High CHT and Oil Temp

I made a short flight of about 30 minutes. No troubles. On the return something unusual happened.

On climb out, I first noticed CHTs getting real hot on 1 and 2. Like 500. Oil temp was up to 220+. EGT was fine. I was quite concerned so I lowered the MP and temps came down slowly. After getting to 5000 feet, I set everything up like normal. It acted normal. No more troubles.

I have flown this Arrow 700 hours and have never seen anything like this. BTW, 3 and 4 were like 320 on climb and down under 300 in cruise. 1 and 2 always did like 360 climb and 300 - 310 cruise.

No dead birds or anything stuffed in the cowl...

I am gonna play with it tomorrow. It is 94 out, but it has been like that many many times before and none of this goofy stuff.



  • What was your airspeed during the climb? Your density altitude?
  • 100kts or so and the DA was about 1200.
  • The JPI manual would say this could be a leaking exhaust gasket. The fact that you got it on both 1 and 2 would mean that it's not probably a blocked air intake. And in climb, if any cylinders are going to get hotter because of outside air temps I would think it would be 3 and 4 since they would have less air flow over them.

    The fact that things evened out when you got to cruise is good but I guess but I'm not sure what it would mean as to why it happened in the first place. Again, since it was happening on two cylinders it's unlikely that it would be faulty probes.
  • Yes, but the EGTs were normal. If there was a leaning the EGTs would be higher too.

    As far as faulty probes, remember... the oil temp was way high too.
  • The symptoms are consistent with preignition - CHT's head for the roof, EGT stays low or goes down. A bad plug could produce that in one cylinder - but not two. Could be a mag going down the tubes.

    Cylinders 1 & 2 also share common intake/exhaust cams. A problem there would not be pretty - but I would expect it to screw up the mixture (to much or too little intake) or the exhaust - either should cause a significant deviation in EGT.

  • I am wondering if it might be the muffler? If the baffle came loose and blocked the outlet, might that keep all kinds of heat in and reduce power?

    I'll have to stick my video scanner up inside and look.

    I looked into the cylinders and they look good. Plugs looked good. Oil looks good. EGTs good. CHTs on 1 and 2 real high. I flew it again (over the airport) and it does not take long for them to go up to 450 and still climbing... but turned down the power and did not let them... If you lower the power to 17MP they go to about the same as 3 and 4... Taxi around and they are the same as 3 and 4...

    When 1 and 2 are hot 3 and 4 are only like 320...
  • You haven't mentioned if performance in terms of power output or fuel consumption has suffered. What are your impressions in those regards?
  • It seems normal but as it gets hotter the power is reduced.
  • I'd suspect a Mag problem.

    The 1 and 2 fire off of the same lobe of the Mag cam. If something was making it fire early, you'd see the CHTs go through the roof on those cylinders at higher power settings.

    Check the timing with a degree wheel on all of the cylinders (not just #1). A quick check would be to simply put the Buzz-Box on the Mags and pull the prop through 2 revolutions and see of both Mags fire at the same time on all cylinders. It would be unlikely (but not impossible) that both Mags fail exactly the same way at the same time).

  • PK Hmmmm. I did not have time to really delve into it past a quick check. But, the data plate calls for 20 degrees advance. The buzz box shows 29 degrees on #1 for both mags... they are very well sync'd at that. That certainly could cause detonation and high cylinder pressures/temps. I wonder why they are so well sync'd at that?
  • So what's the outcome? Mags the problem?

  • The mags seem fine. The timing was consistently off for all cylinders. I set the timing to 20 degrees and the plane seems to have more power, runs cooler then ever as of late, and I had to raise the idle just a tiny bit.

    90 degrees out, full power full RPM from sea level to 7K. Highest CHT was 359. Level off and trim out and it cools to 290 on the hottest. Oddly enough, the EGTs are all 75 to 100 hotter. Runs great. Thanks.
  • PK - Thanks. See, I always think the worst. I'd have looked at all the hard stuff first. Simple is better!
  • Weird that both mags were mis-timed but just now the engine started getting hot (and then just 2 cylinders). When was the timing set last?

    I think you meant to say that you checked the timing (OK for the Owner/Operator to do as long as you have a PPL or better), and found it off. You then, under the direct supervision of an A&P, you re-set the timing and the A&P made the appropriate logbook entry. Right? ;-)

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