The International Cessna^® 170 Association

A good friend of mine is using these sparkplugs in the bottom cylinder positions. He is still experiencing a lot of lead build up and as a consequence cleans and checks all of his plugs at each oil change. He asked if I would see what experience our members may have had with this particular model sparkplug. He is using them in an O300-D. He is considering replacing all his plugs and is wondering if the 37BY's offer others any improvement with lead build up. I have suggested he lean aggressively, but your comments will be passed on to him. Thanks

The advice you gave (leaning severely) will do more to reduce lead fouling than changing to a colder plug. The REM40E is a hotter plug than a “37”. The REM37BY specifically states it does NOT reduce lead fouling. What that extended-nose plug does is allow the plug to continue to fire despite severe fouling. (So unless he’s suffering misfires... that plug will not solve his problem)

What he needs is a hotter plug and aggressive leaning. If he is presently using REM40E plugs (the recommended OEM) and leaning aggresively an d still suffering from excessive fouling...then he probably has either carburetor or timing issues.

If all else fails, he might try Alcor TCP or Decalin “Runup” ....both products deigned to reduce lead fouling.

Is he certain it is LEAD fouling and not OIL fouling? Since you mention lower-plugs only.... that sounds more like oil fouling. This is usually due to worn valve guides and/or rings (usually guides). The solution is to repair the cylinders but a temporary fix is wire-electrode spark plugs.