My farm pickup overheats sometimes

My 2002 Dodge 1500 has developed a recent problem of overheating and then at times you can drive for miles with no problem. Temperature gage comes up slowly not all at once. You can see it raise over 15 to 30 miles when this event happens. Engine is a 4.7 with about 100,000 miles on it. It started about 2 weeks ago when I was trailering about 150 bags of soybeans at about 55 mph. Temperature gage came way up so I pulled over for a few minutes to let it cool down and then only had three miles to the farm. I checked the coolant and added some water - not much was added. You have to add to the little tank on top and then I always squeeze the hose to help it get sucked into the radiator and engine block. Then over the last couple of weeks the temperature gage would come up and the warning noise would go off and I would pull over and let it cool down. Never takes much coolant. I think it did it 4 or 5 times in the 15 - 20 times I drove it. So, this last week I put a new radiator cap on it. Thought that solved the problem as I drove it multiple times with the gauge at normal. Well, I guess not. Hauled 20 railroad ties to the farm yesterday morning and it got hot in the last 5 miles after driving 90 miles with no problems. Told a friend I would haul a lawn mower for him yesterday afternoon. In the 90 miles one way I had to stop twice going and once coming home. But then the last 60 miles the temperature gage was at normal with no issues at all. I bought a new thermostat which I will put in today to see if that is the problem. I also notice I don't get much if any heat out of the heater/defrost - been a problem the last year or two - don't know if that might be helpful information - could the water pump fins be shot?? Hard for me to believe the head gaskets are bad as it holds good pressure in the cooling system when you pull over to let it cool down. Never any white smoke out of the exhaust. Changed oil yesterday and it looked good too. When you start the engine it fires on all cylinders immediately. So I don't think water is getting into the cylinders. I might add that this is not stop and go traffic - down the road at 40 - 55 so I don't think it has anything to do with the fan clutch. Installed a new "parts store" radiator 1 1/2 years ago due to a leak in the side tank. Belt on the front end of the engine is good and also tight driving the water pump. Lastly when it does overheat it does cause the radiator cap to release some steam/water. Haven't been adding antifreeze since this started, just water. I know water boils at a lower temperature than antifreeze but don't think this is the problem? Maybe I should be adding 50/50?? Any more ideas would be helpful and appreciated. Thanks

Sounds like the problem I had a few years ago with my Suburban with a 350. It turned out that the thermostat was sticking in the closed position and wouldn"t open properly. A new thermostat fixed the problem.

Have you added any leak-stop products to your coolant recently? I"ve found that these will effectively stop a leak, but the stuff will also gum up the thermostat and cause it to stick. The old Bars Leak will even clog up the fins in your radiator and cause enough coolant flow restriction to cause an engine to overheat.

It sounds like there may be sludge in the cooling system. Have you ever mixed antifreeze? I've got a 2005 Dodge like yours and was told to never mix antifreeze. I flushed out my radiator last fall and put in new antifreeze from my dealer. I had a neighbor with a 03' that didn't and had to replace the heater core and radiator because of sludge. I have a Chevy that I had to do the same thing because I mixed antifreeze not knowing what would happen.

Always assume bad head gaskets until proven otherwise. Pressure test on a cold engine is the first step.

I had a 98 Dodge 1500 that did that and it was the catalytic converter. It was plugged up. Short trips were ok. More than 15 miles the temp. started to climb. New converter and problem solved. But could tell loss of power with it being plugged too once it started getting hot. You may have another problem or could be the beginning of the same problem.

Could also be the water pump. Had one in a plymouth that wore the fins off the pump and it wouldn't pump good. Didn't leak just wouldn't pump.

rule out the fan clutch first and then proceed with other possible causes, when a vehicle is hot and is shut off the fan should not rotate more then one revolution.

My 2000 Dakota with a 4.7 in it did that one time. I pulled into a dealer and he put a scanner on it. He then opened the hood and put his hand on the fan and it stopped turning. The fan clutch was bad and after a new one was put on I had no more heating. Have a dealer scan it.

quick n easy always first . check fan clutch ,,high failure item . Next Thermostat .Next head gaskets

Is the radiator clean? Maybe it could use a good powerwashing. I've also had to pull bird nests out from between the radiator and the grill the last two times I popped the hood the check oil.

bottom hose sucking shut at higher RPM or thermostat sticking.

Head gaskets are a common problem on the 4.7. It can be hard to nail down. Sometimes a pressure test with plugs out can help diagnose. It is a big job on that engine. Separate timing chains go to each head. Be very careful about machining the heads. When I tear one down, if the heads are warped, I replace them.

Over the years I've had many things cause over heating. Pump spun on shaft, thermostat. Pulling a load will cause tranny to over heat and cause the radiator to get hot, because the tranny cooler is inside the radiator. May not have a heavy duty tranny or need a cooler added.

Is the engine actually geting hot or could it just be a flakey gauge or sensor? The gauge and sensor would be a comparatively inexpensive fix if they are the problem. The radiator cap releasing steam and water could be either over heating or over filling.

Heater not working well indicates silicate drop out in the coolant coating the heater core (a very small radiator).
Did you notice any white coating when the radiator cap was off?
Engine manufacturers (at least the two I have worked for) don't like to recommend coolant system flush as most people don't get the flushing agent out and it decreases the effectiveness of coolant when it is reinstalled.
Another way to check your system is the temp drop from to top of radiator, all of my experience is with heavy equipment but automotive applications should be about the same.
If you have or can borrow a digital surface thermometer suggest checking the top vs. bottom of the radiator. When at operating temp heavy equipment will see a 12-14 deg. drop (plus or minus a couple of degrees). If you see something like a 30 degree drop the radiator is not doing its job, it is plugged internally or something.

I assume you have already checked the general stuff like fan drive, ensuring the fan shroud is in place, etc.

Some vehicles have air conditioning condensers and oil coolers stacked in front of the radiator. Assume none of this is plugged.

Air is also a terrible conductor of heat. If worse comes to worse cut the top radiator hose and install a clear plastic pipe and look for air bubbles with a flashlight.

Hope this helps, I worked in high altitude areas of the world for five years (air is thinner) and cooling system problems were common.

I have drove the pickup enough that I am sure the dash gage is OK. Put the new thermostat in this morning and ran it 35 miles and it stayed slightly below 1/2 way on the gage. Might have found the problem. When I went to drain the radiator, unscrewed the plug and nothing came out. Sort of gunk at the bottom of the radiator. Poked a smaller drill bit in and tried to open it up. Took a sprayer on a hose to blast water in the drain to open it up. Put water in with Prestone cooling system cleaner. Says to drive the vehicle 3 - 4 hours I believe. I think the heater works better now too. Just have to drive it to find out. If everything checks out maybe I better trade it off for a Chevrolet. Sounds like the 4.7 head gaskets give up.

Thanks everyone. I did change the thermostat and it keeps the temperature just a little below the 1/2 way line on the gage. Maybe that was the problem. Running some cleaner too before I put new antifreeze in. I like my 4.7, but should I be sending it down the road??? Are the head gaskets that bad of a problem?? From some of the comments they sound as bad as the Ford 3.8. Did two of them, don't want to do anymore!!!

Blow the cooling stack (rad, condensor, etc) out good. If air can't flow through them to the fan clutch, the fan clutch can't heat up, which allows the blades to free-wheel instead of move the large quantity of air needed to cool the engine. Even if the clutch is new.

If your torque convertor is slipping, the transmission will put a lot of heat into the radiator, not allowing it to cool the coolant before it gets back to the engine as well.