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painless

Well Known Member
I have looked at the archives for an answer here, but need to post this one to the group:

I have an 0320 E2D 150hp, carburated, on two slicks. Mags, wire harness, plugs (finewires) are all relatively new (less than 100hrs). Mags were just timed 4/08. Engine core has just over 1650hrs. Oil pressure at cruise is 76, lowest compression measured early April was 76. Three blade Catto. Engine has been running like a top.

Here's the rub. Taxiing out tonight (OAT about 80F) I noticed that all CHT's were heading over 400F. Actually peaked at over 500 and the warning chime was going off in my RMI micromonitor. Not cylinder-specific. Ran the engine up and all CHT's went back to their usual 350F or so. Took off with no problems... was switching between all cylinders to have them displayed on the RMI ( the one thing I don't like about the monitor) and everybody was happy at about 375F.

Decided to stay in the pattern and reduced power to just over 1800RPM and then up went the CHT's again. Landed, taxiied off the runway and did a runup again, showing normal CHT's. Taxi back to the hangar started the CHT's rising again.

After shutdown, I watched as all temps (CHT and EGT) start cooling off and you could see the CHT's following suit. So I don't think I am dealing with a sensor/guage problem.

Oil temp was 170F for the short around the pattern flight. EGT's never exceeded 1200-1300F.

My theory is a problem with the idle mixture screw. In the past, I have tried to set it so that I get a slight rise in RPM on shutdown, but no joy. If I am too lean, wouldn't it backing out by vibrating make it richer??

Any opinions?
 
High CHT's

Jeff,
Something is wrong for sure.
I would start with taking the cowling off and looking for something obvious
like a loose carb, loose intake tubes, etc.....
Sounds like the problem is coming and going.
Maybe a loose or broken mixture cable or connection.
Good Luck.
 
Thanks Bob.

The thing is the engine runs great. The only thing I am noticing of late is a slight stumble on transitioning from idle to full power....with a steady smooth application of throttle I might add.

Lower RPM in the pattern still has the engine running nice and smooth.

I am going to start with checking all connections to my RMI, including the selector switch for all 4 cylinders. Then work my way from there. Electrons can do funny things sometimes.
 
Seems really odd that the CHT's would trend higher at idle than under power. I generally lean pretty aggressively on the ground to keep the plugs from loading up and have never had the issue you describe, and have a hard time believing the idle screw is to blame (but check it anyway...). I have a hard time believing that CHT's can top 500 degrees at idle under any circumstances, especially on a relatively high time engine that seems to run fine otherwise.

What about an electrical problem? Maybe the voltage is going down at lower RPM and somehow causing a false high temp reading? Faulty engine monitor? Any way to hook another monitor up to verify the temps? Bad ground somewhere? Hopefully someone who knows what they are talking about will chime in, I'm just throwing out ideas.

Good luck!
 
I'd second the suggestion to look at the electrical system. I had strange CHT (and OAT, fuel level) readings in the first few hours on my engine and traced them to a faulty fuel pressure sensor that was pulling down one of the regulated supply voltages in my GRT. Strange but true!
 
Thanks for all the suggestions guys. Now that I have slept on it, I too tend to think it is electrical in nature. My first suspect is my switch on the panel that is required with the RMI unit I have to monitor all cylinders. Seems strange that CHT is the only thing affected.
 
Sounds to me like you got a set of type K cht probes. Most instrumentation system need type J probes for CHT.

A bad ground won't affect readings unless you have internally grounded CHT probes. You can verify this effect but observing a big indication change when switching the alternator off/on while running the engine.


Good luck, Bob
 
For the benefit of others, I wish to report what I found as the cause of my high CHT readings.

I first looked to see if the engine ground strap was loose or disconnected as was suggested. All was secure.

Next, I focused on the CHT/EGT selector switch which was my primary suspect. With the RMI micromonitior on, I jiggled all the wires that are connected to the switch from all the sensors with no effect.

Then I jiggled a molex connector that I have that connects four wires coming from the afore mentioned switch to the RMI. Voila....temps started going screwy.

Turns out I had not inserted the male pins for the CHT connnection into one side of the molex block all the way so they engaged in the block. As a result, with time and vibration, they backed out and started making intermittant contact.


Just thought I would report this finding in case others have a similar problem.


Regards
 
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