Or, you need a long hill going upward with little traffic. Start at the bottom and pedal to the metal. And burn out the carbon. Do it several times. Nothing happens when a car sits. Except flat spots on the round tires. 3 yrs or 30 years. Makes no difference. The knock was there before when the car was run.

Example: I got a turbo Diesel. And it ran okay. Didn't think about the turbo for I never had one. It was driven solely on the ski hill, meaning the turbo never got used and as they were short hops, the engine never really warmed up. So the car was under-driven(no highway) I got the car for cheap and I have a 3 mile straight hill on a highway going up. So I drove it up there(standard shift) and slipped it down a gear and booted it to pass a car. The carboned up turbo "Kicked On" and my head was thrown back into the headrest.

. First time in a turbo. All my other diesels are natural aspiration engines. This power boost was a surprise. I looked out the rear view mirror and only saw a black cloud of diesel smoke as the carbon got burned out. Did this several times and the turbo worked fine. It had never been used. No seafoam, no nothing. Just drove the snot out of it.

And it finally slowed the smoking after the few runs. For I lived in the city, not on a ski hill.

Guessing your car has the same problem. Not driven hard enough(or you got automatic transmission...if so shift it down 1 gear into L2 and drive it up the hill.)

water does not compress and actually cools the combustion temperature. (EVAPORATION DOES THAT).

Back to water doesn't compress....this increased combustion pressure helps to dislodge carbon. only a small vacuum hose not the big ones.

to much water will be a bad thing...it breaks piston rings or worse it can bend a connecting rod.

marvel mystery oil (1/2 cup in a full tank of gas will safely do the same thing.

Is it a carbon knock or a bad rod bearing? you really want to buy a blown up engine? if it was carbon, they could just blow it out. Run, don't walk away from this one

Or if you like, trust a used car salesman, what has he got to gain by lying to you?

The product is called Seafoam. It's a petroleum based product and has instructions on how to put it in the engine. When it comes in contact with carbon, it sinks in and softens it so it will break up and get cleared out.

Was thinkingbof buying a fast project car and found a 92 dodge stealth twin turbo awd with 63k miles for 1000 bucks. Mechanic said it has a carbon knock since its been sitting for more than 3 yrs. What can I do to fix that? I dont know how it sounds im jus going by what my mechanic said since hes seen the car.