Low CHT and Oil Temp before starting

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Piper_EEWL
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Low CHT and Oil Temp before starting

Post by Piper_EEWL »

Hey guys,

I've noticed something odd with the Bonanza. Everytime before I start it the CHT and the Oil Temps read extremely cold and nowhere near related to the OAT which I would expect. Today I loaded a flight at 56s in the Orbx PNW region with the OAT at 15C.

I loaded the flight in the default C172 (FSX:SE) then switched to the Bonanza. The CHT showed -1C and the Oil temp showed 6C. So I'm a little confused since with my other Accusim birds the temps are usually at the ambient temperatures when the plane has been sitting for a while.

Has anyone else noticed that?

My default flight is with the default C172 as well.

Happy flying
B377&COTS, J3 Cub, B-17G, Spitfire, P-40, P-51D, C172, C182, Pa28, Pa24, T-6 Texan, L-049&COTS, Bonanza V35B

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Piper_EEWL
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Re: Low CHT and Oil Temp before starting

Post by Piper_EEWL »

I just rechecked this. Airport is Friday Harbor KFHR. Real world weather from Friday the 14th of September 7:38pm local time. OAT C16C. Hit cold and dark and the CHT reads -2C and the oil temp reads 11C with the battery switch on. And the same right after the engine starts and then it slowly warms up.

Can anyone reproduce this?
B377&COTS, J3 Cub, B-17G, Spitfire, P-40, P-51D, C172, C182, Pa28, Pa24, T-6 Texan, L-049&COTS, Bonanza V35B

Jarek
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Re: Low CHT and Oil Temp before starting

Post by Jarek »

Generally it is not wrong about oil temperature. It is lower than ambient for most of the time, when aircraft stays outside overnight and when temp is above 0 degrees Celsius. Then oil will slowly try catch increasing ambient for several hours, then ambient decreases again after dark. In very cold weather, it's opposite, oil temp is warmer than OAT for like 12h. Even more if put on the cold cover. So Oil temp. amplitude is lower than ambient by few degrees.

This is somehow complex to address, would require complex code, but probably possible in the form like: if you start sim in the early morning then difference is smaller than if you start at noon.

For the cylinder head - it depends on the gauge (thermocouple in fact) accuracy, I would not expect it will be up to single degrees as they are in their operating range (green field).
Last edited by Jarek on 18 Sep 2018, 15:46, edited 1 time in total.

wothan
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Re: Low CHT and Oil Temp before starting

Post by wothan »

Piper_EEWL wrote:I just rechecked this. Airport is Friday Harbor KFHR. Real world weather from Friday the 14th of September 7:38pm local time. OAT C16C. Hit cold and dark and the CHT reads -2C and the oil temp reads 11C with the battery switch on. And the same right after the engine starts and then it slowly warms up.

Can anyone reproduce this?
With Active Sky at Sitka (PASI) I got 9°C OAT
Oil temperature was 9°C, but CHT was ÷12°C.

So Oil temp. seems ok, but not CHT. Then again... It's not ment to be accurate below 100°C I guess, though it seems quite off.

FinnJ
When I like to do basic flying, I turn to A2A Aircraft, cause A2A "basic" flying means "complex" procedures.

simonflight
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Re: Low CHT and Oil Temp before starting

Post by simonflight »

Just took off from Tilamook on the west coast of the US. A new aircraft (deleted log files) with airfield temp of 17 dec C and oil temp -7 deg C and CH -9 deg C

Pretty sure this is the first time its happened to me after many flights so far

Cheers
Simon

Jarek
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Re: Low CHT and Oil Temp before starting

Post by Jarek »

Yup, this is too low, I would expect like more 10 if this was at noon. Ambient extremes are like 7am (low) and 2pm (high) usually.

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Scott - A2A
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Re: Low CHT and Oil Temp before starting

Post by Scott - A2A »

Don't worry about how a virgin airplane is, meaning how it loads just after installing the aircraft (or after deleting the DATS). The next load it should be consistent, but definitely not colder than OAT.

I will do some tests and check this.

Scott.
A2A Simulations Inc.

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Piper_EEWL
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Re: Low CHT and Oil Temp before starting

Post by Piper_EEWL »

Hi Scott,

Thank you for looking into this. For me the issue seems to persist even after a couple of flight. When the Bonanza has been sitting over night or if I hit cold and dark the temps are definetly colder than the OAT. Of course I can only see that through the tool tips but I’m suspecting that changes how the engine starts no?
B377&COTS, J3 Cub, B-17G, Spitfire, P-40, P-51D, C172, C182, Pa28, Pa24, T-6 Texan, L-049&COTS, Bonanza V35B

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Piper_EEWL
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Re: Low CHT and Oil Temp before starting

Post by Piper_EEWL »

Ok. Another test. Plane has been sitting since yesterday evening german time so for about 21h. Flight is at WA05 todays weather at 15:45UTC.

6C OAT: --> CHT -8C
--> Oil temp 1C


So this is definetly reproducable at least on my system.
B377&COTS, J3 Cub, B-17G, Spitfire, P-40, P-51D, C172, C182, Pa28, Pa24, T-6 Texan, L-049&COTS, Bonanza V35B

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Welsch
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Re: Low CHT and Oil Temp before starting

Post by Welsch »

Just noticed this today as well

OAT 21°C
CHT 4°C
Oil Temp 14°C

Yesterday at shutdown, the OAT was also in the mid to low twenties (Celsius).

I use FSX:SE and ASN, but I always let the weather and scenery load and stabilize in the stock FSX Cessna before loading any A2A aircraft.
Oh, and the Auto C&D feature is on... could that be it somehow? Haven't tried without yet...

simonflight
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Re: Low CHT and Oil Temp before starting

Post by simonflight »

Just a further observation...

Started again at Tillamook with 16 ambient and looked at the temperature of the CH after an awkward prolonged start and it was -10 but rapidly increased once the engine was firing.

I don't have the time yet to run any tests but could it be associated ? (showing my lack of knowledge here)

Cheers
Simon

Jarek
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Re: Low CHT and Oil Temp before starting

Post by Jarek »

Probably the best idea (without going into physics and specific heat calculations) would be to display something like "no reading / off the scale" for CHT values below 50degC.
In fact from the cockpit it is not possible to determine CHT prior starting a cold engine, without connecting a specialized diagnostic tool. Gauge starts at 50 or perhaps will start moving a bit earlier. The only important metric here is he rate and time required to heat up the cylinder's heads.

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Welsch
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Re: Low CHT and Oil Temp before starting

Post by Welsch »

Ok, another funny thing with temperatures that I just noticed...

I was sitting on the tarmac after taxiing in, idling at 900rpm, cowl flaps fully open. OAT was 38°C (100F), when I noticed a pretty low CHT of around 108°C, still dropping. Now on previous stops, the OAT had been in the low to mid twenties, but the CHT stayed much higher and dropped much more slowly.
Oil temp at the same time was behaving more like expected, it started out at 72°C and very slowly climbed to 75°C... now I can see that happening while idling under a scorching sun, not much cooling going on, soaking up heat from the hot engine block - but its strange that at the same time I see the CHT drop like I am sitting at a cold Alaskan riverbank.

Now I was not religiously monitoring temperatures all the time during descent, landing and taxi, so I can't say how the temperature developed during those phases - but I know that during cruise everything looked as usual, temperature wise.

Another bit of information: my CHT gauge is flagged yellow, but it is supposed to be "reading a little high", according to the mechanic. That doesn't explain what I am observing.

Edit: reading through the whole thread again, I get the feeling there may be something reversed in the code dealing with CHT temperatures somewhere... the hotter the air, the cooler it seems to act on the CHT, and vice versa.

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Medtner
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Re: Low CHT and Oil Temp before starting

Post by Medtner »

Welsch wrote:Ok, another funny thing with temperatures that I just noticed...

I was sitting on the tarmac after taxiing in, idling at 900rpm, cowl flaps fully open. OAT was 38°C (100F), when I noticed a pretty low CHT of around 108°C, still dropping. Now on previous stops, the OAT had been in the low to mid twenties, but the CHT stayed much higher and dropped much more slowly.
Oil temp at the same time was behaving more like expected, it started out at 72°C and very slowly climbed to 75°C... now I can see that happening while idling under a scorching sun, not much cooling going on, soaking up heat from the hot engine block - but its strange that at the same time I see the CHT drop like I am sitting at a cold Alaskan riverbank.

Now I was not religiously monitoring temperatures all the time during descent, landing and taxi, so I can't say how the temperature developed during those phases - but I know that during cruise everything looked as usual, temperature wise.

Another bit of information: my CHT gauge is flagged yellow, but it is supposed to be "reading a little high", according to the mechanic. That doesn't explain what I am observing.

Edit: reading through the whole thread again, I get the feeling there may be something reversed in the code dealing with CHT temperatures somewhere... the hotter the air, the cooler it seems to act on the CHT, and vice versa.
Yeah, I'm having the feeling that something is amiss. I've had great troubles to get the CHT into the green while doing pre takeoff checks, even with outside temps around 30C. But then again, I'd expect that this is something that A2A has carefully modelled according to their tests, and that the Bonanza behaves like this.
Erik Haugan Aasland,

Arendal, Norway
(Homebase: Kristiansand Lufthavn, Kjevik (ENCN)

All the Accusim-planes are in my hangar, but they aren't sitting long enough for their engines to cool much before next flight!

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Piper_EEWL
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Re: Low CHT and Oil Temp before starting

Post by Piper_EEWL »

Jarek wrote:Probably the best idea (without going into physics and specific heat calculations) would be to display something like "no reading / off the scale" for CHT values below 50degC.
In fact from the cockpit it is not possible to determine CHT prior starting a cold engine, without connecting a specialized diagnostic tool. Gauge starts at 50 or perhaps will start moving a bit earlier. The only important metric here is he rate and time required to heat up the cylinder's heads.
I’m not so much worried about the actual value of the CHT when it is out of the range of the instrument and I’m reading it of via the tool tips. I’m “worried” or curious how that changes the behavior of the engine during startup and warmup and so on. I get a feeling that with Accusim it makes a huge difference if you start the engine at -5C or 25C OAT. That’s what I’m wondering about.
B377&COTS, J3 Cub, B-17G, Spitfire, P-40, P-51D, C172, C182, Pa28, Pa24, T-6 Texan, L-049&COTS, Bonanza V35B

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