Oil Pressure - too high ?
 

Much fun and games yesterday, when I took my car out for a drive. After roughly 30-40 minutes of driving, mostly 30-50 mph but some fast sections up to 70 mph, I pulled up to a set of lights in Wilmslow which are located at the top of a hill on a slope. As I was waiting for the lights to change, smoke starting out from the drivers side of the bonnet - when I managed to park the car up, discovered oil was leaking down the oil filter and across to the exhaust manifold. Left the car to cool down, cleaned up what oil I could and drove it 15 minutes home. When I got home, checked again and the oil leak seemed to have stopped. Looking at the downpipe and underside of the car, it looks as if it's been leaking oil regularly - although regular oil checks by me have not shown drastic oil loss.

A bit of history here, I've been trying to locate the cause of a mis-fire for the last 6 months, the symptoms which ONLY trigger 10 minutes after the car is started from stone cold. The mis-fire typically happens regularly if revs are kept below 3000 revs for those 10 minutes, and has recently been accompanied by a strong smell of oil. Normally, turning the car off for 5 minutes and re-starting it prevents the misfire until the next day.

Yesterday, when the oil leak occured I experimented by revving the engine past 3000 revs before the time the misfire occurred. Roughly 10 minutes in, the car spluttered slightly but kept going unlike previously where the mis-fire was constant. And then, later the oil leak developed and was observed.

Now.... to the point ! I'm wondering wether I have an oil pressure problem ie. the pressure is so high it's being forced past the oil filter gasket ? Is it possible/likely that the engine could develop this much oil pressure, and how could this be a problem ? I'm not sure yet that the oil filter is actually leaking, it could be something above it leaking down. What are the symptoms of a failing oil pressure relief valve - could this trigger high oil pressures ? The oil in the car isn't new, but it isn't that old either - and most (if not all) of the usually leaking engine seals/gaskets have been replaced in the last 12 months.

I know I need to get an oil pressure guage onto it to check, but I'm trying to identify what points in the oil system I should be looking at/suspecting. Any suggestions, thoughts etc would be welcome.

Oil filter plenty tight?