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Thread: Remote oil thermostat

  1. #21
    Senior Member jrevens's Avatar
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    Default Re: Remote oil thermostat

    I appreciate the conversation here... available or not, it's good information and I need all of it that I can get. I didn't start this thread, but thank you all anyway.
    John Evens
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  2. #22
    Administrator DesertFox4's Avatar
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    Default Re: Remote oil thermostat

    FYI guys, you can all vote or rate a thread at anytime for all those folks searching our archives in the future. If you like a thread please rate it and stars will be attached for future reference. Thanks to everyone for another good info filled thread.


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  3. #23

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    Default Re: Remote oil thermostat

    I too have been following this thread with curiosity. The fact that the eng oil cooler is plumbed into the suction side of the eng oil pump disturbs me. Automotive eng oil coolers are rarely used in the gasoline world however they are extensively used in the heavy duty or diesel engs. I have been a Tech for the largest Caterpillar dealer in the world for the last 28 years. Every single Caterpillar eng ever produced has the oil cooler on the pressure side of the eng oil pump and is also downstream of the eng oil filter. To me it is logical to cool the oil after the pump and filter for the following reasons:
    1) Pressurizing oil with a pump produces heat.
    2) Filtering cooled oil has the potential to open the filter bypass valve more often and for longer periods of time allowing unfiltered oil to enter into the lubrication system.
    3) Having the cooler in the suction circuit leaves the system open to extra possible leak points on the suction circuit. This would allow the potential for a constant stream of air to be entering into the lubrication system. Yes air will enter the suction circuit long before a visible external oil leak will be observed.

    With regards to having air in an eng's lubrication circuit as per the original post. I have seen many times the devastating results inside an eng to it's components from air bubble implosions. An implosion is the result of an air bubble collapsing at high pressure allowing the surrounding liquid to impact the metal with incredible force. This can be readily seen on eng bearings, crankshafts, the coolant side of cyl walls, eng oil pumps and the list goes on. I have never seen this damage to a valve train component including lifters however for the most part Caterpillar engs use solid lifters. IMO the air that has managed to enter the system gets purged from the oil prior to entering the valve train components as this is near the end of the lubrication circuit. The comment in a previous post made about ensuring the hyd lifters be completely filled with oil is also very critical to valve train stability. Hyd lifters should always be manually pumped full before installation to the eng.
    Unless someone wishes to convince me otherwise I will definitely be changing the way my Rotax eng oil cooler is plumbed. Because Rotax says so does not count here. My sincerest gratitude to the board members that have brought this fact to everyone's attention.
    Kurt A

    Kitfox II,
    Rotax 912,
    1100 gross
    Fixer Upper Project

  4. #24
    Super Moderator Av8r3400's Avatar
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    Default Re: Remote oil thermostat

    Rotax engines do not have a scavenge pump removing the oil from the engine back to the sump. They rely on crank case pressure to do this. I would not put any components on that side of the oil system that may impede the flow. This is just begging to hydrolock your running engine making for instant total destruction.

    There is no provision that I can see to put the cooler after the pump yet before the engine without modifying the engine case and or pump itself. Additionally I would not do this because it would introduce all of the lines and the cooler itself to holding full engine oil pressure. A failure of any of these multiple connections, lines and passages will result in a pressure oil leak, which can quickly pump all of your engine oil overboard which will totally destroy the engine very quickly.

    There is a lot of overthinking a non problem here. The engineers at Rotax understand their engines and know how to keep them working, reliably. This is the experimental world, so you can do as you wish, but I'll follow the installation and operating manuals.
    Av8r3400
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  5. #25
    Senior Member Slyfox's Avatar
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    Default Re: Remote oil thermostat

    I personally don't see an issue with putting the cooler after the pump. It's done on many applications in automotive. the cooler that is put on is free flow for one. I am disturbed more that the cooler is put on before. first off how do you insure that all air is out of the cooler, you really can't and for first start up that little pump can have problems with air going through or into the bearings of the engine. I know when I first started my engine I had filled all lines with oil first. I took my line from the tank and filled there and removed the line off the pump inlet and had that spot as the leak out. meaning when I had oil coming out of that line my cooler and such was full than I put the line on the pump inlet. this proved very good and it took very little to purge the system and fill the lifters. which I did have the covers off the valves and checked like I was suppose to before firing up the engine.

    again this discussion was on if air or a leak was found on one of the lines. in that case you seal the system and crank over with mags off and look for pressure. that simple. if no pressure you need to make sure and recheck the purge and adding air to the vent is one of them. of course the top of the tank is on as well as the cap. I sit in the airplane with the vent in hand and shop air blown little at a time and crank over the engine until the pressure come up. yes it works real well. take care have a nice day

  6. #26
    Senior Member Slyfox's Avatar
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    Default Re: Remote oil thermostat

    Quote Originally Posted by Av8r3400 View Post
    Rotax engines do not have a scavenge pump removing the oil from the engine back to the sump. They rely on crank case pressure to do this. I would not put any components on that side of the oil system that may impede the flow. This is just begging to hydrolock your running engine making for instant total destruction.

    There is no provision that I can see to put the cooler after the pump yet before the engine without modifying the engine case and or pump itself. Additionally I would not do this because it would introduce all of the lines and the cooler itself to holding full engine oil pressure. A failure of any of these multiple connections, lines and passages will result in a pressure oil leak, which can quickly pump all of your engine oil overboard which will totally destroy the engine very quickly.

    There is a lot of overthinking a non problem here. The engineers at Rotax understand their engines and know how to keep them working, reliably. This is the experimental world, so you can do as you wish, but I'll follow the installation and operating manuals.
    no insult here, but are you an engineer. I've been working on hydraulic systems for years. coolers generally plug up from debris in the cooler created by a failure. also if you are saying there is a chance the cooler being plugged and close off flow. think about this. if the cooler is restricting it can cause problems on the suction side. what I have seen is things will work normally than the vacuum gets to great and than the pump quits without warning. seems to me you can taxi out and take off and than the oil pressure goes to nothing in this case. seen it many times on transmissions. so I guess it can go both ways.

    not sure what the answer is here. I know my system is working fantastic, so I probably won't change it. but to those starting a new engine, they must insure that cooler is free from air from the start up.

    Now this is another thing I do. when I first get to my airplane I burp the engine. I push the airplane out of the hangar and than I get in. turn on the master keep the mags off and pull the choke. than I turn over the engine for 3 seconds. this does two things, it puts fuel in the cylinders, two it makes me aware that the oil pressure is there, if not, it gets more crank time without choke to make sure pressure is there. do any of you insure oil pressure before start. you should. that's all folks, have a nice day.

  7. #27
    Senior Member Slyfox's Avatar
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    Default Re: Remote oil thermostat

    Kurt, you wrote:
    3) Having the cooler in the suction circuit leaves the system open to extra possible leak points on the suction circuit. This would allow the potential for a constant stream of air to be entering into the lubrication system. Yes air will enter the suction circuit long before a visible external oil leak will be observed.

    This is very very true. I have thought of this also on this discussion. this in itself will probably make me change mine over when I change all the oil circuit rubber this next annual. it is much safer to have as little chance of leaks on the suction side of any pump. in our situation having the cooler and the thermostat is a big worry for this. thanks for mentioning.

  8. #28
    Super Moderator Av8r3400's Avatar
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    Default Re: Remote oil thermostat

    Yes, actually, I am an engineer. I work in a different area now, but my background is mechanical engineering.

    This isn't a heavy diesel or automotive application where when you blow a pressure oil line you can stop, shut down the machine and fix it. It's an airplane. When you blow an oil line you will quickly loose the engine. This means you land. Hopefully safely, without injury or loss of life.

    As an experimental, you can do as you please and I wish you luck. I choose to follow the Rotax engineers' advise as to cooler location and operations. They know more than I do.
    Av8r3400
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  9. #29
    Senior Member Slyfox's Avatar
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    Default Re: Remote oil thermostat

    I just looked at my plane and yes it is put together just like rotax says. will I change it. don't know. I run on the premise of, "if it ain't broke don't fix it." I know when I put my lines on I used silicon on the hose to fittings and then the clamp. I've been doing this forever on auto applications. if the clamp happens to loosen a bit it is still sealed. now I don't use cheap silicon I get mine from ford. it really dries solid. Now another thing I did is put that thermostat on the top of the gear box. my theory is it has the line coming out of the tank going up high. makes the oil stay in the tank. I checked my oil level today and it's been since sunday that I last flew it. the oil was all the way up. I also have it plugged in, yup I do that also, I know that is another thread going. but I plug my plane in and forget it. it has the reise system with the thermistor to control temp and a ring around the tank and the element on the engine. engine was warm and the oil at the top of the stick. it's always like that. even after sitting for about a month here recently cus it was real cold and windy, flew the rv instead. the oil was still showing on the stick when I checked it. I think having my thermostat on the gear box does this.

    will I change my line routing, more than likely not. but I do now understand any leak in the lines before the pump can be BAD.

  10. #30
    Senior Member jiott's Avatar
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    Default Re: Remote oil thermostat

    A leak on the suction side can be bad alright, but I agree with Av8r3400 that a leak on the pressure side is much worse. I also think that a cooler on the pressure side is more likely to fail because it is seeing relatively high pressure (way higher than a coolant radiator) cycles all its life. Most oil cooler failures I have seen are from pressure fatigue rather than contaminant blockage.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

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