CHT Differences

[HwkIFan]

Quick question vintage Mooney officianado's, 

I've put roughly 35 hours on my new to me 67 M20F since taking ownership and finally was able to download the EDM 700 data.  The engine is a Lyc remanufactured IO-360-A1A installed in Feb of this year by prior owners.  Normal cowl but it does have the lower cowl cover.  I'm seeing a consistent temp split between my #2 (hottest) and #1 (coolest) cylinder of ~70-80 deg F. (attached pic of data from one flight).  Engine now running Aeroshell 100+...max fuel flow indicated during takeoff ~15-16 gph 

She runs smooth, during runup with the JPI Norm mode, all appears to respond as expected.  Figured I'd ask if there is a 'normal' or expected temp differential between hottest and coldest cylinder...thoughts ?

[MikeOH]

Looks a lot like my '70F.  I have to watch it on take-off to keep #2 under 390.  Normally #2 runs right around 350-360 in cruise (65-70% power).

Used to be a bit higher (405-410 on take-off) until I noticed the upper baffle wasn't sealing against the top cowl on both sides; 1" gap!  Pushed pilot side into place and saw temps drop 10-20 F.  The co-pilot's side still has a gap.  I got a set of new baffles from Guy, but haven't had a chance to put them in just yet.  They do look great!  I'm hoping that will drop CHTs a bit more and also lower my oil temp which runs pretty high (220).

[carusoam]

You need to be aware of the 5 different thermocouples being used on your cylinders...

One of them is not going to be like all the others...

Depending on who set up the monitor... the ship’s CHT is legally sitting in a TC well.  The JPI has 4 TCs that like to occupy the four available wells...

Often one of the JPI TCs gets piggybacked or is sitting in an odd spot.

Do your research to find out where the ship’s TC is and where that JPI’s TC is... that will probably explain why one is slightly different...

a 50°F difference the JPI TC is piggybacked close to the well...

a 100°F difference the JPI TC is spark plug seal type...

PPthoughts only, not a mechanic...

See what I mean?

Best regards,

-a-

[Skates97]

I have an O-360 with the lower cowl enclosure and see the same spread. #2-4 all run within about 5-10 degrees of each other but #1 is consistently 70-80 degrees cooler. I have just attributed it to the difference in the sensors supplying the data. 

[ArtVandelay]

I have an O-360 with the lower cowl enclosure and see the same spread. #2-4 all run within about 5-10 degrees of each other but #1 is consistently 70-80 degrees cooler. I have just attributed it to the difference in the sensors supplying the data. 

#3 for 700/800 use a different ring probe, it will read low (30°-40°). The factory probe takes bayonet position, certified (900 series) replaces it, but 700/800 cannot.

#1 gets direct cooling, I have sheet metal blocking some airflow ( standard on the J) that somewhat balances it. If #1 is too cool, you could replace this with a higher piece.

If the cylinder gets too cool it supposedly can foul with lead.

[flyboy0681]

I've always notice before starting up that all four probes report different ambient temperatures. For example, when the temperature in the hangar is 85 (and the plane has been sitting for a week), the CHT readings could be 83, 86, 85 and 82, not to mention the oil temperature, which also doesn't agree.

[jaylw314]

12 hours ago, teejayevans said:

#3 for 700/800 use a different ring probe, it will read low (30°-40°). The factory probe takes bayonet position, certified (900 series) replaces it, but 700/800 cannot.

#1 gets direct cooling, I have sheet metal blocking some airflow ( standard on the J) that somewhat balances it. If #1 is too cool, you could replace this with a higher piece.

If the cylinder gets too cool it supposedly can foul with lead.

I don't know, my hottest cylinders are #1 and #4.  I assume #4 is hotter because it loses some air to the oil cooler next to it.  I assumed #1 is hotter because the pressure at the very front is not quite as high.  I imagine if you removed the metal baffle in front of the #1 cylinder that it would actually get hotter, not cooler...

[flyboy0681]

Before the age of modern engine monitors, it would have been interesting to see what the numbers were when the planes were delivered to the customer from the factory.

[HwkIFan]

Appreciate the comments from all.  As a Mooney 'nube', I have many questions but am glad to have this kind of information at my disposal.

[Ragsf15e]

It will depend a lot on your cruise power setting, LOP or ROP, IOAT, and altitude, but my 68F generally runs about 290, 330, 340, 300 in cruise at 65% power and 25 degrees IOAT.  So a 50-60 split seems ok.  Definitely different airflow over each cylinder from our old intakes.  I have seen them all 40 warmer on a hot day ROP, and I have seen them all sub-300 LOP on a very cold day in the winter.  Btw, i have the lasar bottom cowl closure and JPI 930.

[pinerunner]

My #1 cyclinder is cooler too. The CHT's look a lot like the ones above.

[Browncbr1]

If you don’t have the optional service instruction metal baffle in front of #1, (which your numbers indicate) you can simulate it with about 2-3” wide aluminum tape across the fins and see how the test flight goes.   I’ve been flying with a few layers of aluminum tape for quite a while now and get very even numbers in cruise.  Note, rain will perforate one layer of aluminum tape..

[HRM]

Here's an IO-360-A1A for comparison:

[Guest]

On 9/11/2018 at 9:19 PM, HwkIFan said:

Quick question vintage Mooney officianado's, 

I've put roughly 35 hours on my new to me 67 M20F since taking ownership and finally was able to download the EDM 700 data.  The engine is a Lyc remanufactured IO-360-A1A installed in Feb of this year by prior owners.  Normal cowl but it does have the lower cowl cover.  I'm seeing a consistent temp split between my #2 (hottest) and #1 (coolest) cylinder of ~70-80 deg F. (attached pic of data from one flight).  Engine now running Aeroshell 100+...max fuel flow indicated during takeoff ~15-16 gph 

She runs smooth, during runup with the JPI Norm mode, all appears to respond as expected.  Figured I'd ask if there is a 'normal' or expected temp differential between hottest and coldest cylinder...thoughts ?

The first thing is what type of probes are installed in the two cylinders? Bayonet or spark plug gasket or gasket under a Tanis heater ?

Clarence