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cold weather = spike in EGT, CHT on #1 & #3

dougknight

Well Known Member
We finally got a little cold winter weather here in the northwest...well cold for us anyway in the mid Willamette valley of Oregon. Teen's at night, 20's & 30's during the day (F) with 2 inches of snow on the ground. Sorry for you guy's in the midwest doing the minus 0* F thing. actually they are saying + 5* F tonight with freezing fog for the next two day's for us , O joy!

So, I decided to take the plane out and circulate the oil and warm it up for a bit. It was mid afternoon the sun was out and it must have been in the mid 30's (F) after being in the mid 20's overnight. Not sure what it was in the hanger where the plane is kept but had to be right around the freezing mark. T Hanger is not heated nor insulated but it is enclosed. I keep the engine on a heated dehydrator 24/7 when not in use which may give it another 10 degrees or so (home made with a 60 watt light bulb in a 5 gal bucket)

Did my normal run-up and mag checks as usual and saw nothing abnormal. Entered the runway and took-off. At about 1000 feet I pulled power back to 2000 rpm and started to lean a little to save some fuel, turn the sterio on and enjoy the sights when the engine stumbled quicker than I anticipated. I'm carburated and lean to roughness then richen to smooth as per lycoming manual. I glanced at my EGT gauge and it was up over 1450* F. I usually see it around 1050 before leaning and maybe up to 1250 after leaning even on a hot 90* summer day!! What the heck Is going on!! I have never seen it this high!!

I pointed it back to the runway, landed and de-cowled (top cowel only) and looked for any obvious indications and found none. I did two more take-off and landings within gliding distance back to the airport so as to gather more information. I figured 1400 wasn't critical. It was unusual, however still safe if I stayed within gliding distance back to the airport should I need to shut the engine down.

Long story short I found that EGT'S on both #1 & #3 peaked aound 200-250* higher than normal even on a hot summer day. CHT'S on both #1 & #3 were running 50-75* higher than normal (375*-425*). CHT'S on all four are usually within 25-50* F of each other in the 325*-350* F range.
EGT'S on both #2 & #4 stayed in the normal range of what I normaly see, 1000-1050 before leaning and 1150-1250 after leaning. CHT'S on #2 & #4 normal in the 325*- 350* range.

I have an idea or two to persue and check once the weather cooperates and warms up enough to work in the unheated hanger (that faces north away from the sun) but I thought I would throw this info out in the meantime and see what ideas others on the forum might provide as to why one side of the engine might see a spike upwards in operating temperature when the ambient temp actually goes down!!

specs are:
RV9A
Areosport re-built O-320 in 2006
475 hrs TT airframe and engine
carburator
STEAM GAUGES! vans EGT and CHT with four position rotary switch
slick mags, left side impulse only
timing=25* BTC

any ideas appreciated.

thanks in advance
doug
 
This may be part of the problem??

I pulled power back to 2000 rpm and started to lean a little to save some fuel, ---------- when the engine stumbled quicker than I anticipated.


any ideas appreciated.

thanks in advance
doug


Cold air is denser, requires more fuel---------mixture knob position will change for same mixture ratio.

Cold dense air will make more HP-----------more HP = higher temps.

I have no idea if this is the total cause of what you saw, but the physics are sound, and must be at least a factor in things.
 
Last edited:
Interesting ....

... that both your hot cylinders were on the R side. Are you carbed or injected?
 
he is carb'd

"I'm carburated and lean to roughness then richen to smooth as per lycoming manual. "
 
Hi Doug,

No idea what's going on, but I'm probably in the same weather (Portland, OR) and my EGT readings the past 1-2 weeks were around 100F higher than normal. Weird, eh? Yesterday I replaced the spark plugs, but EGT was still high this morning. I don't think it's the weather, so next weekend I'm checking the exhaust valves.

Holger
 
I suspect at least some of the changes you are experiencing are due to the cold reference junction for the thermocouples. Google "cold reference junction" for accurate temperature measurement when the ambient temps vary - more than you ever wanted to know but the theory is simple.
 
Quite limey you have very low DA, thus more fuel required.

As for more HP thus higher CHT that is BS right there. When I produce more HP at low DA I get lower CHT, and there is a very good reason, so those who think this way, now is a learning moment.

I suspect you have intake leaks on those cylinders and thus your symptoms.

Check this out and let us know please.
 
Cold air is denser, requires more fuel---------mixture knob position will change for same mixture ratio.

Cold dense air will make more HP-----------more HP = higher temps.
.

Mike: Sounds good but doesn't explain why the temp increase is only on the two starboard cylinders.



deek: haven't had the opportunity to google the cold reference injunction yet. sounds interesting though and I will check it out.


rv10inOZ: G'day mate. Dave I think you are spot on. I'm hoping anyway. Induction leak/leaks seem to fit the symptoms the best and would be the easiest to fix. I will be checking both the induction tubes and carburetor attach gaskets for cold induced shrinkage/looseness. Anybody ever experience either of these two points (or any other spots) effected by cold weather.

Haven't made it to the hanger yet still 2 inches of snow on the roads and runway with freezing fog this morning. Airport is 10 miles away.

doug
 
Ambient temp today 50 F and the snow is gone. went to the hanger de-cowled and checked everywhere I thought the thing might be getting extra air. No smoking guns but I did get two full turns on the hose clamps holding the rubber hoses onto the induction tubes. All cylinders however, not just 1 & 3.

Flew it and all four CHT'S were within 25 F..... EGT's on 1 & 3 were 100 F higher than 2 & 4. I'll live with it for now.

Not sure if I cured anything by tightning up the clamps or it just went back to normal ambient temp mode. Have to wait for colder weather again I guess

Shadowbrush: Have you flown since things warmed up? If so did your EGT'S go back to normal?

doug
 
Shadowbrush: Have you flown since things warmed up? If so did your EGT'S go back to normal?

doug
Doug, I haven't yet. I usually fly down from Seattle (where I work) to Portland over the weekend, but today it was all fogged in, so I had to drive. :mad:

Frankly, what you describe doesn't sound like an intake leak to me. Should run somewhat rough at idle, and less noticeable at higher power settings.

The cold junction calibration is an excellent thought.

I'll report back if I can fly to Portland next weekend.

Holger
 
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