[supersport#69]

My 68 sat a couple of months not driven. It was also due for a coolant swap so I drained radiator and replaced 2 gallons Prestone ready to use.
I started it up and it ran at 180, then got on freeway and it went up to 190-195 going 65 on freeway. As I was driving it expected it’d go down to 180 but didn’t.

Can an engine run warmer after it sits a couple of months or something else going on? I was thinking maybe I could swap the rad cap.

Oh and it’s a stock 400.

[supersport#69]

Oh I also forgot to add when I first added new coolant I left the cap off thinking I’d burp it but before it even got to 180 it started spitting coolant out of the opening so I shut it off. Then I replaced some that spit out and put on the cap.

Why would coolant spit out without the cap on?

[dataway]

By now I'm assuming you've checked the coolant level after it's cooled down? Just wondering what the level is cold, engine not running.

Off the top of my head the only thing I can think of that would make it push out of the cap is more coolant flowing into the rad than out of it, since we know that's impossible it has to have gas (like steam) being introduced the system somewhere, like localized boiling.

How old is the thermostat?

[supersport#69]

I checked after I drove it and it was about 6 inches below the neck or so. I added nearly half gallon for sure after it cooled.. Maybe too much pushed out before I installed the cap and drove it?
Thermostat is maybe 2-3 years old. I don’t have an overflow bottle. Would it have stayed under 200 if thermostat wasn’t opening?

[dataway]

Just wondered if it had an old thermostat that might have been acting up.

I take it for another drive with the coolant at the proper level (cold) and see what it does. Bring it home, don't open the cap, let it cool down, then open the cap and see what the level is. If it's down again, repeat the process ( I'm assuming there isn't a large coolant leak). Sounds like you had air in there somewhere. Car was on level ground when you filled it right?