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Juan Crespo
Juan Crespo, ASE Certified Technician
Category: Dodge
Satisfied Customers: 1526
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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2005 dodge ram 2500 gas. When the weather drops below 50

Customer Question

2005 dodge ram 2500 gas. When the weather drops below 50 degrees, my heating system acts up. This does not happen all the time, I'd say once every two weeks. Once the truck warms up it will blow warm air (not hot air) while driving, but once I take my foot of the gas cold air starts blowing. The truck will start running hot, 3/4-7/8 on the temp gauge, then suddenly drop to 1/2 and the hot air will start blowing. If for some reason I just let the truck idle, it'll blow cold air and run real hot until I depress the gas pedal, then it seems to fix the problem. I changed the thermostat out which stopped the truck from running to hot, but didn't solve the problem. Again, I only have this issue when the temp drops, summertime, no problems. There is no evidence of loss of coolant or coolant in the engine oil. I also can hear the coolant running through the heating coil sometimes, almost like it's leaking through. Any ideas?
Submitted: 11 months ago.
Category: Dodge
Expert:  Juan Crespo replied 11 months ago.

Hi there.

Those are symptoms of air in the cooling system - especially that "gurgling" sound you hear from the heater core. You might take this opportunity to flush out the old coolant and get a fresh 50/50 mixture in there. Start with a cool engine;

  1. remove the reservoir tank cap and open the radiator petcock.
  2. Once all the old coolant has been drained, close the petcock and fill cooling system with the anti-freeze mixture;
  3. fill coolant reservoir to MAX mark
  4. Set HVAC to HEATER and highest temp setting
  5. Start and run engine until the thermostat opens - upper radiator hose becomes warm to the touch
  6. If necessary, add coolant mixture to the reservoir tank to keep coolant level between the MIN and MAX marks
  7. Check coolant level after 3 warm-up and cool-down cycles and refill as necessary

Please let me know if you have any other questions.

Best Regards.

Customer: replied 11 months ago.
I tried that along with changing the thermostat, it worked great all summer and this morning the weather was 47 degrees, first time in VA BCH its been below 70 all summer, and the problem happened. I can try flushing it again, but it didn't seem to make a difference the last time I did it. Any other ideas, like maybe the rely fuse?
Expert:  Juan Crespo replied 11 months ago.

The key to a successful cooling system flushing is patience. Were this my truck, I'd flush it again following the indicated steps - there are relays and fuses that control current to various components such as blower motor, etc. However, there are none that are part of the cooling system itself that could produce the symptoms you describe.

As an optional test, you could get a loaner pressure tester from any of the local major auto parts retailers and make sure there are no weak points such as bulging hoses.

By the way, I recently sold our home in Richmond and retired to the Dominican Republic - goodbye cold winters ;-)