Spark Plug options

Brother

I currently run UREM40 plugs in my O-360 right now, but I see that 38’s are also an option. What differences would you expect to see from running one plug to the other?

Scott Sherer

Hi Paul,
Good topic. Let's see who answers. If you think it's necessary I can forward the question to Erich, our A&P.

Harley Kleemann

The 40 is a hotter plug than the 38. I know guys who switched from 38s to 40s to help with plug fouling problems. Some run 38 as the upper plug, and 40 on the bottom.

Brother

Why bother with 38’s at all?

arrow76r

I put "fine wire" plugs in the bottom positions on my cylinders as a hedge against fouling. Also, something I teach my students, just before shut-down (after checking for "hot mag") lean the engine to the point where it almost quits at about 1000 rpm and run for about 30 seconds to clear out any residual fouling.

BillCampbell

arrow76r, interesting statement about doing the hot mag check. I did that routinely when I was flying Cessnas. But from the time I started flying Pipers in circa 1970 we never had that as part of the engine shut down. It is not on any checklist which I have seen or been required to use flying Pipers. Is that a personal preference or hold over from your Cessna days? Also if you lean the mixture after start up, enriching only for runup and later takeoff, it will serve the same purpose of preventing plug fouling. I counselled my wife's instructor because of the soot accumulating on the nose wheel fairing. He found that my leaning suggestion fixed several problems.

Harley Kleemann

I always lean pretty aggressively when I'm taxiing out to the runway. Right before I do the runup, the mixture goes to full rich. I also lean it out again when taxiing back after a flight.

Jmcmanna

I also lean to max RPM on the ground (except for the run up). No issues with fouled mags. I forgot about the “hot mag” check though until it was just mentioned here...maybe I should add it to my shutdown flow.

Scott Sherer

Same here, Jim. BTW, how's the Arrow engine? When do you get it back?

arrow76r

The engine could lose a "P" lead during flight, hence the "hot mag" check just before shutdown. I insist my students do that from day one. Also, if you must move the prop after shutdown, it is a good habit to turn it "backwards" as then the magneto impulse coupler will not engage. BUT this practice "could" lead to excess wear on vacuum pump carbon vanes since they shape themselves to the normal rotation direction. Best idea is to not move the prop!

Jmcmanna

Based on the initial estimate, I should have the engine back around the first week of June. The only unknown at the moment is the engine mount; hopefully that will be sorted out this week. So far, no surprises with anything else!

Scott Sherer

Good news, Jim. I'm glad to hear it. Thanks for the update.