I have been using Seafoam for a while, as I (still, actually have) a Camry with the notorious sludge monster they call the 5SFE I4... '00 w 298k miles on it and it has never had to have more than regular maintenance (engine and gears are uuntouched aside from pkugs/VCG).
I got it in the early 00's w 49k miles, and it was supposed to just be a means of getting places and then selling it but it is so darn reliable I can't get rid of it.
Anyway, Seafoam has been critical to keeping the immense amount of blow by (the PCV system is poorly designed, so the TB and IM get covered in oil fast) to a minimum.
The first time I gazed into that black void, I knew it would be a perpetual issue, and Toyotanation member recommended SF for manually cleaning the throttle plate.
I have been using it for the vast majority of the long life of the vehicle, and it has only been beneficial.
What I do is, since I run short OCI's due to it being the car used when short trips are in order (3k, now 4.5k w syn; switch around between Rotella T6, RP 0w30, RL 0W30, PP 5w30, and a few very high cleanliness dinosaur juices), is the following:
- 1/4 to 1/2 bottle SI-1 and/or appropriate amount of Stabil Marine per fill up depending on the use it'll see
- Full bottle SI-1 or Techron a tank before the last tank prior to the oil change
- I add about 1/3rd the bottle of Seafoam to the crank about 500mi prior to change, and then 1/3rd to an empty tank immediately before filling up (get about 460 before light comes on), and then drive normally. Once the gas light comes on again, I dilute down the remainder of what's in the tank by adding 2 gal or so of gas 2-4x.
- When ready to change oil, I use the Deep Creep to manually clean the TB, PCV valve (which is replaced every 15k or so but this actually keeps the lines from sludging), and use my judgement regarding the condition of the parts as to whether or not to do the next part.
- if they're bad (more than light varnish), I make sure that the oil is fully up to temp, immediately shut off the car, and with the help of another person (sitting in the driver seat to start and stop the car), I let the engine suck about 1/3rd a can of Seafoam through the brake booster line as quickly as possible without stalling out (I also spray it through the throttle body throat at the same time, getting the entire intake tract covered), and the car is shut off immediately before it's all in. I have borrowed a friend's digital scope, and it's clear that this distributes the stuff very well and very evenly.
- Wait 30-120min, and then start the car (everything reassembled). I take it out for the literal clouds of smoke to dissipate (well, hasn't been terrible in a long time), and get the oil hot and then run the car hard to burn off anything sticking around and especially off the cats.
- Come back, wait the 3min it takes to get the car on my lift, and drain the oil hot (the lift allows me to angle the car, about 8 degrees, in any direction, which helps ensure everything is out).
- Once it hasn't dripped for 5min, the engine is empty and also cool, so I just finish the change.
Car has never burnt so much as a mm on the dipstick worth of oil, and there iszero asludge as determined when the VCG was replaced a second time just this summer (also dropped the pan), and all seals are in excellent condition.
I love the stuff, and it does work semi-preventatively for cases like mine. However, I would not be pouring it into my M cars' cranks (I do use it in the gas and to manually clean intake manifold and TB's).
MOST IMPORTANT THING is that you have an extremely Stout oil in there, and it has to be changed well before you would even begin to think about additive wear out or loss of TBN, making oils like RP (PAO), the insanely additive packed Rotella T6, and especially the ester based RL (holds its TBN insanely well, and I have used RL alone to clean sludgy Bimmers due to the strong reaction of the ester base stock), ideal.
Anyway, that's gotten me this far on that car, and I bet it will hit half a million without a hint of drama.