R

RV7ator

Well Known Member
My question is do Millennium cylinders tend to run hot? Hotter than Lycs? How much hotter?

My 6th RV-7 is now flying. Prior builds used 360s and 375s with ECI jugs or Lycomings flowed by Lycon, up to 9.6:1, with updraft RSAs or carbs. This one, "Gooney Bird", a Superior IO-360-M1B has a cold sump, FM-150 servo, 9:1. My other aircraft would run in the 350-390 range (ambient, power, speed, leaning variables). #6 has cruise CHTs into the 400s in 40 degree ambients; in short, unserviceable. Its temperature range is barely affected by such experiments as blocking advance by the P-mags and retarded timing to 20 BTC. (Yes, the P-mags are on TDC for set-up. I've verified that the ring gear's timing marks are correctly positioned.) Allowing the A curve advance and such curiosities as removing the lower cowl intake seals had NO effect on CHTs. Seems air's just not getting through the system.

Gooney under the cowl looks like all the other happy installations except for the Superior engine and the Vetterman exhaust system accommodating the horizontal sump; it seems to have more piping across and near the cowl exit that it might be blockage. My suspicions start with the cylinders themselves.

Any thoughts?

Anyone want to buy a hot RV-7?

John Siebold
 
If it’s new instrumentation and thermocouples an engine monitor setup for type J thermocouples connected to type K thermocouples will read 420 when the actual temperature is 340. It will only read 10F too high at 40F. If there is any doubt wrap the thermocouple and an oven thermometer in aluminum foil and heat it up with a heat gun.
 
Mikeyb, I’ll look into it. That does fit indications. I’m only slightly skeptical because the JPI indicates the hangar temp, though the k/y error difference compared to a wall thermometer could be too small to notice.
 
Change your temperature serttings on the JPI from reading F to reading C... that will bring them right down from 400 degrees to 200 degrees straight away. :D

(Stick with me for more engine tips!)

I like Walt's idea.

I'm running a Superior IO-360 in XTC (Vetterman Exhaust but vertical sump) and to begin with the CHT's were all on the high side however they've certainly settled down now. During Phase I we had to be mindful of the CHT's prior to take-off and even on a typical Spring day with temps around 40F the takxi time was kept short. We saw temps peaking up to 410 F in the first 5 hours. Now, after 150 hours of operation these are always steady around 340 F all day long with peaks on a hot day of 375 F as we launch.

How many hours has your engine got on it now?
 
I would also check you flashing between the intake/exhaust valve cylinder fins. Blockage in those can lead to higher temps but not like what you are seeing. Out of curiosity, are you cylinders painted in some nice polyurethane paint. Looks great, however, that can block heat exchanging abilities. I believe Lycon alodine's the aluminum end of the cylinder and paints the steel barrel portion. In engines with higher than normal compressions and EI, you could be at the tipping point of potential heat exchanging abilities.
 
-Upper ramps in place?
-What's your fuel flow at full power?
-Any chance there is excess flash between the cylinder fins?
-Inter-cylinder baffles correctly installed?
-All baffle gaps well sealed with RTV?
-What are the lower cowl intake seals you mention?
-How many hours into Phase 1 are you?
 
Many good suggestions, all have been considered or investigated. For those watching, it's not an instrumentality problem; the engine monitor is displaying reality. Fins are clear, paint is not an issue - out of the box Millennium. Plenty of fuel for climb (therefore cruise, obviously), baffling, seals, and wraps are sufficiently tight. 13 hours as of today. The break-in drop happened in the first hour. Since, almost no further reduction.

What has me stumped is this airframe and installation are identical to prior builds except for being Superior and horizontal; the engine is actually more mildly turned than the two previous 375s since we don't know what kind of corn squeezins and grass clippings lie in our fuel future.

I can manage temps with power, leaning, and speed right now. Summer's going to be a problem. I'll keep hoping this is something of a plateau and continued operation will lower temps (ala Planenutz) I've never seen this sort of persistence. Some points to chew on: CHTs stay within a range of 10 degrees, swapping between cylinders with variations in operation. Therefore I haven't bothered with #1 or #2 dams as there's no particular cylinder needing attention. As to those seals attached to the lower cowl that overlay the baffle ramps: installed or not makes no difference. Interesting.

Any other thoughts? I appreciate the suggestions.

Changing to centigrade!

John Siebold
 
I had high cht’s as you describe for the first 10-20 hours on my Titan 370 with 9.6:1 & pmags. It’s got a Sam James cowl and home brew plenum. I added the lower firewall bump and everything dropped at least 10 degrees. I also gained a few knots. I then cleared all the claptrap from the exit area and dropped a few more degrees. I added the anti splat cowl flaps just incase I needed them on a hot day, but have yet to really need them.
 
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