A couple of months ago I was heading off on a 400 mile journey. I checked my oil levels at a service station on the way and it was very low, so I promptly filled it up, but I put in too much, prob 1cm higher up the dipstick than it should have been. I didnt think too much about it at the time, and off I went. The car drove fine and there was no difference in performance or economy. The level is now as it should be, well maybe slightly over but not much.

The past couple of weeks I get the feeling that power is down in the car, it's just a gut feeling but ofc without putting it on a rolling road I wont be able to say for sure. Do you think it's possible that the over filling of oil may be having an effect a few months down the line? The engine sounds fine.

Whenever my previous car was serviced, the oil level when checked on its return was always higher than the maximum on the dipstick...

It says on the Oil Cap filler too much oil can damage catalytic converters....

A couple of months ago I was heading off on a 400 mile journey. I checked my oil levels at a service station on the way and it was very low, so I promptly filled it up, but I put in too much, prob 1cm higher up the dipstick than it should have been. I didnt think too much about it at the time, and off I went. The car drove fine and there was no difference in performance or economy. The level is now as it should be, well maybe slightly over but not much.

The past couple of weeks I get the feeling that power is down in the car, it's just a gut feeling but ofc without putting it on a rolling road I wont be able to say for sure. Do you think it's possible that the over filling of oil may be having an effect a few months down the line? The engine sounds fine.

It has probably partially blocked the cat. That will take a bit of time to happen, but when it does it will reduce power output noticably.

Hmm, dont know if you've noticed my other thread about the eggy smell usually associated with dodgy cats on petrol cars? Maybe the 2 are linked to this issue of over filling the oil.

Have been reading that diesels dont need a cat to pass an mot, so might just get it removed and replaced with a straight through pipe.

It says on the Oil Cap filler too much oil can damage catalytic converters....

You learn something new on here ever day - in six years of owning a vRS I'd not read that!

Anyone care how much of an overfill would be the critical point? As I've said when the car's come back from service it's always been slightly above the cranked point on the dipstick - say up to 5mm. Not that I noticed a problem on my old car up to 64,500 miles when I sold it.

And how to solve it? (New cat?)

Edited 16 October, 201015 yr by DRJ

Shouldn't produce an eggy smell ona diesel, it's only a two way cat with no chemical activation unlike a three way petrol cat.

Depending on how overfull a little is ok, to much and the engine will start running on it's own oil and will rev flat out until either air is removed or it pops.

Yeah I read it shouldnt produce the smell on a diesel, but it does seem a bit of a coincidence.

So how do I find out if my cat is damaged then?

Depending on how overfull a little is ok, to much and the engine will start running on it's own oil and will rev flat out until either air is removed or it pops.

Yes - I see - so if the OP hasn't experienced that, the fact his car feels down on power is probably something else?

Not sure of the engine similarity ,but there used to be a problem on Vauxhalls ( I've seen it on Astras )with diesel engines ( usually the turbo version) and had it confirmed by AA , that too much oil contributed to engines failing to shut down on switch off - burning the sump oil by compression and over revving as per Techie's reply ( SMIDSY) .

Edited 16 October, 201015 yr by VWD

Surely, you'd only be down on power if the catalytic converter got so clogged that airflow through it was reduced and an increase in back-pressure up the line towards the engine occurred. That's not to say of course that oil loss through the CC won't seriously impair its exchange role and lead to failure of the MOT exhaust emissions test.

Given what's officially deemed as acceptable oil usuage for the Fabia range i.e. 1 litre per 1000Km and the well-known problem with blow-by of oil into the combustion chambers caused by blocked crankcase breatther induced crankcase overpressure, I would suggest that you would have to consistently overfill with oil before anything deleterious in the converter took place.

I would say that's what's more likely to happen is that the combustion chamber gets coked-up and that this effects the combustion efficiency reducing engine power.

Perhaps using Vpower or equivalent fuels, which i understand have better detergent properties, for a short while would do a minor decoke for you, if you think you have lost power.

Postscript

Dont know whether this helps

http://en.wikipedia.org/wiki/Catalytic_converter

Recently, on top-up before going on hols, I slightly overfilled my 16V 1.4 BBZ petrol engine with oil. Within a couple of miles of leaving home the engine management light came on. Presumably oil had reached one of the oxygen sensors in the exhaust. Anyway, all other parameters were OK and the engine wasn't misbehaving so I pushed on. Light was on all the way from London to Portsmouth (M25/M3/M27). When I re-started after on disembarking the ferry light was out and engine as normal. Presume that the high speed run had burn't out any of the excess oil out of the exhaust. Above wiki article seems to support that proposition. Vehicle then did 500 + miles on French Motorway at high speed without probs.

Again, given the standard operating envelope of these engines and the light grade of modern engine oils shouldn't be a problem. Only problem might occur if you were refilling with oil which had a zinc additive and apparently that would diminish the functionality of the CC.But the CC is probably designed with a certain degree of redundancy and all you would be doing is reducing its life as far as emission testing is concerned.

Nick

Edited 16 October, 201015 yr by Clunkclick

Ok will use the better fuel for the next few tanks. Is there any kind of additive anyone can recommend that will help de-coke?

I think dealer fill to a specified volume rather than checking on the dipstick and this volume seems to be above the top mark. Either dealers are overfilling, or perhaps the max mark is intentionally low to help prevent unintentional overfilling by the user.

It should just burn off the excess and I dont have a cat so it doesnt matter. Saying that, people who have Cats, it shouldnt matter that much really as there not needed for MOTs

Been out and bought some Redex Advanced fuel system cleaner, was quite pricey at £15 but figured it will do no harm.

Thinking about getting a Magnex de-cat too, not too expensive and gets rid of a part that can go wrong that I dont even need.

the other danger of putting too much oil in is it causes the seals to swell up as there is greater pressure in the crankcase. The oils looks for the best way to expell itself and usually this means damaged seals and bearings.

Been out and bought some Redex Advanced fuel system cleaner, was quite pricey at £15 but figured it will do no harm.

Thinking about getting a Magnex de-cat too, not too expensive and gets rid of a part that can go wrong that I dont even need.

Forte are very good and it does work.

Getting a decat is fine except it could increase the risk of turbo failure if it is over boosting. So it could be a false economy...i.e. you remove the cat only to **** the turbo

Edited 17 October, 201015 yr by newskoda

I can't see oil residues sticking around for long on the cells of a cat at - what? - 650 degC?