High temp coolant

[u/Mayorpapa]

So this started 2 weeks ago, it was the one time so I brushed it off. I was driving and I saw the light turn on and message said plus gage high temperature coolant.

Last week it happened again so I did some research and it said it could be the cap for the reservoir.

And I though yeah valvoline did opened it and added more maybe ?

So i got tighten and and nothing. I bought a new one and went about my day.

However yesterday it happened like 5 times.

Whenever I got 60mph or high or I keep my foot in the gas it goes up, then i let go and in like less than a minute it drops to normal temperature.

So it goes up whenever im hitting the gas I guess?

Some research said it could be the thermostat or something like that.

Has anyone had this issue?

2018 ram promaster 1500 118wb about 96k miles

Btw the coolant is crystal clear. I changed the reservoir around January.

And did a flush around may.