Carbon Buildup Bilk?

Just paid $733.00 to my mini dealer for what they indicated was Carbon build up on intake valves, ports and injectors. Told me that this was a chronic condition with minis since most gas contains ethanol which leads to this build up- caused engine check light to come on. Indicated it was not covered by my extensive extra warranty since mini considers this cleaning and not covered maintenance. Just wondering - seems to me this ought to be covered since it’s a designed in flaw of the engine. Solution I paid for was having the carbon blasted off with walnut shell sand blasting??? The additive to the engine and one time fuel additive. Have I just fallen for a real bilk job??

Since you haven’t given a year, mileage, maintenance history, OR - perhaps especially - any info about whether or not you’ve been having any problems with car, I’d say its going to be impossible to say. Was the car running poorly? Is it running better now? What else was done to it at this time

I will say that frequently those services subsidize the companies that make the equipment for doing the services, and the shops that buy the equipment. And once you buy the equipment - you have to use it.

It’s a 2009 and goes in for the usual maintenance intervals at the dealer, since the warranty covers all of this (normally) Mileage is just over 50,000. No problems were noticeable before hand; I do think it was a bit peppier when I picked it up. No other substantial work beyond the cleaning was needed.

Sounds like a load of male bovine droppings to me. Ethanol is a great solvent, so it would actually help prevent carbon buildup. Gasoline is also required to have detergents that also help prevent this. However, so-called “top tier” brands go beyond the required minimum and many manufacturers recommend that you use only such brands.

@Jimbob64…Let me break this down for you: They now have $733 of your money and you won’t get it back. Don’t fall for this type of thing in the future.

You might want to go poke around some mini forums and see what people have to say. You might find this thread to be of interest: Engine Carbon Buildup Problem census count

Here’s an old thread from here on the CarTalk boards

I had this problem on a previous car of mine

The carbon buildup was so severe, you could actually hear it rolling around

After the cleaning, all was well again

cigroller posted an interesting thread. Certain Minis are prone to excessive carbon buildup in the cylinder heads, the pics in his post show that. Let the carbon buildup get bad enough and you’re buying an engine rebuild or replacement. The walnut shell treatment has been around for BMW for as long as I can remember and it is effective.

Many years ago BMW(Mini), Toyota, GM, and a few others came out with specifications for detergent ability in gasoline that they thought would be the best for their cars. At that time, only one or two gasoline brands made the grade. Now many do. Stick with name brand gasoline.

$700 every 50K doesn’t seem like that large a price to pay for driving a Mini. You bought it because it’s fun to drive, not because it’s economical right?

I’ve read reliable reports from other mini owners with this problem, so I guess it was warranted. But I have no idea what a good price would be.

Any engine can get carboned up and is the root cause of a lot of EGR system problems.
It sounds like the situation was severe in your case because they had to resort to bead blasting with the intake removed, etc.

Sounds like an engine design poorly suited to the general public.
What price performance??

This sort of thing isn’t unheard of in direct-injected gas engines, which I believe this car has.

"De-cokeing cylinder heads on 1950-60s British autos was maintenance. Fortunately removing/replacing the cylinder head was not difficult. It required a brass scraper. For some reason U.S. engines were not plagued with carbon with the same fuel. They were coated with lead deposits.

Since it has come up, I have gotten curious about the internal “steam cleaning” of engines.


It seems a little weird, but make sense - I think. Presumably if one has an engine prone to carbon build up, then doing this once in a while would take care of it. Anyone have any thoughts about that method? Nonsense? Damaging? Plain crazy?

@cigroller, I have no experience with steam cleaning, but I know that spark plugs in cylinders with coolant leaks will get steam cleaned. So if steam will clean carbon off a spark plug, I guess it will clean carbon off other surfaces too.

And, hey, Nick Berry says it does work, so I’ll take his word for it.

And to prevent carbon buildup, never drive her under 3000 rpm in a forward gear. Ever.

Seems an unusual problem, but if it needed to be done, you didn’t have much choice but to do it. I guess that’s the question. Did it actually need to be done? Since the engine seems to be performing better, maybe it did need to be done. Probably best to assume you simply had a job done that needed to be done and forget about it. If presented with such a conundrum again, maybe get a second opinion is about all you can do. If you are a DIY’er type, this would give you a reason to buy one of those cool bore hole cameras to look at that area, threading it through the intake manifold. So an opportunity for a new tool, that’s one advantage.

The intake valves, ports, and injector area also are in the path of the intake airflow. It’s possible another contribution to the carbon build up is from the PCV system. Might be worthwhile to have the PCV valve assessed.