Inconsistent heat

2019 Limited Double cab, 5.7L non flex fuel

Now that the leaves are changed and the mornings are cool, I have been running my heat.

At idle , or cruising at 55mph (1200rpm), the heat blows cool/warm. If rev'd up to 2000rpm, heat blows hot.

With an infrared temp gun, we checked temps in parking lot. Let the truck warm up (truck's guage was just shy of half way).
At idle the temps as follows....
Temp at radiator 160 degrees
Upper Rad hose 160
Lower rad hose 90
in hose through firewall 140
out hose through firewall 114

If rev'd to 2000 rpm the firewall hose temps are 140/135. all other temps remained the same.
Ran the truck down the road a few miles and came back. temps remained same.

Coolant flush at dealer 6 months ago. coolant level full. popped rad cap, no bubbles.

Am I looking at a thermostat? other?

 

Have you owned since new? Is it possible someone put a 165 degree thermostat in place of the OEM?

 

I bought it new. Never noticed this issue prior....but maybe?

My tinfoil hat was on tight this morning blaming the dealership as I was just in for oil change/brakes last week. After that is when I first noticed.
I guess I wouldnt know the part # without pulling it first.

 

Welp...took it to a dealer and they determined it was a thermostat (144.5 degrees) They didn't have one in stock so I bought an OEM thermostat and had a local indepedant shop put it in. Didn't fix my issue. Still cold/warm.

Can one of ya'll put a thermometer on your vents and offer your readings? With an infrared gun I get 110 at idle and 135 at 2000rpm. Curious if yours is the same.

Thanks in advance.

 

Fan speed and water pump speed will cause temperature differences. Try reading the temps at a given RPM and fan setting. I have a 21 and a thermometer and can repeat your test and provide my results.

 

fan setting is high as it will go, vent only, 800rpm/2000rpm (110/135 degrees)

 

Lemme warm mine up to operating temp

 

Thank You....results?

 

Ambient temps 60°F. Coolant temps stabilized at 180° per scangauge II. Took a few minutes for air temps to stabilize at dash vent between steering wheel and radio. 152° at idle and 162° at 2,000 RPM.

 

wow. Big difference. Thank you for the input. its appreciated.

 

You are most welcome. That's what this place is all about.

 

Is the passenger side output warmer than the drivers side

 

Blend door/actuator sticking?

 

Passenger side is cooler than drivers. I can hear blend door actuator when adjusted. At dealer now having thermostat installed. Will update in a bit if fixed or not.

 

Welp. Dealer replaced stat and bled system. Blows hot now.

 

Just in time for spring. How does the AC work?

 

So the independent shop didn’t bleed the system correctly?

 

It looks like either the stat was bad or the independant didnt bleed correctly, i guess? Will check the a/c later today.

I spoke too soon. After a 25 min commute it is testing cold again. 115 at idle and 140 at 2000 rpms.

Apparntly their fix, didn't fix it. I wonder if I have a small leak someplace causing air bubbles?? It worked great after yesterdays service. 135 at idle and 170ish on the way home at 70mph.

Temps are taken with an infrared handled temp gun held to the vent between steering wheel and radio with temp and fan on high.

Well, I put a temp gun on all the vents. There's a 30degree diference between pass and driver. Heater Core? Blend Door stuck? Oh, A/C worked great

 

I had a partially blocked heater core. It was hot on passenger side andcool to lukewarm on driver side. Not a fun job.

 

Replace the radiator cap.

 

Radiator Cap?
How do I know its bad?
Details please.

How did you deal with teh heater core? backlush it?

 

It's just a guess. I'm in a preventive maintenance mode right now. I happen to read a review a few days ago about the radiator cap. They have rubber seals that wear out. Its a maintance item. It's cheap and should be swapped anyway so it's worth a try.

Ps don't buy it on Amazon. Buy it your dealer or look up a direct quality fit at your local parts store. Don't get a universal one.

 

hmmm. okay. will get one on the way. thank you

 

Good luck! Hopefully it's just the cap and not a blocked heater core. I think it wouldn't be too soon for a clogged heater core. Unless a piece of the rubber on the cap fell inside.

This is why I'm replacing my cap and doing a coolant drain and fill on mine this week... amongst other things.

 

The radiator cap has no bearing on any of this. Beyond keeping coolant from spilling, its only job is to raise system pressure in order to increase the fluid’s boiling point.

 

Not sure you have fully nailed it down as a cause yet. You sometimes get heat and not other times a plugged core is low heat all the time.In my case, i back flushed for hours. Ended up replacing the core. Good heat now