Overheating

[Roy]

Hi guys I bought Bearhawk with a 540 in it I have #6 cyl heating up to 450. On climb out any ideas on how to cool it down

[Steve W]

What's 5, 4 and 3 doing?

[Battson]

Hi Roy,

Welcome to the forum and the "Bearhawk family"! Great to have you here!

Let me start by saying, overheating is a common problem with the -540 in Bearhawks, especially in the climb. But it doesn't have to be that way! Mine runs very cool.

Next, 450 is a very hot temperature - too hot. I know that is where Lycoming sets their redline (460*F), but it's too hot if you want your engine to last as long as possible. At 450*F the aluminium the cylinders are made of has lost 50% of it's tensile strength. At 400*F, the metal is exponentially stronger, and you reduce the chance of damage considerably. I strongly recommend a "personal redline" of 400*F. My caution area starts at 380*F (yellow line), above that point I take active steps to cool my IO-540 down immediately.

Is your problem just with no.6 cylinder, or are all your cylinders running over 400*F?


So, what can you do to cool it down? Here are some ideas:

(A) Perhaps obviously - until you can implement a long term fix, I suggest you do one of the following to keep the temps below 400*F at all times

• climb at a lower nose angle / higher airspeed
• keep the mixture full rich during climb below 6000 ft DA
• climb at lower power settings
• if you have a fuel injected engine, learn how to climb lean of peak EGT (cruise climb at partial power)

(B) Longer term fixes include the following, I will order these the order I would approach it:
​
1.Improve the baffling:

• liberal use of CRC 556 red liquid gasket in any and all gaps between baffles
• replace worn or poorly sealing baffle rubber / fabric
• ensure there are NO holes, some builders have a pretty loose idea of what good baffles look like, every hole makes your engine run hotter. My tolerance is zero, if there's a toothpick sized hole I am filling it. Holes around the engine mounts are a common area where builders slack off.

2. Install a cowl outlet lip. This is an easy modification which takes an hour or two, not days. I have installed one, and it makes a measurable difference.

See this image for the idea in terms of how you want to change the airflow. Most Bearhawks have the first picture, you want to build the third one, using a simple bit of hardware store aluminium tube which you cut and flatten a part of:


You can see mine in this image:



3. Install cowl louvres - this is going to increase cooling drag permanently, and isn't my favourite solution for that reason...Here is an image of what I mean:


4. Install plenum at the cowl inlets. I put in a short plenum, on each side, to ensure there is no loss of cooling air in the transition from the cowl inlet and the area above the cylinders. The area around the prop and starter gear / flywheel is another classic area for cooling air losses and extra cooling drag. There are baffle seals around the cowl inlets.

Here is a photo which shows you what I mean:


5. Install cowl flaps - this gives you more control over the airflow through the engine cooling fins, but would be a lot more work to retro-fit, probably not worth doing unless you have a mind to start a big project and take the plane out of the air for a month or two. Here is a link to a thread where I discuss my cowl flaps:

• http://bearhawkforums.com/forum/bear...571-cowl-flaps

6. Install a complete plenum over the entire engine baffling area. This is a huge job, I would say a last resort...

[jaredyates]

What a great post by Jonathan. Also read this article:

http://eci.aero/pdf/EngineCoolingProblems-SAE.pdf

This tells you how to test your air pressure differential, which you can do before and after the mods he suggests.

[Battson]

Ahh the manometer, the oldest pressure measuring device I can think of and the origin of inches of mercury unit of measure.

[Baloo]

I had the pleasure of flying with Roy today. His aircraft is a beast and he is a pretty nice guy to boot! Welcome to the family Roy!