Yet another high temp post... but with a twist.

[FasGlas]

RV7 with a 390 and Hartzell carbon prop... First flight of the day the CHTs will go to 425 degs cyl #3 and cyl #2 410 degs , oil 193 degs. Slow climb 20in 2400 RPM. I gain some altitude and try to cool it down. Fly to my destination.. Now the twist.... after a few hours I take off and the CHTs for #3 and #2 are much lower climbing. High 300s, oil is the same at 193 degs. I installed cowl flaps but that didn't change anything. I'm running Shell 100w plus. My first thought is the oil thinning during the first flight and warmed up thin on the flight back. Anyone heard of this?

 

[Walt]

Nothing to do with ‘oil thinning’. I would first suspect a fuel flow issue.

 

[bjdecker]

Check baffles, timing, fuel flows.

 

[FasGlas]

Nothing to do with ‘oil thinning’. I would first suspect a fuel flow issue.

Fuel flow is the same ~18 GPH down to ~15GPH at 20in 2400rpm while climbing. Timing - Slick 20degs, Lightspeed (don't know). Baffling - just replaced all the silicon, resealed all the joints, taped any gaps. The temps are lower on the second flight from the reseals but does not solve the "First Flight temps". So it's not fuel, timing or baffling.

 

[bjdecker]

Fuel flow is the same ~18 GPH down to ~15GPH at 20in 2400rpm while climbing. Timing - Slick 20degs, Lightspeed (don't know). Baffling - just replaced all the silicon, resealed all the joints, taped any gaps. The temps are lower on the second flight from the reseals but does not solve the "First Flight temps". So it's not fuel, timing or baffling.

Verify that the Lightspeed hasn’t advanced the timing beyond 20 degrees during high power ops.

Climb at 2700 RPM…

 

[Mikeyb]

I am almost always wrong about this but it could be instrumentation. If the temperature was significantly higher on the second flight the difference suggests the remote possibility the instrumentation isn’t properly applying the cold junction compensation.

But with the outflow of the fat blade Hartzell propellor and an IO 390 I would guess the CHT would never exceed OAT+300F climbing at full power and 100K airspeed.

 

[Mikeyb]

As an avid VAF reader I think your CHTs could be 75 degrees lower than indicated. These symptoms fit the possibility that the thermocouples are type J and the instrument is set for type K.

 

[dmattmul]

Post CSV's in zip format. CHT's for an AV engine should be below 400 F, OT is normally the issue with an AV 390. Something is amiss, suspect timing. Fuel flow looks "ok". Is this a new engine? If not how many hours? Cowl flaps not normally needed and just add drag. Mine (390 AV) don't go above 350 F in climb and in cruise LOP below 320 F. That's in Florida.

Type J vs K is a good guess, how are your EGT's ? What are ambient readings for your CHT's? Again, posting your CSV would help solve this issue.

 

[D-Dubya]

If you can safely do it at altitude, turn the Lightspeed ignition off in flight when the CHTs are high and see if that has any effect. If the CHTs start heading back down, then something in your Lightspeed ignition may be advancing timing. If that's the case, a call to Klaus would be in order. You could isolate the other ignition as well to test the Slick mag. But with what should be a fixed timing mag, that's less likely to be changing the timing...at least in my mind.

 

[FasGlas]

I have been questioning the if the Lightspeed is causing a problem. I have a gauge on the Lightspeed (Timing/RPM/MAP), I need to closely monitor that next. I need to check to see if it's got the right flywheel (Magnets at 40deg). I didn't build this plane, it has about 1000 hours. I don't think the probes are the problem, it's a Garmin G900X panel with Garmin probes. The Mag is set to 20degs. It has to be something that changes from flight 1 to flight 2.

 

[Walt]

I have been questioning the if the Lightspeed is causing a problem. I have a gauge on the Lightspeed (Timing/RPM/MAP), I need to closely monitor that next. I need to check to see if it's got the right flywheel (Magnets at 40deg). I didn't build this plane, it has about 1000 hours. I don't think the probes are the problem, it's a Garmin G900X panel with Garmin probes. The Mag is set to 20degs. It has to be something that changes from flight 1 to flight 2.

Just flip the LS off and see what happens.... you're not gonna die.