While performing minor maintenance on a family member's 1990 240, I discovered that a mechanic had installed a NGK BPR6ES spark plugs, gapped at 0.40-INCH!!! I thought this was too wide, so I checked my manual. Haynes specifies a gap of 0.28 - 0.32-inch for a standard Bosch plug or equivalent. Then, I called a local parts store, and a clerk said the NGK plug gap should be 0.40-inch!

TO GAP, OR NOT TO GAP --- WHAT IS THE CORRECT GAP?
Should I re-gap the plugs to 0.28-inch? Or should I leave them at 0.40-inch?

I checked past Brickboard posts, and most guys recommend 0.30/0.32 as the norm. Why would a mechanic gap them at 0.40-inch? What damage could this have caused to the engine? If I change it to 0.30, what difference will this make on Fuel Economy? How will it affect Performance? I assume it will not correct a rough idle, since all plugs are gapped the same.

When I re-gap to 0.30, is there anything else I should adjust at the same time?

Also, which is better for a warm Southern US climate: NGK BPR6ES or BPR7ES ???

TEST CAR: 1990 240, 117k mi. New fuel filter, air filter, plug wires, flame trap OK, engine oil changed to Mobile-1 10W-30 synthetic fluid.

[[ southern fried volvo ]]