2002 4.7 ram overheats only under heavy load (mountain pass unloaded, or pulling a trailer) but fine for months around town even after a few hours of driving on a hot day... it will also spike up real fast when it has this issue...

I recently had the system "open" at the heater hoses attempting to check flow through the heater core.

I expect air in the system of course, i would imaging that if it was the t-stat or pump it would be flaking out after a few hours of driving loaded or not?

As for the air, I have tried the hose massaging with the cap of, putting the rig on an incline... any other ideas?

When it does overheat, open the cap slightly and let what appears to be air out, and then let it idle it goes back down quickly as it rose...

I may pick up a new cap today, any other ideas?

 

fill the rad up while shes off, leave the cap off and run her untill the t-stat opens, you'll be able to tell when the water stops coming out and it looks like there is no water in the rad anymore and the temp gauge is at the normal operating area.fill her up while she's running,Then put the cap on and shut her off.fill up the over flow bottle.and drive it around.If nothing else is worng IE: water pump going out,t-stat out,bad rad cap...est. it should be fine.

 

I'm subscribing, I'm having the same issues. I had to run with the heat on this past weekend for 500 miles and it stayed perfect. I shut off the heat and it starts creaping up. Pissing me off.

 

Check for cold spots on the radiator when its hot and running. Friends radiator plugged up and did the same thing. He had the bottom half plugged and it was cold as ice with the upper half smokin hot. Just a thought and easy to check.

 

Radiators are plugged gentlemen,

 

Ill give the radiator a feel, bought a new cap yesterday. One odd thing is when it does start to spike and i pull over, vent the cap a little and it drops about as fast as it rose back to normal range... its like air is getting into the system or something... The challenge is that it never really shows any signs of distress until we are loaded up for a camping trip or something, seems like it would be hard to reproduce the problem at the shop.

 

Is it possible the head gasket is blown and pushing combustion gases into the water jacket as the engine heats up? Thought I read that the 4.7's have a issue with head gaskets or something like that. Just a thought.

 

this is exactly what i was thinkin +1

 

Running at highway rpm, when the radiator is clogged, the coolant passes thru the unclogged part too past and doesn't have time to pull the heat out.
Had this problem on my buddies 97 Ram. Idle and around town it ran normal, on the highway for 10 minutes and it would creep up until it boiled over. I replaced the head gaskets the first time and told him to get a radiator. He cooked the engine the second time. I upgraded from the 5.2L to the 5.9L and would not let him have the truck back until a new radiator was bought. No more problem.
My Mustang ran warmer than I likes on the highway as well after 165K miles. Would creep up to 215 or so. replaced the radiator, now 180 on the highway in 85 degree weather.
You may be able to have it rebuilt by a local radiator shop for much less than a new one.

 

Yea im thinking the radiator. I pulled the upper and lower hoses off and ran clean water thru, top to bottom, flow seemed a little restricted. So i put it back together filled it with prestone premix (does it really need the dexcool stuff if there is a complete flush? If so do i have to get that from the dealer?), bled the air using the bleed bolt on the upper hose to block connection. Then we took a 2hr trip...

It really seems to be a cooling capacity issue, took that trip with it over the holiday weekend, 1500ft climb with a full bed and tuggin a trailer, was fine until we heat the peak, temp slowly climbed going up the pass and then i pulled over mid way between the midpoint and "H", just left it running, started coming back down, steadied at the normal spot, put her back in drive and hot back on the highway, we crested the pass and it was fine the rest of the trip (30 min down about about an hour through stop and go small town(s) traffic. Coming home i was a cpl hundred pounds lighter, it climbed a little as i was cresting the pass, quickly retuned to normal once i was going down the hill, fine the rest of the way home.

So... agree i need the radiator rodded? Replaced? Do they make aftermarket radiators with more capacity?