False positives are the normal failure mode of the coolant level sensor. I had to replace the one in WMBO's 1993 300E within the last year. About $20 for the part, IIRC.

Keep tabs on the coolant level. If it doesn't drop, then it's time to convict the level sensor. BTW, if you have the reservoir more than half full, you might lose some coolant due to normal heating and expansion. In that case it will, over time, drop to the normal level and remain there.

No pressure in the hoses is not right - they should be quite firm with the engine at 90C. Pressure cap on the plastic tank is the first item to replace. The plastic tanks are known to not last forever either.

Only 84 degrees? Must be nice.

- JimY