Overheating issues

Question by onopolk7675 posted 8 months 3 weeks ago in SL-Class

1998 sl500 keeps overheating. Changed radiator, water pump, thermostat, hoses, clutch fan, resevour, checked head, no oil in water, no water in oil, no smoke or water at tail pipe, runs fine until temperature reaches 90 degrees +\- then starts to heat up. Water in reservoir boils. Hoses are hard with water but see or feel any circulation of water. Pump is new. What else could I check? Could it be a bad sensor or vacuum signal of some type for coolant to go to heads for cooling? I'm stumped. Please help