Not sure exactly...would depend on also if there's any water diluting it I suppose...
Not under pressure, (as in not in a radiator ) I think it's something around 250? Somebody correct me if I'm wrong...

If I had to estimate a temp. for soaking an engine, I'd say somewhere under 150...probably 120-130 would be close enough...

It will clean an engine at room temp. but it takes longer.

The best way I have found is to just look for wisps of steam just barely forming as you remove the lid off your slow cooker/crockpot...

Or...just hot enough for you to go "eeeooowww"[X(] when you go to pick up an engine out of there without using tongs, or something...

You can also smell it...like a melting candy bar or something...so you should do it in a ventilated area, because you don't want anybody or any pets close by when you're doing this.