De-coking petrol engine cost

tkharri

HELP!!!

I’m not really sure where to go and hope someone can help. 
I have a Peugeot 308 (65 plate) auto transmission. It’s had many, many parts replaced over the past 2-3 yrs. Eventually the whole engine was replaced (all under manufacturers or extended warranty). The problem is the new engine is now starting to fail. 
The original engine was de-coked as this was the first step in the process of fixing the engine issue. As the issues continued more and more parts were replaced, again I was told by the dealership they had to follow a process. 
Now the new engine has been in for a year, the same issues have cropped up again. So, the process starts again. De-coking was done this week and extended warranty have decided they won’t cover the cost (even though manufacturers warranty covered it previously).

My question is - why does a modern, new petrol engine need de-coking? I average 10k miles per year. It’s either sat on the drive (I work from home) or its up and down the motorway (albeit only 1 or 2 junctions South - 30-40 miles) and a short journey to Tesco once Or twice a week. 

Both the mechanic and I believe there’s something fundamentally wrong with the car but how can I prove it to the manufacturer and who is liable to pay for the de-coking that the dealership went ahead and completed because they were on the understanding extended warranty were paying. They’re now chasing me even though they didn’t give me an option to decline the work - just completed it. 

angrycrow

I guess this is a prince vti engine. These are direct injection engines which simply means fuel is injected directly into the cylinder.

On non direct injection engines fuel mixes with air in the intake and passes over the intake valves. The petrol acts as a solvent to clean any oil or carbon deposits off the valves keeping them clean. 

In your engine no fuel passes over the valves so contaminants build up and can eventually reduce the size of the intake port reducing the engine power. 

The issue is made worse by the Peugeot engines using a lot of oil which finds its way to the intake valves via the oil breather system. 

What they are doing is not decoking as used to be done where the cylinder head and pistons were cleaned. What they do is media blast the intake valves and then suck out the debris. This works fine until it builds up again. 

Does yours use a lot of oil, 1 litre of oil per 1000 miles is not unheard of and not considered a problem by Peugeot. 

roddydogs

? Are we back in the 1950s? Engines still need de-coking?

daveyjp

De coking was needed previously because the tolerances in the manufacture of engines, fuel and oil quality and the timing of the combustion cycle were woeful.

We now have engines and components made to microns, fuel and oils manufactured to excellent standards and combustion constantly monitored by computer and adjusted accordingly.

Any build up of carbon due to incomplete combustion of fuel is therefore down to fundamental issues in the design of the engine and combustion cycle. Get it fixed and shift it on.

Dr_Crypto

De-coking? Is this the 1940s? Maybe on an Austin Princess you needed to but hardly now! 

AdrianC

It's a genuine issue that's returned with direct-injection engines - but, as angrycrow said, differently. It's not the piston crowns and heads that need decoking, like it used to be. EGR and crankcase breathing means oily vapours in the intake air, especially if the engine's burning a lot of oil - but direct injection means there's no petrol acting as a solvent and detergent in the intake tracts.

waamo

I had a car with a Prince engine. Get rid. It will be nothing but trouble. 

Mutton_Geoff

Dr_Crypto said:

Maybe on an Austin Princess you needed to but hardly now! 

Reminded me of the old "Will Carling goes into Halfords and asks for a packet of condoms" joke ;-)

mattyprice4004

Dr_Crypto said:

De-coking? Is this the 1940s? Maybe on an Austin Princess you needed to but hardly now! 

You've clearly not had the joy of dealing with these awful engines then...! 

Paula_Smith

Mutton_Geoff said:

Dr_Crypto said:

Maybe on an Austin Princess you needed to but hardly now! 

Reminded me of the old "Will Carling goes into Halfords and asks for a packet of condoms" joke ;-)

Please remind us of that one.

AdrianC

Mutton_Geoff said:

Dr_Crypto said:

Maybe on an Austin Princess you needed to but hardly now! 

Reminded me of the old "Will Carling goes into Halfords and asks for a packet of condoms" joke ;-)

Topical jokes go a bit stale by the time the subject's been out of the news for a quarter of a century...