haha i was thinking the same thing and probably not.

You'd most likely have to add a lot of liquid at a much lower temperature to shock it in such a way that something breaks.
and when you put seafoam in your vac line your adding a tiny bit at a time and not a lot anyway. I don't think the quantity is enough to affect very much.

Thinking out loud.

 

X2. 96 with 243k

 

Like someone above you said, you'd have to alot a good amount to potentially do harm. I guess when those places drain the oil and refill the engine is already cooled down a lil bit.

 

I had an employee tell me he wanted to use the old water trick to clean carbon out of a customer's car that only gets used for short trips.
I told him not to do it - just put cleaner in the tank to slowly dissolve it.
Next thing I knew the place was smoking up - he did it anyway! Using water or any kind of snake oil liquid is dangerous.
A chuck of carbon of stuck on the piston, hitting the top of the chamber. We had to take off the head and scrape it off! I made him do it. I deducted the costs from his paycheck and the cost of renting her a care for the weekend, then fired him.
He sued me - and lost!

Do it at your own risk!

It does NOT dissolve carbon - try it!

 

Ive never tried seafoam or anything claming to clean a block until After I bought a 94 zj 4.0 with 220000 miles I got tired of changing the oil and 2-3 weeks after I changed it its black as hell as if it was months since I changed the oil filter ect. So I
ran gunk motor flush as directed in the crank ran idle for 5 minutes. I was skeptical but to be honest I cant beleive the difference its night and day difference. just checking the oil in how much cleaner it is. I cant speak to any change idle gas mileage ect. My wife drives it. It definitely cleaned the heck out of that motor. It just looks like it should after an oil change not black 2 weeks later

 

Speaking of Seafoam anyone try/use Deep Creep? It seems to be WD40/PB Blaster based any reviews on it. No Sense starting a new thread on Seafoam.

 

I just started using deep creep on my last few projects and I gotta say it's worth the 11-12$ a can. It works like 5x better than pb blast does.

I recommend it, get a can and try it yourself, that's about the only way you'll be able to make your personal decision.