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Runs hot with A/C on.

7K views 14 replies 8 participants last post by  RogerRamJet 
#1 ·
Hello all, I have an '05 1500, 3.7l engine. The temp guage usually reads right on the center mark in hot and cold weather, around town or on the highway. With the A/C on around town pointer reads 1/2 way between 1/2 and 3/4. But on the highway pointer quickly reaches top mark ( black line in what I would call normal range ) . Then it climbs toward the red, when warning on dash comes on saying check guages (duh), and stop engine. I've never let it overheat to the point of spewing coolant. Engine also stumbles when warnings come on. I've got new thermostat, bottom hose, and Mopar 5 yr coolant. Have not installed them yet pending complete diagnosis. Then I started thinking fan clutch might be going bad. Also NO coolant leaks.

Is there a way to check fan clutch? I appreciate any input .Thanks in advance.
Chris:doh:
 
#3 ·
still runnin' hot

Warlock, thanks for the response. The clutch does have resistance and no apparent leakage. I can't believe this truck has a 1 row radiator. I do like the electric fan idea tho. Chris
 
#4 ·
still runnin' hot

86 views and 1 response ( much thanks Warlock ). I'm bummin' here people. I'm a " certified shadetree mechanic ", but I need help with this one. Hopefully I can return the favor. Must not be enough V6 enthusiasts here. If fuel wasn't such a rip off scam, I'd love to have a V8, which probably gets better mileage than the 3.7.

Hopefully one of you pro mechanics (no disrepect here either) can help me diagnose this. Thanks everyone.
Chris:4-dontknow:
 
#5 ·
have you tried cleaning out the fins? squirt a hose from the inside.. other than that maybe corrosion on the inside of the radiator. Might be worth it to take it to a radiator shop to be rodded if you can see any signs of corrosion from the cap.

A coolant system is fairly simple. Fan, Radiator, heater core, pump, thermostat, coolant passages, hoses, temp sensors and the cap. just check off each part of the system and rule it out. process of elimination. it's how the pros do it. Diagnostic trees.

Edit: almost forgot the most important part- The coolant.
 
#6 ·
I would probably change the thermostat refill with straight water and see how it does. Check everything shroud,fan and blades,bottom hose for sucking together. If the thermastat fixes the problem then put your anti-freze in and your good to go. If it does'nt then I would be suspecting the water pump. I have heard of a few going out. I dont think its your fan. They will heat up idling and around town,not going down the road,unless pulling heavy with a/c on.
 
#9 ·
running hot with A/C on

Thanks fellas, I sure appreciate the input.

Simple guy, the fins are clean. I haven't looked inside yet. The coolant in expansion tank looks brand new. Speaking of coolant , the Mopar stuff isn't cheap. I've learned alot about coolant recently. It does get confusing.


deanhinsley1963,good idea with plain water. I did get a fail safe thermostat that stays open if overheating occurs.

RogerRamJet, that's a great idea with the heat gun.

I'll let y'all know the outcome. Thanks again, Chris
 
#11 ·
OK im going to school to become a tech and i just went through A/C. What you just described tells me that everything is fine but your radiator is bad. the tubes in the radiator are plugged up and not letting it dispate the heat from the condenser that sits infront of the radiator. Dont waste any time one anything else and just replace the radiator....i guarantee your problem will be fixed.
 
#12 ·
Does the AC Condenser sit in front of the radiator on 05 Rams, on my 06 hemi its off to the side and has its own electric fan, curious if that's a redesign or something only on the hemis. Regardless, I do agree with TJBiker, the engine is cooling well at low speeds which rules out the fan as a problem, which leads me to believe its an airflow problem or coolant flow problem. The fan doesn't really pull in any extra air at highway speeds. If there were much in the way of air ducting or front spoilers I would recommend you check that first but my truck doesn't have any so to speak and I am guessing your truck is similar so I would say check out the radiator. Either give it a good flush, a close visual inspection to replace it with a new one. My 2 cents is that a thermostat, fan or other parts wont change your problem
 
#14 ·
Problem solved

Haven't been online in a while. Thought I'd update this thread. I kept putting off repair until I noticed the radiator was weeping coolant on bottom corner. Power steering cooler slight leak as well.

New radiator, hoses, coolant ,thermostat, and power steering cooler and what a difference. Gage never gets above half way.
tjbiker , your diagnosis was absolutely correct.

06HemiRam, wchnu , and simpleguy were also correct that it was the radiator.

Thanks to everyone who posted.:wavey:
Chris
 
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