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High CHT readings

S

svanarts

Well Known Member
I've been noticing my CHT climbs to almost 420 F during climbs and slowly settles down to the upper 390's or 380's on cool days. This seems a little high to me. First of all, is this too high? It seems to have gone up about 10 degrees or so lately. Incidentally, I'm taking my reading from the #4 cylinder and there is a large hole cut in the rear baffle for the oil cooler which is mounted there.

Assuming this is a little on the high side what can I check? I'm going to look for things like debris in the cooling fins on the cylinder and loose exhaust gaskets, and check the probe for proper operation of course. Maybe close up the hole that feeds air to the oil cooler.

Is there anything else I could be looking for?
 
svanarts said:
I've been noticing my CHT climbs to almost 420 F during climbs and slowly settles down to the upper 390's or 380's on cool days. This seems a little high to me. First of all, is this too high? It seems to have gone up about 10 degrees or so lately. Incidentally, I'm taking my reading from the #4 cylinder and there is a large hole cut in the rear baffle for the oil cooler which is mounted there.

Assuming this is a little on the high side what can I check? I'm going to look for things like debris in the cooling fins on the cylinder and loose exhaust gaskets, and check the probe for proper operation of course. Maybe close up the hole that feeds air to the oil cooler.

Is there anything else I could be looking for?
Click to expand...

Scott: I dropped my temps by 30-40F across the board by cleaning out the flashings in the fins between the spark plugs. It was truly dramatic.

Vern
 
How to run CHT's cooler in the green.

svanarts said:
I've been noticing my CHT climbs to almost 420 F during climbs and slowly settles down to the upper 390's or 380's on cool days. This seems a little high to me. First of all, is this too high? It seems to have gone up about 10 degrees or so lately. Incidentally, I'm taking my reading from the #4 cylinder and there is a large hole cut in the rear baffle for the oil cooler which is mounted there.
Click to expand...

HI Scott, if you do some searching around on VAF under this issue or under my posts you'll find some good information. I've had several VAF folks call me about how I reduced my CHT's and they have called me back to thank me as they saw 40-50F degree changes with some minor work on the baffling. It's all about air management and using it correctly. Cowl inlet design, baffling design, exit gaps, oil cooler location,etc. and NO air leaks is the key. Probably 80% of the baffles that wrap around the cylinders that I've seen are done incorrectly. If you'd like to call me sometime, send me a private message and I'll give you my phone number. BTW I'm cooling my IO-360A1B6 200HP + engine with very high compression pistons and only 2 1/2" round inlets in hot summer temps. I spent many hours days months trying this and that and learned what not to do and what worked.
Click to expand...
 
#3 is usually hottest

svanarts said:
I've been noticing my CHT climbs to almost 420 F during climbs and slowly settles down to the upper 390's or 380's on cool days. This seems a little high to me. First of all, is this too high? It seems to have gone up about 10 degrees or so lately. Incidentally, I'm taking my reading from the #4 cylinder and there is a large hole cut in the rear baffle for the oil cooler which is mounted there.

Assuming this is a little on the high side what can I check? I'm going to look for things like debris in the cooling fins on the cylinder and loose exhaust gaskets, and check the probe for proper operation of course. Maybe close up the hole that feeds air to the oil cooler.

Is there anything else I could be looking for?
Click to expand...
Usually its #3 is hottest in cruise due to the fin orientation. If you are not looking at #3 and frankly #2 and yes #1 in climb, than they might be higher (depending on phase of flight).

Remember one cylinder fits in any position and the cylinder is NOT symmetric front to back. When the cylinder is mounted on the right side, the intake side is aft. When mounted on the left side of the engine, the exhaust valve is on the aft side. The deeper fins are on the exhaust side. When you smash the shallow fins against the baffle (#2 and #3) you choke air off around the cylinder and to the bottom fins. (see pic below)

I gather you have a single CHT just on #4. That is OK but #3 might be higher.

There are threads to search but I'll re post the pictures that show why #3 runs hot. I would not be too concerned about the oil cooler but it may have something to do with it.

Is the engine NEW, breaking in. Why do new engines run hot? NO it is not that they are tight, common mistake. Sure close or tight fit may raise the temp a little, but the main reason is the fact the layer of Carbon deposits has not formed on the piston dome and head combustion chamber and valves. That carbon film acts as a thermal barrier or coating. Some deposits are good.

Why #3 jug runs hot: (short fins against the baffle #2 and #3 cylinders - click pic once or twice for full size)




Usually an increase in gap between the baffle and fins on #3 helps improve cooling. #4 should not have a baffle/fin gap issue, but you may try increasing the gap a little. Also consider blocking the cooler. From my experience it does not make much difference on the CHT to #4. However play with it. Block some of the oil cooler hole off and see what happens to OT.

To increase baffle gap, one trick is add a washer between baffle and cylinder mount screw.

Good Luck
 
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Thanks for the suggestions. Just got back up in the air again after my false start with gunked up plugs (thank you Harbor Freight). The firs thing I have tried is to glass in the "holes" in my inlet ramp that was letting air spill to the low pressure side of the baffles. The CHT seemed a little lower today then started climbing rapidly. I'm going to try a couple of things. First, I want to rule out the obvious and test the sensor to see if it is working properly. This is a bayonet probe hooked to a Rocky Mountain MicroMonitor. My plan is to boil some water and see if the probe and monitor measure the right temp. I have seen some odd fluctuations in displayed temperature so I want to give that a try.

If the CHT probe seems to be operating normally I'll try to close off the hole in the baffles where the oil cooler is mounted.

Thanks for the pictures George. That's something I understand! :)

Alan, if this doesn't work I may take you up on that offer of a phone call.
 
cooler temps all around thanks A.J.

I own /fly an 8A. fought cooling issues for about a week every day in early testing. I called Alan for advise. Great guy , took time to email me several fixes. the short storey is -They Worked-. In one afternoon I lowered my temps 35 to 40 degrees. great advise here!!!! ;)
 
UPDATE - CHT temp down by 25 deg

I did two things and both together helped.

#1 I glassed in the sides of my air inlet ramps. Don't leave them open. Thanks for that suggestion.

#2 I paid more attention to timing my mags correctly per suggestion by Bart LaLonde.

#1 cooled the temps down a bit but not enough, when I timed the mags again (with no one around yacking) the temps came down even more. I saw about a 25 degree drop in cruise. I've got to wait until the Central Valley temps really kick in to find out how much cooler the cylinder is actually going to run but it looks very promising.
 
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