Heater problem? - Ford Powerstroke Diesel Forum
6.0L Performance Parts Discussion What has or has not worked for you?

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post #1 of 3 Old 01-15-2014, 05:36 PM Thread Starter
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Heater problem?

So I replaced the T-stat this past weekend. Ever since when my truck idles cold air blows out of the vents.

-ECT is near constant on 190 at 65mph or at idle. (+or- a couple degrees)
-Heat t-stat set on 90
-Doesn't matter if it defrost, dash, floor or combo.
-If the engine is under load the temp is fine.
-Back out of throttle and drift air gets cool.
-Stop at a light and it goes cold
-As soon as I take off and get a load on the engine it's back to hot.
-All ambient temperatures.

Any ideas what could be causing this or ways to fix?


2005 F-350 Lariat DRW, Asheville Engines Performance 20 Long Block with ARP studs and a Stage 2 Cam. EGR Delete. SCT tuner. Salvaged Banks High Ram Intake Elbow, Ram Air Filter and IC. Amsoil lubricants, Sinister Coolant Filter, Edge Insight CTS, SP Performance Rotors and Hawk Tow Pads, Motorcraft fuel and transmission filters, Mishimoto radiator, thermostat and silicone hoses. BulletProofDiesel water pump and Heavy Duty Oil Cooler. Marty's Diesel Regulated Return
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post #2 of 3 Old 01-15-2014, 05:55 PM
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Have you checked the coolant level? When my egr cooler went out years ago the coolant level would get a little low and do the same thing. Good luck.

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post #3 of 3 Old 01-15-2014, 05:58 PM
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Have you ever flushed your heater core or looked at the condition of your water pump?

When thr trucks idling, and you have the heat turned on pop the hood and see if both lines going to the heater core are hot, if not your heater core could be plugged or your water pump may be worn out, also check the little heater core control valve that's on the passenger side under the hood. It controls water flow to the heater core. It has a gray vacuum line going to it.

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