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912 Cylinder head coolant temperature Gauge

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hgmckay

Joined: 23 May 2006
Posts: 397

Posted: Sat Apr 14, 2018 11:08 am Post subject: 912 Cylinder head coolant temperature Gauge

I have the new cylinder heads on my 912 UL engine. I am measuring the  coolant temperature using the normal Rotax (VDO) gauge. During engine operation  my gauge needle is quickly fluctuating (swinging) as much as 10 to 30 degrees  Celsius between zero and 80 degrees C. After landing and engine ignition  circuits are cut off and the engine stopped, but with current still on the  instruments (i.e. key on the “on” position the VDO gauge needle is steady at 80  degrees C. As the engine cools the needle drops. The wiring and connections from  the sensors to the gauge are sound and tight. Could I have a problem with the  coolant pump on the engine varying the coolant flow and thereby causing the  sudden temperature variation indications on the VDO gauge? Any ideas or  suggestions?

  

 Hugh G.  McKay III, P.E. Fellow, L.M. ASCE

Senior Consultant

Worldwide Engineering  Inc.

4090 North NC Hwy. 16

Denver, NC 28037



Ph. 704-661-8271

Fax  704-483-5466

email  hgmckay(at)bellsouth.net

http://www.wwegeo.com

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John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Sat Apr 14, 2018 11:17 am Post subject: 912 Cylinder head coolant temperature Gauge

Make sure all the air has been bled out of the cooling system.  

 

How is your coolant recovery tank behaving?  Normal?

 

john h

mkIII

Titus, Alabama

 

From: owner-rotaxengines-list-server(at)matronics.com [mailto:owner-rotaxengines-list-server(at)matronics.com] On Behalf Of hgmckay(at)bellsouth.net

Sent: Saturday, April 14, 2018 2:08 PM

To: Rotax Engines

Subject: 912 Cylinder head coolant temperature Gauge

 

I have the new cylinder heads on my 912 UL engine. I am measuring the coolant temperature using the normal Rotax (VDO) gauge. During engine operation my gauge needle is quickly fluctuating (swinging) as much as 10 to 30 degrees Celsius between zero and 80 degrees C. After landing and engine ignition circuits are cut off and the engine stopped, but with current still on the instruments (i.e. key on the “on” position the VDO gauge needle is steady at 80 degrees C. As the engine cools the needle drops. The wiring and connections from the sensors to the gauge are sound and tight. Could I have a problem with the coolant pump on the engine varying the coolant flow and thereby causing the sudden temperature variation indications on the VDO gauge? Any ideas or suggestions?



 



Hugh G. McKay III, P.E. Fellow, L.M. ASCE

Senior Consultant

Worldwide Engineering Inc.

4090 North NC Hwy. 16

Denver, NC 28037



Ph. 704-661-8271

Fax 704-483-5466

email hgmckay(at)bellsouth.net

http://www.wwegeo.com

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

williamtsullivan(at)att.n
Guest

Posted: Sat Apr 14, 2018 12:41 pm Post subject: 912 Cylinder head coolant temperature Gauge

I am thinking the same way John is.  You have an air bubble, and is has to be burped.  The other option, as always, is a loose wire.



                                                       Bill Sullivan

                                                       Tarboro, NC (recently escaped from Connecticut!)

--------------------------------------------

On Sat, 4/14/18,  <hgmckay(at)bellsouth.net> wrote:



 Subject: 912 Cylinder head coolant temperature Gauge

 To: "Rotax Engines" <rotaxengines-list(at)matronics.com>

 Date: Saturday, April 14, 2018, 3:08 PM

 

 

 

 

 

 I have the new cylinder heads on my 912 UL engine. I am

 measuring the 

 coolant temperature using the normal Rotax (VDO) gauge.

 During engine operation 

 my gauge needle is quickly fluctuating (swinging) as much as

 10 to 30 degrees 

 

 

 Ph. 704-661-8271

 Fax 

 704-483-5466

 email 

 hgmckay(at)bellsouth.net

 http://www.wwegeo.com

johnelling

Joined: 23 Feb 2013
Posts: 18

Posted: Sun Apr 15, 2018 10:12 am Post subject: 912 Cylinder head coolant temperature Gauge

I had a problem like this and finally solved it with a resistor, 1kohm I 

think, in line with the probe.  It is the same fix they recommend for 

the tach.



 	  Quote: 	
		   I have the new cylinder heads on my 912 UL engine. I am measuring the

 coolant temperature using the normal Rotax (VDO) gauge. During engine

 operation my gauge needle is quickly fluctuating (swinging) as much as

 10 to 30 degrees Celsius between zero and 80 degrees C. After landing

 and engine ignition circuits are cut off and the engine stopped, but

 with current still on the instruments (i.e. key on the

 =9Con=9D position the VDO gauge needle is steady at 80

 degrees C. As the engine cools the needle drops. The wiring and

 connections from the sensors to the gauge are sound and tight. Could I

 have a problem with the coolant pump on the engine varying the coolant

 flow and thereby causing the sudden temperature variation indications on

 the VDO gauge? Any ideas or suggestions?



 Hugh G. McKay III, P.E. Fellow, L.M. ASCE

 Senior Consultant

 Worldwide Engineering Inc.

 4090 North NC Hwy. 16

 Denver, NC 28037



 Ph. 704-661-8271

 Fax 704-483-5466

 email hgmckay(at)bellsouth.net

 http://www.wwegeo.com

hgmckay

Joined: 23 May 2006
Posts: 397

Posted: Tue Apr 17, 2018 12:27 pm Post subject: 912 Cylinder head coolant temperature Gauge

Bill,



I know how to "burp" the oil system, but I have never heard of "burping" the 

coolant system. How is that done?



Hugh G. McKay III, P.E. Fellow, L.M. ASCE

Senior Consultant

Worldwide Engineering Inc.

4090 North NC Hwy. 16

Denver, NC 28037



Ph. 704-661-8271

Fax 704-483-5466

email hgmckay(at)bellsouth.net

http://www.wwegeo.com

--

williamtsullivan(at)att.n
Guest

Posted: Tue Apr 17, 2018 12:47 pm Post subject: 912 Cylinder head coolant temperature Gauge

I have to plead ignorance on Rotax, but a number of automotive engines will hide an air bubble in the cooling system.  The old Jeep 4.0 liter straight 6 was always doing that.  You filled it up after working on it, and had to keep filling it for a few days until all of the air worked out of it.  Maybe John Hauck knows.  It used to drive me nuts, thinking I had a leak and not finding it.  I would just fill it, run it, fill it, and run it over a few days, cooling off in between runs.



                                                           Bill Sullivan

--------------------------------------------

On Tue, 4/17/18,  <hgmckay(at)bellsouth.net> wrote:



 Subject: Re: 912 Cylinder head coolant temperature Gauge

 To: rotaxengines-list(at)matronics.com

 Date: Tuesday, April 17, 2018, 4:27 PM

 

 

 <hgmckay(at)bellsouth.net>

 

 Bill,

 

 I know how to "burp" the oil system,

 but I have never heard of "burping" the 

 coolant system. How is that done?

 

 Hugh G. McKay III, P.E. Fellow, L.M.

 ASCE

 Senior Consultant

 Worldwide Engineering Inc.

 4090 North NC Hwy. 16

 Denver, NC 28037

 

 Ph. 704-661-8271

 Fax 704-483-5466

 email hgmckay(at)bellsouth.net

 http://www.wwegeo.com

 --

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Tue Apr 17, 2018 2:59 pm Post subject: 912 Cylinder head coolant temperature Gauge

Here is how I do it.  After draining and refilling, I raise the tail higher than the nose, MKIII is a tail dragger, and back down.  Top it off and rock it up and back down until I can't put any more coolant into the header tank.



I bleed air the same way you describe Bill S.  Until the header tank is completely full after a flight, shut down, and cool down, I check the header tank.  I keep doing this procedure until all the air is gone.  Do the same thing with all my other water cooled engines to bleed air.



When all air is gone the coolant recovery tank will hit its high mark with the engine hot and suck coolant out of the coolant recovery tank as it cools.  This keeps air out of the system.



john h

mkIII

Titus, Alabama



--

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Tue Apr 17, 2018 5:22 pm Post subject: Re: 912 Cylinder head coolant temperature Gauge

The coolant system in the 912 is an open system. The fluid seeks its own level and rarely ever needs more after filling. Because it is an open system it is also very easy to evacuate the entire tire system.



Fill and go. With all the hoses changes I do every year I never have trapped air that made a difference.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Tue Apr 17, 2018 6:28 pm Post subject: 912 Cylinder head coolant temperature Gauge

I thought I was flying with a closed cooling system all these years.  If it

has a pressure cap and coolant recovery system, I call that a closed system.



An open system would be like my old antique tractors, unpressurised and open

to the atmosphere.   



I really don't know of an open system on a modern water cooled engine.



Set me straight if I am wrong.  Not trying to be argumentative.



I do know the three 912 engines I have owned since 1993, all required

bleeding air and fill/top off through the header tank.  There are places in

the engine that do trap air.  Maybe the newer engines have different

castings.



john h

mkIII

Titus, Alabama





--

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Tue Apr 17, 2018 6:51 pm Post subject: 912 Cylinder head coolant temperature Gauge

Roger Lee:



Took a quick look in the Rotax 912 Installation Manual.  It describes the

cooling system as closed.



john h

mkIII

Titus, Alabama





--

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

daberti(at)sbcglobal.net
Guest

Posted: Tue Apr 17, 2018 6:54 pm Post subject: 912 Cylinder head coolant temperature Gauge

You’re right on. And without the overflow tank with a hose submerged in coolant you will never get rid of the air. 



Dave Alberti 



[quote] On Apr 17, 2018, at 9:28 PM, John Hauck <jhauck(at)elmore.rr.com> wrote:

 

 

 

 I thought I was flying with a closed cooling system all these years.  If it

 has a pressure cap and coolant recovery system, I call that a closed system.

 

 An open system would be like my old antique tractors, unpressurised and open

 to the atmosphere.   

 

 I really don't know of an open system on a modern water cooled engine.

 

 Set me straight if I am wrong.  Not trying to be argumentative.

 

 I do know the three 912 engines I have owned since 1993, all required

 bleeding air and fill/top off through the header tank.  There are places in

 the engine that do trap air.  Maybe the newer engines have different

 castings.

 

 john h

 mkIII

 Titus, Alabama

 

 

 

 

 --

dougsnash

Joined: 14 Apr 2008
Posts: 281

Posted: Wed Apr 18, 2018 3:16 am Post subject: 912 Cylinder head coolant temperature Gauge

Another source of temperature spikes I have found is with the absolute junk VDO gauges that tend to develop erratic needle swings as they age.  I spent one summer changing out well over 1000 dollars worth of electrical components chasing "voltage spikes" on  my CH-701 only to find out the problem was a bad VDO gauge.  I had even tried another (albeit used) VDO voltage gauge and still had the same "spikes".  Turned out it was the crap VDO volt meters and there was actually nothing wrong with my electrical system.  Since then, I have been slowly converting my panel over to Stewart Warner gauges and have been happy with the results.  I have an erratic oil temperature gauge right now that will be getting replaced at annual.

While I won't claim to be an expert and know very little of the OP's problem, he did mention he has a VDO gauge and I would replace that before getting to carried away chasing a potentially phantom engine problem.

Doug M

CH-701/ 912-UL

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Wed Apr 18, 2018 4:31 am Post subject: 912 Cylinder head coolant temperature Gauge

Since the early days, ultralight pilots have freaked out over instrument indications.  They spent hours and lots of money, and probably destroyed lots of engines and airplanes chasing engine instruments, trying to get that two stroke engine dialed in perfectly.  I think of all the other two stroke engines in my life back then that had no instrumentation.  Never worried about EGT and other temps.  They seemed to run forever with good fuel and oil, and a new spark plug every once in a while.  Usual the problem was improper prop loading.  Rotax did a good job of setting up the engines at the factory, but if the Westach instrument told them their EGT was a little high or low, they'd start chasing their tail, changing jets, needles, spark plugs, and anything else they could find to change.  I was one of them.

 

I have a situation with my 9121ULS that irritates me.  I randomly get low oil pressure and high engine oil temp indications.  I was on a flight to Oregon many years ago when this first started happening.  Was irritating, but proved to be harmless.  It is still happening, but the temps are always reading the same, even though they are incorrect.  Annoying, but not critical.  BTW, they are VDO marine gauges.  I can shut down the battery and the indications return to normal.  Must be wiring, probably poor grounding, or the gauges.

 

john h

mkIII

Titus, Alabama

 

 

 

From: owner-rotaxengines-list-server(at)matronics.com [mailto:owner-rotaxengines-list-server(at)matronics.com] On Behalf Of MacDonald Doug

Sent: Wednesday, April 18, 2018 6:16 AM

To: RotaxEngines-List Digest Server

Subject: Re: 912 Cylinder head coolant temperature Gauge

 

Another source of temperature spikes I have found is with the absolute junk VDO gauges that tend to develop erratic needle swings as they age.  I spent one summer changing out well over 1000 dollars worth of electrical components chasing "voltage spikes" on  my CH-701 only to find out the problem was a bad VDO gauge.  I had even tried another (albeit used) VDO voltage gauge and still had the same "spikes".  Turned out it was the crap VDO volt meters and there was actually nothing wrong with my electrical system.  Since then, I have been slowly converting my panel over to Stewart Warner gauges and have been happy with the results.  I have an erratic oil temperature gauge right now that will be getting replaced at annual.



 



While I won't claim to be an expert and know very little of the OP's problem, he did mention he has a VDO gauge and I would replace that before getting to carried away chasing a potentially phantom engine problem.



 



Doug M



CH-701/ 912-UL

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

rampil

Joined: 04 May 2007
Posts: 870

Posted: Wed Apr 18, 2018 11:52 am Post subject: Re: 912 Cylinder head coolant temperature Gauge

My 2 cents as an EE:



There are NO rapid temperature changes. Not physically possible.

How much energy do you think is available to heat and COOL the coolant

through wide swings.



VDO are cheap crappy mechanical gauges, emphasis on cheap crap.

Automotive or snowmobile quality, no better. I like Rotax hardware, but the

VDO garbage should be thrown away on delivery and replaced with

airworthy meters.

The temp. swings are most likely vibration induced mechanical resonances

in the needle/coil/spring system in the indicator.

_________________
Ira N224XS

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