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Assuming the above is all correct, then the question is why so little heat in the cab? Plugged heater core could be the case.
Yep....
Originally Posted by Dodgevity
The top hose is supposed to be much hotter than the bottom. It's the intake coming from the engine and the cooled coolant flows back out via bottom hose. That said, it shouldn't be hot/cold... more like hot/ very warm.
I'd run a prestone radiator flush through it. If that doesn't help, the radiator or heater core could be clogged.
Edit: Yeah, get that flush in there asap. It does sound like radiator or heater core. Try back flushing heater core too. You never know if someone used some stop leak crap to clog the system.
"If you are having heater problems, then you may have a problem with the heater core, which can become blocked and need to be replaced. Find the two hoses that are smaller than the engine hoses, they run to the back of the engine compartment (bulkhead). One of these hoses should feel slightly warmer than the other when the engine reaches operating temperature and heater turned is on. If one is significantly cooler than the other, the heater core is closed off and may need to be replaced"
Hey Kat,
Just rethinking this a bit. Is your engine truly running cold? Or are you saying you have no heat? Two different things entirely.
It sounds like you have an accurate coolant temp gauge and you have tested the Tstat to make sure it's opening when it should. And you can verify the lower radiator hose is definitely cooler than the top hose. I'd conclude from this information that the system is cooling as designed, especially since your truck is not overheating. The heat's got to go somewhere afterall, and it is.
Assuming the above is all correct, then the question is why so little heat in the cab? Plugged heater core could be the case. Apparently that is an issue with some of these trucks. I'll offer my theory but that is all it is.
I think you could well have some heater core issues, but it seems to me on these trucks the radiator may be a one size fits all, designed with enough capacity to cover all the engines offered from 4-cylinders to 8. So it may work so well on a 3.9 that the lower hose is always cool. My guess is the heater cores may be on the small side, perhaps just barely large enough to heat the cab. I've noticed in really cold weather the heat in my 3.9 is tepid, because that little heater core is trying to warm up some 20-30 degree air. When it's 50 outside, the heater will run you out of the cab.
I intend to flush my heater core soon to see if the heater temp improves. But I'll try to check my own lower radiator hose to see if it stays cool or not. We might both learn something here.
Keep us posted!
I think the engine temp is running normal now. I changed out the Temperature Sensor today and the gauge did jump up some compared to the old sensor.
I also flushed out the heater core as well. Still not getting good heat inside the cab. The intake hose is hot and the outlet is luke warm. Even after flushing both directions. It did puke out some cruddy brown fluid, but NOT nearly as much as I expected.
During the flush out, as I poured in the Flush it DID come out the other hose. So I know I have "some" fluid passing through the heater core. How much ? I dunno. ??
I took the truck out for a 10 mile drive afterwards. Heater initially was blowing luke warm air. Then by the time I got home it was blowing COLD. ??? Air pocket in the cooling system perhaps ???
Anyways, I have some Prestone Cooling system flush sitting in the heater core right now. I'm letting it sit over night in hopes of losing up some more crud.
I've watched a bunch of videos on YT on flushing heater cores and picked up a few tips. Including burping all the air out of the system.
We'll see in the AM if I'm successful...... or not! LOL!
Last edited by Katmandu; Dec 16, 2014 at 02:28 AM.
This one is out in far left field, but you do have a 98 so it's possible. The mode doors are vacuum op, is it remotely-though-unlikely possible that the mode door is moving from heat to vent?
I'm a little confused about what is cold or should I say not warm/hot?
I'm wondering if part of your problem is cold air leaking into the cab from the HVAC unit the older Dakota's have a problem with a foam seal between the dash and the HVAC unit under the dash. Sometimes it rots off sometimes if the HVAC unit has been removed to be worked on the seal falls off or not replaced/installed.
This air leak can be very bad especially if its very hot or cold outside so no matter how hot your heater is its being drowned out by freezing cold air leaking into the cab.
I have some Prestone Cooling system flush sitting in the heater core right now. I'm letting it sit over night in hopes of losing up some more crud.
I've watched a bunch of videos on YT on flushing heater cores and picked up a few tips. Including burping all the air out of the system.
We'll see in the AM if I'm successful...... or not! LOL!
We have SUCCESS !!!
After today's round of flushing using an pressurized air blowing both directions, I was able to get more crud out of the system.
Finally have nice hot air blowing out the floor and air vents. Not perfect, but good enough for me. I believe the heater core still does have some crud build up in it.
In summation, what I have here is a truck that was severely neglected over the past 16 years. As a result, the cooling system had multiple issues that made it very difficult to diagnose.
I found the following issues.
- Heater core clogged with crud....... Repeatedly flushed/back flushed
- Temperature Sensor bad...............Replaced
- Fan clutch bearing bad/seizing up....Replaced
- Coolant filthy and under-filled.........Flushed out and refilled.
- Thermostat stuck open (probably from all the crud)........ Replaced..... TWICE.
I also replaced the radiator cap as well.
The above was all done under $150. That includes taking it to a local shop to do the Flush-n-Fill.
This truck should serve as a good example of WHY regular maintenance is absolutely essential and the consequences of neglecting to do so.
The truck does have air leaks inside the cab as well. Someone suggested the air box seals. I believe this and weak door/window seals as well as a cracked windshield are reducing the efficiency of the heater core's output and fogging of the inside the windows. But oh well !! Good enough for this beater truck!
I thank all you for your valuable input!
I hope others can learn from this thread as well.
Last edited by Katmandu; Dec 16, 2014 at 08:48 PM.
Wow if your cooling system was that badly clogged up with gunk and it took three cleanings to clean it out I'm wondering if the previous owner used some kind if leak seal in the cooling system.
Watch very carefully that you don't develop any cooling leaks in the next month look under that truck every day to be sure and check your coolant fluid levels every day also.
That could explain things nicely especially the thermostat getting clogged up possibly 2 times you may need to change the thermostat one more time.
definitely poorly managed or like Dakaz says, somebody used some stopleak. Keep an eye for drips- particularly under the radiator and at the front of the passenger footwell.
