Bad Heater core or t-stat?
 

my truck will not warm up at idle even if you let it idle for an hour. But once you get moving the gauge moves to 190 and stays there. The problem is the heat doesnt work. I mean it somewhat works but its warm air not hot air so i will freeze during the winter. Is this a t-stat problem or heater core problem? truck has 240k on it so it could be do for both lol.

my truck will not warm up at idle either unless high idle is on. as for the heat i'd start with t-stat, cheaper of the two. if not you can always flush the heater core and see where that gets you.

probably a combination of the t-stat not working properly, and the evap core being clogged up not allowing much air flow to reach the heater core.


there is no air filter in these trucks for the cabin. so all air must go though that evap core first regardless of if the AC is on or not, then it can flow to the heater core, and to your vents.


this was my evap core when I went to do my heater core replacement:

Attachment 34693

all of that junk was in there clogging up the air flow...

works 100% better now that I replaced both the heater core and the evap core. (I tried cleaning it but there was too much junk deep inside the fins and I really didn't want to pull the dash again)

wow thats a dirty sob. glad my heat is hot as hell when its up to temp.

btw if you want faster idle warmups:

DAP is selling IAT foolers and has a smarty rental program going on so you can use a smarty for a couple weeks to flash a tune, then revert to stock with the smarty which will enable the factory cummins option of 3 and 6 cylinder high idle modes.

then the IAT/ECT fooler will give you several functions once the high idle feature has been enabled in the programming.

it has a 4 position switch that does the following:

1 - stock passthrough (no fooling of ECT or IAT sensors)

2 - MPG setting (makes your engine think it's a hot summer day, so engine fueling and timing run in summer mode...great for winter time when your fuel economy typically drops 2-3mpg)

3 - 6-cyl high idle + ECT fooling for continuous run (makes your truck think it is below 32* outside to activate 6-cyl high idle mode. truck will idle at 1200rpm. also fools ECT to make truck think coolant is at a constant 123* to keep the mode running indefinitely until switched off)

4- 3-cyl high idle (makes your truck think it is below 15* outside to activate 3-cylinder high idle. this mode will rev the engine to 1200rpm after 1 minute of run time and then cut fuel to 3 cylinders causing an artificial load on the engine to warm the engine faster. this mode will raise EGT's to around 500-600* while idling. mode will shut off automatically when coolant temp reaches 170* or if throttle/brake pedals are touched.

once either of the modes start, you can change the switch back to stock or mpg mode and the high idle will continue till coolant temp reaches 170* in either mode..

also 6-cyl mode can be changed to 3 cyl mode even if 6 cyl mode is already started just by changing switch position to 3 cyl mode.

3 cyl mode can also be held indefinitely by changing the switch to 6-cyl mode after 3-cyl mode was already engaged.

also note your coolant temp gauge will not work while switch is on 6-cyl mode because of the ECT fooler.

I have personally tested this mode with large competition injectors on a warm day in my own truck to verify that the engine will not overheat with this mode using an external coolant temp gauge. my coolant temp peaked at 205* and never got past that. the cooling fan still engaged fine on its own without the ECT communicating with the ECU since the clutch fan is mechanically controlled, not electronically controlled.

(I was a beta tester for the fooler)


also to answer questions about the smarty: you just need to flash any tune, then revert to stock with the smarty to enable the high idle feature. (smarty's version of stock is not the exact same stock that dodge put in there originally, hence high idle being enabled. the change is permanent unless you take the truck to dodge and have the ECM re-flashed)

the IAT fooler is not required for high idle to work once enabled by a smarty. It will enable on its own if the outside temp conditions meet the conditions of the software.

conditions = if intake temp < 32*F enable 6-cyl high idle mode
if intake temp < 15*F enable 3-cyl high idle mode

the IAT fooler just lets you enable those modes on demand regardless of actual outside temperatures, and gives the added bonus of the MPG fooler which fools the IAT into thinking it is over 100* F outside.

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no kidding! I was shocked to find it that dirty, but it explained the slight musty smell, and the fan sounding like it was laboring and low air flow...

it's all brand new now :tu:

new evap core, new heater core. no more leaks, and no more clogged air flow. flows great now! :rocking:

ok, ill replace the t-stat since its cheap. also, i got the truck warm and had the heat on and both heatercore hoses going into the firewall were both hot. does that mean it isnt clogged?

likely means inside the heater core isn't plugged up, but doesn't mean airflow in the box isn't working...

so your truck does warm up to 190+ and stays there on the gauge?

if so it's not a t-stat problem...

likely either a plugged up airbox, or your blend door actuator motor isn't working.

you will need a flash light to check that.

How do I check that? Do I need to pull the dash out?

no. under the dash just just below the floorboard on the passenger side towards the center console is a little motor mounted to the bottom of the hvac box.

that little electric motor controls the temperature blend door. (not the vent door as that is vacuum controlled...this one is electronic and controls air temperature only)

turn your temp knob side to side and you will see the small shaft between the motor and the airbox turn side to side slowly. if it turns fine, then that isn't your issue...if it doesn't turn at all even when you change the temp, then either the motor or switch is bad, or a wire got chewed through by a rodent...

Just checked it and motor turns in both directions