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Thread: no heat at low speed

  1. #1
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    Question no heat at low speed

    Been running my 96 SeaSport alot this summer since purchase in May. I am tickled to death with almost all of the features and the way she handles. One problem that I do not understand and have not spent time looking into yet is the heater.
    This is an Acuheat system running off of the engine block.Fan and heat exchanger are located in storage area under cuddy cushion. Two hoses running to form the loop just like the heater in your car is set up.
    Problem I have is no heat at idle and low speeds. I have to start working her over 1600 RPM's to get things hot. Then it works great.
    Guy I bought it from said he changed out factory 160 degree thermostat to 180 for more heat. Works great when she's got a load on, but cools quickly when down to idle.
    I also have an Almar riverboat with 351. Virtually the same set up and distance from engine to heater and it pours out tons of heat at idle all day long.
    Anyone out there got any clues as to whether this is how it is supposed to work, or can I do something to get heat when idling? Advice and tips are much appreciated.

  2. #2
    Member Dupont Spinner's Avatar
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    Default

    Does your engine temp drop when trolling. If so then you have a stuck thermostat. If not then it's a circulation problem. The system may be plugged with rust.

    My Bayliner runs about 180 running hard and about 160 at troll speed but the heater doesn't change much.

  3. #3
    Sponsor potbuilder's Avatar
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    maybe its getting some kind of air bubble at low speed that won't let the water circulate???

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  4. #4

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    Replace your thermostat. ....And check the lever that switches the heater from the dash vents to the floor vents, my lever is down below the helm seat, something might be plugged.

  5. #5
    Member jrogers's Avatar
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    I think the heater core is plumbed in wrong - well, maybe not wrong, just not the way you want it. I have seent his on cars before. The heater core for the interior heater should be on the engine side of the thermostat, so that fluid is flowing through it all of the time instead of just when the thermostat is open so that the anitfreeze cuirculates through the heater core at all times. This way you will get some heat off of it when the engine is just warming up, or when the engine is not at a big load.

    Jim
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  6. #6

    Default What Jim said is correct

    Water costantly flows through the core, the thermostat keeps it hot. A stuck (open) t-stat will leave you cold at low speed. A bad water pump or air gap would likely cause the engine to overheat. Not good.
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  7. #7
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    Default Still looking for answer

    Air flow is strong from blower to defroster and cabin heat vents, nothing plugged up there.
    Also engine runs at a pretty consistant 180 degrees from warmed up idle, to high rpm cruising, accotding to temp gauge.
    Just seems like its pouring out hot air while cruising, then cools off quick when back to idle rpm's.

  8. #8

    Default Obstructing Water Flow

    If your motor is 180 degs, so should your heater core. If not, I'd guess the water flow is obstructed or plumbed wrong.
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  9. #9

    Default

    The heater core is always the highest point in a cooling system therefore the first place to suffer loss of coolant flow if the system is low.

    Check the cooling system fluid level before anything, if that appears to be full then check for a restricted heater core, it can easily be done by removing the two hoses attached to it then place a garden hose on 1 pipe and flush thoroughly then, switch to the other pipe and repeat. If, as you do this you see rust and such flush out, be sure to flush the entire cooling system of the engine.

    The thermostat has nothing whatsoever to do with the heater core function provided the engine temp is running normally.

    If the engine does not reach operating temp. then replace the t-stat.

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