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maillemaker's avatar
maillemaker
Explorer
Jun 11, 2018

Can anyone tell me what this coolant line is for?

I have a 1990 Winnebago Warrior RV built on a Ford E350 van.

There are, of course, two bypass lines that come off of the water pump and manifold. Normally, these would route to the heater core. On my RV, there are tees in these lines that also run back into the RV house cabin, to heat a heater back there as well as heat the water heater (this is called "Motor Aid" - it will give you hot water by using the engine heat to heat your water heater tank).

In addition, there is a thinner (3/8"?) line running off of a T that goes to a fitting on the bottom of the radiator near the drain ****.

Can anyone tell me the purpose of this line? It is difficult to find a replacement radiator with an extra fitting for this line.

Schematic:


Here is where it tees off of one of the bypass lines:



Here is where it terminates at the radiator:



This line is a metal hard line that runs down behind the alternator. It has permanently crimped-on rubber ends at the T and down by the radiator. This line makes me nervous as it is 28 years old and I would like to replace the rubber portions due to age but as they are permanently crimped onto the metal middle run I'm not sure what to do about it. I could replace it with plain rubber tubing and just carefully zip-tie it out of the way. But it makes it problematic for replacing the radiator as I can't find an aftermarket replacement with a fitting for it to go to.

Steve

17 Replies

  • That line is there to help keep the transmission fluid up to temperature. Note that it delivers hot coolant over the top of the transmission heat exchanger in the radiator end tank.


    Thanks, Richard. That makes sense, given the proximity to the input/output of the transmission cooler lines, but I am not familiar with the internal layout of the radiator.

    I'll take some more pictures/video tonight that shows the complete routing of the system. I'm not sure which of the bypass lines is the output and which is the input from/to the engine. I believe one line terminates in the intake manifold near the thermostat housing, and the other terminates in the water pump itself. I'm guessing the output is from the manifold, not the pump.

    Steve
  • wnjj's avatar
    wnjj
    Explorer II
    RLS7201 wrote:
    That line is there to help keep the transmission fluid up to temperature. Note that it delivers hot coolant over the top of the transmission heat exchanger in the radiator end tank.

    Richard

    So I assume that line is connected to the pressure side of the heater core loop, effectively bypassing the thermostat? That would allow both cabin heating and transmission heating as a priority on a cold (t-stat closed) engine.
  • That line is there to help keep the transmission fluid up to temperature. Note that it delivers hot coolant over the top of the transmission heat exchanger in the radiator end tank.

    Richard
  • Looks like a bypass for when the heater valve is shut. If the heater is fed directly off the water pump, when the thermostat is closed and the heater valve is closed, there's no flow through the pump, causing it to cavitate and heat up.

    Just a guess.


    Thanks for the info. Where is the "heater valve" located? I'm not familiar with that.

    Steve
  • Looks like a bypass for when the heater valve is shut. If the heater is fed directly off the water pump, when the thermostat is closed and the heater valve is closed, there's no flow through the pump, causing it to cavitate and heat up.

    Just a guess.

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