Thermostat is acting as if it does not close, or close completely. Engine warm up fine if idling, or running in slow traffic. Speed up to 80 KPH and the engine temp drops to half way between cold and normal. Speed up to 100 KPH and it drops right to the cold mark. Slow down again and it will come back up to normal.
Never runs hot. - It works great in regulating during hot running conditions.
I have replaced the T'stat and seal twice - same deal, assuming I have gotten a bad T'stat. I have heard that the rubber gasket/seal that goes around the t'stat can leak internally, allowing coolant to flow by the t'stat causing this type of symptom.
Has anyone heard of this - or experienced this?
Is there a solution better than keep on trying? I have used non OEM T'stats and seals. Might this be part of the problem? Might the OEM seal be a better choice in this particular instance?
TIA Mike