Help interpret my spark plugs

[alpinelakespilot2000]

Over my first 80 hours I've been chasing a relatively high #3 CHT. At ROP cruise, #3 generally tend to run about 20F higher than #4, and 30-40F higher than #1 and #2. Once OATs get above 75F or so, low 400's (400-410) on #3 is not unusual to see at 75% climb, and high 380s to low 390s is common if I'm running 75% or above at cruise. FWIW, #3 and #4 both come right down to match #1 and #2 if I run peak or LOP at 65% or less. I've been working at various baffle solutions but today during my condition inspection I pulled all the plugs and, as I guessed, the #3 plugs look significantly different than the others:



Is this an indication that my #3 is probably running leaner than all the others or simply that it is running hotter than the others? Anything else I can learn about my CHT symptoms simply from the visual condition of the plugs?

Thanks

[Russ McCutcheon]

#3 is running lean, the rest look good.

[PCHunt]

Carbureted or injected?

If Carb, I would first look for an intake leak.

If Injected, you might have an intake leak, or a "bad" (clogged maybe?) injector.

Now the experts can chime in.

[LifeofReiley]

Steve,

Looks like you're flying an O-320... look for an intake leak. Good Luck!

[alpinelakespilot2000]

Originally Posted by LifeofReiley

Steve,
Looks like your flying an O-320... look for an intake leak. Good Luck!

Yes, I am carbureted, thanks. Where and what do I look for to identify an intake leak? (Still learning much about aircraft engines!)

[LifeofReiley]

Originally Posted by alpinelakespilot2000

Yes, I am carbureted, thanks. Where and what do I look for to identify an intake leak? (Still learning much about aircraft engines!)

Check the hose from the sump to the intake tube and the flange gasket at the head.

[LifeofReiley]

Originally Posted by LifeofReiley

Check the hose from the sump to the intake tube and the flange gasket at the head.

I have also found the sump tube itself loose in the sump and sucking air.

[alpinelakespilot2000]

Originally Posted by LifeofReiley

Check the hose from the sump to the intake tube and the flange gasket at the head.

Thanks Reiley. So, is it mostly a matter of checking to see if the clamps at the sump and the bolts through the flange are tight, or is there also ever any visual indication of an intake leak?

Originally Posted by LifeofReiley

I have also found the sump tube itself loose in the sump and sucking air.

Would I be able to tell this just by feeling for a secure sump tube from the outside of the sump? Thanks again.

[LifeofReiley]

Hi Steve,

There should be a gasket at the flange going to the head.

If you are VERY careful and have some help, chalk the plane. With the cowling off, have someone you trust that knows your systems well start your plane and just idle it. You can then spray carb cleaner, start fluid heck even WD40 lightly around these intake areas we're dicussing. If you get an RPM rise, you are sucking air and have a leak. Always walk the wing tight, and do not get near that spinning prop.

[AK4x4]

A much safer way to check for intake leaks is to (with engine off) use a (emptied)shop vac with the hose attached to the blow side of the vac to mildly pressurize the intake system. Disasemble as nesassary and attach hose to intake with duct tape. With vac on blow spray everything with a dishsoap (recomened dawn)and water solution. Bubbles indicate leaks. Good luck and be safe, Russ