around town on a hot so cal day it runs around 200-230ish. but as soon as i turn it off but keep the key on i see the temp spike very rapidly. i can hear a gurgling sound from the reservoir, even while sitting in the drivers seat.

once i turn the engine back on the fans kick in and it drops down to normal. i tested the fans while idling and they cycle. i recently had a tank on the radiator crack so i replaced those along with the upper & lower hoses, cap, and stat. i did the TB bypass awhile back however i have no current coolant leaks.

any ideas?

 

any ideas?

 

Low coolant or radiator cap is bad. Sound like the coolant isn't staying in the block and goes back to the reservoir. Don't see any other reason for the temp to go up that fast after shutdown.