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Ron, ASE Certified Technician
Category: Ford
Satisfied Customers: 35515
Experience:  23 years with Ford specializing in drivability and electrical and AC. Ford certs and ASE Certs
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A 2005 F-350 diesel. Heater won't get warm when in an idle.

Customer Question

A 2005 F-350 diesel. Heater won't get warm when in an idle. After motor is accelerated it will heat. New heater core, new thermostat. Temp door and selector have been check by the dealer and said it works. Fluid level is correct and correct antifreeze is in the engine. Nothing will make it heat in an idle. What is wrong?
JA: How old is the transmission? Have you checked the fuel filters?
Customer: Fuel filters have been changed monthly. Transmission is the original one to my knowledge.
JA: Are you fixing your F350 yourself? What have you tried so far?
Customer: We have worked on it here. Sent it to two different dealers and have over $2,000.00 in parts and labor and no luck.
JA: Anything else you want the mechanic to know before I connect you?
Customer: Other that I am frustrated, no.
Submitted: 6 months ago.
Category: Ford
Expert:  Ron replied 6 months ago.

Hello. My name is ***** ***** I am happy to assist you today. Give me just a moment to review your post, and I'll be right back with the help you need.

Expert:  Ron replied 6 months ago.

The common cause for this type of problem is usually a flow issue due to either you have trapped air in the system or the water pump is weak and not pushing the coolant as it should. Has the cooling system been properly bled?

Customer: replied 6 months ago.
I am not total sure, but the dealer changed all the coolant and heater core and thermostat. Where do you bleed it or how?
Customer: replied 6 months ago.
They also changed the water pump
Expert:  Ron replied 6 months ago.

The best way to bleed this system is with a vacuum bleeder. It work very well to get all the trapped the trapped air out and if it is trapped air it usually ends up in the heater core. It take a special bleeder tool to do this. See it in the link below.

See this link for the procedure to do it as well.

Expert:  Ron replied 6 months ago.

Since the pump is new then I would try having the system vacuum bleed.

Customer: replied 6 months ago.
Any other things that we can do to fix this that we should consider also
Expert:  Ron replied 6 months ago.

If the pump is new and the heater core is not restricted then there really in not much else that can cause this type of flow issue. If it produces heat when you get the engine up off of idle then it has to be a flow issue.

Expert:  Ron replied 6 months ago.

Give this a try and let me know the results and we can work from there is need be.

Customer: replied 6 months ago.
We have got the pickup bled with a vacuum bleeder and after sitting outside running for 15 minutes the air is cold. Same problem and same results.
Expert:  Ron replied 6 months ago.

Are you sure the heater core is flowing freely with no restrictions? Did they back flush it?

Customer: replied 6 months ago.
It was a new heater core. The dealer put it in. Not sure if they back flushed it.
Expert:  Ron replied 6 months ago.

It should not have needed back flushed if its new, when the heater stops blowing hot air if you place your hands on both heater hoses at the firewall where they connect to the heater core are both hoses hot or is only one getting hot?

Customer: replied 6 months ago.
We asked the dealer specifically that question and he told us that the flow was great. We did not observe it ourselves, but have to trust the dealer that he is telling us the truth, but who knows. By now, they just want us out of the their dealership and to forget about us.
Expert:  Ron replied 6 months ago.

Okay this is something you can check your self, warm the engine up , turn the heater on and when it start blowing cold air go out and check the hoses. If you have good flow through the core both hoses should be to hot to hold. Check this for me and let me know.

Customer: replied 6 months ago.
After working on it all day, here are some observations. When you take the hose loose from the water pump going to the heater core, it appears to be pumping a fair amount of water, estimated at close to 3 gallons a minute. On the return side where it goes into the engine block the amount of water is considerable less, estimated at half to one third the amount of water going to it. I suppose that the flow coming out of the heater core would be reduced because it has to pass through all the little tubes in the heater core. Speeding the engine up increases both sides by an similar amount. The water pump is new as we can see the pump in a few places and it new. We have no ideas. The amount of water coming out of the heater core appears that it should be enough to provide with some heat but who knows. We are not Ford mechanics, just an glorified version of shade tree mechanics.
Expert:  Ron replied 6 months ago.

Did you ever check both hoses with a warm engine and the heater running to see if they are getting hot?

Customer: replied 6 months ago.
they are. The water coming out on the heater side is steaming in the open air when we took it loose. Just wasn't a lot of it.
Expert:  Ron replied 6 months ago.

Okay so you back to a flow issue, If the system has no air in it as you have indicted then you have to wonder why the new pump is not pushing the coolant as it should.

Customer: replied 6 months ago.
What should the volume be? Is 3 gallons a minute enough or should it be more? We don't know. You have about 3 gallons a minute leaving the water pump and this is reduced by the heater core to about 1.5 gallons a minute coming out. Is this enough or is this too low? We don't know. If this amount is too low then either the tube coming off the water pump is blocked or the water pump is faulty
Customer: replied 6 months ago.
What do the specs call for the amount of water. The dealer is not going to just change the pump because we are unhappy. They have no idea and wish we would disappear off the face of the earth as we have been all over them. Like I said we have over $2,000.00 in this project right now.
Expert:  Ron replied 6 months ago.

The amount entering the heater core should be the same amount coming out. There should be no restrictions in the core. The problem seems to be with the amount flow you have from the pump. Ford dose not list any flow amounts . With having spent $ 2000 they should have been able to get you great heat. Something is being overlooked here and I am not sure what from here. I will open the post back up for you and perhaps someone else will have something new to add.