4G15P 's coolant intake should be @ #3 ( hottest ) cylinder

, then coolant can go to #2, 1 & 4.
Present intake @ #1 causes #1 to be the least hot : spark plug ( even the hottest type - NGK 5ES ) fouls > 3 other cylinders', if oil used is synthetic & very viscous i.e. conducts heat fast.
I insert steel wool into gap betw coolant pipe & exhaust manifold, to transfer heat into coolant to heat up #1 spark plug, but the other 3 cylinders are now hotter than necessary i.e. less effficient.