Hi
4 days ago, my (2.5 V6) engine developed a knocking noise. The noise was only just audible initially, and seemed to be coming from the top of the engine.Over the last few days it's become noticeably louder.
At first, I thought it was down to the fuel I was using. I normally use the high octane stuff, but I was running short of fuel one night and I had to fill up with lower octane Jet petrol, and the problem started soon after this. When I'd used all of that up, I refilled with high octane fuel but the problem persisted.
The car has done 37k miles and has been properly serviced. It hasn't lost a drop of oil. It hasn't been thrashed, and I've never revved it hard when the engine has been cold. It's done mainly motorway miles.
I took it to a garage and the mechanic said it was possibly a worn tappet, and that it would cost a fair bit of money to put right. While I have to defer to his superior knowledge, in over 30 years of driving, I've never had an engine suffer this type of wear with that kind of mileage. I suppose there's always a first time though.
I took the car away without having it repaired, because I wanted to get a second opinion before having the engine taken to bits.
The performance of the car hasn't been noticeably affected. Once the engine revs abouve about 3,000 RPM, I don't hear the noise. Of course, that may be because the extra noise of the engine at the higher revs drowns the knocking noise out, but I don't think so.
Is there any chance the noise could be caused by something other than tappets, such as a faulty anti knock sensor for example?
Cheers
Pete