My 98 Ram 1500 5speed 318 seems to overheat. I changed the thermostat twice now and it still over heats.. But when I remove it completely, it doesn't overheat. It doesn't burn and water, there's no water in the oil, the water pump and rad are new. What could it be. I have not noticed the water level going down. I am not 100 % sure the clutch fan is working properly.

 

What kind of temps are we talking about?

 

Have you tested the thermostats to make sure they work?

 

Does the fan engage when the temp hits operating temp?
Check the fan/clutch for any play.
Spin it [engine off], there should be some resistance-too much or too little is bad.

Also just read somewhere another test is that if you get the vehicle up to operating temp, shut it off and try to spin the fan, it shouldn't move. <--not sure if that applies to our trucks though...

 

Coolant levels? I was leaking coolant from a bad freeze, plug...fixed that, fixed my over heating...

 

+1 and check the part numbers you are using

I have been sold a bad part - figured out on the stove top.
and I have been sold the wrong part - figured out on the side of the road

 

I am betting it is a burping problem. Park truck at andgle with tstat installed. Fill with appropriate amount of coolant and water and run it. Turn the heater on and let it run. Front end needs to be higher (front right I think - been so long since I looked under my hood...) Gotta get all of the air out of the system. If there is air trapped, it can prevent the tstat from opening...

 

Yes I have tested them .. Put them in a pot of boiling water and they open and close... so I'm lost.

 

I would try the burping thing as gdstock suggested, go from there (yep front right )

 

the t-stat opens and closes to maintain engine temp at some predetermined level, such as 195 or 180. everything then depends on the cooling system to work properly to cycle in cooler liquid back into the water pump.

so if your cooling capacity is reduced, and you reintroduce hot water back into the engine, then everything gets out of whack and results in overheating.

removing the t-stat can mask the problem by letting the coolant out of the engine at about 160 or so, and a poor cooling system can keep up with the reduced demand.

so any component could be bad:
you already changed the t-stat, so move on.

radiator could be stopped up and not cooling. you can try spraying the water hose from the engine compartment out the front, and wash all the mud, grass seeds, weeds, and other clutter out of the fins. that might help. or you can replace it for 100-150.

as said, clutch fan should have some resistance. if it freewheels, then its slipping too much and not moving air properly.

at normal (or hotter) temp, feel the upper and lower radiator hose. upper will be scorching hot. lower should be cool enough to touch, WATCH OUT FOR THE FAN.

if you have pressure blowing out your overflow tank, you have a blown head gasket and the compression entering the water jackets is preventing coolant from flowing properly.

with engine off check your water pump to make sure it feels solid and that its not wobbling or shaking.

check that the radiator cap is holding pressure properly and not letting too much bleed out into overflow.

check that coolant is about 50/50 and not 0/100 or 100/0.

if none of this helps and you find no obvious problem, replace radiator.