My car has developed a slight oil leak. It looks like it's coming from the oil filter cap, the part that unscrews holding the filter.

There's no visible signs the oil is leaking above the filter cap so I presume it's leaking from the seal.

I noticed the rubber seal was slightly bulging at one side. I replaced the seal and filter and all looked fine. Turned the engine to check and top up oil and the new seal bulged again and a small amount of oil leaked out.

Anyone know how to fix this?

I would suggest replacing the O rings that seal the filter. Best thing to do is just a full oil and filter service.

Have a word with your local kwik fit, I had an oil and filter service with brake fluid done for £40, was better than the other options I had.

When you fitted the new filter, did you ensure the seal was in the groove correctly and not 'rolled up' at any point? Never had this problem with an oil filter before so I'm only guessing

Could be a ventilation problem causin abit of too much pressure an the seal might be the weakest part?

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Yes seal was fitted square and snug, looked to be fine once tightened up. It was just when the engine started the seal bulged.

Too much pressure sounds likely, do you know where to start looking into this likely cause?

I noticed the filter cap actually has a hole in the side where the thread is. I initially thought this was the problem and was going to buy a new one, only to find the replacement would have the same hole.

What is this hole for?

This is a tread I started a while a go but the problem remains and is becoming increasingly annoying!!

After further investigation it appears the leak is actually when the engine is off (not what I originally thought). As the oil settles at the lowest point the seal may as well not be there as the it just leaks out (slow drip). The car is parked on a slight slope hence the leak is to one side, could this cause the problem?

I've also noticed when looking at possibly replacing the oil filter housing, all images show the cassette screwed snug to the housing. I checked mine and the cassette will not screw tight to the metal, a gap of about 3mm is visible, presumably for the seal?!? I tested this by removing the seal and refitting without filter or seal but the gap remains. Can anyone confirm what is correct here.

see here for example picture

On another note, does anyone know how to get oil off of tarmac??

unless the threads are stripped on the recieving side of the filter, I would still be looking at getting a healthier seal and checking the threads on the other filter.

threads look good, filter screws in with no problem.

The seal (o-ring) look fine - not sure how changing this could help? Are there different types of O rings?

I better point out this wasn't a genuine Ford oil filter, i'm starting to think this may be the problem.

Are Ford seals better than after market products??

Thanks,

They are more suitably designed. And if you didn't change the seal removing it and replacing would never be the same again. Definitely worth considering a genuine filters

Ford filter on order.

I think I have been fitting the O ring at the wrong point. Is it supposed to roll to the bottom of the cap or sit a bit off the bottom?

The way mine is fitted now the O ring is visible, I'm starting to think this is wrong.

Theres a recess just above where the cap meets the filter housing. An it sits in there.

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The filter should be snug against the I ring which should be unseen when it's all put together

Yep, I'm clearly fitting this wrong. There just doesn't seem to be a deep enough recess for the O ring to fit.

I'll check again.