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Hi all. Can anyone please clear this up for me regarding the plumbing of the Thermostasis unit P6-H-190 as it is driving me potty!

The instructions that come with the unit (see pic 1) have the oil routing from the sump/ tank connected to the lower port of the Thermostasis unit. The oil routing the pump is connected to the upper outlet port of the unit. Depending on whether the thermostat is open or closed the majority of oil flow will either flow via the bypass (bottom to top), or route via the cooler. I get this.

However another set of instructions for the same unit which also shows the internal components (see pic 2) shows the unit plumbed 'upside down' (Ie. Oil from tank routes to upper port and oil to pump routes from the lower port therefore bypass oil flows from top to bottom within the unit).

Looking at the unit itself and its internal construction (see pic 3) it seems to me that the second set of instructions should make more sense because if the oil is routed from the tank to the lower port there is no restriction to flow rate to reduce oil flow to the cooler and instead encourage oil to flow up and through the bypass valve. The lower bore is straight through with no obstruction.

If the oil tank is indeed connected to the lower port as per the instructions that come with the unit is the oil from the tank encouraged to flow upwards through the unit and the oil bypass to exit via the upper port to route to the pump merely due to the effects of lower pressure/ suction from the returning oil flow above?

I want to understand the reasons why there are two seemingly conflicting ways of plumbing this unit and what the effects are of each method with respect to operating temperatures.

I have seen many photos of different installations and they pretty much all have the oil tank routing to the lower port. 

Can anyone help?

 

8351_1_image.jpeg (You do not have access to download this file.)
8351_1_image.png (You do not have access to download this file.)
8351_1_image.jpeg (You do not have access to download this file.)
  • Re: Rotax 912 Thermostasis unit plumbing confusion

    by » 6 days ago


    Sorry instructions supplied with unit attached

    28145_2_image.jpeg (You do not have access to download this file.)

  • Re: Rotax 912 Thermostasis unit plumbing confusion

    by » 5 days ago


    You are over-thinking this.  It is a six of one an a half dozen of the other situation.
    You are thinking that if the flow hits the side you can't see clear through, it will tend to bypass more than passing through the clear opening.

    Consider that if the Oil passes through the clear side first, then passes through the cooler, it is going to encounter the "Restricted' side on the return trip.
    The back pressure on the return trip is going to reflect back through the cooler to the clear exit side of the thermostat making the oil prefer to bypass the cooler just as much as if it were plumber the other way.
    It makes no difference in flow byypass.
    The  Flow Steering Force is Not in the Thermostat, it is in the Hoses to and from the Cooler and the Cooler itself.
    Take the two inch path or take the three foot path ???

    The only real difference, which is probably also insignificant, is that once closed, the temperature sensing element will either be on the warmer or cooler side producing a slight operating temperature offset.
    The Thermostats have more varialbility in there calibration than the difference in closing temperature.
    No mater how you connect it as long  as the engine is on one side and the cooler is on the other it will work.

    Just be sure the outflow of the cooler is at the top to allow any air to rise and be purged.

    Remember, the purpose of the thermostat is Not to keep the Oil Cool, it is to keep the Oil Hot!


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


  • Re: Rotax 912 Thermostasis unit plumbing confusion

    by » 5 days ago


    Hi Bill. Thanks for the reply. I've done some more digging and have found the attached amendment to the Thermostasis installation instructions. It seems that in 2012 they changed the recommended installation such that the oil tank connection routed via the lower port of the unit (straight through bore with no restriction) rather than the upper port.

    It seems that the only difference between the two installation methods is a difference in the returning oil temperature going into the pump (either 88deg C, or 79Deg C). Still 10deg C is still quite a difference.  

    Thanks 

     

     

    28148_2_7C8951EF-7E82-4BD2-9EC1-644AADF5B4FE.png (You do not have access to download this file.)

    Thank you said by: Bill Hertzel

  • Re: Rotax 912 Thermostasis unit plumbing confusion

    by » 4 days ago


    That all makes sense.
    Keep in mind that no matter if the Tstat closes at 79 or 88°C; neither installation will have any effect on getting the Oil up to 100°C or more.
    It only effects how quickly you warm up to ~80°C++.
    Once the Tstat closes, it is out of the loop and no longer has any effect on controlling the temperature.

    There are 4 differnet orientations you could install the Tstat; None of them are Wrong.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


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