There is a better method than just a simple pour-and-go for things like
Seafoam, Marvel Mystery Oil, and such.
My method for Seafoam is rather extensive. Ready for it?
Go and buy 4 cans of SeaFoam. Best price I've seen is at Advance Auto Parts.
This is a driveway method.
With your tank around 6 gallons (typically about half in most cars) pour a
full can into the tank. Drive the car about 1 mile, then allow to idle for a
few minutes, then kill it. Take the other can, and find the best place to
pour the liquid. The throttle body or carb is typically best, but anything
that flows evenly to all cylinders will do. After about 15 minutes of cooling,
fire it up again. Begin SLOWLY pouring in the SeaFoam. The engine will
stumble, but do not let it die just yet. If you need to, manipulate the
throttle a bit to keep it alive. When about 1/4-1/2 of the can (depending on
engine size. More for big 454 V-8's, less for 1.5L I-4s) is in the engine,
pour enough to kill it. Allow it to sit for about 1/2-1 hour. After it has,
fire it up. It will likely be flooded, so do what you must, BUT DO NOT REV IT
JUST YET. Allow to idle for 20-30 seconds, then floor it. Rev it from idle to
4 or 5,000 RPM. After a few bounces, maintain 2500RPM for 15 seconds. You
will be visited by a dark greyish cloud that ranges from annoying to the
firetrucks showing up. Drive the car around for a mile or 2. Idle for a few
minutes, then shut fown for 15. Repeat for the last half of the can of Sea-
Foam. After this is done, drive the car to as low as you dare, then pour in a
can of Seafoam and top it off. Save the last can for your next tank. This
method will blow away dang near any carbon that can be removed without a wire
The water method typically involves closer to 2 quarts of water, but it is
very important to do it slowly. With this method, try to keep the car running.
After you've done as much water as you want to (a pint will help, but 2
quarts will blow away) drive the car until all steam stops. Otherwise you'll
have water in your oil rusting your block inside and water in the exhaust
rusting it out.
Catalytic converters are designed to run hot, but not too hot. Overheat a
catalytic converter and the element inside begins to melt, blocking flow, and
if hot enough, will cause a fire.