Keeping CHT temps in range on climb-out

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Hans
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Re: Keeping CHT temps in range on climb-out

Post by Hans »

-I recently changing the cooling baffles in my DA-40...it made a difference in the climb-out temp...mine were old,worn and 'wavey'...also sealed all the holes....time consuming but easy to do
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Re: Keeping CHT temps in range on climb-out

Post by dwurfel »

Thanks Hans. think I am in good shape there. All cylinders are in the same range for the most part. I did that on my 172 and it did make a difference.
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Re: Keeping CHT temps in range on climb-out

Post by dwurfel »

Again thanks for everyone's input. I now have found that keeping my climb out speed at 90 KT, 24-25 squared and a bit richer mix ( leaning while climbing ) really keeps my CHT's cooler eg: 360 380 versus 390-410 that I was seeing before.
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Kurt h
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Re: Keeping CHT temps in range on climb-out

Post by Kurt h »

My CHTs have been steadily creeping up over the years during climb out. I’m sure my 2000 hr baffling is getting a bit stiff with some air gaps. If I maintain best climb during summer (in Houston!), temps will climb to about 405-410 F. Used to be 380 F. about 1000 hrs ago.

For what it’s worth, I have mentioned this to 3 separate Lycoming factory guys and they all say these temps are a non issue for our engine even for a 20 minute climb to altitude. Of course they want to see cruise temps below 400, but they shrugged their shoulders and said any climb temp below 430 is not going to accelerate engine wear.
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Re: Keeping CHT temps in range on climb-out

Post by rwtucker »

Kurt h wrote:My CHTs have been steadily creeping up over the years during climb out. I’m sure my 2000 hr baffling is getting a bit stiff with some air gaps. If I maintain best climb during summer (in Houston!), temps will climb to about 405-410 F. Used to be 380 F. about 1000 hrs ago. For what it’s worth, I have mentioned this to 3 separate Lycoming factory guys and they all say these temps are a non-issue for our engine even for a 20 minute climb to altitude. Of course they want to see cruise temps below 400, but they shrugged their shoulders and said any climb temp below 430 is not going to accelerate engine wear.
Interesting comment from the Lyco guys Kurt. I wonder if it means that there have been changes in the metallurgy over the years. One IO-360 manual says:
For maximum service life, cylinder head temperatures must be maintained below 435°F.
(224°C.) during high performance cruise operation and below 400°F. (205°C.) for economy
cruise powers.
I have seen older references suggesting that lower than that is better. Maybe someone can explain why higher temps are OK with higher power. Seems counterintuitive. I guess I can quit panicking when I see 402 on one cylinder.

Oil temps might be a different issue. At some location in the engine, oil will be 40-50 degrees hotter than indicated and high CHTs might contribute to premature oil breakdown.
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Kurt h
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Re: Keeping CHT temps in range on climb-out

Post by Kurt h »

rwtucker wrote:
Kurt h wrote:My CHTs have been steadily creeping up over the years during climb out. I’m sure my 2000 hr baffling is getting a bit stiff with some air gaps. If I maintain best climb during summer (in Houston!), temps will climb to about 405-410 F. Used to be 380 F. about 1000 hrs ago. For what it’s worth, I have mentioned this to 3 separate Lycoming factory guys and they all say these temps are a non-issue for our engine even for a 20 minute climb to altitude. Of course they want to see cruise temps below 400, but they shrugged their shoulders and said any climb temp below 430 is not going to accelerate engine wear.
Interesting comment from the Lyco guys Kurt. I wonder if it means that there have been changes in the metallurgy over the years. One IO-360 manual says:
For maximum service life, cylinder head temperatures must be maintained below 435°F.
(224°C.) during high performance cruise operation and below 400°F. (205°C.) for economy
cruise powers.
I have seen older references suggesting that lower than that is better. Maybe someone can explain why higher temps are OK with higher power. Seems counterintuitive. I guess I can quit panicking when I see 402 on one cylinder.

Oil temps might be a different issue. At some location in the engine, oil will be 40-50 degrees hotter than indicated and high CHTs might contribute to premature oil breakdown.
RW, the impression I received from all 3 of these discussions at airshows with the Lycoming guys is we are overthinking this. At SNF this year when I quizzed him on temps (after a long discussion) he said "change the oil and fly frequently, it's hard to hurt an IO-360."

The 435 max temp you mention is for "high performance cruise". I assume that is 75% power, continuous operation at the POH recommended leaning. Maintaining full power climb temp <430 would not seem to conflict with this recommendation.
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Re: Keeping CHT temps in range on climb-out

Post by rwtucker »

Kurt -- All of this makes sense except the max temp guidance being higher for high power cruise than for low power cruise. As with EGT, lower power settings produce less pressure, uneven spot heat, etc.
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Kurt h
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Re: Keeping CHT temps in range on climb-out

Post by Kurt h »

Hi Rob - I'm confused, do you mean the Lycoming guidance on cruise CHTs you quoted contradicts itself?
Last edited by Kurt h on Tue Jun 12, 2018 3:46 pm, edited 1 time in total.
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Re: Keeping CHT temps in range on climb-out

Post by rwtucker »

Taking standard definitions for high performance and economy, they are saying it is destructive to your cylinders to operate at 434 degrees at 55-65% power but OK to operate at 434 degrees at 75-80% power. Does that make sense? Is there something about the mechanics of higher power that makes it safer to run at higher temps than at lower power settings? That seems to be what they are saying but it could be bad writing and not counterintuitive mechanical facts.
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Kurt h
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Re: Keeping CHT temps in range on climb-out

Post by Kurt h »

Good points about the discrepancy in the Lycoming statement. I suppose I feel ok with my temporary <430 climb temps based on the factory rep statements, and at least one part of the Lycoming guidance allowing 435 F. continuous operation.
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