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  1. #1

    Changing Coolant 1984MY

    I feel that it is time to change the coolant for the first time since I have owned the boat. The coolant that is presently in the 12 V 71 engines is a purple type colour and smells slightly of vinegar. Perhaps this is okay?? Regardless, what would be The simplest way to change out the coolant? The only way that I can see it happening is to drain all of the old coolant into the bilge and then suck it up? About 20 gallons per engine?

  2. #2

    Re: Changing Coolant 1984MY

    In going to change mine as well. I’m looking for a plastic sleeve similar to what you would put a wet umbrella in. Wrap it around the petcock and drain into a bucket to keep the bilge clean. Looking forward to what the pros say.
    SEVEN
    1979 53' MY Hull #563
    Antioch, California

  3. #3

    Re: Changing Coolant 1984MY

    I don't like the idea of draining into the bilge so I bought a bunch of small petcocks with nipples on them.
    After cleaning up the mess of emptying the coolant from the fresh water side, remove the old petcocks
    and install the new one's with the nipples. After they are installed you just slide an appropriate size
    small length of hose onto the nipple and drain the flush fluid into empty 5 gal drums for disposal. Now
    in the future you will thank yourself for making the job easy, neat and clean.

    Walt

  4. #4

    Re: Changing Coolant 1984MY

    Good idea Walt.
    SEVEN
    1979 53' MY Hull #563
    Antioch, California

  5. #5

    Re: Changing Coolant 1984MY

    Quote Originally Posted by Walter P View Post
    I don't like the idea of draining into the bilge so I bought a bunch of small petcocks with nipples on them.After cleaning up the mess of emptying the coolant from the fresh water side, remove the old petcocks and install the new one's with the nipples. After they are installed you just slide an appropriate sizesmall length of hose onto the nipple and drain the flush fluid into empty 5 gal drums for disposal. Now in the future you will thank yourself for making the job easy, neat and clean.Walt
    Did same. Very worth the effort.
    Semper Siesta
    Robert Clarkson
    ASLAN, 1983 55C #343
    Charleston, SC

  6. #6

    Re: Changing Coolant 1984MY

    Thanks for the petcock idea. I can see this project becoming quite involved given the amount of coolant. My previous boat had 8v92s and I changed the coolant twice during my ownership but the fluids were about 1/3 the volume. Which would be the main petcocks to drain from? Also would you flush with a cleaner prior to refilling with coolant? In Australia we have all different brands. I am thinking of using the very best long life truck engine coolant I can find which is mixed 50:50 with water.

  7. #7

    Re: Changing Coolant 1984MY

    Scott, Be sure to use a coolant that is proper for Detroit Diesels. I know that DD Powercool has something
    in it that prevents cavitation corrosion and it needs to be checked regularly other wise you may be asking
    for major problems. If DD Powercool is available in Australia I would use it. If not then be sure to check
    the specifications on alternate products to insure compatibility with your engines.

    Walt

  8. #8

    Re: Changing Coolant 1984MY

    Quote Originally Posted by scottinsydney View Post
    Thanks for the petcock idea. I can see this project becoming quite involved given the amount of coolant. My previous boat had 8v92s and I changed the coolant twice during my ownership but the fluids were about 1/3 the volume. Which would be the main petcocks to drain from? Also would you flush with a cleaner prior to refilling with coolant? In Australia we have all different brands. I am thinking of using the very best long life truck engine coolant I can find which is mixed 50:50 with water.
    unless the coolant has some other properties to prevent corrosion etc why would you use it in Aussie land? it never gets cold enough there to worry about freezing. plain distilled water with additives may be best solution in that climate.

    on my 6-71s I have petcock drains on water pump, oil cooler and exhaust manifold. Guess all three need to be opened to drain as much a possible. when I changed it last time I run the distilled water in the engine for an hour and drained all again before filling with the coolant.

    you can buy coolant analysis strips from DD to test the properties of the coolant which will tell you when it is the time to replace it. testing it once a year or more often dependent on the running hours.

    simple colour based chart that will show when you need to act.
    M/V BONAZZA
    1980 Hatteras
    37 Convertible
    Hull# - 405
    Twin DD 6-71NA
    Vancouver, Canada

  9. #9

    Re: Changing Coolant 1984MY

    Quote Originally Posted by scottinsydney View Post
    Thanks for the petcock idea. I can see this project becoming quite involved given the amount of coolant. My previous boat had 8v92s and I changed the coolant twice during my ownership but the fluids were about 1/3 the volume. Which would be the main petcocks to drain from? Also would you flush with a cleaner prior to refilling with coolant? In Australia we have all different brands. I am thinking of using the very best long life truck engine coolant I can find which is mixed 50:50 with water.
    Put a valve and nipple on the oil cooler drain. I also added a valve and nipple to drain the heat exchanger.

    IMG_8673.JPG

    I'd advise to apply a cap as extra insurance.

    You can't do much with the petcock behind the starter, but you could add a nipple to the block drain on the other side. Either way, you'll get most of if out the cooler and the HE drain. From there you can refill with fresh water, circulate a couple of minutes and then drain again. That'll get the majority of the old coolant out. Repeat as necessary until you're satisfied the old coolant is out.

    If the coolant is in bad shape, I'd advise opening all the petcocks. Make a shield to keep the starter dry. If a drain is slow or plugged, insert a wire or apply some low pressure air to break up the sediment. There'll also be gunk in the bottom end of the water manifolds. I'd take the drain hoses off in that case. Hopefully all this won't be necessary.

    As long as the coolant is in decent shape, future coolant changes will be a lot easier.
    Semper Siesta
    Robert Clarkson
    ASLAN, 1983 55C #343
    Charleston, SC

  10. #10

    Re: Changing Coolant 1984MY

    I guess I am dumb, but what are the additives you add to plain water and where do you get them. Are they a DD product or a general product. Sounds to me you guys are recommending fresh water with additives in mild climates is that correct? John
    Mahalo V
    1974 53 Motoryacht
    Hull Number 406
    San Diego, Ca. Ready 32 Nordic Tug, Brunswick Ga.

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