Adding Seafoam to the gas tank is a normal use for it. Its a cleaner like anything else you’d dump in. Its routine & nothing to stress over. I add a can of that or Techron once every 6mos or so to each of my cars. I have no idea if it does any good. But it makes me feel good.
The tops of the pistons should not be clean and shiny and how/why do you think the compression is too high?
I used Casite Motor Tune-up in the cars I used to own that had carburetors. I would add a can of the stuff to the gas tank and sometimes add it directly through the carburetor. I would then take the car out for a run on the highway–I would run the car up to a good speed in 2nd gear on the cars with a manual transmission or floor the accelerator to put the car in passing gear if it was an automatic. The black smoke would spew out of the exhaust for a few minutes and then I knew that the treatment was completed. This treatment would take care of the spark knock problem. However, with the cars I now own with fuel injection, I find these treatments unnecessary. If the OP is not having a spark knock problem, I don’t think that there is a real need for Seafoam. However, if it makes a person feel better to use an additive, it doesn’t hurt anything. I was taking Geritol to stave off the onset of geezeritis. I thought it was working well because when I would purchase a six pack of beer at the grocery store, the checkout person would ask to see a picture ID. When I found out that it was a newly enacted state law that anyone has to show an ID to purchase beer, my bubble was burst and I quit using Geritol. It did make me feel good for a while, however.
“The tops of the pistons should not be clean and shiny and how/why do you think the compression is too high?”
I did a compression test recently and all four cylinders were around 215 psi. According to my manual standard is 195.
If ALL the cylinders are reading 215 but the spec calls for 195…then it’s NOT that the compression is too high…it’s that your gauge is faulty.
Compression can build up due to increased carbon deposits. But NOT so uniformly. Carbon deposits are NOT common with fuel injection vehicles.
I’m also not convinced how well Sea Foam is going to remove carbon builup (if there is any).
It’s possible the gauge could be faulty but there are a few other possibilities. (Keep in mind that my Mazda experience is limited.)
The manual could be wrong on that spec. I’ve seen a few engines that would carry 210 PSI in good shape.
It is possible that if the piston tops are heavily caked up with carbon deposits that this could raise the pressure a bit. Whether it would bring it up to 215 is debateable.
Timing belt change and the cam timng is off; too much advance maybe. This affects compression pressures.
If the piston tops are heavily caked with carbon it’s unlikely that diluting SF in a tank of gasoline is going to remove it. You might need to feed some SF straight through an intake manifold vacuum line. If you do this the engine will smoke afterwards but it will clear up shortly.
You can also take a squirt bottle and slowly spray plain water into the intake system while operating the throttle by hand to keep the engine from dying. Water under combustion will cut through carbon deposits.
In the old days, if an engine had pistons that were heavily caked up with carbon deposits, the carbon would retain heat and cause pre-ignition (spark knock). In severe cases, the engine would turn over slowly when hot because the hot carbon would ignite the fuel coming into the cylinder and tend to push the piston down in the cylinder opposing the direction the starter motor was turning the crankshaft.
The OP didn’t state that he was having this problem. I think he is worrying about a problem that doesn’t exist with his engine.
“Timing belt change and the cam timing is off; too much advance maybe. This affects compression pressures.”
Yeah, I’m gonna check the timing marks to see if they’re off a tad when I do the stem seals. It doesn’t seem likely though, because the belt was replaced professionally by a quality shop with quality mechanics but I guess even they can make mistakes.
“You can also take a squirt bottle and slowly spray plain water into the intake system while operating the throttle by hand to keep the engine from dying. Water under combustion will cut through carbon deposits.”
Would the brake booster intake port work? How about the PCV port? Because I know when decarbonizing an engine through the intake it would make sense to use a port that feeds all the cylinders but how can you tell what feeds what?
The brake booster hose could be used but that creates a pretty large vacuum leak and could cause problems keeping the motor running while doing this. If a spray bottle nozzle fits snugly into the booster hose then it would work and feed all cylinders.