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I noticed coolant level is low on the upper radiator hose (when I open up fill cap) Is this normal? I filled to the top a few times and later it lowers again to same level. I think it's going into coolant reservoir.

yeah thats normal. youll notice that if you keep adding coolant to the top of the fill cap your coolant bottle will start to fill up (over time). when your car reaches running temperature the coolant inside the system expands as it heats up. to relieve some pressure the thermostat dumps excess coolant into the overflow bottle. when it cools and contracts its supposed to suck the coolant back into the system, but it never gets it to 100%. youll notice the fill cap is the high point in the system so its not that huge of a deal. just check it periodically and fill if and when you think its too low...

Did you fill the overflow reservoir to the fill line when you topped it off? It should vary slightly, but not a huge amount.

If I remove the fill caps on either of my cars, I lose a little bit each time(They stay to the top of the filler neck)

That's bad design, especially having coolant temp sensors there. They probably don't read accurately and possibly has air pocket. On most other cars if I remove cap it's always up to the cap. I know my reservoir is full, unless I fill it all the way up?? Worse thing that can happen is it will leak some out as the car warms up.

I keep both reservoirs within 1" of the fill line, and it's to the cap every time I check it...

i guess so. on my old mx3 it worked the same as your describing. on my current one the actual upper rad hose is suctioned in a bit (when cold) and i assume the fluid level is at the top of the fill cap. if i loosen the cap the suction is released and the hose expands and coolant level goes down slightly.

i also dont think it would affect the temp sensor that much. when its cold the sensor knows its cold (lack of fluid for proper reading), by the time its up to temp the coolant has expanded and filled in the gap giving the sensor the everything it needs to send to the ecu. i may be wrong...


maybe your thermostat isnt working properly?

Probably nothing wrong, but coolant on my car is at the top of the filler cap.

The level should stay high enough that you can still see it from the fill cap. If it doesn't, try buying a new lower rad cap (with 12-15PSI spring and the little return valve)