Hey everyone,
It's been a while since I needed to post, so I guess it's past due for me to have an issue with my dakota...
About a month or so ago I had a rad leak. I replaced the rad and flushed the coolant system and filled her back up. All seemed good until about 4 days ago. I had to travel up north...just under 200 miles. Whole trip seemed fine, got to my destination, but one day while idling at a stop, the check gauges light came on. Looked at the temp and it was near the red and going up. I turned the engine off, let it cool and checked the coolant. It was low. Filled it up and was fine until my trip back (yesterday) halfway home started overheating again. Stopped, let it cool, filled it up with some water and since then seems fine. This time, noticed a lot of fluid coming from the overflow from the reserve/overflow tank. And that whole area was wet. This morning did a more in depth check...checked the coolant level. Ran it all morning. Ran it with the cap off to bleed any air...a few bubbles for a few minutes. Also loosened the bleeder screw after putting cap back on and got some air bubbles from that. Ran it this way with and without heat on for about half an hour. Put all back to normal and ran some more. seemed fine. I then checked other stuff the manual said to check...mechanical fan works fine...jumped electric fan to battery, that worked, checked the resistance of the temp. sensor and checked all fuses. When I put the A/C on, electric fan kicked on, so I know that's working. And of course, looked all around for a while to see if I saw any leaks by the rad and all the hoses. Nothing and the ground below was bone dry
Anyway, my concern is it's probably gonna happen again. What I didn't do was change the thermostat yet, and the cap. What I did change, as mentioned earlier, was the radiator and the upper hose assembly, which had a crack in it (the "t" where the cap goes) Since then, can't see any leak or any signs of one.
I also checked the oil for any foam or water, and that looks fine.
So, basically, it will run fine, but seems to be losing fluid from the overflow.
Could this be a bad thermostat? I was gonna change that and the cap tomorrow. I am not sure how the system works, but was trying to troubleshoot. See, I figure the coolant after it reaches operating temp. starts running through the system. Correct me if I'm wrong, but the direction seems to be from the top end of engine to the top hose (by filler cap) to the top end of rad to to bottom of rad/hose then to the lower part of engine via the thermo housing, through the engine then back to upper engine outlet... in this direction. In my case, could a bad thermo cause the coolant to not circulate and overflow out the overflow tank. Could it have been air in the system? Could it be a bad cap? From my symptoms, does any of these sound like the culprit? Like I said, now it seems to be fine, but supposed to go away next week and didn't want to happen again. Never had a problem till I had the leak and changes out the rad. and even still, all seemed good for a month till now. I used a 50/50 mix of coolant and water, and also, when I had the cap off and was running the engine, I shot it with thermometer, and got about 185-190 degrees and it appeared to be flowing, which makes me think the thermo is working properly. The inside-cab gauge the whole time I was running it was at a steady temp (just shy of the 12 oclock mark on the gauge. Took it out for a ride for 20 minutes...fine.came back and let it run for another 10 minutes...fine. Thanks for any help. With the money I've saved from this forum and not having to go to a mechanic, I could probably buy a new truck. lol. So, really, thanks everyone.

 

I don't believe the thermostat is bad from your description. The cap is a possibility and is easy to swap.

It sounds like you got some more air out of it.

Coolant always flows through the block and heater core. The thermostat just controls how much passes through the radiator to maintain temp.

 

thanks for the reply. I got a few ideas from a friend of what it could be. I guess worst case scenario would be the head gasket(s). As of now, I was using it most of the day and it seemed to be running fine. I don't seem to be getting any white smoke from the exhaust on cold start and the oil filler cap appears to be clean. I didn't pull the plugs yet to check those, but I am hoping it isn't the head gaskets. I've been trying to notice any patterns, but since it's been running good, it's hard to notice anything. I just popped the hood to check again after getting home, and noticed no leaks or puddles. I did notice the upper hose was pretty tight and expanded, as if it were under a lot of pressure. Is this normal? When that fitting that houses the cap broke and I had to replace it, the part was just that, no cap came with it, so I used the old one. Could it be a faulty cap, where it's not allowing the proper pressure relief/release into the overflow. The only time I noticed an obvious leak was when it was coming out of the overflow spout on the overflow tank, and squirted all over that area. So it's obviously getting into the tank. But, and I am just guessing here as I am not too familiar with how the system works, but if the pressure setting on the cap were too high, could it allow the system to build up too much pressure, then finally let loose and overflow the overflow tank? From what I see, the design looks like once the cap reaches enough pressure, it pops up and allows fluid to reach the little hose that leads to the overflow tank. in my case,could the antifreeze expand that much, where it flows out the overflow, then when it finally cools enough, leaves the system too low and then overheats. The overflow always seems to have fluid in it, even the times when it was overheating and the system was low on coolant. By the way, I see how the overflow receives coolant from pressure, but how does the cooling system retrieve it from the overflow tank?...Again, thanks so far for the help. It seems the more I learn how the system works, the closer I get to finding the problem.

 

A bad cap could have caused the other part to fail.

The cap maintains pressure on the system. It will allow fluid into the overflow tank when it heats up and then as it cools back down it should draw the fluid out of the tank.

Caps can fail. Get a good one, Stant for example, or one from Dodge.

 

Unfortunately I am pretty sure I got a head gasket leak, which sucks. lol. I changed out the thermostat and got a new cap, but after topping it off, I was burping the system and it just didn't wanna stop "burping". With the the truck running with the cap off, I was getting consistent bubbles coming from the engine side. I decided to take a sniff and the bubbles did indeed smell like exhaust, which is not a good sign. Then, just this morning, my engine light came on. Checked the codes and got p1491 and p0304. One has something to do with the A/C fan fuse or relay....I'll check that later, but the other is a misfire in cyl. 4, which I never got before. It makes sense. System runs fine at normal temp until enough pressure from leak builds up air pressure in the coolant and forces it out the overflow, eventually making the engine overheat from lack of coolant and too much air. Fill her up again and she runs fine until the next cycle. Also, this morning noticed a rough idle start and some white smoke, another tell-tale sign I never had noticed before. I guess overnight, engine cools and coolant has enough pressure to leak into cylinder. Start it up and the coolant burns off into the exhaust. Engine gets hot enough and either expands heads to stop leak or opposite pressure from firing sends air into the cooling system, which seems to be my problem? Sound like I'm right? Wish I wasn't. lol. Anyway, gonna bring it into the shop to do a compression check, but I am pretty sure that's what it is. Any one got any other possible causes?... Also, what should I be looking at as far as cost to have the head gaskets done on the 4.7 v8's. It's a 2002. I'm sure it ain't gonna be cheap. SOmeone told me if my mechanic is gonna have to go that deep into the engine, I should probably do the timing as well? Any pointers. Most things I try to fix myself, but this seems like a big job beyond my skill set. I am just thinking ahead. Have it scheduled to go in tomorrow to be looked at, but am fearing the worst as far a what it's gonna cost me.

 

I have 2000 Dakota 4.7L with 205,000 miles on it that is doing exactly as you have described below. I have replaced the water pump, t-stat, fan clutch, both hoses, radiator cap, and flushed and fillled with new coolant. Ran great for 1 day afterwards, no overheating even when I let it sit idling in 90 degree heat with the a/c on for 20-ish minutes. Next day it started overheating again. I have noticed a lot of scale in the coolant even though I flushed the radiator and the block prior to refilling with a new 50/50 blend of coolant- this could be the problem, but I doubt it. I too have some white vapor exiting the tail pipe at times.

I have a leakdown tester, but have only used it on motocycles in the past. Would like to use it on the Dak if I can figure out how to determine piston position on a V8 engine. I'd like to be as certain as I can that it is a head problem before I tear the d@mn thing apart.

 

It's funny, cause all the other sh@t that went wrong with this truck, I was always proud to say, well, the engine works great. lol. (i.e ball joints, bearings, bad brake design, etc.)
Anyway, yeah, all the research I've been doing leads me to the head gaskets with those symptoms. The air in the system made the most sense. Especially when it smells like exhaust and/or gas fumes. Some people told me your not always gonna see symptoms of water in the oil. As far as smoke in the exhaust, I saw youtube vids of crazy white smoke coming from the exhaust, where as mine only puffed a little when giving it gas on cold start. I guess a little is all it takes. Again, it makes sense, though. You figure after sitting and letting the engine cool, with no back pressure, coolant will leak into the cyls. and then burn off when you start her up (i.e white smoke). And I spent alot of time looking for leaks and found nothing. I guess a pressure test would rule that out better, considering any external leak would most likely happen while driving and/or strain on motor, usually in a hard to find place. I heard also of a co test that would test the coolant for any combustables. But my nose worked pretty good. Well, I bring it into the shop today to see, so I'll keep you all updated. I'm just wondering how much more poor this is gonna make me. I know it won't be cheap. I'd be willing to give it a try myself, but just don't have the time and can't risk messing it up further. lol.