#3 Running cool

[mike newall]

Just noticed our #3 running cool. CHT down 25f, EGT down 100f in the cruise at 23/23. IO-360, 350 hours from new, no other issues.

Pulled through 4 great compressions after the flight with no differences.

EGT probes are old on 1, 2 and 4 - planning on changing soon.

Ran comprehensive ignition check in the cruise, no difference so can't see it is a plug or lead issue.

Suggestions welcomed, may get the shufty scope down the plug hole next weekend.

 

[BillL]

Slipper cam? Hours? Have you owned since new? Did it happen suddenly?

 

[mike newall]

Std cam, 350 since new, new when we built it - 7 years in operation, well looked after, noticed recently, not suddenly.

Had heat issues for first year - all cylinders up to 400f, #3 was regularly highest but sorted. All run fairly evenly, say within 10f of each other, crept down lower.

Heck - it may have just run in !!!!!

 

[Toobuilder]

Curious to see what you come up with, as my #4 is doing the same thing. Still need to do the wobble test and check lift on the cam.

 

[Boyd Birchler]

I would look at whether there is a difference in egt/cht evident at full throttle altitude. When cruising at 23 square at say 3000 feet the inside of the manifold is below ambient, so it can suck air through a loose fitting or gasket. At say 8000 feet full throttle the pressure inside the intake manifold is virtually the same as the ambient pressure, a loose fitting or gasket will pull in very little or no air.

If the difference is gone at full throttle altitude, look for a intake system leak.
I would check the rubbers on the intake tubes, the elbows at the cylinders and on 200 Hp angle valve engines the "O" rings where the intake tubes go into the intake plenum.

Another issue is, did the idle change? At throttle closed idle, the difference between manifold pressure and ambient is the highest, potential leaks should(but not always do) leak the most. This would cause a change in Idle speed and often cause a "lean" miss during idle
.