Heat not as hot as it used to be.

[jer]

Looking for ideas as to what might be going on here. I find that the heat in the TJ is no longer as hot as it was a few weeks ago. The thermostat was replaced this summer along with a new blower motor resistor. I have the blend door actuator for the heat blend unplugged and door set to full heat to eliminate that from the equation. I replaced the rad cap as well. With vehicle running, if i put my hand on both the thermostat outlet hose and the upper hose going to the heater core, they are roughly the same temperature. Oddly enough I can hold my bare hand on them and not feel they are unpleasantly hot. The return hose from the heater core is only slightly cooler than the feed line. I have noticed recently the coolant temp gauge in the dash seems to fluctuate at random times (maybe once every 100kms) from 91-about 98 degrees. Though because the needle "jitters" sometimes I suspect the sensor may be on its way out. I have checked that the vacuum line connection on the intake manifold that runs to the heater core is not leaking. So now, I'm not sure where to go in figuring out why the heat is cooler than usual. Perhaps a flush of the heater core? Or maybe the thermostat is failing prematurely?

[Dewie]

Sounds to me like maybe the thermostat is stuck open and it's just constantly cooling - when up to temperature the thermostat outlet should be quite warm...

[jer]

Though in being stuck open, the temperature on the dash reads properly 99% of the time. When it does start to climb, to add insult to injury I completely shut the heat off to see how high it will go. Once it reaches around 97-98 it returns to normal. Its very sporadic. The speed I'm driving seems to have no relation either.

[Dewie]

temperature reading properly isn't what I expected to hear... hmmmm

[T-Dogg]

I had a vehicle I had to partially block the rad in the winter to get heat.
which would also relate to a stuck open stat I think.

Da
Dogg

[jer]

But thats just it, the jeep heats up in the usual amount of time, and its not running colder than it should. Even sitting idle the heat does not change. The whole winter its had piping hot heat. Even on the days it was down into the double digits.

I replaced the rad cap because the relief valve no longer had tension against the seal. If the Rad cap had any issue perhaps there is air in the system?

[The Garagemahal]

I doubt there is air in the system after all this time
A heater core flush / cleaning might help ?
Or it's possible to have a faulty thermostat ?
I assume the over flow bottle has antifreeze in it ?

[derekmac]

When our old Grand Prix wasn't heating like it did previous years, I reverse flushed the heather core. Worked like a charm!

My Jeep's doing the same thing now, just haven't had a chance to flush it.

[frankenjeep]

*vote*
Flush the core

[jer]

Overflow did not empty. I'll flush it out this weekend and take measurements of air temp to see any change.

[Nightpath]

Jan 25, 2016 17:10:42 GMT -4 The Garagemahal said:

I doubt there is air in the system after all this time
A heater core flush / cleaning might help ?
Or it's possible to have a faulty thermostat ?
I assume the over flow bottle has antifreeze in it ?

This. I'd flush the core, it takes all of 20 minutes and is probably your problem. White gummy crap gets stuck up there, a quick flush will get rid of it.

[jer]

Just as an update. Have code P1281 in there now for "thermostat inactive". Seems like I'll find it to be stuck open.