I've used seafoam several times on my own 240s, and couple of times on my boys cars. Usually after all the smoke is gone and yada yada yada, the typical reaction is HOLY SHIT.. Actually, thats the reaction every time. On my KA is smoothened out the idle, acceleration, and improved my fuel economy. I used it everywhere.. My buddys wrx went from being fast, to being a rocket ship.. The amount of smoke that came out was amazing.. His entire neighborhood had it's own cloud. Nevermind the highway.. that was absolutely rediculous.
On a side note.. if you run it, stay off the street as seafoam is potentially dangerous to other drivers due to the PLUMES of smoke shooting out of the exhaust.
On my Sr'd s14, I only use it in the intake. Nissan clearly states don't use any shit in the gasoline, as the cars are sensitive to fuel additives. So I stay away...
I don't use it in the crank case.. because.. well shit, if you need to clean anything in the oil system, your motor is fucked anyway. A motor with proper oil changes should never need chemical cleaning. Only sludged motors would need such service, in which case they are junk anyway. Or if you bought the car from a negligent owner...Yea maybe then too.
****************** PLEASE READ*******************
If for whatever reason you find the need to use it through the oil system, and the motor has not seen regular oil changes.. there may be raw chunky shit from the cleaning process in your oil pan. AKA.. you will need to remove the oil pan, and clean this raw chunky shit out. Motors with proper oil change intervals will not have raw chunky shit in the oil pan =)
Seafoam is known for ruining 1) Spark Plugs 2) O2 sensors. If you are going to run seafoam anywhere in your system, either be ready to change out the plugs and sensor(s), or swap in oil sensors and plugs before Seafoaming.
For example.. I have an old O2 sensor and 4 old plugs I swap in when I do seafoam. I run the car with the old o2 and plugs in for 2-3 days. Afterward, I swap in my newer O2 and plugs so as not to ruin them.
Like someone mentioned before.. Seafoam is a GREAT way to find exhaust leaks. Exhaust leaks will smoke like a mofo!!!!
Be safe kids
-Bart