Higher CHTs after maintenance

Bavafa · #1 09-24-2011, 05:23 PM

Last week as part of my routing oil change and maintenance, I added another cooling hose (typical ½”) for the fuel pump and replaced the spark plugs which I had been mistakenly gapping them at .019-.022 until now and this time I set the gap between 0.015-0.018 which I think it is a correct gap for the slick mag.

Now my CHTs are running a bit higher, still with the reasonable range of 360s for cruise but during take-off, it gets to 400 quickly. So, I am wondering which of these two had the main affect. I suspect it is a combination of both but thought to get others thoughts and experience on this. My RMP drop is less during Mag check with the new gap setting.

Thanks in advance

MauiLvrs · #2 09-25-2011, 01:44 AM

I would not expect adding another 1/2" cooling hose to have an impact...

rwhittier · #3 09-25-2011, 07:53 AM

I suspect your widening the gap to the spec increased to efficiency of ignition and the flame front to the engine manufacturers spec, before it was a little delayed by spark plugs not being wide enough to really get the flame front going. Advancing timing beyond spec will also increase CHT's so assuming you didn't do that... without more data that is just my best guess.

Your engine is hotter because you are putting out a tad more HP and now have to dissipate the additional heat that comes from that power output. Have you noticed a slight drop in EGT? If so it's because you are burning more of your fuel during the power stroke and have a little less left over to burn in the exhaust stack. in short, this is a good thing, now you are getting rated HP. Now watch those CHT's.

Bavafa · #4 09-25-2011, 10:21 AM

Thanks for chiming in here, my own feelings say same thing. The little more efficiency is hard to notice but the mag check and less of RPM drop should be an indication of that.

Now, I have been contemplating to change one of the Mag to PMag and I am wondering how much I can expect my CHT to rise as a result?!?!

NDrv8r · #5 09-25-2011, 07:22 PM

any possibility of getting some of the baffle seals turned backwards during cowl reinstall? I don't think the plugs or blast tube would have that kind of effect.

On RV7A I have to reach through the oil door and verify they are all facing forward so they seal to the cowl with the air pressure on the top of the engine.