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water temp guage

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clemwehner

Joined: 02 Feb 2009
Posts: 32

Posted: Sat Jan 02, 2010 10:30 pm Post subject: water temp guage

We're getting near done on a KFIV-912. 

  

 But, when I planned the panel a few years ago, I  included a Westach quad gauge with CHT, and also made a hole for a  separate water temp guage. Now that I think about it, why would I need  both? Doesn't CHT equal water temp in an engine with water cooled  heads?

  

 Am I missing something?

  

 thanks for the help,

 Clem

 Lawton OK

 KFIV-912 getting near done. 

    [quote][b]

_________________
Clem
Oklahoma
Kitfox IV-912, under construction since 1991

lcfitt(at)sbcglobal.net
Guest

Posted: Sat Jan 02, 2010 11:00 pm Post subject: water temp guage

Clem,



I was looking at the cad drawings for my first Kitfox to see how I wanted to 

set up the panel for the new one, and I too had the temp gauge slotted in 

there.  I also used the Quad gauge and as you are suggesting, filled the 

hole with something else - had an extra turn and bank.



Lowell



---

Paul A. Franz, P.E.

Joined: 02 Dec 2008
Posts: 280
Location: Bellevue WA

Posted: Sat Jan 02, 2010 11:15 pm Post subject: water temp guage

On Sat, January 2, 2010 10:26 pm, CLEMWEHNER wrote:

 	  Quote: 	
		   We're getting near done on a KFIV-912.



 But, when I planned the panel a few years ago, I included a Westach quad gauge with

 CHT, and also made a hole for a separate water temp guage.


	


Good design choice. You won't regret that decision.



 	  Quote: 	
		   Now that I think about it,

 why would I need both? Doesn't CHT equal water temp in an engine with water cooled

 heads?


	


In a word - no. I definitely would have both CHT and water temp gauges.



If it were mine I would use water temp gauge also.



 	  Quote: 	
		   Am I missing something?


	


The quad CHT is important if you want to run lean of peak because you know the

temperatures in each cylinder head. However, without fuel injection you still might

not elect to run lean of peak. But if the cylinders run close in temp, you definitely

can get significant fuel savings running lean of peak in cruise.



The water temperature gauge is an essential instrument too. It will let you know if

you're exceeding that T-stat controlled temp or that your operating temperature is too

low. The cyl head temp reading will be much higher than the water temperature since

the sensor is generally placed against the head under a spark plug. CHT is also

effected by power setting whereas T-stat controlled water temperature should remain

constant at all power settings.

-- 

Paul A. Franz

Registration/Aircraft - N14UW/Merlin GT

Engine/Prop - Rotax 914/NSI CAP

Bellevue WA

425.241.1618 Cell

425.440.9505 Office



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one party of the citizens to give to the other.

-- Voltaire (1764)

_________________
Paul A. Franz, P.E.
Registration/Aircraft - N14UW/Merlin GT
Engine/Prop - Rotax 914/NSI CAP
Bellevue WA
425.241.1618 Cell
425.440.9505 Office

Fox5flyer
Guest

Posted: Sun Jan 03, 2010 5:00 am Post subject: water temp guage

Clem, way back when I ran my 582 with my KF2 I used  CHT sensors along with EGT and coolant sensors.  I don't know whether they  CHT sensors did me much good, but (IIRC) they always ran about 40 to 50 degrees  hotter than the coolant temps.  I always thought that if I had some sort of  coolant blockage that allowed boiling in the heads (highest point), I would know  it immediately with the CHT.  I don't know if this would compare with the  912, though.  Mainly, I like a lot of instruments so that if something  suddenly is different it gets my attention.

 Deke Morisse

Mikado Michigan

S5/Subaru/CAP  438+ TT

"If you put the federal government in charge of the Sahara

Desert,  in five years there'd be a shortage of sand."

-- Nobel prize-winning  economist Milton Friedman (1912-2006)

  

  

  

  

  

 [quote]   ---

Dick Maddux

Joined: 24 Jun 2008
Posts: 516
Location: Milton, Fl

Posted: Sun Jan 03, 2010 7:14 am Post subject: water temp guage

Paul,

  By T-stat do you mean thermostat? Unless I am having a senior moment (I have many) I am not aware of a thermostat in the 9 series (unless you install an oil thermo) If there was one it wouldn't take 5-8 min for my engine to warm up enough to fly, or check the mags.

  I also have the quad gauge that includes the CHT.The CHT pretty well equals a water temp gauge although both would be useful for comparison.

                                     Dick Maddux

                                     Fox 4

                                     Milton,Fl

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rdmac(at)swbell.net
Guest

Posted: Sun Jan 03, 2010 11:21 am Post subject: water temp guage

Clem,  

            I too have the quad gauge with CHT but it is good insurance to know what the over all temp of your coolant is running. I installed the sensor for my water temp in the spider tank on top of the engine.  

     

Roger McConnell, Duncan, OK  

Model 7 Trigear, Rotax 912uls   

Flying sense Jan. 06  

  

         

  

From: owner-kitfox-list-server(at)matronics.com [mailto:owner-kitfox-list-server(at)matronics.com] On Behalf Of CLEMWEHNER

 Sent: Sunday, January 03, 2010 12:27 AM

 To: kitfox-list(at)matronics.com

 Subject: water temp guage  

  

     

We're getting near done on a KFIV-912.   

    

   

    

But, when I planned the panel a few years ago, I included a Westach quad gauge with CHT, and also made a hole for a separate water temp guage. Now that I think about it, why would I need both? Doesn't CHT equal water temp in an engine with water cooled heads?  

    

   

    

Am I missing something?  

    

   

    

thanks for the help,  

    

Clem  

    

Lawton OK  

    

KFIV-912 getting near done.   

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       [quote][b]

Av8r3400

Joined: 22 Sep 2008
Posts: 83
Location: North Central Wisconsin (KRRL)

Posted: Sun Jan 03, 2010 1:35 pm Post subject: Re: water temp guage

Correct, there is no thermostat in a 900 series Rotax unless it has been modified to accept one.



The cylinder head temp probe and coolant temp probes both read from the head casting, but from different places.

_________________
Thanks,
Av8r3400

Kitfox Model IV-1200 W/912UL & IVO
Kitfox Model IV-1050 W/912UL & Warp
YouTube Videos

pwmac(at)sisna.com
Guest

Posted: Mon Jan 04, 2010 9:16 am Post subject: water temp guage

Correct Paul.

Both are the prudent way to go. Of course the Stat is a feature that 

Rotax forgot, but is usually required unless one lives in the more 

temperate clims. However I note that some builders use the shutters 

on the radiator instead, which means a T gauge for coolant is even 

more critical due manual control of the shutters. I don't think that 

gauge should be engine mounted, but S/B in the coolant lines.

Paul W

=============

At 11:13 PM 1/2/2010, Paul F  wrote:

 	  Quote: 	
		  On Sat, January 2, 2010 10:26 pm, CLEMWEHNER wrote:

 > We're getting near done on a KFIV-912.

 >

 > But, when I planned the panel a few years ago, I included a 

 Westach quad gauge with

 > CHT, and also made a hole for a separate water temp guage.

Good design choice. You won't regret that decision.

 > Now that I think about it,

 > why would I need both? Doesn't CHT equal water temp in an engine 

 with water cooled

 > heads?

In a word - no. I definitely would have both CHT and water temp gauges.

If it were mine I would use water temp gauge also.

 > Am I missing something?

The quad CHT is important if you want to run lean of peak because you know the

temperatures in each cylinder head. However, without fuel injection 

you still might

not elect to run lean of peak. But if the cylinders run close in 

temp, you definitely

can get significant fuel savings running lean of peak in cruise.

The water temperature gauge is an essential instrument too. It will 

let you know if

you're exceeding that T-stat controlled temp or that your operating 

temperature is too

low. The cyl head temp reading will be much higher than the water 

temperature since

the sensor is generally placed against the head under a spark plug. 

CHT is also

effected by power setting whereas T-stat controlled water 

temperature should remain

constant at all power settings.

--

Paul A. Franz

lcfitt(at)sbcglobal.net
Guest

Posted: Mon Jan 04, 2010 10:36 am Post subject: water temp guage

I'm strugglin to understand this.  It has always been my understanding that 

temperatures relate to engine performance and longevity.  I am personally 

comfortable knowing my engine's temps.  I need a bit of help understanding 

how knowing the coolent temp in addition will help me protect my engine.  I 

flew lots of hours getting temp readings only from a cylinder head sensor 

and an oil temp sensor.  I have found that even then, both needles pretty 

much follow each other during a warm up and flight and in the early days 

were typically on the low side.  That is where the small oil cooler and the 

shutters came in.  Then the same gauges showed the temps of the engine. 

What am I missing?  I could understand the need for numerous temp sensors 

and gauges if the operation temperature ranges were critically narrow, but 

when the ranges are over 50°?  I'd rather save the ounce or two.



I found the following at:



http://www.rotaxservice.com/rotax_tips/engine_instruments.htm



Cylinder Head Temperature (CHT)

We found that many pilots confuse this instrument with a coolant temperature 

instrument, and sometimes label it as such. The probe to this instrument 

actually measures the temperature of the metal in your cylinder head. It 

allows you to monitor the proper operation of the liquid cooling system that 

cools your cylinder heads yet it does not measure the actual temperature of 

that liquid.



Coolant temperature

No provision for a coolant temperature probe is provided on Rotax 4-stroke 

engines and for good reason: the Cylinder Head Temperature instrument offers 

a better insight into the proper operation of the liquid cooling system and 

may reveal problems, such as the formation of air bubbles, that a coolant 

temperature instrument would not.



Lowell



---

Paul A. Franz, P.E.

Joined: 02 Dec 2008
Posts: 280
Location: Bellevue WA

Posted: Mon Jan 04, 2010 7:04 pm Post subject: water temp guage

On Mon, January 4, 2010 9:59 am, Lowell Fitt wrote:

 	  Quote: 	
		   



 I'm strugglin to understand this.  It has always been my understanding that

 temperatures relate to engine performance and longevity.  I am personally

 comfortable knowing my engine's temps.  I need a bit of help understanding

 how knowing the coolent temp in addition will help me protect my engine.  I

 flew lots of hours getting temp readings only from a cylinder head sensor

 and an oil temp sensor.  I have found that even then, both needles pretty

 much follow each other during a warm up and flight and in the early days

 were typically on the low side.  That is where the small oil cooler and the

 shutters came in.  Then the same gauges showed the temps of the engine.

 What am I missing?  I could understand the need for numerous temp sensors

 and gauges if the operation temperature ranges were critically narrow, but

 when the ranges are over 50°?  I'd rather save the ounce or two.


	


I didn't realize there is no T-stat to regulate coolant temperature. In that case, I'd

expect coolant temperature to track power setting and because of capacity design,

coolant temperatures will be often lower than ideal. Here's what I mean,

thermodynamically speaking. The compression of an ideal gas follows:



    PV**n = C  P is pressure, V is volume and C is a constant.



For the two extremes of compression for air, adiabatic and constant temperature

compression, n = 1.41 (adiabatic) and n = 1.0 for isothermal compression. Adiabatic

compression occurs when there is no heat transfer to the surroundings and isothermal

compression is where all the heat of compression is transferred to the surroundings.

We would like to have the highest possible thermal efficiency of the engine which

would ideally be with adiabatic compression. This would be the condition with the

highest possible coolant water temperature (closest to adiabatic) and hence the least

heat of compression lost.



A coolant T-stat (Thermostat) would be ideally set for the highest possible

(allowable) temperature to do the following:



1) maximize the thermal efficiency of the engine



and



2) minimize the warm up time period where the most damage to the engine occurs due to

water vapor condensation and degradation of the engine oil and corrosion from the

formation of sulfuric acid in the crankcase.



Since Rotax has chosen not to provide thermostatically regulated coolant temperature

probably due to a desire for weight savings, I would expect water temperature and

cylinder head temperatures to both track power setting.



An additional benefit of having a T-stat and consequently a higher coolant temperature

would be more cabin heat if you have coolant routed to a cabin heater.



I plan to incorporate a T-stat in my 914 installation and a coolant temperature sensor

immediately upstream of the T-stat. I will also use CHT on each cylinder. In this

configuration coolant temperature will not track CHT. CHT will track power setting and

mixture. One thing that I also wish were possible on the 914 would be an intercooler

which would greatly extend engine life. (The 914 is turbo supercharged.)



 	  Quote: 	
		  

 I found the following at:



 http://www.rotaxservice.com/rotax_tips/engine_instruments.htm



 Cylinder Head Temperature (CHT)

 We found that many pilots confuse this instrument with a coolant temperature

 instrument, and sometimes label it as such. The probe to this instrument

 actually measures the temperature of the metal in your cylinder head. It

 allows you to monitor the proper operation of the liquid cooling system that

 cools your cylinder heads yet it does not measure the actual temperature of

 that liquid.



 Coolant temperature

 No provision for a coolant temperature probe is provided on Rotax 4-stroke

 engines and for good reason: the Cylinder Head Temperature instrument offers

 a better insight into the proper operation of the liquid cooling system and

 may reveal problems, such as the formation of air bubbles, that a coolant

 temperature instrument would not.

-- 
	


Paul A. Franz

Registration/Aircraft - N14UW/Merlin GT

Engine/Prop - Rotax 914/NSI CAP

Bellevue WA

425.241.1618 Cell



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_________________
Paul A. Franz, P.E.
Registration/Aircraft - N14UW/Merlin GT
Engine/Prop - Rotax 914/NSI CAP
Bellevue WA
425.241.1618 Cell
425.440.9505 Office

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Tue Jan 05, 2010 7:31 pm Post subject: water temp guage

I guess if you noticed your CHT climbing and the water temp holding steady

or even going low, you might guess that you were getting low on coolant.



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

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