little to no heat when at idle
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little to no heat when at idle
I have an 04 F-250 4X4 CC 6.3 Diesel.
I have just started to notice this since it's been cold, but it could have been going on for a while now.
I only get hot air from the vents/defroster when accelerating. If the engine is at idle (sitting at stoplight or going down a hill) it will blow cold to lukewarm air. I have checked the coolant level, and it is topped off.
I don't have any issues with it switching to the different settings for vents/defroster.
I tried checking out vacuum lines, but they all seem to be ok.
One thing I have noticed is the valve that controls the amount of coolant allowed to flow to the heater core doesn't seem to move when I move the temp control from cold to hot or vice versa. I just thought it was odd.
Does anyone have an idea as to what could cause this?
I have just started to notice this since it's been cold, but it could have been going on for a while now.
I only get hot air from the vents/defroster when accelerating. If the engine is at idle (sitting at stoplight or going down a hill) it will blow cold to lukewarm air. I have checked the coolant level, and it is topped off.
I don't have any issues with it switching to the different settings for vents/defroster.
I tried checking out vacuum lines, but they all seem to be ok.
One thing I have noticed is the valve that controls the amount of coolant allowed to flow to the heater core doesn't seem to move when I move the temp control from cold to hot or vice versa. I just thought it was odd.
Does anyone have an idea as to what could cause this?
FTE Leadership Emeritus
Joined: Jul 2002
Posts: 42,561
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From: Long Island USA
Might want to make sure the thermostat isn't stuck open.
It could also be a clogged heater core.
BUT - you most likely have a heater core shutoff valve inline in one of the heater core hoses. It might very well be stuck partly closed.
It could also be a clogged heater core.
BUT - you most likely have a heater core shutoff valve inline in one of the heater core hoses. It might very well be stuck partly closed.
Logistics Pro
Joined: Nov 2006
Posts: 3,685
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From: Fallon,NV & Bainbridge OH
Did you buy the truck new or used? If you got it used somebody probably put in a vacuum controlled valve as described on earlier posts. If it has one it sounds like it is hooked to the manifold instead of the vacuum pump. Typically the diesels don't pull vacuum but sometimes there will a slight negative pressure(vacuum) upon acceleration prior to the turbo spooling up which would allow the valve to open allowing hot water to flow throught the heater core. Look for a valve in the heater hose and either remove it or at minimum disconnect the vacuum line. Let us know what you find.
Good luck.
Good luck.
Logistics Pro
Joined: Mar 2002
Posts: 3,881
Likes: 84
From: Wake Forest, NC
The heater shutoff valve defaults to the open position, allowing hot coolant to flow at all times if it fails.
I'm not positive, but I think the superduties that came stock with the shutoff valve only did so with a/c on or in max a/c, so you may want to check those positions to see if it is moving.
Ruling that out, blockage may be evident at slower engine speeds. Does revving it up improve the heat flow?
I'm not positive, but I think the superduties that came stock with the shutoff valve only did so with a/c on or in max a/c, so you may want to check those positions to see if it is moving.
Ruling that out, blockage may be evident at slower engine speeds. Does revving it up improve the heat flow?
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Joined: Aug 2008
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From: DPR Kalifornia
You might wan to check that you have enough water/coolant in your cooling system.
With the syptoms you mention, it sounds like the water level could be low and it takes higher pressure from the pump to send water into the heater.
Good luck whatever it turns out to be.
With the syptoms you mention, it sounds like the water level could be low and it takes higher pressure from the pump to send water into the heater.
Good luck whatever it turns out to be.
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Thanks all for the great info.
I did buy the truck used, but I do not see any modifications to the stock vacuum system.
I have checked the coolant level, and it is full.
I did notice that the problems seems to go away if I have it running for 45-60 minutes or more. Most of my trips are short (5-10) miles, so didn't notice that until yesterday when I did alot of running around.
I don't believe it is the thermostat, as the engine temp does rise. With the current temp outside (10 degrees) I would expect it to stay quite low if that were the case.
Revving the engine does improve the heat drastically.
I did have the heater core flushed, which did make a small difference. It makes it acceptable to drive now.
I did buy the truck used, but I do not see any modifications to the stock vacuum system.
I have checked the coolant level, and it is full.
I did notice that the problems seems to go away if I have it running for 45-60 minutes or more. Most of my trips are short (5-10) miles, so didn't notice that until yesterday when I did alot of running around.
I don't believe it is the thermostat, as the engine temp does rise. With the current temp outside (10 degrees) I would expect it to stay quite low if that were the case.
Revving the engine does improve the heat drastically.
I did have the heater core flushed, which did make a small difference. It makes it acceptable to drive now.
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Logistics Pro
Joined: Mar 2002
Posts: 3,881
Likes: 84
From: Wake Forest, NC
Which means it is clogged. Higher revs push more water and more heat. To get it any better it will probably need to be replaced.
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From: Stephensville WI
Did you have the radiator flushed also? Was the coolant pump checked out?
If the heater core was plugged up, the rest of the cooling system is probably clogged up also. A weak water pump on top of that will make for little coolant flow while at idle.
If the heater core was plugged up, the rest of the cooling system is probably clogged up also. A weak water pump on top of that will make for little coolant flow while at idle.
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