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AQ125a losing coolant (not in the oil)-gctid385368

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    AQ125a losing coolant (not in the oil)-gctid385368

    I just bought my first boat a 82 19' Capri with a aq125a/270. Before I put it in the water I flushed the cooling system, replaced impellar, new cap, thermostat all for good measure and changed the oil. The boat has lots of power and will jam at 5100rpm with power to spare. The problem, the boat runs at 185 at 4000rpm for about an hour then the temp marches up. I check the tank and its a gallon low. Refill and run same thing. No leaks and deffinetly no watet in oil, checked it constantly and changed it twice to ensure, no water no burning. Still trying to wrap my head around the whole heat exchanger thing but, if the exchanger core has a leak is it possible the coolant is leaking into the fresh water when the closed system is pressurized?

    #2
    I just bought my first boat a 82 19' Capri with a aq125a/270. Before I put it in the water I flushed the cooling system, replaced impellar, new cap, thermostat all for good measure and changed the oil. The boat has lots of power and will jam at 5100rpm with power to spare. The problem, the boat runs at 185 at 4000rpm for about an hour then the temp marches up. I check the tank and its a gallon low. Refill and run same thing. No leaks and deffinetly no watet in oil, checked it constantly and changed it twice to ensure, no water no burning. Still trying to wrap my head around the whole heat exchanger thing but, if the exchanger core has a leak is it possible the coolant is leaking into the fresh water when the closed system is pressurized?

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      #3
      The only place that I know of that they (raw water and coolant) get close it in the heat exchanger itself. There is a core (think radiator) and the raw water circulates thru the core and cools the coolant. It it possible the core is cracked or one of the internal o rings is bad (I think there's an odd gasket in there too), allowing the coolant to escape thru the manifolds.

      If you put the drive on muffs or a shallow tank (covering the raw water inlets) you should be able to see the coolant escape via the exhaust outlet (triangle flap above the prop)

      2850 Bounty is the VP expert on this site, although several members have this engine/drive setup. I'm sure they'll check in soon. Remember, it's a holiday weekend.

      side note: I'll have to double check, but your RPM's are high. I think the AQ125A's range is 4400-4800.

      I also merged your threads, then deleted one post as they were identical.

      :wel-

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        #4
        if i read you right then, I'd be running the impeller dry? I wonder if i drain the raw water out of the heat exchanger and topped off the coolant tank the coolant would fill the exchanger tank to the level of the leak? the coolant tank being higher than the exchanger tank this might work. would still like to hear from any other members who wish to put there 2 cents in here.

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          #5
          Well i cant say for sure but it is possible that you are losing coolant thru the exchanger. In my case the coolant reservoir was leaking at the bottom of the casting itself, due to a crack in the tank. It could also be blowing off thru the cap, but you say it is not leaking into the bilge so i dunno. As for you tach, you are way too high. Your should be maxing out at 4800 rpm and cruising at around 42-4400 rpm

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            #6
            yes 5100rpm is too high to run it but, it took it and felt like it had more to give. learning about the motor i now know probably not to smart. no leaks, new cap. it's going someplace else.

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              #7
              See if you can beg, borrow, a cooling system pressure tester like this

              http://www.harborfreight.com/radiato...kit-65053.html.

              I used i on mine when i noticed i was loosing coolant. If you can get one of these i would empty the heat exchanger of all sea water via the drain on the bottom, pressure test it for say 30 mins, relieve pressure from the system then open the drain on the heat exchanger and see if there is coolant there. As far as i know (and i may be mistaken) this is the only place coolant and sea water meet. Since you say there is no coolant in the oil, this is where i would start. If that test passes(ie no coolant in heat exchanger) one other test you can do and we do it at work all the time, is run the engine with the rad cap off and check for constant bubbles. Bubbles mean a failed head gasket on the exhaust side. But i would lean more on the side of the heat exchanger, and rad shop can repair this for you, or shop on ebay for a used one, i have seen a few there myself

              Comment


                #8
                just got a clean and tested heat exchanger today. going to install and cross fingers

                Comment


                  #9
                  Well, the new exchanger brought down the running temp considerably but, after a few hours of running the temp climbed and missing coolant again. Combed over the eingine again looking for leaks, nothing. Drained the oil again! I don't see any indication of watet but, put a sample in the mail for analysis. I gurss a head gasket leak on the exhaust side? Does the cam and all that have to be removed to change the gasket or is there a way to pull the whole thong off one piece?

                  Comment


                    #10
                    caprinaz wrote:
                    Well, the new exchanger brought down the running temp considerably but, after a few hours of running the temp climbed and missing coolant again. Combed over the eingine again looking for leaks, nothing. Drained the oil again! I don't see any indication of watet but, put a sample in the mail for analysis. I gurss a head gasket leak on the exhaust side? Does the cam and all that have to be removed to change the gasket or is there a way to pull the whole thong off one piece?
                    Have you had a look around the thermastat? it sounds like something is happening once the engine warms up, if you are overheating the water may be turned to steam so you wouldn't see a leak?.

                    If that fails then I think you may be on the right track with either a leaking head gasket or a cracked head.

                    Hopefully someone that knows about engines can help you with the cam issue.

                    Good luck

                    Comment


                      #11
                      Ok, the oil came back, all is well within perimeters (no water) negligible metal deposits). I am getting minute air bubbles forming at the coolant filler neck which leads me to believe its a exhaust side leak. So, I'm not getting a great deal of AQ advice from any experts on here and since I have no idea if i can pull the head without removing the cam and serious effort I guess its Bars leak head gasket repair time

                      Comment


                        #12
                        Bubbles in the expansion tank are indicative of a head gasket problem on the exhaust side. You can pull the head without removing the cam from the head. There are only 10 bolts in the head all around the perimeter. You will need new head bolts though. You should be able to re & re the head in a few hours. Just make sure you set your timing marks up before you remove the head.

                        Comment


                          #13
                          tbear wrote:
                          The only place that I know of that they (raw water and coolant) get close it in the heat exchanger itself. There is a core (think radiator) and the raw water circulates thru the core and cools the coolant.
                          I would agree. The heat exchanger core would be the most likely place to look and test.

                          caprinaz wrote:
                          if i read you right then, I'd be running the impeller dry?

                          I wonder if i drain the raw water out of the heat exchanger and topped off the coolant tank the coolant would fill the exchanger tank to the level of the leak? the coolant tank being higher than the exchanger tank this might work. would still like to hear from any other members who wish to put there 2 cents in here.
                          A coolant leak will not affect the sea water pump impeller, or visa-versa unless a bad impeller was causing over-heating.

                          Even at that, the coolant is escaping somehow.

                          The bad head gasket is certainly a possibility if it's allowing coolant to escape without entering the engine oil side.

                          caprinaz wrote:
                          yes 5100rpm is too high to run it but, it took it and felt like it had more to give. learning about the motor i now know probably not to smart. no leaks, new cap. it's going someplace else.
                          NOTE: your WOT RPM is a test RPM ONLY. Not an RPM intended to operate at.

                          With a WOT of 5,100 rpm, you may be able to prop UP one pitch or so.

                          If you can reach a WOT of 5,100 rpm with the boat not loaded down, you will want to test again with the boat loaded as you would normally load.

                          IOW, a load that you are more likely to be using routinely.

                          Always error on the high WOT RPM side. Just don't run at that RPM for sustained durations.

                          .
                          Rick E. Gresham, Oregon
                          2850 Bounty Sedan Flybridge model
                          Twin 280 HP 5.7's w/ Closed Cooling
                          Volvo Penta DuoProp Drives
                          Kohler 4 CZ Gen Set

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