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chillie
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Discussion Starter #1
Good morning
I have a 98 dodge 1500.5.9. I have a heat problem. I have installed 2 new tstats.flushed system 3 times. Truck will heat up if truck is sitting idle the heat gets warm unless it is on high then luke warm at best. If I keep it around 2000 rpms it will blow hot air. I did find 1 vacum leak and fixed. If i drive the truck it will blow cold air until I hit the gas around 2000 it blow hoy then will go back to cold. Also I hear all doors moving. Any Ideas
 

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Probably still a vacuum leak somewhere..

Also, you sure you don't have air in the system somewhere? Might be some air that needs to be burped out.

My truck has average heat right now too. It gets cold and there's all these new threads from guys with no heat in their trucks. Search around the forum too eh.
 

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You have a vacuum issue. Check the vac line coming in to the cab and see if you have constant vacuum (idle and +rpm). I think there is a check valve on that line to before it gets to the heater box.
 

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chillie
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Discussion Starter #4
Ok So I replaced both Valves and when I move the dial for heat to cold it gets cold when I move the direction dial it goes to where I want it Def or floor. I found 3 leaks and 1 bad valve ( one way check valve). I was the line for Cruise. The other was the main going to the 1st valve. Where would I find the vacuum Reservoir? Also There is one line that goes through fire wall to under wiper cowl that was broke.Where does this go?..
 

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The power brake booster is your reservoir. The line you speak of sounds like the vac line. there is only one vac line that comes into the cab(small black hard plastic). It should go to the check valve before going to the main dial control valve.
 

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Theres a vac. resevoir (black rectangular...) under pass. side wiper cowl, that I believe is shared by HTR/cruise, but I am "unsure". Try reverse flushing the HTR core itself (powdered dishwasher soap,CLR,or...???) If you have A/C, select MAX/AC position, see what happens. I have same low RPM/poor heat issue, but I found a guy in Edmonton that still does acid flushes, will try that, or new core.
 

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chillie
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Discussion Starter #7
ok here an update.I went to a couple of auto stores to get a radiator flush. Only one they had and this was 4 stores was prestone super flush. Followed directions and flushed heater core then back flushed system. Heat is a lot better,Wish there was a stronger flush but all stores say that they do not sell anymore. Going to try to flush again I think this is the way to go. Will check some radiator shops see if they have the old way. or may just change the core.Will let you know what happens.
Thanks and Happy New year!
 

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Had the same problem. I finally took my 1998 Ram in and had the garage flush the system with a strong anti-corrosive agent they use and I also had them disconnect the heater hoses and flush out the heater core separately. I've now got plenty of heat. I've got a feeling that the heater core is just very prone to plugging up from hard water. Cost a $150 total, but I'm warm here in Wisconsin.
 

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sander06. very prone to plugging, X2; but on any type of water/fluid!!!. Ive owned 3 handfulls of used vehicles and never, ever, ever, had core and or poor heater issues like this. Half of them never got a flush. Ive got a feeling that the magnum pump/crossover may also be at fault.
 

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had the same problem, i just disconnected the hoses on either end of the heater core and blew compresses air thru it both ways, and then hooked a waterhose and flushed both ways, and once again compressed it, was all jammed full of gasket/gasketmaker from waterpump/ tstat changes probably, blows hot now after that
 

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mjans20 Is my jealousy showing? lol.
 

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Ok someone let me know if this is the fix I have had everyone around trying to figure it out.
 

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chillie
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Discussion Starter #13
Happy New year To all
So I have changed all Vacuum check valves,Replaced Vacuum hoses, Flushed the radiator,Changed the temp stat twice,I flushed the system 3 times with a little better heat but not enough. This week after the snow storm I said thats it.I went and picked up a heater core after finding out the price to flush the heater core $125. Thank You for the instruction on heater core change out. 2 hrs and I had heat wow I mean heat. pulling the dash was not bad. I did cut the tubes off the old. So After reading all with the same problems. The heater core was the problem.Also did have a bad Vacuum check valve. All learned from this site. Thank You all Again
 

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New core=Happy new year. Good for you man, and THANKS for update. Sounds again like going new is the the right choice. Have you got any info on the new core, etc?
 

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chillie
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Discussion Starter #15
Went to Auto zone for the core. $62.00. They make the tubes flexable so it is easyer to install. the foam around the tubes Fire wall came out so I used spray glue and sprayed around the hole put foam on and let dry. also only installed foam on core bottom and top 1 side. it is a tight fit so don't be afaid to apply some pressure.
 

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Has anyone noticed a heat difference from the 195 thermo compared to the 180 thermostat?! I put in a 180 this past summer, now I don't have very much heat, either the heater core is plugged or the thermo changed did it. I find it coincidental that my first winter on the 180 I have no heat, but I may just need to flush my coolant since it hasn't been done in 7 years, will do that and see if i have any heat after.
 
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