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Rotax 912ULS & oil temperature thermostat


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Is there anybody out there that has successfully installed a Perma-Cool Oil thermostat to their Rotax 912?

 

I imported a thermostat a while back and a LAME fitted it in accordance with the instructions supplied, however I still cannot get the oil temperature into the green band other than by taping the oil cooler.

 

The thermostat was initially installed as per Fig.B however it made absolutely no difference to the oil temperature, so I contacted Perma-Cool and they told me to try Fig. D which I did, but nothing changed and the engine oil temp. continued to run way too cool.

 

I have now spent $750 on this installation where in the past a 5 cent piece of tape did the job quite adequately. The only reason I installed the thermostat was to have a permanent fix so that I could operate year round without having to install/remove tape on the oil cooler :black_eye:

 

Ideally I would like to see around 100C oil temperature but at 9500 ft on a trip during winter I could not get it above around 62C.

 

I test flew it again today in Config D. and these were the engine readings:-

 

Altitude 3000 ft

 

RPM 4710

 

MP 26.3

 

Fuel Flow 20.5 LPH

 

OAT 11 C

 

TAS 116 kts

 

EGT 801/779 C

 

CHT 98/104 C

 

Oil Temp 80 C

 

During descent and approach with about 2500 RPM, the oil temperature dropped to 69C.

 

Any advice would be greatly appreciated.

 

Regards

 

Dave

 

Config. D

 

 

 

 

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If you have too much cooling, a thermostat should be arranged so that the oil bypasses the cooler.

 

I usually put a piece of tape across the hole in front of the oil cooler during the winter to restrict the air flow and get the temperature up to 100 C. As you say it is cheaper. After a while you get a feel for the amount of tape you need.

 

David

 

 

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David....yes that is why I installed the thermostat but it appears that the oil is still passing through the cooler before it reaches 180F/82C. (the thermostat is supposed to start to close at 180F/82C)

 

I am sure that the thermostat is not defective as I checked it was in the open position prior to installation. The thermostat is designed to be 'fail safe' so that if the thermostat stuck closed (i.e. in opposition to the spring) then the oil would all continue to pass through the cooler. My problem is that it appears to be going through the cooler whether open or closed? Like electricity, the oil should take the path of least resistance and flow from E1 to E2 (see diagram) when the oil is cold and the thermostat is open.........why it is not doing that...I am not sure?

 

There must be someone out there that has installed one of these?

 

(BTW I am sure that my oil temp. indications are valid as the ambients look good prior to start and the time taken to 50C is in line with other 912s)

 

 

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  • 2 weeks later...

Just a thought - its very hard to read the instructions that you posted - but is it possible that you have the wrong type? (Auto transmission not engine oil?

 

OR

 

Has the valve in the unit been played with? In other words has it been installed incorrectly?

 

regards

 

 

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Peter.....thanks for your input. Perma-Cool only manufacture one type of oil thermostat (I phoned the factory in California).

 

The thermostat was purchased new from California Power Systems (USA) and correctly installed by a L.A.M.E. in both config. B and config D. as suggested by the manufacturer.

 

We are going to remove the thermostat tomorrow to make sure that it has not 'stuck' closed. If indeed it is open, then I am tending to conclude that this thermostat is not suitable for the 912. The only reason I have persisted this long is that I am getting reports from 912 owners in the USA that they have installed this thermo. and it works fine.

 

I have just had a call from an owner of a CTsw here in Perth that had a Perma-Cool thermostat factory installed by Flight Design (as an optional extra) and he can't get the oil temperature much above 75C either. I won't comment further until I have a look at his installation, however there seems to be a fundamental problem somewhere ???

 

Regards

 

Dave

 

 

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Guest Nelson Smith

Dave, I had one of these thermostats fitted to a Jabiru and after nine months removed it.It wasn't doing anything for the oil temp,so I figured i'd be in front with less weight

 

Nelson

 

 

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Nelson.....that's interesting and I am fast coming to the conclusion that this thermostat is just not suitable for the Rotax 912. What I don't understand is that owners in the USA keep installing them and are telling me they work OK??

 

Just yesterday I received the latest Rotax catalogue from Lockwood in Florida and they are still advertising them as suitable for Rotax applications.

 

I also wonder why Flight Design would offer this thermostat as an optional extra if they are inneffectual.

 

Very puzzling!

 

Dave

 

 

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Now you've really got me in - I love a good mystery. ;)

 

1. Are you sue that the temp gauge is accurate? (not reading low...) 049_sad.gif.af5e5c0993af131d9c5bfe880fbbc2a0.gif

 

2. There MUST be oil still flowing thru the cooler which means,

 

a. thermostat stuck open, or :black_eye:

 

b. pipe partially blocked causing high preassure and unit is working in "fail safe mode" or ;)

 

c. your aeroplane doen't like you. 051_crying.gif.fe5d15edcc60afab3cc76b2638e7acf3.gif

 

3. It might be time to try for a refund?

 

regards

 

 

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I have just come back from the hangar and having removed the thermostat have established that it is not stuck closed (see my explanation of how the thermostat functions above) and while open the oil should take the shortest route back to the engine (ie in E1 and out E2) effectively bypassing the oil cooler.

 

We then removed the circlip and opened up the thermostat....everything appeared intact and normal, however stamped on the bi-metalic copper core inside was 77C / 171F . Now the description supplied by Perma-Cool says that the thermostat should begin to close between 82C (180F) & 88C (190F) however I fail to see how this could be achieved with a 77C core??

 

This could explain why we cannot get the temperature above 80C, however it does not explain why the oil temperature drops to as low as 69C on approach with 2500 RPM set as it should regulate at around 77C if the numbering on the plug is correct.

 

I intend phoning Perma-Cool in the USA tonight and ask them about it, but if you happen to be considering buying one of these thermostats....hold off for a while as currently it is about as useful as an ashtray on a motorbike!

 

PS. Peter, I am 100% sure that the Dynon temperature indication is correct and there are no blocked oil pipes etc.

 

 

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as useful as an ashtray on a motorbike!

Dave - obviously a Dick Johnson fan - I can remember when he made that statement just after he turned the corner at the end of pit straight to start going up the mountain!

 

 

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Perhaps you still have too much air passing through the cooler, so that it only requires a very small flow of oil to stop the temperature from rising once the thermostat starts to operate. My 912UL only has an air hole in front of it about the size of a tennis ball in the summer and about half that during the winter. You might be expecting to much of the thermostat.

 

David

 

 

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Guest grantisaac

Hi, Try placing the thermostat in a jug of cold water and place boiling water in,read the temp that it begins to open at.Should give you an idea when it is opening

 

 

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Hiya Dave,

 

We have just had delivery of two trikes from France last week, one with a factory installed oil thermostat and another with retrofit kit for installation.

 

It was intersting to note that whilst these are similar to yours, they bolt onto the oil filter housing between the filter and it's original plate.

 

I will check for you this weekend on results from these units and report back to you with our findings.

 

These are stats for the Rotax 912ULS and I will let you know what we have paid for these from Europe.

 

I will attempt to snap these and send you pics with the installation piping to confirm the most appropriate route.

 

Regards

 

Perry

 

 

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Thanks Perry....I would be very interested to see details & pics of the thermostats (I assume they are not Perma-Cool).

 

I have just got off the telephone after talking to Perma-Cool in the USA and they admitted that they are primarily suppliers to the automotive industry who apparently require oil temperatures around the high 70C s.

 

Curiously on their data sheet, they state that the thermostat closes at between 82C & 88C, however from my experience this is clearly not the case which has been confirmed since I found the temp. rating stamped on the core.

 

I am sure the Perma-Cool unit would be great if we could only get a higher temp core for it, but Perma-Cool only do the one temp. (77C / 171F).

 

It has been a very expensive exercise as being a SLSA registered aircraft I have had to use a LAME to do the work, so including the purchase of the stat, it has cost me almost $1000 for no benefit.:confused:

 

Regards

 

Dave

 

 

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  • 4 weeks later...

Just a thought on a possible thermostat design problem, one of which I have run into previously when messing around with farm hydraulic systems.

 

Hope I can explain this OK.

 

Oil, and viscous fluids generally that are flowing at velocity and have considerable inertia, are very reluctant to make a right angle change in their flow direction.

 

When they do so there is an abrupt drop in flow rates and a great deal of turbulence in the oil flow

 

The flow will preferably continue straight on in a straight running pipe and just about totally bypass a right angle take off unless there is a large increase in the back pressure in the straight pipe.

 

The thermostat design has a triple whammy.

 

Two straight pipes with high oil flow velocities so both flows will preferably bypass the right angle take off.

 

Even if some oil is diverted through the thermostat body, the oil flow through the thermostat will in the first couple of seconds, be a lot lower pressure than the return oil flow from the cooler so there is a real problem here in getting the bypass flow through the thermostat to actually start.

 

This reluctance of the oil to go through the thermostat body is compounded by the flow restriction that the actual thermostat imposes on the bypassed oil between the cooler inflow and return flow so you actually have a lower pressure on the bypassed oil which has to join the cooler return flow of the thermostat body.

 

The only way you will get this thermostat to work reliabily is if the cooler itself has quite a high back pressure or if you put a flow restriction into the cooler inflow line between the thermostat and the cooler.

 

This would increase the pressure to force the oil flow to divert through the thermostat.

 

Probably a good way to kiss an engine goodbye due to low oil at some point.

 

 

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The cooler on a 912 is fitted on the suction/inlet pipe to the oil pump. Perhaps the internals of the thermostat/bypass valve are designed to work under positive pressure. i.e. Oil pump then thermostat/bypass then cooler then engine. You may consider a ‘sandwich’ type thermostat housing fitted under the filter. However fitting this type would require a flatter filter to allow clearance between the exhaust header pipe. Another way of increasing oil temps would be to fit a jacket around the oil tank.

 

 

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Hi Dave I look at the photo and cringe. i hope this is just temp. installation and the suggestions are not needed

 

At risk of upsetting those involved i recommend that you redo this installation and use proper clamps, the ones you have will fail. use full length proper fire shield and banditcamp to each end of the hose. this will not only protect the hose from fire/heat but if the hose splits it will stop the oil spraying all over your hot exhaust. the white zip ties you have go brittle with the heat. how much you pay for this installation?

 

just 10yrs of working in GA talking here.

 

Ozzie

 

 

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I don't know what you paid for the thermostat, but if it isn't working, why not go back to the old way of doing things and fit adjustable cooling flaps to reduce the amount of air through the cooler.

 

Simple and I would think safer.

 

 

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Thanks everybody for your comments and suggestions with regard to my problem with the oil thermostat.

 

ROM...I think you are right.....the way this thermostat is designed, a large proportion of the oil would still tend to flow through the oil cooler due to the 180 degree reversal it has to do at the thermostat. As you mentioned, restriction is an option but we also dismissed that for the reasons you gave, however unless I can source a higher temp. core, I will remove it entirely from the engine.

 

OZZIE...your comments are noted and I agree that with uncertified aircraft, things could be done a lot better. You may or may not be aware, but the CTsw is delivered from the factory with exactly the same setup with regard to fire shields (including the white zip ties) as well as the type of hose clamps pictured.

 

Your comments regarding full length fire shields on the oil delivery pipes is particularly valid and I will arrange to have that done. I will also make enquiries about Band-It clamps.

 

The LAME that did the work for me has been in the industry for over 45 years and is a meticulous engineer, but installed it exactly as per the factory approved (LSA) modification schedule.

 

I am unfamiliar with the LAZAIR, however understand it is a Canadian ultra-light (does it come as a kit or is it factory built?)

 

I would be interested to see photographs of your engine (Rotax?)

 

YENN...cowl flaps are certainly the way to go but getting approval from the FD factory to modify (as required under SLSA) would probably be impossible.

 

GMZEZ...will make enquiries about the thermostat you mentioned.

 

BRUCE...thanks...will try and contact Wally at Narrandera.

 

Thanks again.

 

Dave

 

 

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