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6.4L believer
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Discussion Starter #1
Hi guys I have a question see if anybody can help, my friend has a 2003
F-350 with a 6.0L and we live in Canada but his truck when coming up to stop lights it will lose it's heat. He has checked the oil for antifreeze and vice versa, no coolant leaks, thermostat has been changed. Just looking for some ideas on what it could be any help would be appreciated.
 

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Sounds like a vacuum issue going on. It loses heat at idle, how about sit there in park and rev it up to about 2,000 rpm's and hold it there; see if the heat comes back.
 

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6.4L believer
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138 Posts
Discussion Starter #4
coolant is right to the full line and it never loses it
 

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matt
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Sounds like a vacuum issue going on. It loses heat at idle, how about sit there in park and rev it up to about 2,000 rpm's and hold it there; see if the heat comes back.
why would rpm affect that when theres a electric vaccum pump?
 

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Administrator
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it wouldn't but i see people post that all the time lol

there have been several of these threads and no one has posted the resolve ?
I think it's a coolant flow issue myself
maybe a bad impeller (common) of failed collant bypass valve , that is partially closed ??

when rpms are increased the pump flows more and gets it going to the heater core again ??
 

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matt
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it wouldn't but i see people post that all the time lol

there have been several of these threads and no one has posted the resolve ?
I think it's a coolant flow issue myself
maybe a bad impeller (common) of failed collant bypass valve , that is partially closed ??

when rpms are increased the pump flows more and gets it going to the heater core again ??
sounds to me like its a water pump bad if the coolant level is good and theres not a air pocket in the system
 

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How fast does the heat drop?? Give a bit more detail.
 

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It is bad headgaskets. Air gets trapped in the front cover and causes a vapor lock. Coolant flow stops to the heater core. Once you rev the engine up the water pump speeds up and blows the air out and it works like normal again.
Seen lots of these over the years. New headgaskets fixes them ever time.
 

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now there is an answer i never would have guessed, but it makes perfect sense. check the water pump first but if it looks good, sounds like HG's. if the pump was croaking you would think it would start overheating,so if operating temp is normal, pump is prob ok.

is there any other possible causes for vapor lock or is HG's about it?
 

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I heard that if the hg was blown it would get residue on the coolant cap.. Well mine in the mornings is cold untill I get some miles on it ,but the when I stop to its does the same it gets cold. And another thing Im always having to fill up my coolant like every 2 weeks but I cant see any leaks and I just replaced the Water pump last week.. I also checked all the hoses and the little grey line by the turbo and all the parts under the glove box.
 

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I have the same problem and it started before new gaskets, core flush and water pump. I figured the above would have fixed it but still no luck. I am thinking it has to be a vacuum line
 

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Fixing Broken Stuff
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I'd try flushing the hearer core.
 

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unexplained coolant loss good chance its HG's, before you actually pull them look very hard at every hose connection on every hose just to be sure. ideally with a pressure tester on the system(many times the leak is only while its cool)
 
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