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Oil Thermostat
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mikenjulie.parkin(at)btop
Guest

Posted: Tue Jan 24, 2006 4:05 pm Post subject: Oil Thermostat

Dear Richard,  (and all)



Thanks for the information, I am watching with interest to see how you get 

on.  I have applied to the PFA for the Mod details so that I can fit the oil 

thermostat.  Andy Draper did tell me that he thinks that Francis Donaldson 

has done an about turn on the waxstat approval.  I await developments with 

anticipation.



For all those with reservations about this mod.  In 40 years of motoring, I 

can recall only one thermostat failure and that was a long time ago.  What 

are the consequences of operating an engine with a lubricant that never 

reaches the optimum operating temperature.  In the modern world this is a 

straight forward risk assessment. (ie.  the likelihood of thermostat failure 

versus possible accellerated engine wear, corrosion or oil cooler matrix 

rupture).



Bearing in mind that there is air and water cooling of the Rotax engine I 

cannot understand why the oil temperature would soar quickly to the limits 

if the oil cooler is out of circuit.  If the CHT temperature is operating at 

say 80degs (typical this time of year on GJULZ) in the cruise why then would 

the oil temperature suddenly go out of limits.  Bob Harrison said that he 

rarely has to put his oil cooler in circuit.  The fact that his Jabiru is 

totally air cooled is irrelevant.  As the Rotax is water and air cooled at 

the top end, then it is feasible that the requirement for oil cooling is not 

always necessary, particularly in temperate climes.



Originally, I had the oil cooler mounted directly behind the radiator.  In 

that configuration the oil temperature was always identical to the CHT 

temperature.



Since I lowered the oil cooler to the alternative position, the oil 

temperature NEVER reaches that of the CHT.



The expert engineers among our group might draw some conclusion from this.



The point I am making is that with the Thermostat in the oil circuit, it 

should never inhibit the full flow of oil from the tank to the engine via 

the pump.  Thermostat failed or not the oil should always either bypass the 

oil cooler, go totally through the oil cooler or, a combination of the 2 

situations.  Therefore, if it can be shown that a failure of the thermostat 

that results in total bypass of the oil cooler, does not create an 

unmanageble oil temperature situation then there is no reason why this 

should not be an advantageous modification.



Bob H, your comment is not really valid with modern aircraft.  Automation is 

the name of the game.  With modern systems, many performance indications are 

not even presented to the pilot until a positive action/decision is actually 

required by the 'human' systems supervisor.

If one can automate a system then why not - the idea is to reduce pilot 

workload so that he may concentrate on flying the aircraft and not be 

distracted by systems management.



I am most grateful that the wheel was invented before the birth of the 

Europa - otherwise we would still be bouncing along on skids!!!



regards,



Mike.



Do not archive.

---

mikenjulie.parkin(at)btop
Guest

Posted: Tue Jan 24, 2006 4:12 pm Post subject: Oil Thermostat

 	  Quote: 	
		   The heated and expanded wax causes the thermostat to open against spring

 pressure. As the wax cools, the valve is closed by the spring pressure, 

 not

 "suction" of contracting wax, which would probably cavitate anyway.

 As such, when the wax is lost there is nothing to push the valve open and

 the spring returns it to the closed position, so failing in that position.



 I agree that the older mechanical versions fail closed.



 The Mocal version of oil thermostat bypasses the cooler when "closed".




	




Forgive me Duncan, but if I follow your logic then the Mocal thermostat 

would fail in the cooler bypass position - that is opposite to the ideal 

failsafe position.



regards,



Mike

ptag.dev(at)tiscali.co.uk
Guest

Posted: Tue Jan 24, 2006 4:21 pm Post subject: Oil Thermostat

Thanks Duncan.

That is precisely my point, sort of been there done that and I wouldn't

be writing this had I been on a long flight particularly over long legs

of water ! So in the established cruise since it overcools anyway I

disconnect the cooler from circuit and therefore no dramatic oil loss if

the cooler is ruptured.

I guess if then the Rotax system is pressurised when stopped the

pressure will back feed to the cooler and then leak ?

So without priming does the oil pump still fetch oil once running ?

Regards

Bob H  G-PTAG Europa MKI/Jabiru 3300



--

ptag.dev(at)tiscali.co.uk
Guest

Posted: Tue Jan 24, 2006 11:06 pm Post subject: Oil Thermostat

Hi! Mike

Trying to answer your question on running with cold oil..... I'm

convinced that caused my engine to need new rings at 450 hours (but

being a Jabiru!!!)

I hope to be able to confirm this when I do my annual leak down tests in

April and compare them with the pre- ring change figures and the

knackered ring figures.

I am hopeful that this is correct since hand propping indicates some

good compressions still but that may also be down to my choice of oil

too.



But to look at the logic I'm not aware of oil circulation being used to

cool an engine so in most applications except the old side valve types

the oil is generally in the hottest places, pistons cylinder heads and

rocker boxes etc. so therefore you would expect it to be designed to be

in its best lubrication quality at the high temperatures especially so

when it's viscosity is least to throw up into the bores.

The exception to this I think is around the turbo when it is bad news to

stop the engine without a short cooling off period for the turbo.

Regards

Bob H G-PTAG Europa MKI/Jabiru3300



--

rholder(at)avnet.co.uk
Guest

Posted: Wed Jan 25, 2006 12:46 am Post subject: Oil Thermostat

R.C.Harrison wrote:



 	  Quote: 	
		   But to look at the logic I'm not aware of oil

 circulation being used to cool an engine so in most

 applications ...


	


This, Bob, is complete rubbish. IMNSHO.



All engines with no water cooling always have an oil

cooler. Why - to cool the oil ! And why does it need to be

cooled ? Because it gets hot. And why does it get hot ?

Because it is taking heat out of the engine !



The cooling air can only reach the outside of the engine.



I hope your statement was a typo !



Richard

ptag.dev(at)tiscali.co.uk
Guest

Posted: Wed Jan 25, 2006 3:45 am Post subject: Oil Thermostat

Hi! Richard.

I appreciated the error of my statement as soon as I pressed the send

key.

My point was that in air cooled engines the oil isn't the primary

cooling medium. In the Jabiru case the sump has cooling fins BUT when

over filled the thing overheats, half fill it and it stays cool!

Thus in the established cruise there is no need for an oil cooler

whatever. But when major power is required during which I accept the oil

is obviously taking heat to the cooler as is the sump a heat sink on a

conventional engine without an oil cooler but the primary cooling is by

water circulation.

Regards

Bob Harrison G-PTAG Europa MKI/Jabiru 3300 



--

nigel_graham(at)btclick.c
Guest

Posted: Wed Jan 25, 2006 9:36 am Post subject: Oil Thermostat

Way to go Gilles.

You have created the ideal oil cooling system that I was describing (albeit 

with manual control).



Since this discussion is nicely "on-the-boil" (pun totally intended) - here 

is another aspect to consider - weight.

 	  Quote: 	
		  From the postings on this group over the years, it would seem that there is 

more concern with new builds running too hot - than too cool.
	


The thermostats primary purpose is to increase engine temperature (it cannot 

improve cooling) so its main benefit is to get the engine up to temperature 

more quickly following start-up. For the entire rest of the flight - the 

thermostat, its pipework, clips, mounting brackets and the additional oil 

needed to fill the new pipework is simply dead weight being lugged around 

the sky increasing fuel consumption and reducing performance.



A well designed duct with a lightweight vane to control airflow (operated 

either manually or by servo) would weigh grams rather than the kilos of an 

oil thermostat system.

On a heavier certified aircraft this is not such an issue, but on the Europa 

any weight saving improves performance.



Nigel



---

rholder(at)avnet.co.uk
Guest

Posted: Wed Jan 25, 2006 10:11 am Post subject: Oil Thermostat

Nigel Graham wrote:

 	  Quote: 	
		  > From the postings on this group over the years, it 

> would seem that there is

 more concern with new builds running too hot - than too

  cool.

Mine (912 S 170 hours) runs too cool except in the climb.

 	  Quote: 	
		   The thermostats primary purpose is to increase engine 

 temperature (it cannot improve cooling)

It can improve cooling. Mine was running cold so i blanked

off half the oil cooler and it was like that throughout

the summer of 2003.

With the thermostat the oil cooler can be completely

uncovered as the thermostat will control the amount of oil

going through it and therefore its cooling effect. So in

very very hot weather the thermostat directs all the oil

through the cooler which can be used to its fullest

extent. In cold weather it is almost completely blanked

off keeping the oil nice and warm.

The flaw in this argument as I have found is that in the

cruise the oil just doesn't get enough heat pushed into it

to even reach the 80 degrees at which point the thermostat

will control it to 80 degrees. I am considering lagging

the oil pipes AND the oil tank to keep the heat in ! This

was found in 2 degree weather ! Maybe in 10 degree weather

it would be OK !

 	  Quote: 	
		   A well designed duct with a lightweight vane to control

 airflow (operated

 either manually or by servo) would weigh grams rather 

 than the kilos of an oil thermostat system.

Oil thermostat - 251 grams !

This is gonna run and run and run 

Richard

mikenjulie.parkin(at)btop
Guest

Posted: Wed Jan 25, 2006 10:38 am Post subject: Oil Thermostat

 	  Quote: 	
		   more quickly following start-up. For the entire rest of the flight - the

 thermostat, its pipework, clips, mounting brackets and the additional oil

 needed to fill the new pipework is simply dead weight being lugged around

 the sky increasing fuel consumption and reducing performance.



 A well designed duct with a lightweight vane to control airflow (operated

 either manually or by servo) would weigh grams rather than the kilos of an

 oil thermostat system.

 On a heavier certified aircraft this is not such an issue, but on the 

 Europa

 any weight saving improves performance.



 Nigel




	




Nigel,



I don't agree with your weight argument.  The thermostat is very light and 

requires no extra hose to speak of - just 4 jubilee clips.

For a start, the MAC servo weighs 4oz without any fittings.

The objective is raise the oil temp and keep it at the optimum operating 

temperature.  Which seems more unlikely as the story unfolds.



regards,



MP

nigel_graham(at)btclick.c
Guest

Posted: Thu Jan 26, 2006 7:34 am Post subject: Oil Thermostat

H Richard



 	  Quote: 	
		  Oil thermostat - 251 grams !

Yep....I'm holding my hands up. Thats much lighter than I expected.
	




 	  Quote: 	
		  ......"This is gonna run and run and run "

No, I think we're about there now.
	


In your original posting of the 23rd, you were so unhappy that you were 

contenplating  taking your oil thermostat off and I agreed with you.



.......My oil did not warm up quicker. ......

....My feeling is that the waxstat in the thermostat is

opening too early

..... I am contemplating ripping the whole thing off ...........



and now you are arguing robustly in its defence. By a process of cunning 

reverse psychology, I have persuaded you to keep it.



Nigel

rholder(at)avnet.co.uk
Guest

Posted: Thu Jan 26, 2006 9:56 am Post subject: Oil Thermostat

Nigel Graham wrote:

 	  Quote: 	
		   H Richard

 	  Quote: 	
		  > Oil thermostat - 251 grams !

 Yep....I'm holding my hands up. Thats much lighter than

 I expected.

> ......"This is gonna run and run and run "

 No, I think we're about there now. In your original

 posting of the 23rd, you were so unhappy that you were

  contenplating  taking your oil thermostat off and I

 agreed with you.

 ........My oil did not warm up quicker. ...... .....My

 feeling is that the waxstat in the thermostat is 

 opening too early ...... I am contemplating ripping the

 whole thing off ...........

 and now you are arguing robustly in its defence. By a

 process of cunning reverse psychology, I have persuaded

 you to keep it.

 Nigel 

I don't do psychology - just practical  And hating to

be beaten, liking to know what is ACTUALLY happening.

The original intention in fitting the thermostat was

primarily to keep the oil temp up in the cruise (keeping

the oil out of the cooler) and as a secondary effect I

could uncover the oil cooler (1/2 covered up) which would

allow better cooling in the summer. I needed the oil temp

up in the winter to keep the water temp up so that the

carb heaters would work properly !

I flew it again today. It was only 4 degrees when I took

off ! On a hard climb to 2495 feet (LTMA at 2500) the oil

went up to 80 and didn't go above (although this wasn't a

really long enough test). I went to Stapleford for lunch

thinking that it would only have a short time to cool so

the oil would start hotter, but got lumbered with filling

in on Air-Ground for an hour so the oil HAD cooled).

In the cruise the oil temp went down to 60.

I have the coolers in the standard position now with no

baffling at all.

So I have come to the conclusion that in the cruise (25.5

MAP 4600 rpm) the engine just doesn't produce much heat -

not enough to keep the oil at 80. A little baffling on the

water radiator might generate more heat in that which

would then cross to the oil. More experiments to come.

Perhaps a half blocking of the air intake that feeds the

cylinder cooling shroud.

And what was different this time compared with last time

when the oil went to 95 in the climb ? The widening out of

the ports to 10 mm (in particular the one that goes to the

oil pump) meant that in the fully extended position the

waxstat wasn't blocking off the by-pass completely. So

that means that as the oil would MUCH prefer to bypass the

cooler rather than go through it, the oil wasn't getting

much (any ?) cooling and so the temp went up. So for today

I had modified the thermostat to give an extra 1.3 mm

movement, and although I didn't give it a conclusive test,

I think the thermostat is opening and achieving at least

the secondary effect.

This is all done of course in 4 degree weather and that is

not representative of the likely operating conditions in

the spring summer and fall (I mean autumn !)

So anyone who is contemplating putting on this thermostat

should chat with me first about how and where to widen out

the ports, before getting their drill out ! Just drilling

out all the ports to 10mm will mean that the thermostat

will always bypass the cooler - which would not be a good

thing !

Maybe the oil tank needs a nice woolly jacket (fireproof

of course) to retain the heat !

-- 

Richard

Richard F.W. Holder                      01279 842804 (POTS)

Bell House, Bell Lane,                   01279 842804 (fax)

Widford, Ware, Herts,                    07860 367423 (mobile)

SG12 8SH                    email : richard.holder(at)avnet.co.uk

Europa Classic Tri-gear : G-OWWW, High Cross

PA-28-181 : Piper Archer : G-JANA, EGSG (Stapleford)

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