Pulling a 7-8K load at 60 mph, had already traveled about 150 miles with no issues when in about 20 seconds my ect went from 196-198 and jumped to 230 and I immediately backed off while trying to find a place to pull off of the road and in the next 20-30 seconds the ect went down to a low off 177 and then eased right back up to 196. This confuses me because the eot stayed at 202-204 the whole time that this happened. After stopping I checked the degas bottle and it had puked just a little around the cap, not everywhere, and I installed a new cap about 6 wks before. After temps returned to normal I came on home without any more hiccups. Yesterday I ran the same route again with the same load and everything was normal.
Just wondering what is going on or about to happen.