Piston Slap: Oil Burning and Carbon Cleaning?

Sajeev Mehta
by Sajeev Mehta
piston slap oil burning and carbon cleaning

Arley writes:


I have a 2003 Jetta TDI with 178k miles. Runs 100%. My mechanic recommends a carbon cleaning. What are the positives and negatives? To be more succinct, what can go wrong?

You can tune a piano but you can’t tuna fish. (Good to know! – SM)

Sajeev answers:

Conventional wisdom (for both diesel and gas engines) is carbon buildup occurs more often when the owner subjects the engine to excessive idling and a severe lack of full throttle acceleration. Today’s direct injected, EGR equipped diesels (and direct injected gas engines lacking a piggyback port-EFI setup a la Toyota V6s) are sensitive to carbon buildup due to idle time, EGR design and cooling system inadequacies, and perhaps even fuel (i.e. varying quality of bio diesel). Don’t take my word, this company’s blog did a good job assessing the problem.


So carbon cleaning is commonplace and a good idea. And be it a seafoam-alike treatment or physical removal/cleaning of critical parts, there’s no downside if performed with even a modicum of care.

Question is, do YOU have a problem?

Considering your mileage (less idling and more highway driving?) and engine performance: probably not. Watch this video (go to 1:39) and DIY if you are even the least bit handy. From the video, make a trip to the parts store for vacuum lines too!

Or just do nothing aside from performing an Italian Tune-Up. That’d work for sure, and it’s totally fun.

[Image: Shutterstock user sasha2109]

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

Join the conversation
4 of 21 comments
  • Speedlaw Speedlaw on Jun 11, 2015

    I had my MDX carbon cleaned out, and it passed pollution and got a few more hp....definitely felt better after 100k. Worth the $175 for whatever they did. The car has been done by the book and then some, so it was up to date and always got The diesel TDI has been driven hard since oil change #2. Full temps and rpms are not unusual. I've some highways and one or two long uphills in the area. Hoping not, have read too much on BMW forums...I had a mad crush on the 335d but carbon appears to be the tragic flaw. There is much debate as to if US regs cause this. One must assume BMW and VW know how to make a diesel, but MB is on record as saying half of their engineers work on US emission issues.

  • Sjalabais Sjalabais on Jun 11, 2015

    When Volvo started selling its first V40 with the T4 engine - a petrol machine - there actually was a Volvo service note recommending an Italian tune up for every service. The instruction was to drive at 5000rpm for so-and-so-many-kilometres in order to reduce internal carbon buildup. I can't fathom how this could be a problem for any car blog reader though.

  • 415s30 415s30 on Jun 17, 2015

    One of the first things I did when I bought my W123 was cap off the EGR. Diesels are exempt.

  • TammyRice39 TammyRice39 on Mar 13, 2019

    Engine Carbon is headache for me, but you clear my thought regarding Carbon. thanks for the information. bets of luck for future.