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sprinkles08, Chrysler/Dodge/Jeep master tech
Category: Dodge
Satisfied Customers: 22816
Experience:  ASE Master and Advanced Certified, Chrysler/Dodge/Jeep Master Certified, Trans and Hybrid Specialist
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2003 Dodge Ram 1500: overheats on highway..runs fine..kit..flushed

Resolved Question:

I have 2003 Dodge Ram 1500 that overheats on highway only. Around town runs fine. Changed thermostat, installed cooling flush kit and flushed system. Can see water flow in radiator with cap off. Cooliant mixture correct also. Oil clear no water in it. Went ahead and had oil system flushed anyway no help. Don't know what it could be. Help!
Submitted: 6 years ago.
Category: Dodge
Expert:  sprinkles08 replied 6 years ago.

Hello and welcome to JustAnswer!


This isn't uncommon on anything with a 4.7, more so on the DR body trucks for some reason. Some of the cores in the radiator will get restricted and not flow, and it effectively reduces the size of the radiator. It will heat up more under a load when this happens because of the increased engine heat being produced. I've seen this in the shop, and have had first hand experience with my own 2004 truck at around 70,000 miles.

With the truck hot, use an infrared thermometer or your hand to feel the temperature of the outside of the front of the radiator (away from the fan). The top left of the radiator should be the hottest, the bottom right should be the coolest. There should be a gradual temperature change across the radiator. When cores get restricted there will be spots in the radiator that are cooler than the rest because there is no flow through them.

Flushing the radiator seems to have no effect on the problem, since flushing it will not force through the restricted cores. It's easier for liquid to flow through cores that aren't restricted, and it just takes the path of least resistance. The radiator will need to be pulled out and taken to a radiator shop to be rodded out, or replaced.

Customer: replied 6 years ago.

Forgot to mention heat not working properly. Once engine heats up if you turn heat on only blows hot for few seconds. Does that help?

Expert:  sprinkles08 replied 6 years ago.

That makes it sound as if there is air in the cooling system, either from not being bled or from a combustion leak into the cooling system. Did you bleed the air from the system when the work was done? If not then that may be all that needs to be done. If the air was properly bled from the system then a combustion leak test should be done to check the cooling system for presence of exhaust gases.

Customer: replied 6 years ago.
How would you bleed air from the system?
Expert:  sprinkles08 replied 6 years ago.
Any time the cooling system is opened it has to be bled when refilling it. Follow the top radiator hose back to the timing cover and you will find a pipe plug that accepts a 5/16" allen wrench. When filling the system this bleeder plug has to be removed. You would fill the system with the plug removed, then when a full stream of coolant flowed from it then the plug is replaced. Then the engine is ran to normal operating temperature before the radiator cap is reinstalled to allow the rest of the air to escape from the system. Once no more bubbles are coming up and the engine is at full operating temperature then the radiator cap can be installed, and the system is considered bled.
Customer: replied 6 years ago.

So a combustion leak would be costantly putting air in system?

Why would'nt it overheat all the time?

Expert:  sprinkles08 replied 6 years ago.
Yes, a combustion leak would be constantly putting gases into the cooling system. If that was the case it would hard to say exactly why it only overheats under a load, other than the engine producing more heat and more combustion gases would enter the cooling system at higher engine speeds.
Customer: replied 6 years ago.

Will try bleeding and then the radiator. Thank's for your help. This has been driving me nuts!

Expert:  sprinkles08 replied 6 years ago.

I does sound like it's been driving you nuts!


I'd bleed it out and see if the heat then works normal and see if it still overheats. If it still overheats but you don't have a problem with the heat then I'd replace the radiator.


If it's ok for a while and then the same symptoms occur and there is air in the system again or you are having unexplained coolant loss then I'd do a combustion leak test.


Good luck with your truck! If I have been helpful clicking the Accept button will give me credit for helping you this afternoon. Have a great weekend!

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