Help! What's this leak?

I was driving earlier and smelt petrol. On investigation I saw this…

What’s the problem and what do I do to fix it please?

That’s the cam position sensor and the oil way for the VVT, oil concentration looks more around the cam position sensor, nothing fuel related there. I wouldn’t be concerned with that small amount of oil misting, give it a clean up with some brake cleaner and monitor it. The fuel smell will be something else.

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I’ll do that, go for a drive, and report back.

Could be wrong but can see what may be fuel in the area where a faulty injector seal might dump it. Be careful if you drive her. I would run the car stationary first to try a see if there is a petrol leak - don’t take any chances.

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If it’s the Injector seal, is replacing that seal a DIY job? Or is there more to it than remove and replace?
I’ll run it stationary first and watch to see if I can see anything happening.

The leak looks and smells like oil. Not sure why I smelt (or thought I smelt) petrol.
It has dried overnight and running the engine stationary didn’t create any more leaks. I wonder if that had built up over time…

The used oil in a petrol engine will always smell of petrol because of residues of the combustion process - this is totally normal and it will smell stronger the longer the oil has been in the motor.

The key to being able to differentiate is whether it smells of fresh petrol or not.

So, take off your oil filler cap, give it a good sniff and if it smells like that, I.e not neat fresh petrol, then it’s most likely the Cam position sensor seal.

Take it out by removing the single bolt retaining bolt give it a good clean with a rag and some brake cleaner or other evaporative solvent, do the same for the mounting hole and then check the O-Ring seal - is it in good condition? Overly compressed? Torn?

Make a judgement on it, then refit it and tighten the bolt up properly and see what happens.

Clean all of the spilt oil from the area thoroughly before refitting and then keep an eye on both the sensor and the cam cover gasket.

Ok, thanks. I’ll give that a go tomorrow.

Done. It’s all nice and clean now. The bolt came off very easily, I wonder if it was loose… The O ring looks in good condition, almost new.
I’ll post again if I notice further leaking.
Thanks everyone for your tips! :+1:

There’s still a slight leak from the Cam Sensor so I’m going to buy a new O ring. However I need more advice please…


MX5 Parts lists two different O rings


This one is relevant to the Mk2.5 VVT only (my model) and differs in description by including the word “Inlet”.


It says that I also need to buy an SI111 O ring as well.


The SI111 is the other one listed.


So my questions are, do I need both for my 2003 Mk2.5 VVT and do they both go in the same place or is the one for the inlet intended to go elsewhere?


I don’t think the ones you link to are correct. Much smaller o ring type seal is required, Autolink show a similar seal but they don’t mention it’s for the cam position sensor if as Robbie says above that’s what you need.
I might be inclined to smear some silicone gasket seal around that if you can’t track down the correct o ring. Take it off again clean it up and smear a little around the mating surfaces before reassembly.

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Or, you could spend £18 and be sure of a permanent fix…

I’m guessing the sensor seal is definitely defective, I.e torn?

If it’s complete/undamaged I’d be really surprised if the seal itself was actually the problem, unless it’s the wrong seal of course…

Most decent car parts places will stock o-rings of all types… Take the sensor to the shop and they will find one that fits for you.

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