I have a 1998 plymouth neon that is leaking oil from the filler cap, I have replaced the cap 4 times and it still leaks from this same spot. Any ideas on what it might be?
If oil is coming out of the filler cap, that would seem to indicate that there is a build-up of excess “blow-by” pressure inside the crankcase, and that situation would most likely be the result of a clogged PCV valve.
Even though a PCV valve is perhaps the cheapest engine part that you can buy, it seems that many people completely overlook this item when doing maintenance. Instead of cleaning the PCV valve, I suggest that you replace it, as well as the hose that connects to it. More than likely, you will find that both the valve and the hose are completely clogged with gunky material.
“If oil is coming out of the filler cap, that would seem to indicate that there is a build-up of excess “blow-by” pressure inside the crankcase, and that situation would most likely be the result of a clogged PCV valve.”
…or worn out piston rings and/or cylinder walls. :neutral: Hope it’s the PCV system!
Or both. It’s a 1998.
All engines have some blowby… That’s combustion gasses being forced past the rings. In new engines it’s miniscule. Old engines can have way too much. Blowby pressurizes the crankcase, which is openly connected to the space under the valvecover, on which the fill cap lives, through the oil return channels. Normally the excess pressure is vented into the engine’s intake through the PCV (Positive Crankcase Ventilation) valve, but if that’s plugged, and especially of the blowby is also excessive due to wear, the pressure buildup can blow oil up into the space under the valvecover and force it past the fill cap.
My guess is that both the PCV valve is gummed up, probably from oil being forced up under the valvecover, and your engine is worn to where you have excess blowby.
If replacing the pcv valve and making sure the hose is clear and air is flowing thru it doesn’t work, you have excessive blowby. You can minimize the oil loss by making a small hole in the top of the oil filler cap.