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  • Aq131 exhaust manifold hot

    Hello fellow boat buffs!! This is my first post on iBoats and I hope I can get some answers. I recently completed a total restoration on a 1986 Bayliner Capri bowrider 1950. It has the Aq131 with the 275 Penta our drive. I have replaced the stringers, transom, floor and reupholster the entire boat. I also had that engine completely rebuilt with new pistons, new bearings, and all new seals. I have replaced all the bushings and O-rings in the outdrive and also replace the raw water pump and heat exchanger and exhaust manifold...and that problematic water neck and seal. I put a clear hose on the suction side and out on the lake I don’t see any bubbles. The engine runs about 170° or at wide-open about 175°. The problem that I am experiencing is that the exhaust manifold gets hot. It is brand new and I’ve been shooting it with an infrared temp gun and it’s about 200°. Besides that hot manifold problem everything else is great. With three people on board I can get 35 mph out of this little motor! So hopefully someone can let me know if the hot exhaust manifold is normal or if I should be concerned?

  • #2
    I'm not seeing a problem with the exhaust manifold so long as it is also part of the closed cooling system of the motor. The exhaust elbow (riser) on top of the manifold should be a bit cooler. Now if the manifold and elbow is raw water cooled, then maybe your not moving enough water
    94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
    95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
    07 Seadoo GTX
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    G-Dad always said "First Liar doesn't stand a chance"

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    • #3
      It is raw water cooled. The water goes straight from the heat exchanger to the manifold. The bottom stays cool as if water is running through the bottom but the top and middle get very hot to the touch at lower rpms. The higher rpms do cool it enough to put hand on but not nice and cool... could my exhaust gasses be abnormally hot for some reason??

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      • #4
        FYI, the AQ131 does not have a riser.
        I never measured the temperature of my manifold, maybe next time out I'll take along an oven thermometer.
        I know it is too hot to touch.

        When on muffs, do you get good water flow out the exhaust?
        Does the big rubber donut look melted at all?

        Exhaust gases could be abnormally high if the valve timing is off; exh. valve opening too soon.
        Dennis
        20' 1987 Renken Cuddy Cabin
        AQ131C 270 drive
        Southern NJ

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        • #5
          In the expansion tank there's a heat exchanger.
          Take it out and try back flushing.
          Or take it to a radiator shop for a dip.
          Some use muriatic acid and it sometimes helps clean the stuff out.
          Just don't let it set as it can eat the metal and you'll be buying a new one.$1237.00
          Used on eBay $99
          New On eBay $750


          Buy American made Cars and Trucks!!!Towing insurance for a boat,a GREAT thing.
          ​Tools to make my life easier: Battery tester, die grinder, temp.gun, compression tester, DVA meter.

          In Scenic , Beautiful San Sebastian by the sea Florida

          88 Bayliner 21CC 2001 Mercury 225 HP EFI

          PLEASE,NO PERSONAL MESSAGES IF THE QUESTION CAN BE ASKED ON THE OPEN FORUM

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          • #6
            Originally posted by jerryjerry05 View Post
            In the expansion tank there's a heat exchanger.
            Take it out and try back flushing.
            Or take it to a radiator shop for a dip.
            ...0
            He said he replaced the heat exchanger, so, unless he replaced it with a used part he should be OK.
            He reported an engine temperature that looks normal for summer fast cruising.

            The 200 degrees on the exhaust manifold may be normal, I know mine is usually too hot to touch.
            Dennis
            20' 1987 Renken Cuddy Cabin
            AQ131C 270 drive
            Southern NJ

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            • #7
              Hey Guys thanks for all the responses! The heat exchanger i put on was used but seemed to flow water nicely! It is the heat exchanger off of the aq171 so it has a slightly higher cooling compacity. Coolant going in is 170 degrees and coming out is 120 degrees. Also in response to the question about my rubber buffer being melted...I actually replaced that with a piece of flexible silicone hose and it is not melting at all. I do have a decent amount of water coming out of the exhaust with muff on in my drive way but i dont have any thing to compare it to to see if it is good enough?? It is definitely spitting out water though, not just steam. The timing is set at 10 degrees and seems to idle nicely there although it has a hard time idling back down below a thousand after i run it wide open... Think i am ok??

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              • #8
                probably OK,
                FYI, I added a second throttle return spring. The boat only had the spiral spring on the throttle shaft on my boat, perhaps a previous owner mistake. I would make note of the idle jet position, then open it up 1/2 turn see if that makes a difference.
                Dennis
                20' 1987 Renken Cuddy Cabin
                AQ131C 270 drive
                Southern NJ

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                • #9
                  Great! Thanks! I will let you’ll know how it works!

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                  • #10
                    Used parts
                    The running temp can be as much as 180d on the AQ131
                    The gauge might be off??

                    The manifold shouldn't be so hot you can't hold your hand on it.
                    How hot is the rubber boot on the end of the exhaust?

                    Running on a hose, it might not have enough water.
                    The raw water pump can push a lot more water than the normal hose can supply.

                    The AQ131 is 120hp.
                    To get the best results from these little motors, you need to use the OEM props.

                    One of my friends had a AQ125 117hp.on a 24ft.
                    Said it wouldn't perform right.
                    Did a bunch of tests and didn't find anything.
                    Then I noticed a brand new prop on the drive.

                    I asked when did the problem start?
                    He said when he put on the new prop.
                    The new prop had short blades almost like a chopper.
                    Changed it back, the problem went away.


                    Buy American made Cars and Trucks!!!Towing insurance for a boat,a GREAT thing.
                    ​Tools to make my life easier: Battery tester, die grinder, temp.gun, compression tester, DVA meter.

                    In Scenic , Beautiful San Sebastian by the sea Florida

                    88 Bayliner 21CC 2001 Mercury 225 HP EFI

                    PLEASE,NO PERSONAL MESSAGES IF THE QUESTION CAN BE ASKED ON THE OPEN FORUM

                    Comment


                    • #11
                      I have the exact same boat in Cuddy config: Bayliner Capri 1950, AQ131A, 275 O/D. I bought it new in 1986(!) and it's still giving great service. At idle, the temp gauge shows 175 degrees; at 4000 RPM, temp goes to ~190, but quickly returns to 175 at lower RPM's. The exhaust manifold is uncomfortably hot to the touch when running at 4000 RPM, but cools a bit at lower RPM.

                      I've seen a Youtube video where the guy hooked a clear plastic tube to the drain spigot on the input to the copper exhaust manifold cooling tube. By elevating the free end abut 2-3 feet above the engine you can actually measure the water pressure going into the exhaust manifold. A 2 foot rise in the water column represents ~ 1 PSI. Might be worth a try..

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                      • #12
                        Interesting! I will have to try that! I will let you know what I find! Thanks guys

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                        • #13
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                          Originally posted by djhinca View Post
                          ...
                          I've seen a Youtube video where the guy hooked a clear plastic tube to the drain spigot on the input to the copper exhaust manifold cooling tube. By elevating the free end abut 2-3 feet above the engine you can actually measure the water pressure going into the exhaust manifold. A 2 foot rise in the water column represents ~ 1 PSI. Might be worth a try..
                          Could that be me?
                          https://www.youtube.com/watch?v=sSk7GpihQVs

                          Last month's shakedown, checking out things before going fishing
                          https://youtu.be/SGcP1E56HmQ
                          Dennis
                          20' 1987 Renken Cuddy Cabin
                          AQ131C 270 drive
                          Southern NJ

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