Our Peugeot 306 1.4 1998 is noticably 'popping' when sitting in neutral at 2.5k rpm (most noticable then, but certainly present at lower rate at
2k and possibly lower revs). Car has done about 101,000 miles.Engine runs otherwise fine, always starts first time and pulls away fine
- plenty of power etc.
When the car is at 2.5k rpm the popping is very quiet (from inside the car) - not loud - but clearly there in the background. Noticable enough for our 2 year old to say "pop pop"!! If I had to describe the sound and frequency at these revs, it's actually not dissimilar to the sound/frequency a bag of microwave popcorn popping! Certainly a 3+ pops a second.
Oil, oil filter, air filter, fuel filter and coolant (including flushing) were changed last month. Spark plugs were changed just over a year ago and have a new set ready to go in when I get the chance. We do around 10k a year. Most journeys are short to/from shops + work, but generally at least once a week do journeys 20+ miles. Maybe every month or so do 100+ mile journeys.
There has been a slight amount of mayo type gunk in the coolant - although I understand that lots of stop/start journeys can make this worse. Small amount of oil leaking from the front of the engine at the head gasket level (not rocker cover) - but don't really have to top up the oil much, if at all really (maybe every few months - less than 1/2 a litre each time - min to max is 0.5l I think, and probably half that is lost/replaced every few months). Coolant temp sits around 90 degrees (as has always been the case).
I wouldn't be surprised if the head gasket needed doing at some point (been leaking slighly like this probably most of the time we've had it - had the car since Oct 2001).
I don't have a compression tester (yet) - and when I tried changing the plugs before, I had difficulty in accessing the 4th - I think I didn't remove enough of the gubbins sitting on top of the engine - so I got a garage to change it just before an MOT. Once I've changed the plugs myself (and confirmed I can get access to all 4), I might invest in a compression tester and see what it might be.
Any suggestions as to what the cause of this popping might be - and is it serious (eg. for the cat etc)?
Thanks
David