6.0L Power Stroke Engine and DrivetrainDiscussion of the 6.0L Power Stroke diesel engine and drivetrain in the 2003-Up Super-Duties and Excursions. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 6.0L Power Stroke engine.
Can any body answer me the question of which way does the coolant flow in the heater circuit of the 6.0. On the 6.0 bible pages it says that coolant goes out of the steel pipe on the top of the right side of the engine to the heater core. but a few pages later an arrow pointing to the pipe says that it is the heater return line. also has any body noticed if there heater output temp changes when they stop at a red light then warms up as soon as the engine rpm's come up when the light turns green. the temp gauge on the dash does not change when this happens.
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2003 F250 Larait Grey/Black 3.5" lift 33" tires Bully Dog Tridog with Outlook monitor MBRP 4" ex. KC sunshine out front
Your heater uses coolant to create heat in your heater........ Diesels cool at idle (though at a stop light it should cool enough for you to notice)......... Chance are, your headgaskets, EGR cooler or oil cooler (or any combination of those) is bad.......
__________________ 2003 Toreador Red/Arizona Beige CC, DRW, Lariat, FX4, 6.0 PSD, Torqshift, born early Feb. 03, AIC, MBRP turbo-back exhaust, Tuning by Tony Wildman (Total Diesel Performance), ARP studs & some "other" work done by River City Diesel, AFE PG7, Fumoto valve, B&W hitch, Di-Pricol gauges, Voyager brake controller, DIESELSITE Coolant filter, Timbrens, Rancho RSXs, Michelin XPS Traction's, a whole bunch of "bling", Connex 4300hp, JL Audio 275w amp w/ 12" sub, Alpine door and rear seat speakers.
The "gauge" is a three position idiot light. Not warm, normal, and OH SHt. If it get to the red, stop immediately, you're already in trouble. Ford doesn't want pasky real gauges troubling the 90% of the driving public that doesn't pay any attention to them any way. Hell, if a gauge moved, somebody might bring it for warranty repairs.
I'd pay an extra $1000 for a good gauge set if offered as a factory option.
OMC
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Feb 03 6.0 Silver F-250 SD SC XLT long box, 6-spd 3.73ls, Fx4, Stock, Spray-in liner, Contico box.HARPOONED.
To answer the original question, the coolant flow through the heater core is correct the way you listed it. It's not uncommon for a heater core restriction to cause the issue you are having. A quick way to check is to feel both heater hoses when your concern is present. If the inlet is hot (almost too hot to touch) and the outlet is cool to warm, chances are your heater core is resticted. If both hoses are cool, then you should look into a cooling system issue.
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2003 Toreador Red/Arizona Beige CC, DRW, Lariat, FX4, 6.0 PSD, Torqshift, born early Feb. 03, AIC, MBRP turbo-back exhaust, Tuning by Tony Wildman (Total Diesel Performance), ARP studs & some "other" work done by River City Diesel, AFE PG7, Fumoto valve, B&W hitch, Di-Pricol gauges, Voyager brake controller, DIESELSITE Coolant filter, Timbrens, Rancho RSXs, Michelin XPS Traction's, a whole bunch of "bling", Connex 4300hp, JL Audio 275w amp w/ 12" sub, Alpine door and rear seat speakers. 
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