So I have a 01 dodge ram that has been constantly overheating. I've done just about everything I can think of besides taking it into a shop for further repairs. It started overheating so I changed the therm and the water pump. Recently starting overheating again and realized the radiator was leaking. So I replaced that. Since replacing the radiator it overheats and redlines much faster than before. Through doing research I figured out that I could tell if the therm and water pump was bad by checking the upper radiator hose. If there is circulation and when it reaches temp if the hose is hot then I was informed its neither of the two. It has a brand new radiator and no leaks from anything my buddies or I can tell so its not the radiator. I don't see any collapsed hoses. I don't have heat so I was told it could be the heater core. I'm at a loss and don't want to take it to a shop cuz I know they will try to overcharge me and I frankly don't have that kind of money right now. Any help would be greatly appreciated. Thankyou in advance.

  • Welcome to Motor Vehicle Maintenance & Repair! Did you properly bleed the system of all the air in it? Did the thermostat get put in the right side up? Commented Jul 3, 2018 at 23:56
  • If the system has been properly bled as @Pauls term asked, then It is time to check for combustion gasses in the coolant.
    – Milison
    Commented Jul 4, 2018 at 0:57
  • 1
    It could be a blown head gasket since you have no heat check your oil and see if its milky Commented Jul 4, 2018 at 2:50
  • I doubt anyone is going to overcharge you. Some smaller shops only charge .5 for diag. Since you don’t have heat, try bypassing the heater core or bleeding the system. I’d also make sure you didn’t leave a plastic cap on one of the radiator pipes.
    – Ben
    Commented Jul 4, 2018 at 12:27
  • Ok the upper radiator hose is hot when its overheating. Honestly I do not know how to bleed the system. If anyone could explain I will def try that
    – FuccedRam
    Commented Jul 5, 2018 at 1:27

2 Answers 2


When the engine is at temp, there are 2 hoses which come out of the top of the engine which should be hot.

The smaller one goes to the heater core (Hot to h.c. on diagram). The larger one goes to the radiator (hot to rad). I colored the thermostat in green. enter image description here

At all times, the water pump is pumping coolant at a rate determined only by the engine RPMs. The rate does not change depending on whether the thermostat is open or closed. Coolant is also being sent through the heater core at all times.

When the engine is cold, the thermostat is closed, and the water pump is pumping (technically pulling) coolant through the heater core. Because the (small) heater core hoses are restrictive, excess coolant is sent through the bypass.

As the engine begins to warm, the Hot to h.c. hose will begin to warm up. If you do not have the heater turned on, the cold from h.c. hose will also be warm, because there heater core fan is not extracting heat from the coolant running through the heater core.

When the engine gets hot, 1 of 2 things will happen:

  1. If the temperature outside is cold and you have the heater on in the cabin, the thermostat might not open, because the heater core may be providing all the cooling the engine needs. For example, if you are driving on the highway and the temperature is 15° F, hot coolant will be sent through the heater core, and the freezing air being blown over the heater core will cool the hot coolant. Combined with the cold air flowing around the engine, this might provide all the cooling the engine requires.

  2. If the temperature outside is hot, the coolant inside the engine will get hot enough to open the thermostat (green). The water pump will then begin pumping hot coolant into the radiator, and "cold" coolant out of the radiator into the engine. Because the radiator hoses are quite large, the bypass is no longer needed. (Note: hot coolant will still be pumped into the heater core, and it will be coming out of the heater core hot.)

A few possibilities (when engine is HOT)

  1. If the Hot to h.c. hose is not getting hot, you might have a clogged heater core. Sometimes rust gunk can build up inside the heater core. This is not a big deal, as the main purpose of the heater core is to provide the cabin heat. It cannot cause the engine to overheat.

  2. If the hot to rad hose (aka upper radiator hose) is not getting hot, you can consider yourself "lucky", because the problem is almost certainly in the cooling system, and not the engine. Did you uses the correct temperature thermostat when you replaced the thermostat? They range from 160° to 195°. You could try putting a 160° thermostat in. This would cause the thermostat to open when the coolant reaches 160°, which would in theory prevent the engine from getting as hot. Also, try unplugging the hot to rad hose from the radiator. It should start shooting (very) hot coolant out. If it doesn't shoot hot coolant, you either have a bad water pump, or a clog in the cooling system.

  3. If the cold from rad hose (aka lower radiator hose) is very warm or hot, your radiator is not cooling the coolant enough. This could be causes by a bad fan clutch

  4. It could be as simple as having a bad temperature sensor. There are probably 2 temp sensors located near the thermostat. One sends info to the dashboard temp gauge, the other sends info to the ECU. Since they are pretty cheap, it wouldn't hurt to replace them both.

  • So should I not replace the heater core yet if it can't make the truck overheat?
    – FuccedRam
    Commented Jul 5, 2018 at 1:31
  • @FuccedRam If I was you, I wouldn't bother replacing the hc until you get the overheating problem figured out. You probably won't need the cabin heat until the Spring anyway. Best case scenario: the hc/no-cabin-heat problem will "fix itself" when you fix the overheating problem. My guess is that the 2 problems are linked, but the heater core is almost certainly not causing the overheating problem.
    – sam
    Commented Jul 5, 2018 at 18:32

Firstly you need to determine where in the system you have heat and where you lose it. carefully feel the top and bottom of the radiator hose, whichever one is hot to the touch is the side that's closest to the engine, the coolest one is where you need to begin your troubleshooting. things to look out for. -proper installation of thermostat. -Clogged hoses, mainly heater core hoses are the trouble makers, due to them being so small, the smallest particles can become trapped and create a blockage. -Contaminated system. What i mean by contamination is the lack of maintenance in the past has deteriorated the system internally and now you have this rust colored fluid with chunks of sludge. This is the worst case scenario which has light at the end of the tunnel but requires patience and determination.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .