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TimO, ASE Certified Technician
Category: Dodge
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Experience:  7 years tech
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2002 Dodge ram 1500: Truck started running hot..cap..leaks

Resolved Question:

2002 Dodge ram 1500, 4.7, auto, 95000k. Truck started running hot about three weeks ago, and i have noticed a coolant near cap recently. no other coolant leaks of any kind, in or out. replaced t-stat at that time and the cap about a week ago. when i drained the factory coolant then, it came out clean and bright fact it looked brand new, no rust, dirt, gunk of any kind. refilled 50/50 w/ peak. neither made a difference. about three days ago the truck began to get hot while in town driving, but would cool back down at highway speeds. today, truck has overheated several times. highway speeds make no difference. running the heater makes no difference. i believe the pump is good, as the return hose swells bigtime when the engine is revved. both core hoses are hot, so i have ruled out the heater temp sensor for now. the truck runs excellent and i haver never had an issue before this. any ideas? thanks in advance for any guidance or help.
Submitted: 8 years ago.
Category: Dodge
Expert:  TimO replied 8 years ago.
The 4.7 engine has a problem with the head gaskets. Its starts as slight overheat condition and as it grows it gets worse fast. The heads are aluminum and dont handle heat well. The heads cam warp and the more it overheats the worse it gets. If you run it untill it is warm and then park it for the night, When started in the morning it will blow smoke for a bit then clean up. It can start runing rough at the same time. You can also test this by adding pressure to the cooling system and let it soak for an hour or so. Then removed the spark plugs and look down the holes with a pen light and look for coolant. If this has happened the heads might need replaced as they are not machineable.
Customer: replied 8 years ago.

Thanks for your reply and insight. I have heard about the head warpage issue and this could be the problem, but from what I can see, I would think there has to be something else. Let me give you a few more details that I forgot to include in the first email.


Up until today, the truck has never really overheated(moved to the right, but stayed in normal range). Twice today I, shut the truck down when it passed the normal range and approached the red. I let it cool for about 30 minutes, then drove on.


The truck burns no oil, never has. I have checked the oil for coolant and there isn't any.


There is no oil in the coolant.


For the pastcouple of months, before the overheating issue began, when I would park the truck at night, I would hear the radiator rumble slightly as I walked in front of the truck. I have seen a trace of coolant present around the cap area during this time.


From, I assume the overheating pressure, the reservoir tank on top of the radiator has developed a pinhole leak that the coolant bubbles out of.


I believe that this is a seperate issue, but over the summer the AC/heater developed an issue where the fan motor works only on high speed. On AC, the driver vents blow cold, and the passenger vents blow warm/ambient. Conversely, with the heater on, the passenger vents blow warm(not hot), and the driver vents blow cold/ambient. This may be an unrelated issue that involves...the actuator on the vent gate?


Anyways, when I wrote, I was at Autozone trying to figure it out w/ a few of the guys there. As we ruled out the possibilities, we came down to maybe it is the radiator that is clogged and not allowing the coolant to flow. In your expert opinion, could it be the radiator? This vehicle has a history of radiators going out at sub 100k mileage. If so would a flushing be worth a try, or just replace it? Let me know your thoughts and I appreciate your knowledge and help.


PS- funny thing, when I left Autozone to go home, about 3 miles, the gauge went to the middle after about 1 mile. It did not go past there or get hot the rest of the way home. I let it run in the driveway for about 3-4 minutes, thinking surely it would begin to get hot, but it didn't.

Expert:  TimO replied 8 years ago.
Well I havent seen a lot of rediator problems, that is to say not from getting cloggedup. I have seen a few the cracked around the tanks and they needed replaced. To flush a cooling system is prevenative matainence. If it is over heating then it is to late and even if it helped it would not cure it and theproblem would return, and during the flush paticals can break free and get lodged in the heater core glogging it up. You could take it to the radiator shop and have them rod it out. That is not a bad idea, but it always seen to cost as much as the new radiator would have. I really beleave you are just starting to see head problems. I know that coolant in the oil is a good sign but in the cases of the 4.7 we dont see that. The gasket just lets coolant into the cylinder. since the compression is higher than the coolant pressure, Its pushes into the cooling system. This would get worse at higher rpms. If you have a digital temp scanner you can run it around the radiator and look for cool spots and that can help solve that problem also. During our test on the 4.7 it was hard to tell if we had exhaust in the coolant when we tested it with a block tester and took time to finally prove it. The truck was just slightly overheating for almost 2 months before it was bad enough to find the problem. I really hope it is just the radiator as it is alot cheaper than performing the head replacement.
Customer: replied 8 years ago.
Your idea makes sense. the only problem is that there is nothing in the is clean, no white or dark smoke...and the truck runs great. just to clarify, when you use the term overheating, is that a temperature outside of the normal range on the gauges? because other than the situation today, the needle has not went outside of the normal range, which makes me wonder when it would have gotten hot enough to warp the heads.
Expert:  TimO replied 8 years ago.
Good question. The rest of the ones I have seen, I didn't see how hot they got when the damage was done. I know it really doesn't take much. We could drive them down the highway and it would not always get hot. However it was random, It might run somewhat normal on one trip out and overheat on the way back. I have seen a few fan clutches go bad and that caused them to overheat. If it was a fan clutch it would overheat around town or at an idle.
Customer: replied 8 years ago.

in the past few days, when the gauge would get a little warm(but not overheat), it would be in town at stop and go speeds. then highway speeds would cool it down to normal. running the heater seemed to make a momentary, but not lasting, difference as well.

today though, it got hot at all speeds. when i was limping it to the house, the temperature seemed the most stable at about 40-45 on the highway. running the heater had no effect at all. if there was a radiator or system clog, would a backflush help this at all? as far as coring or replacing a radiator, i agree with you, not much cost difference, and when you consider that a new one is...well...a new is a no brainer. also, at autozone, when we held the top hose and revved the engine, it didn't distort the shape of the hose, but man it expanded like a firehose priming(i would guess about 1 inch in diameter). would that seem excessive as if there were a blockage in the radiator?

Expert:  TimO replied 8 years ago.
Yes it does seem excessive. A clogged radiator could cuase that. Bad head gaskets could also cause it. could you see the lower hose and if it was also flexing?
Customer: replied 8 years ago.
i did not put my hands on the lower one, but could check it in the morning. what should i look for?
Expert:  TimO replied 8 years ago.
Just see if acts the same as the upper hose. If the radiator was clogged it would act the opposit and it would suck flat. If it acts the same as tha upper hose the radiator would not be the cause.
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Customer: replied 8 years ago.
fixed the problem. took it to a reliable radiator shop yesterday morning that has worked on my dads vehicles for about 50 years. he said that he fixes on average about 15-20 4.7 dodge rams a month. he pulled it(i watched), took it apart(it looked like it had 10 pounds of peanut butter inside of it), hooked it up and it put out as much water as a coffee maker. tried to clean it with the rods, but couldn't get them even a third of the way through. he said he couldn't believe that i didn't have a problem this past summer. put a new aftermarket one in that he says is a better radiator, and all is running perfect. on the warped head possibility...he agreed with you, he said that it definately can happen, but in all of the 4.7 rams he has worked on, he has only seen that problem twice, and that they still needed the radiator repaired. he thinks the problem is that the mopar radiator tubes are too small and that the red 100k dodge coolant is too thick, especially when people take it to the limit like i did. he says that to maintain radiator life in most cases, you should dump it and flush it about every 3yr/50k. thanks for your all your help, the multiple replies and your expertise. have a great new year. boyd