When do you need to decoke an engine

[thexav]

When is it necessary to decoke an engine or is this something that only applies to older cars. Do modern engines suffer from coking up?

Also how is it done, do you have to dismantle the engine or can you do this with tools and sprays through the manifolds and with fuel additives?

 

[HDi fun]

It used to be a 10,000 miles process 40-50 years ago. Modern ones can coke up. The biggest culprit is short journeys coupled with poor quality fuel. Although some engines are far more prone to problems that others.

Disassembly is the old way, however, chemicals can work wonders. They can also wreak havoc.

Stick with decent fuel, drive the car properly and the occasional can of BG44K or similar is very good at maintaining a clean engine.

The Turin technique is a good one, just make sure the engine is fully warm before undertaking this particular process.

 

[thexav]

Thanks for that. How do you know if an engine needs a decoke, are there noticable symptoms?

 

[HDi fun]

It can often suffer from pre-ignition (knocking or pinking) due to bits of glow carbon which ignites the compressed fuel air mixture.

Generally the performance will be down on standard, although the deterioration is a gradual one so often goes un-noticed.

I have never needed to decoke an engine mechanically - even going back to a couple of early 1980s cars I had, years and years ago.

There's much to be said for good fuel and purposeful driving (ie. use the rev range properly, none of this 5th gear at 34mph rubbish, which, incidentally is bad for the whole drivetrain.

 

[obi_waynne]

Just adding to this thread. Older engines injected the fuel which was sucked into the intake. Fuel acted as a cleaner and kept the intake tract nice and clear.

Newer engines employ direct injection where the fuel goes straight into the cylinder. They also recirculate waste engine gases which contain unburnt fuel, oil vapour and other byproducts. These stick to the intake and build up over time into a hard coating. This really reduces an engines performance and economy so a decoke will be required.

New processes involve spraying cleaners into the air charge or using cleaners and small brushes and other tools to clear out the intake to the valves without requiring engine disassemble!

 

[T9 man]

I am not even sure if such a process is still even viable with all the super fuels with cleaning agents available these days

 

[obi_waynne]

The trouble is these fuels go straight into the engine now and not through the intake where the cleaning is needed.

The direct injection petrol is the worst. I know Audi quite well and the V8 TFSI Quattros and 2.0 TFSi all have an issue with this. Even the smaller tfsi engines are prone to some carbon build up.

 

[RobBentley]

You should have seen the intake on my B7 RS4 at 40k miles - what a mess. Felt like a new car after it was cleaned!

 

[RobBentley]

Fortunately for me the V10 TFSI seems to suffer a whole lot less. A guy I know locally with one took his intake off for a look at 55k miles recently and it wasn't that bad at all really.

 

[davalav]

My Cooper S and any car with the' PSA/Prince Engine' coke up. Around 40,000 miles is the regular decoke interval. I have seafoamed mine and performs much nicer.

 

[andy206]

Terraclean seems to be the way forward now.

I know a garage near me started this a few months ago and some of the results are pretty amazing

 

[obi_waynne]

BG also have a cleaning process which I'll be trying out next week so hopefully I can write up a report on it for you all.