Car fogs up and the heat is very weak. Could it be a thermostat?

Does the engine reach normal operating temp? Do you live in an extremely cold region? Are the heater hoses hot? Also, there could be a problem with temp door, under the dash.

This is normal if your A/C doesn't work. When set on defrost the A/C kicks on and off to keep the fog from appearing. the fog goes away once the heat inside reaches a certain temperature. Unless the drain is clogged and the plenum is holding water. Do you have ice on the inside? clean the drain. It's on the passenger side, near the bottom of the firewall. A rubber tube coming out, that goes to nothing.

no heat is probably low coolant or bad thermostat,although you have fog and smell ! the heating and cooling systems are closed systems the only way the windows fog is the coolant is hot and steams inside the car due to some leak inside the heater core box. as well as the smell being present. Now it is possible that a little leak has occured where the coolant supply or return line connects to the heater core and is running into the car which is running onto the core and creating steam and smell. hopefully it is a easy clamp tighten fix for you.

If it is fogging your windows, you have a leaking heater core. Dash removal is required to fix it.

New thermostat may be faulty. May be stuck open. Remove rad cap and with rad full and eng cold - start vehicle. The coolant should not circulate until eng reaches design temp of thermostat. Let me know if this helps you.

lets start with the heating up problem!
replacing the thermostat and relay has nothing to do with it. common causes of heating up are improper valve setting timing, mismatch air-fuel ratio, worn-out piston rings, poor oil flow, poor radiator coolant flow.
i suppose you have changed your car motor oil. recheck if its on the right amount.


loss of power:
Common Causes
loose piston rings (causing insufficient compression: indications fog like smoke), air-fuel ratio incorrect, blockage in air intake.

check also for air on the fuel hoses if you experience often jurking problems regularly clean fuel strainers or filters.

check the thermostat and heater core

Had the same issue .. turns out that the thermostat was stuck open .. replaced it, and all is fine now

chances are the heater core is clogged and wont allow proper circulation for the heater.i would suggest getting a new one put in and see if that dosent fix it for you.

If your smelling coolant in cab, and window fogging up, check fog if green heater core is going. Over heating could be a couple of things, plugged radiator, water pump, thermostat. To check for water pump Find the top hose, run car check for leaks on ground. While warm or hot wear glove oven mitt or something that you can feel through but will protect from heat, If you feel flow of coolant more the just a trickle its a good thing to replace thermostat. Also check for bubbles in the coolant tank, if there are bubbles your S.O.L. the head gasket is blown