never mind the jury-rigged street elbow + pipe nipple on the port side. It's obviously custom for increased horsepower and speed.



    Also, remember to use a wire or something to poke in the holes as it's draining. My block drains were just sort of trickling out until I poked in there with some welding-wire. A bunch of mud globbed out then the water drained more freely at about 10x the flowrate.

    I also had to remove the hose from the power steering cooler. I didn't see (or feel) a drain fitting on the cooler, so I just pulled the hose off the low end.



    All in all, I drain about 2 gallons out of my engine.



    I read in another forum post somewhere that some people get up to 5 gallons. Not sure how to get any more, unless I missed a drain plug. I just had it running with the hose and muffs yesterday too when I did the fogging oil, so it didn't drain out from being un-level.

    Also, on a final note: should I keep the plugs out over winter? Logic says it's not necessary, but I put them in a ziplock baggie anyway.


  • #2
    Re: Water drain plugs locations on Mercruiser V8. (pics)

    I would consider replacing that galvanized street elbow with some brass fittings.
    1989 Four Winns 170 Cobra 3.0

    Comment



    • #3
      Re: Water drain plugs locations on Mercruiser V8. (pics)

      Originally posted by Bluestream View Post
      I would consider replacing that galvanized street elbow with some brass fittings.
      Yeah... if it's not already rusted and fused to the manifold. Not sure if it's worth screwing with. Kinda one of those "if it ain't broke, don't fix it" situations.

      Comment



      • #4
        Re: Water drain plugs locations on Mercruiser V8. (pics)

        I remove the drain plugs/petcocks and store them in a baggie as well.
        1978 Glastron/Carlson CV23
        429/Berkeley JE

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        • #5
          Re: Water drain plugs locations on Mercruiser V8. (pics)

          I also like to take the plugs out and leave them out. Also leave all the hoses unhooked... Not really any reason, just makes me feel better.

          On all of our boats the manifold drains are on the back of the manifold. Dont see a problem with taking those hoses off though. Pretty sure the engines Ive drained have not had 5 gallons of water in them.
          2007 Four Winns H180
          Volvo 4.3GL-G SX

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          • #6
            Re: Water drain plugs locations on Mercruiser V8. (pics)

            Im kinda confused, I have the merc 5.0mpi that has the single point drain plug in the front that drains the water out. Does that drain all the water out eventually or do I need to find all these other drain plugs and take those out too? Thanks good info and pics.

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            • #7
              Re: Water drain plugs locations on Mercruiser V8. (pics)

              Originally posted by ScotWithOne_t View Post
              Yeah... if it's not already rusted and fused to the manifold. Not sure if it's worth screwing with. Kinda one of those "if it ain't broke, don't fix it" situations.
              Your call on that, but its only going to get worse with rusting
              1989 Four Winns 170 Cobra 3.0

              Comment



              • #8
                Re: Water drain plugs locations on Mercruiser V8. (pics)

                Originally posted by Bluestream View Post
                Your call on that, but its only going to get worse with rusting
                I suppose I could hit it with some PB-Blast, and try to turn it. My biggest worry is that I'd crack the cast-iron manifold if I really wrenched on it hard to break it loose.

                Comment



                • #9
                  Re: Water drain plugs locations on Mercruiser V8. (pics)

                  Try some moderate pressure and if it doesn't move, leave it be.

                  If it comes loose, clean up the internal threads and put some grease on the new brass fitting and install and tighten just a bit more than snug.
                  1989 Four Winns 170 Cobra 3.0

                  Comment



                  • #10
                    Re: Water drain plugs locations on Mercruiser V8. (pics)

                    The winterizing debate; an annual occurance. I remove all the plugs, hoses and such, and then take off the thermostat housing. This is a good time to check and/or replace the thermostat. I believe in adding the pink stuff - antifreeze - to the system. I pour it in through the open thermostat housing. As it comes out the bottom openings, I reinstall the plugs and hoses and then top off the engine. I do this to prevent further rusting in the block and manifolds. I know air can't freeze, so some people prefer leaving the system empty. But, cast iron can rust when exposed to the damp air of winter. The $25 or so I spend on antifreeze is, in my opinion, worth it. The pink flowing out also gurantees that I got all the water out. On newer Mercruiser engines, look for the drain plug in the "cool fuel" system down in the back on the starboard side. I didn't know about that one until it was posted on the Chaparral Owners Forum. When I removed it, more water came out, even though I had already filled the engine with antifreeze. The 2000 Mercruiser 5.0/5.7 has six plugs. Think spring. Hy

                    Comment



                    • #11
                      Re: Water drain plugs locations on Mercruiser V8. (pics)

                      I put everything back together. To many mice like to get into my engine.
                      1986 Century Riviera 6 Meter 350/260 Alpha 1

                      Comment



                      • #12
                        Re: Water drain plugs locations on Mercruiser V8. (pics)

                        Originally posted by littlebookworm View Post
                        The winterizing debate; an annual occurance. I remove all the plugs, hoses and such, and then take off the thermostat housing. This is a good time to check and/or replace the thermostat. I believe in adding the pink stuff - antifreeze - to the system. I pour it in through the open thermostat housing. As it comes out the bottom openings, I reinstall the plugs and hoses and then top off the engine. I do this to prevent further rusting in the block and manifolds. I know air can't freeze, so some people prefer leaving the system empty. But, cast iron can rust when exposed to the damp air of winter. The $25 or so I spend on antifreeze is, in my opinion, worth it. The pink flowing out also gurantees that I got all the water out. On newer Mercruiser engines, look for the drain plug in the "cool fuel" system down in the back on the starboard side. I didn't know about that one until it was posted on the Chaparral Owners Forum. When I removed it, more water came out, even though I had already filled the engine with antifreeze. The 2000 Mercruiser 5.0/5.7 has six plugs. Think spring. Hy
                        I'm assuming I didn't miss any plugs in mine, but I only had 2 in the block (one on each side) and one in each exhaust riser.

                        Where are the other two in the 2000 model year? I'd like to check to be sure my 1996 doesn't have them.

                        It's gotten below freezing a couple nights now, but nothing super cold, so freeze damage isn't really a concern just yet, but double checking is something I should maybe do now before it starts dropping into the teens.

                        Comment



                        • #13
                          Re: Water drain plugs locations on Mercruiser V8. (pics)

                          I agree. I did the pink-stuff-in-the-container-with-the-flusher-hose thing last year and thankfully I had no issues this year. However I did the same thing this year, opened the petcocks and saw NO pink stuff in the water. So I said "not taking the chance" and opened the 2 petcocks in the block and the blue ones in the exhaust manifolds and let ALL the water run out and reinstalled the petcocks. Then I loosened the thermostat housing and poured the pink RV AF (-50) down the thermostat opening in the intake manifold with a funnel. It took less than 2 gallons.
                          I opened the block petcocks slightly to check for the AF and there it was. The only disadvantage I can see to this is the AF does not get to the power steering system, which needs to be winterized also according to Merc. I may manually disconnect the p/s steering tubes to get the water out and then reconnect them. IT wouldn't hurt to pour some AF down the hose that the freshwater comes in from also and down the hose that goes from the Stat housing to the water pump.

                          As far as draining the block and leaving it with no AF, I had an overheating problem this year and fixed it by backflushing the block with the garden hose through the petcocks in the block until it ran out the top of the Stat housing. I saw quite a bit of scale and rust come out and no more overheating (Merc Alpha 1, 270 HP) If you've got air and iron, you're gonna get rust. I would not leave it dry, I would definitely put AF in there.

                          Good luck.

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