I replaced my radiator, (after tank froze and split), with an all aluminum. I am having the same issue. I'm pretty mechanical and have checked all the obvious: leaks, oil, (oil is clean, constant level), etc., yet the radiator and coolant reservoir is always low after a long drive. Jun 06, 2016 · I have never seen a car with inadequate coolant with the reservoir having coolant up to the full mark when the engine is cold. If you want to be very sure, there is an easy way to do so - when the engine is running for some time, the coolant level in the reservoir will rise to above where it is when the engine is cold.
Guess what, empty! Checked dipstick and oil cap, no mayo and, interestingly very little by way of deposit on the tank cap since cleaned (same time last checked coolant level). Filled back to level and ran until warm checked all ok and took on run, level ok and temp bang on where always sits. Heater working perfect etc.