T-stat & control valve acting funky

[Magister88]

Hi everyone,

So about 1.5 years ago I replaced the t-stat as part of the cooling system refresh (hoses, sensors, rad, ET, WP etc..) and it was working fine engine temp around 93C.

1. Recently i started to observe the k-temp (my android unit shows the coolant temp all the time) and noticed that the engine reaches the 93C fairly quickly and stays there between 91 - 96 driving locally. However on highway driving while accelerating it can drop as low as 81 degrees. before slowly climbing back up, given i keep thing constant. it does take some time to go back to 93 and if i speed up it can drop back quickly to 88, 84 etc..
this t-stat is almost new from FCP Euro: Mahle Behr 11537509227. could it have started sticking open?

2. on another note seems my amazon heater control value acts up from time to time (also replaced it about 1 year ago). where the driver sides starts to blow really hot air while passenger side is normal. connected a scan tool and while the value shows as closed, the heater exchange on left shows 88-90C and right side shows closer to what the set point is. I guess it sticks open, did anyone of you replace it with the non oem version, seems OE it pretty expensive at $180 or is that the only way to go? rockauto has the gates and other brands for around $100. the amazon one was $40 (didn't think much of it when i got it).

Note: the t-stat temps still act the same way even of the heater value is working normally. so i do not believe its related.

Any input would be highly apricated.

than you.