My 91 Cherokee says it runs under 210 degrees and the heater will not blow hot air it only blows warm air. I just replaced thermostat, tested the heater core flow, replaced the heater hoses, and checked the heater control value.

 

You need to verify actual Temps with either a probe or IR thermometer first. Factory guages are notorious for being incorrect. It's also recommended by well known members to eliminate the heater control valve as they commonly fail.

 

Did you put in a 195 F thermostat? When i used a 180 F, my XJ would never warm up all the way, it would pretty much stay at 180 unless it was a long highway drive. You can always test the thermostat in hot water to make sure it is opening up when it is supposed to. I have had 3 bad thermostats and always test them now before I put them in.

 

Yes I put in a 195

 

The heater control valve may be opening only halfway etc.
Are both heater hoses hot ?
Temp sensor may be lying to you too.
Did you have heat before, or did you do the thermostat to get heat ?

Just wonderin' ...

 

Yep. My normal operating temp (according to the temp gauge) is 155*F. But that doesn't explain your underperforming heater. You did thermostat after weak heat?

 

Your blend doors inside the heater box may not be operating correctly. Also, what is the average outside temperature in your area when this problem occurs?

 

Recently had the same problem.
The solution was to replace the bad thermostat that was stuck open with a new 195deg one.

Your mileage may vary.

 

My weak heat was contributed to a leaking heater core. I replaced other parts when I did the core. Evap coil, blower motor and resistor.

 

Verify the temp of the heater hoses. I would eliminate the heater control valve as a matter of course anyway.

 

Approx. how much under 210?

Was it a 195 "FailSafe" stat?

 

The top hose gets extremly hot and the bottom hose gets warm and last time I checked the top hose was just getting steam in it I believe. I changes the thermostat to get heat.

 

Yes I changed the thermostat because of the heater not working well and the temp gage reading low but it did not change anything. My dad and I believe it may be caused by air getting into the cooling system but we cannot figure out how.

 

Right now it is around high 20s low 30s and even if it runs for a long time nothing changes. I have to have the heat coming from the window vents constantly because the heater is not warm enough to keep the windows defrosted

 

I say bypass the heater valve