Remote oil thermostat

[jiott]

One thing I have learned after 40 years as a hydraulics engineer is that there is always more than one way to do something, as we see here in this thread, so choosing the best way is usually a compromise between many factors such as:

• Proper function
• Longevity
• Ease of installation
• Ease of maintenance
• Failure modes & probability
• Results of failures
• Likelihood of errors in installation & maintenance
• First cost & life cycle costs
• Overall reliability
• Environmental factors
• Cosmetic appearance

I have probably missed several areas, but you get the idea. The engineer has to weigh all these things, and I tend to trust the factory engineers who focus their whole effort and have many years of product experience to call upon. That is compared to those of us on this forum having fun trying to second guess them in a few minutes of our spare time. Hey I know this is experimental aircraft and there have been many new and better ideas come out of it, but be carefull, you are dealing with your life and a $20,000 engine. My 2 cents.

[Slyfox]

but in my line of work, these type of coolers have not been a problem. now the ones in the radiator, oh my. but those generally will fail with pressures over let say 80psi. and have seen it. aka the Nissan radiator failures which is a direct result of cooler line pressure up tward the 120psi area. which can be controlled with a different spring. the stacked cooler like we use can even withstand that pressure. but those radiators not a chance. not trying to muddle anything just saying. mine will probably stay the same for it is WORKING the way it is and I like the fact that my system keeps the tank level up. but knowing that there is like 8 connections between the tank and my oil pump inlet has got me to say the least, interested in keeping things sound.

[Kurt.A]

Did not mean to get under anybody's skin with my previous post. Yes we are all allowed our own opinion, we have many to thank for our freedom of speech. I fully understand the potential for an external leak being disastrous but no more disastrous than any other eng failure which could easily be caused by a variety of reasons. The plate coolers are very tough units as compared to the coolant radiators. They live right in prop wash and can be subjected to stones and pebbles even on a paved strip. something as simple as a pebble strike could cause a cooler to leak. With the cooler on the pressure side the leak would be obvious and draw immediate attention. With a leak on the suction side through the same pebble strike would still cause the eng to go down after many hours of aerating the eng oil and creating huge dollars in repairs. With the environment that I will be flying in I can definitely see that eng life would be increased with plumbing the cooler in after the filter. Just honestly makes more sense to my brain.

[jiott]

Kurt, just curious if you plan to plumb your cooler after the filter there is nowhere on the 912 to put it except in the scavenge line from the bottom of the crankcase to the oil tank. Or are you planning some modification to the engine case to get an oil in & out port on the pressure side?

[jrevens]

Kurt, just curious if you plan to plumb your cooler after the filter there is nowhere on the 912 to put it except in the scavenge line from the bottom of the crankcase to the oil tank. Or are you planning some modification to the engine case to get an oil in & out port on the pressure side?

I had the same question in mind with one of my previous posts. There's a lot to consider here, and I tend to agree with Jim and some others who like the cooler where Rotax says to put it. I'll say again that I believe the engine will see higher oil temps if the cooler is piped between the engine & the oil tank. Is it enough to be a factor worth thinking about? I don't know. But how do you propose to install the cooler "downstream of the oil pump & filter"? The only access I know of is downstream of the whole engine. The only pressure on that line is crankcase pressure. It seems to me there might be more chance of potential clogging of the cooler on that line than after that big "engine moisture, sludge & any other crap that may come out of the crankcase" trap called the oil tank.

[Kurt.A]

Tapping into the oil supply is relatively simple. I agree that plumbing the cooler into the return to tank line would not be wise. What I would propose is to spin off the oil filter. Fabricate or purchase an adapter plate that installs in place of the filter with an inlet and outlet port. These are readily available for automotive use but would require some research to find one that fits the filter mounting dimensions. From the adapter plate you would run steel braided hose to a remote mount filter housing then to the cooler and then back to the filter adapter. You could also do this using thin wall 4130 tubing which would probably be the safer route. A word of caution to those reading in, steel braided hose will harden after about 3000 hrs and become a serious safety concern. A cooler bypass valve would be wise as well with a pressure differential setting of about 20 PSI for cold starts. I am not saying that Rotax engineering is wrong, but I am saying that in cold climates where I live and intend to fly a cooler on the suction circuit scares the bejesses out of me far more than the potential for an external leak or even a total rupture.

[Av8r3400]

One last point I'm going to make here.

I have a 912 UL (80 hp) in my yellow plane. I have NO oil cooler on it. Zip, zero, nada. On the hottest of summer days, after long sustained full power climb, my oil temp may get to 250 degrees Fahrenheit. Yes I live in Wisconsin, not Arizona or Nevada. But it does get into the high humidity, 90s here during the summer.

I use Mobil 1, Racing 4T oil. With this oil my temp redline from Rotax is 280 degrees Fahrenheit. I've been told by LEAF, that this oil remains stable and will not coke well above 320. I don't need an oil cooler. I don't want the complexity of tubing and weight of an oil cooler on this already nose heavy plane.

With modern oil technology, high temps usually aren't the problem. I've seen more problems with prolonged low oil temps.

Just something to think about.

[Slyfox]

does anybody have the info on the oil circuit for the 912 internally. just curious on the thoughts here on the crankcase pressure for the return line. I don't see how crankcase pressure alone can burb the engine for normal use. I believe it's also mixed with oil pressure from the pump. just trying to do a mental on this. the reason I say this, there is a big line coming off the bottom of the engine. I would be interested in a flow of this line. I have a device called a sonna flow that I can put on this line to do just that, it checks flow. I don't have any time now to install this on mine at time being but would be interesting to see what it is. think of this. if the engine needs so much oil from the tank to operate, the return has to be as much to keep the level up. see my meaning. the flow back to the tank is the same as what is leaving. with that in mind why wouldn't it work on the return line the cooler that is, just saying.

[jiott]

The reason it wouldn't be wise is that the scavenge line coming off the bottom always has oil in it (the same amount being pumped out of the tank) but it also has some air (combustion blowby) in it. I doubt an oil cooler in this line would work very efficiently with a mixture of oil and "air" in it. The oil tank is designed, with its screen etc. to separate out the air before it gets pumped back into the circuit. If you don't think there is air in this line, think again. The only thing pushing oil out of the crankcase back to the tank is crankcase pressure; there is no oil pump pressure down there because the crankcase is common with the oil tank which is vented to atmosphere. I know engineers are clever fellows but there is no way they can design the crankcase blowby pressure to push EXACTLY the right amount of oil back to the tank without any air in it. If the flow rate was even a teensy bit too slow the crankcase would eventually fill up with oil and hydrolock the engine. The only choice is to always blow more than enough oil back to the tank, keeping the sump "dry", which means that there is always some air in this line. By the way the Rotax maintenance manuals which show the oil circuit details are available free to all on the rotaxowner.com website.

[Slyfox]

thanks for explaining, makes more sense now. must be why I get a little oil out the vent line. I'm sure if I make my vent longer and loop it higher than the tank might help. another project to do. that's what makes an experimental so fun, lots of little things you can do to it. have a nice day. oh also, will have to download the engine manual one of these times. hope you all have a nice Christmas.