mercedes question
 

hi.. i have a question will a bad monovalve cause the upper radiator hose to have pressure my hose is very tight also no interior heat thanks for the help.

Monovalve will affect cabin heater operation, so if that's your issue fix it.

Your rad hoses will do what they do and have enough of their own circulation paths that monovalve is not going to slow them down. If hard hoses are your issue, get your coolant system pressure tested.

mercedes benz question
 

ok.. will do thank you sir.

Plus, your hoses should be pressurized while the engine is running at operating temp...

A higher pressure means a higher boiling point (for your coolant) which is why your radiator cap will say something like "15lbs".

Disconnect your monovalve - it should provide full heat in all settings. They mostly fail by letting too much heat, not no heat, but it could be stuck or your climate control unit may not be sending it a signal. I'd check the aux pump right next to it; it's what pumps hot coolant through the heater core.

mercedes benz question
 

i disconnet the monovalve still no heat i check the valve and its working good is there anything else to check for i need some heat bad its cold thanks.

I had a similar situation. The thermostat was broken and stuck open. Little heat, car having a hard time reaching operating temp in cold weather and pressure in the upper hose almost all the time.

Not knowing your car model or year, if you have an auxiliary coolant pump (electric) and it's not working, that will affect how much heat you get inside the cabin, especially at lower RPM.

mercedes benz question
 

hi.. sorry its a 1993 300se w140 and yes the auxilliary pump is working.