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I recently started to see spotting of oil on the drive way when I parked up my 78 C3, oddly it appeared to be just behind the drivers side front wheel. After a run yesterday I popped the hood to try and locate a leak and found the oil being pushed out the rocker cover through the PCV valve bush.
I appreciate the oil pressure gauge in these old cars are probably not the best, but during the run it was at 80 and barely dropped when warm, its colder now then it was so I know the viscosity will be higher, but it should not be high enough to force oil out the seals - any ideas what might be causing this? Its a new issue, nothing has changed on the car for a good long time, engine temps seem fine so I guess the oil circulation is OK but the pressure seems really high
Its running fully synthetic 10w-30 (Castrol edge), oil has been in the car a couple of years, but its clean (very low mileage) - I know an oil change will probably be the best start, but is there anything else I should look in to while its up?
From: At my Bar drinking and wrenching in Lafayette Colorado
Oil pressure has no effect on whether or not oil is leaking from the PCV grommet. That's a non-pressurized area that only sees oil splash, irrelevant to pressure.
If oil is boing pushed out the PCV grommet it is an indication of the crankcase getting pressurized to force the oil out. This can be caused by:
Plugged or inoperable PCV. If the PCV is not allowing airflow/suction on the crankcase, oil can be pushed out by pressurization
Restriction on the suction side of the PCV system. If the car is stock, it wil have a PCV filter clipped inside the air cleaner. Is the filter clean and open?
Excessive ring blowby. If you have worn or broken piston rings, the amount of ring blowby will exceed the capacity of the PCV system, the crankcase will pressurize, and it will leak at the grommet as well as push oil out the PCV breather tube
You can easily test for ring blowby by getting the engine nice and warm and then pulling the PCV out of the valve cover. Observe if it's "puffing" oil smoke out the PCV hole, or hold your hand over the PCV grommet to see if you feel pressure or outward flow.
Lars
Awesome, thanks chaps some great advice, I will replace the PCV see if there is any improvement - for this "it wil have a PCV filter clipped inside the air cleaner" - any pics what this looks like, the car is not stock and I dont really have any history of it so not even sure what is/is not stock and I will also replace on the offchance (if I have/need one)
From: At my Bar drinking and wrenching in Lafayette Colorado
There has to be a breather in the passenger side valve cover, whether the car is stock or not. Verify the breather is installed, and that it's flowing freely. If there is no breather/fresh air inlet in the passenger side valve cover, that's part of your problem.
The PCV inlet air Air Cleaner Breather Crankcase Filter looks like this:
It installs in the air cleaner like this:
If you have modified your car to eliminate the stock system, you must replace the filter with some other alternative means of crankcase inlet air for the PCV system or it will blow oil out the PCV seal.
As usual mate you are a super star, the passenger side valve cover does have a breather and its only a year old, but ill get it off and give it a good clean but hopefully thats not an issue - the airbox looks nothing like the one pictured so Im going to say not original so I will follow the pipe and see where it goes, from a quick look it looked like it went in to the carb directly not via the filter housing.. but Ill double check
From: At my Bar drinking and wrenching in Lafayette Colorado
Only the PCV should be routed to the carb's manifold vacuum port. The passenger side breather must be vented to atmospheric air pressure, either inside the air cleaner or by being a free-standing vented cap to atmosphere. The passenger side vent should not be routed to any port on the carb.
This diagram shows the PCV system operation at idle and at light throttle cruise when there is plenty of manifold vacuum. When you "get on it," there is little or no manifold vacuum, and ring blow-by is at its greatest, so the crankcase gasses then reverse their flow and blow up through the passenger side air inlet supply, into the air cleaner, and get sucked down the carb's air inlet. If you do not have the fresh air inlet tube from the air cleaner, but have a vented valve cover cap instead, the blowby gasses are simply vented to atmosphere under high power settings. If blowby under power is excessive, or if the fresh air inlet system is restrictive, the blowby gasses will pressurize the crankcase and attempt to blow out the PCV with resultant oil leaks around the PCV grommet.
Oil Pressure Question
