Seafoam in high mileage vehicles

I was thinking about using seafoam on my 89 honda accord which has (sadly) about 270,000+ miles. It's still pushing, but im doing an oil change soon and i want to clean out the engine, fuel tank, and vacuum line. but is seafoam safe?

i heard mixed reviews saying it's safe and unsafe. Is it true that if i add to oil crankcase, it might actually clean up too much carbon that the engine needs to seal?

And is it also unsafe to add it to brake booster line?

If the vehicle has had good maintenance for those amount of miles than there is no reason to use an oil system cleaner. Running half a can for 15 to 20 minutes and then changing the oil won't hurt anything. Dump the other half in the fuel tank and your good to go. Unless you can see the intake/throttle body is caked with carbon deposits than there is no reason to run it through the intake through the booster hose. If you do poor it in slowly on a hot engine. Use about half the can and then add enough to stall the engine. Let it soak and restart. The directions for this are all on the can.

I know for a fact that my vacuum lines have at least some carbon build up. i really want to seafoam it. so its it safe to use? im afraid of it hydrolocking. is that something i should be concerned about?

You can't run fluid through a vacuum port fast enough to hydrolock an engine....used to dump a quart of tranny fluid directly into the carb as fast as we could to clean up induction and combustion chambers back in the day....even that wouldn't come close to hydrolocking them.

Biggest concern in the crankcase is that if the engine is really trashy with deposits you can conceivably break enough crud loose all at once to plug the oil pump screen...then you've got trouble.

This happens in severely neglected motors though....if you've had reasonable maintenance, it won't happen.

i understand. thanks guys for your help!

For a little humor, do the seafoam in a ritzy area. After the soak, you'll wanna take her for a spirited drive. I kid you not, you'll smoke out a city block as the seafoam goes through the engine... hence the ritzy area.

I smoked out a biker gang back when I used some in my WS6. :)