New guy here, so, there's that, but, anyway, 2003 dakota 5 speed, 3.9 XRT. 172,000 miles. Overheats when driving. doesn't overheat when idling in the yard with full radiator. Will idle for hours. Replaced the thErmostat. Did a radiator pressure test by connecting the device with full rad. Will sit for hours without a prob, no excessive pressure, or, overheating. My conclusion, not bad head gaskets, but, a bad waterpump. BTW, there is no visible water loss, or noise from the pump, but driving the car under load results in overheating. Could the heads be cracked, but, not leak until under load? I'm confused. What do you guys say?

 

Welcome to the forum Duh.

What happens if you turn the heat on while it's overheating? Does the temp drop?

How about a flow test on the radiator? It may not be moving enough water through it at speed.

 

Could be clogged radiator try flushing it out and refill make sure to get all the air out of cooling system. if that dosen't work I would look into replacing radiator.

 

While the motor's cold, remove the radiator cap.

Start the motor.

Keep an eye on the water in the top of the radiator.

When the thermostat opens, if the pumps' working, you'll see water running. You may also get a bit of a geyser, so don't be looking STRAIGHT down at it ... *grins*

Odds are, more likely the radiator's gotten plugged, or the thermostat's not opening right.

And yes, new ones CAN be bad.

One more thing to try - if you have a IR camera, take a picture of it hot, and see if there's cold spots on the radiator. Bonus - if you can feel a radical difference in the heat off the radiator, that much cooler spot is the plugged spot.

RwP

 

Fan clutch if it has one? Just another thing to check.

 

Water pump, thermostat or Rad, fan possibly but it stays cool at idle.


Have any of these parts ever been replaced beyond the stat?

 

Thanks for the replies, nothing other than the stat has been replaced by me in the 2 years I have owned the truck. Tonight, weather willing, I'm going to reverse flush the radiator, but, not the block, since getting the stat out is a PIA, and, when I replaced it the other day everything was bright and clean. I have a new water pump, but, the old one is not leaking or making noise, so, I dunno. Will report back later, wish me luck.

 

Well, upon further review I have a 2002, but says 2003 on the title, no bigee, but, good to know. Also, the electric fan does not come on, A/C on or not. swapped relays, no diff. Haven't found the 10amp fuse in the junction box yet. The clutch fan moves with a bit of resistance, doesn't wobble, so, seems O'K. I do wonder about the serpantine belt though. How do you check if the tensioner is up to snuff? The stat works as it is supposed to, top rad hose gets hot after it opens, lower hose also hot.So, we will see.

 

If the tensioner wasn't working I think you would have bad belt noise squeal. I'm still going with Rad or pump, at cold start and cold engine pop off the rad cap start run till warm take note of the coolant flow down the rad cap hole it should be flowing at a good pace as it gets hot. Doing this will get any air out of the system as you could have air lock I don't think so but you never know.

 

Yeah, I've burped the heck out of the thing, I have kept the cap off till I get good flow, then put on the cap, let it cool, then refill. The stat is working properly, the rad is clean inside and out, clutch fan seems proper, water pump is pumping, unknown how well, only thing not working is the electric fan. As I always say, we will see.