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Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 22903
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Hi - My Skoda Octavia 1.9 TDI MK 2 has developed a sort of

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Hi - My Skoda Octavia 1.9 TDI MK 2 has developed a sort of rasping\throaty\low noise when accelerating - this does not happen when not under load or idling. There is no appreciable loss of power and no whistling. I did overfill engine oil recently above upper dipstick mark by mistake. Any ideas would be much appreciated?!

I'd 1st check for an exhaust leak

The best way to find an exhaust leak is to run the engine from cold and feel around the exhaust joints with your bare hands - you'll have about 30 seconds before it all gets too hot and you should feel any escaping gas blowing over your fingers

if this is OK then remove the air filter and check that it is seated properly , not blocked up with leaves and that the intake trunking after the air filter box is all intact with no splits or leaks
Customer: replied 4 years ago.

Hi Matt - I did what you suggested but can't find anything. I've noticed a warning on the engine regarding damaging the cat in relation to overfilling the oil which I did (and have done on several occasions). Could it be the cat on the way out as I've haven't renewed it in 350K?!! It has also got a valeo replacement clutch with single mass flywheel which has covered 80k - could it be the release bearing? Many thanks.

Hello Richard

Blimey thats a lot of miles for any component

and yes if you overfill the engine it'll tend to burn the oil which then hurts the cataylst

that said one or two events won't immediatly kill the cat as they run very hot and burn off pretty much anything

and if the car is still passing MOT's then its likely the cat is fine

another thing to check for is an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for causing rough running.
As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.
Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.
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