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Hi everyone!

in another thread it was mentioned that oil pressure has  „a very strong relation with oil temp“. I would like to know more about that and would appreciate if anyone can provide some more detailed information about that. 

Thanx a lot for direct comments or links to relevant sources.

Peter

 

  • Re: Relation of oil pressure and temp

    by » 5 days ago


    Thank you Sean Griffin for your earlier reply in the other thread: „ Sorry Peter - no link from me but I am sure the information is out there - its the relationship of viscosity and temperature. Oils viscosity goes down as the temperature rises (it gets thinner). As it thins the ability of the pump to maintain the cold(er) pressure drops. This is why cold engine start up usually sees a relatively high oil pressure that then reduces as the engine/oil  temperature rises.

    So, if you see an oil indicator pressure drop but no rise in oil temperature you most likely have a faulty pressure sensing system. The corollary is also fairly true.“

    That’s the part I happen to experience with my 912, too - understood and confirmed. Viscosity in a given set up is a function of oil temp. My thoughts are more in the direction of „what if the mushroom (or ball) is set up to give a higher or lower level of oil pressure“ to start with. Is it likely that the oil temp level is directly affected by the oil pressure one can adjust in some range?

    Regards

    Peter


  • Re: Relation of oil pressure and temp

    by » 5 days ago


    I use Mobil 1 Racing 4T 10W-40 Synthetic Motorcycle Oil in my RV-12 w/ Rotax 912ULS.  The oil is multi-viscosity, so at cold temps it acts like a thin 10W oil and at elevated temps it acts like a 40W oil.  I see nice steady oil pressure when the engine is at operating temperature ~ 50 psig.  My engine is early SN with mushroom head pressure relief valve.

     

    Mobil 4T has correct additives for use in engines that share oil between crankcase and power transmission gear drive.  This is a very important consideration for the Rotax 9-series engines.  


  • Re: Relation of oil pressure and temp

    by » 4 days ago


    Oil pressure on startup tends to be a bit higher especially on cold mornings until it warms up a bit and then settles down to your normal running pressure. It can do this in many different types of engines. If your oil pressure is normal and then you advance the throttle and it drops to lets say 25 psi, but goes back up to 50 psi when you reduce the throttle it's most likely a poor ground. It the pressure drops way down or goes way up like 100 psi it's more likely the sender. There are a few other scenarios, but these seem to be the most common.


    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


  • Re: Relation of oil pressure and temp

    by » 4 days ago


    Maybe I am being misunderstood. No worries about sender, ground or type of oil.

    If there is a strong relation of oil pressure to oil temp and shims are put underneath the mushrooms spring that will surely increase indicated oil pressure. Will I get higher or lower oil temps? 
    With Bernoulli in mind the product of speed and pressure remains the the same, right? Thus, do I get reduced oil flow speed when pressure is shimed up. And if the flow of oil is slower due to increased oil pressure, will the flowing oil get better cooling cause it stays in the cooler a longer time?

    Any experience with that?


  • Re: Relation of oil pressure and temp

    by » 4 days ago


    No, Bernoulli would not apply in this case because it is based on a fluid with constant energy (strictly speaking it is about constant enthalpy, the product of pressure and volume).  The temperature of the oil is determined by the temperature of the engine because the oil absorbs energy from the engine. It also loses energy through the oil cooler, so the rate of heat loss from the cooler will affect temperature too. The pressure of the oil depends on the force with which it is pumped, the backpressure due to the flow rate and the viscosity of the oil, which is a function of temperature.  Yes, I don't understand your question.   


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