PSRU Oil Operating Temps

Discussion in 'General Auto Conversion Discussion' started by TXFlyGuy, Dec 14, 2019.

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  1. Dec 14, 2019 #1

    TXFlyGuy

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    What is considered too hot when it comes to oil temp in your PSRU?

    Most Titan owners are running syn oil. And typical operating temps for the Honda V6 are from 105-110F.

    For the LS3, closer to 170-180F.

    Note the gearbox oil also runs the prop governor, in the Titan Mustang.

    Reading about engine oil temp and high tuned cars, temps of 200-220F are not only acceptable, but desirable.

    Mobil states their syn oil can withstand temps of 500F.
     
  2. Dec 14, 2019 #2

    Toobuilder

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    What does the manufacturer say?
     
  3. Dec 14, 2019 #3

    wsimpso1

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    The oil might stand very short exposures at 500 F, but not for much of the oil nor for long.

    The big issue is not what the oil will stand, but what the propellor and governor will stand for a long and reliable life.

    Aluminum alloys do not like being above 400 F. Seals and gaskets and internals will need to be lower and they are what deteriorate over time. Temps they should stay below is all a matter of exactly what materials were used. What do the prop and governor makers have to say about their max oil temps? My guess is redline same as Lycoming and Continental. 170-180 F ought to be fine.

    Billski
     
  4. Dec 14, 2019 #4

    TXFlyGuy

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    Thanks. Might you know offhand what the Lycon redline numbers are?

    The manufacturer states operating temps of 110 to 180 are standard.
     
  5. Dec 14, 2019 #5

    TXFlyGuy

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    This is a general question about oil temps in gearboxes. Not a Titan specific question. What is your experience?
     
  6. Dec 14, 2019 #6

    Chris Matheny

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    Many oils exhibit a significantly lower load capacity at lower temperatures. The additive packages they use in modern oils are specifically designed to run in the 200-230 F range and often offer the best protection there. In auto engines this temperature is desired to off gas any water vapors that can form when shutting an engine down and condensation can occur. For this reason it would be a good idea to change the PSRU oil regularly if the oil doesn't get very warm.
     
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  7. Dec 15, 2019 #7

    TXFlyGuy

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    The guys I know are changing oil every 10 hours. That seems excessive to me. But the temps are on the low side, being 110-175F.

    I would think you really want the temp to be 200, or a little higher?
     
  8. Dec 15, 2019 #8

    Chris Matheny

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    If you're running an automotive engine oil then change it regularly. If running a good hypoid gear oil they contain emulsifiers to keep any moisture suspended since differential's are more susceptible to heat cycles without getting warm enough to rid themselves of moisture.
     
  9. Dec 15, 2019 #9

    TXFlyGuy

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    Good advice. Yes, my friends are running full synthetic auto-engine oil.
     
  10. Dec 15, 2019 #10

    wsimpso1

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    You asked for it...

    In automatic transmissions used in cars and trucks, we had a variety of extended warranty issues that always appeared to be temperature related during an era when 273 F was the top allowed temperature at the end of any of several heat protection tests (corrected for a 100 F day). The fact that it was sometimes not held tightly and some folks cheated by calibrating the tranny around the tests did not help either. In any event all of the majors moved to lower standards, around 250-255 F for these same tests, and quite a few of the extended warranty issues disappeared. These issues were worst in Florida and were much better in Arizona, presumably because the airconditioner condensor drops heat on the other heat exchangers while there is more thermal load with Florida's humidity than with Arizona's dry heat. Yep, dry heat really is easier to deal with, at least for road vehicles. We can safely presume that the rest of the duty cycle for automatic transmission was reduced by folks getting the law laid down on absolutely meeting the lower required temps and without invoking heat protection strategies in the calibration.

    Failures seen on extended warranties (these are bought to cover the vehicle to 100k or 150k miles) were always tough to nail down, rarely a "smoking gun", and a variety of issues. We could tell that the oil, friction materials, seals, gaskets, bearings and gears, and polymeric components were not doing well with the higher temps and did MUCH better after the policy changes were made to run cooler. All warranty, both nominal and extended mileage, ran with substantially lower failure rates and root causes became easier to determine too.

    Something else to remember about this era - the industry was doing a lot of work to raise capabilities of seals, gaskets, polymeric parts, friction materials, and even investigated oils. Many upgrades were made in this era, going in when they could be launched, and only caused a modest downward drift in all types of warranty, but oil temps dropping showed strong across the board reductions in warranty failures.

    So, there you have it, automatic tranny cooling in cars and trucks should not allow worst duty cycle events to go above 255 F. Lower temps may even be better, but the data is even harder to come by because field failure rates had been dropping to the point where end-of-life failures are rarely seen even on extended warranties. When I retired, most broken boxes were due to transient quality and build issues and tended to happen early in the vehicle lifetime.

    So, 160-180 F sounds like a pretty good territory to me. But then a PSRU is not a nine-speed torque converter launch automatic transmission...

    Billski
     
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  11. Dec 15, 2019 #11

    wsimpso1

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    In the automatic transmission world, we just did not see much in the way of moisture, even when we went looking for it. These machines are pretty much lifetime fill in the field, with few folks changing the oil in them EVER. If I had a PSRU with its own oil supply, I would probably send some oil for analysis each annual or 50 hours so I would get some warning if a gear or bearing is beginning to go.

    Now engines, they make lots of water, carbon dioxide, unburned hydrocarbons and oxides of nitrogen. Those chemicals get past the rings and into the crankcase where the water plus those other things are acids. You are also circulating the oil and purging air and other gases from the crankcase, so you do not accumulate a lot of water if you get the engine warmed up on each run. When the engine cools down after shut down, the resident water condenses, and you get a slug of acidic water through the oil system on the next cold start, then as the engine warms up, most of it evaporates and some remains thoroughly suspended in the oil.

    Engines are pretty good at handling water during lower temperature starts, but if you run a sump heater AND a blanket over the cowl to keep everything the same temperature, you keep less of that water for your next start. Leave the blanket off the engine, and all the heater does is move water from where the temps are highest to places where temps are lowest, like the camshaft on Lycomings and valve covers on many engines.

    I can tell you that the engines actually handle the modest amounts of water they cycle through pretty well, but the other chemicals become acids in the water suspended in the oil, and they do nothing but accumulate. This is like you or I trying to live without functioning kidneys, and is why we periodically change engine oil. Let's not get wrapped around the axle on this, the oil guys know how to put additives in to buffer the acids and reduce oxidation, and we have lots of history of long lived engines running their oil 25 to 50 hours in our Lycosaurs. The LS based engines can probably run those kinds of intervals too, being as they run a lot less blow-by gases than the traditional air cooled engines.

    But changing the oil in the gearbox? Make sure it stays full and that a little bottle goes in for analysis now and then. If you get back news of a lot of iron, aluminum, copper, etc, by all means, investigate. But change it like it was an engine? Maybe for the first 50 hours...

    Billski
     
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  12. Dec 15, 2019 #12

    TXFlyGuy

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    Billski - Great advice, and insight into this area. It would seem that 10 hour oil changes are not needed. In the PSRU, that is. But an oil analysis is worthy of the price of admission!

    Thank you.
     
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  13. Dec 15, 2019 #13

    Chris Matheny

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    I would say maybe 10hrs the first change then 50hrs after that. They usually don't hold much oil so it's not a big cost savings to run it longer. Oil analysis is always a good idea.
     
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  14. Dec 15, 2019 #14

    TFF

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    Rotax for the 912 like you to run motorcycle oil because it has additives for gears. I would only run what the gearbox designer says without question. It’s their box. They had an idea when they designed it. All the gearboxes I have been involved with had either turbine oil or gear oil. Only manufacturers recommended oils used.
     
  15. Dec 15, 2019 #15

    cheapracer

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    30 hours is reasonably standard fare for an unfiltered small capacity machine operating at temps.

    I'm not going to suggest it because aircraft, but my own personal experience with mobile core drilling heads (mobile rigs drilling through coal seams looking for gas) is that what we call Moreys, and you call Lucas Oil Stabiliser, actually does what it claims to do, specifically lowers temps and offers protection in your gear driven application.

    Because it's vicious, sticky stuff, at oil change, we would drain the heads, then run gear oil without Moreys for a shift, monitor the (high) temps on the head, drain that (like a flush), then refill with gear oil and the Moreys, and down came the temps.

    The owner of the drilling company swore by it, gear failures were very rare after he started using it compared to previously.

    Close enough to call the same as this type of rig, at the back of it 13 hours a day, 24 hours a day non-stop by 3 teams of 3 (10 days, 10 nights, 10 day's rest) rain, sun or hail. We could drill down a half mile.

    We were more complicated than this as we were drilling for gas, with the explosion risks that go with it, and indeed, a team of 3 for another company were killed during my time.

     
  16. Dec 15, 2019 #16

    pfarber

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    Wouldn't a gear oil be better than an engine oil? Different additives making the biggest difference.

    A PSRU is closer to a manual transmission than an engines rotating assembly. There are dino and synthetic gear oils, so the base oil can't be the biggest difference.
     
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  17. Dec 15, 2019 #17

    pfarber

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    A car engine has multiple methods for handling water. The most critical being PCV. Back in the day (aka late 30s early 40s) you had a simple 'road tube' to vent the cankcase. But PCV and detergent oils started to be a big thing in the 40s.

    Today, certified engines have no PCV so water vapor is still an issue, wheres an auto engine has a sophisticated PCV system.

    In a PSRU that is vented, normal operation would heat (well, more like warm) the oil enough to evaporate water (no, it doesn't have to reach 100C) as any amount of heat above freezing will aid in water evaporation. Also most PSRUs I have seen have an aluminum case. Al can corrode, but water, without oxygen, sitting on the surface of an alodined part, just isn't going to start a lot of corrosion.
     
  18. Dec 15, 2019 #18

    TXFlyGuy

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    It is my understanding that the Autoflight-New Zealand PSRU has an operating limit of 180F. That is a hard limit for the gearbox.

    Titan uses 80W90 Gear Oil.
     
    Last edited: Dec 15, 2019
  19. Dec 16, 2019 #19

    AdrianS

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    I agree that the manufacturer's recommendation is the way to go.

    Slightly OT
    I had a manual transaxle gearbox Volvo once that had a really baulky shift after a service.

    A bit of research, and I found the garage had changed the oil and filled with manual trans oil.
    Draining the box and refilling it with the Volvo specified ATF fixed the problem for good.

    I don't know why Volvo specced ATF for a manual box, but it worked.
     
  20. Dec 16, 2019 #20

    wsimpso1

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    Not to quibble excessively, but road engines vented the crankcase, usually with draft tubes, until PCV became common in the 1960's as the first piece of emissions control hardware.

    Elaborating on venting of crankcases and airspaces in gearboxes....

    PCV is still part of evaporative emissions equipment on road vehicles today. PCV originally vented the crankcase to the intake manifold, but evap emission systems also capture fuel vapors from the tank and crankcase, and vent to the intake manifold for burning while running. Fuel vapors are captured and released using a canister of activated charcoal. Water absorption and release is NOT a part of the evap emissions. Water vapor passes through the system with the rest of the gases that will not absorb and release from charcoal.

    In airplanes, we run breathers to keep from building pressure in the crankcase, and crankcase gases are driven overboard by the influx of new blow-by gases on a continuous basis. Liquid water will only accumulate to the levels that will suspend in the oil and in the air based upon the temperatures and pressures present.

    Go to transmissions and other gearboxes, and they almost universally are vented to the atmosphere. Jiggle caps used to be universal on road vehicles, but relocated vent openings have become common to prevent gearboxes and axles from "inhaling" water during water trench testing. Even modest amounts of water in these systems will mess with seals, gaskets, friction materials, bearings, gears, etc, so all vents for these things really should be placed and routed to prevent water ingestion while sitting and while in operation. Temperatures in the 150-180 F range WILL keep them from accumulating significant water if they only aspirate ambient water vapor.

    Billski
     

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