Oil Caps for Honda Civic ED

An oil filler cap closes the opening used to top up the engine oil and keeps the crankcase sealed, so the ventilation system works as designed. The range holds aluminium filler caps made for particular makes, a 12AN cap, and sump plug adapters and magnetic sump plugs in metric threads.

The crankcase is not a closed box. Blow-by gas is drawn out through the ventilation system, and many engines hold the crankcase at a slight vacuum. A cap with a hard or cracked seal lets unfiltered air in, unmeasured too on engines with an air mass sensor, or lets oil mist out under load.

Most caps are made for one maker’s filler neck, as thread and locking styles differ. A sump plug adapter replaces the drain plug with a body carrying a 1/8 NPT female port, a common way to add an oil temperature sender in the sump.

Choose by fitting first, then finish:

• Filler caps: listed by make, in aluminium with black, red, blue, silver or gold finishes. One cap has an M37 × 3 thread, another is a 12AN cap, and slim caps save height where clearance is tight.
• Sump plug adapters: M12 × 1.25, M12 × 1.5, M14 × 1.5, M16 × 1.5, M18 × 1.5 and M20 × 1.5 male threads. Each has a 1/8 NPT female port, and an M18 × 1.5 blind plug is listed as well.
• Magnetic sump plugs: M12 × 1.5 and M18 × 1.5, in black, to hold steel particles at the bottom of the sump.

Tighten a filler cap by hand until it seats, and replace its seal when it is flattened, hard or cracked. Oil mist around a new cap points to a poor seal or to crankcase pressure; the latter means heavy blow-by or a blocked breather, not a faulty cap. NPT threads are tapered and seal on the thread itself, so the sender needs a suitable sealant.

Fit a sump adapter with a new sealing washer and tighten it to the engine’s drain plug figure. On a lowered or rally car, check that the sender is not the lowest point underneath.