Hello everyone! I am the proud owner of a dark green '99 Dodge Dakota with a stock 3.9 V6.

Currently, need has forced me to replace a cracked head on my truck, and it is because of this evolving overheating problem. I am not a mechanic by any stretch of the imagination, but I am learning! I bought the truck late last year with an inoperable heater, so my thermostat was probably not working from the start. I should have dealt with it then, but it was driving ok so I just let things go (damn it if I'll do THAT again) until summertime came and the truck overheated while towing a trailer. I changed the thermostat then and then put the problem away, until I started encountering some odd, intermittent sputtering problems. It really reminded me of an ignition problem (done that already). The problems got worse as time went by, and the truck started getting more and more sensitive to overheating again. It was ok for a while until the power dropped through the floor and I finally took it to the dealership for that, and for some console bus problems. They fixed the console bus (various lights on the dashboard acting strangely), replaced the ABS sensor; and then told me that they found water in the #1 cylinder, aka cracked head. I could not afford to have them do it (the quote of $2500 sounded reasonable considering I've had higher quotes from other places for other vehicles; if I'd had the money, that is). I then parked the truck and took the opportunity the replace both heads (just for the hell of it, while I had it open). I then changed the oil, refilled the coolant, and then took it test-drove it that night. It immediately overheated AGAIN, but then cleared up just like that as I was watching it. I figured it was just an air bubble and put it out of my mind.

I drove my truck to work that next day, and it drove very well, except that it was edging a little high on the engine temp. I chalked it up to the hot summer weather, but made the day quick, just to make sure I would not be stranded. I was on my way home when things got bad. One second things were fine, and then the temp went through the roof! I pulled over and left it running, and sat there for a while with the inside heat on at full blast to take the edge off. I watched it for a few minutes, even tried trying racing up the engine a bit to increase the circulation, but it made it worse. The temp would NOT go down. I ended up borrowing some water from someone and dowsing the engine just to get it cool enough to safely shut it down. And yes, I know that was a bad idea, but there was no other way to made the temp go down! I got it back home and inspected my work, and found that the front (toward the front of the truck) of the head on the alternator side of the engine was leaking coolant. I then removed that head again and reworked the gasket... I'll cut to the chase.

I'll figure out the heads, but what I need to know is if the overheating problem could be caused by the leaking. Would the overheating be solved by fixing the leak? It really sounded like it was sucking air... Could that be replacing and limiting the water flow?

I took apart the water pump and it looks new. NO WEAR.

I ran water up through the radiator, and it seemed like it had a good flow.

Also, I replaced the thermostat with one rated at 160 (I'll replace it with a 180 before I drive it a lot. My truck had a 195 previously, and THAT just seemed to exacerbate the overheating problem), and it seemed to control the overheating somewhat. Before, while testing, I encountered a weird but constant temperature cycling, and the 160 thermostat seemed to lower the overall temp of the cycling.

Any ideas, anyone?

 

Have you tried to do a cooling system flush? I had an issue a couple years ago that was about the same, minus the cracked heads. It would be fine for a short distance, then it would spike. I'd let it cool some and it would be ok for a bit. It got worse to the point you could hardly drive it around the block without it overheating. I started by replacing the thermostat with no luck. Then I bought a Prestone flush kit and flushed it good. Haven't had a problem since then. So your radiator might be flowing fine, but you might have a clog somewhere else. You might have got a crap thermostat too. I understand why you ran a cooler thermostat, but 195 is stock, most people say it runs better with a 180, but it's not recommended to run one colder than that. It starts to hurt performance then.

I don't think the cracked head is your only cause of the overheating. Seems like it would have to be leaking really bad to overheat like that. But, I'm not positive on that. I would get the head fixed, do a good coolant system flush, put a new 180 or 195 thermostat back in, fill up with coolant and distilled water, and try it again.

 

A cooling flush. That is a good idea. I'll try that after I work the head again. Thanks!

 

Cooling flush is a good start. I would also take another look at your water pump. Try replacing it and if it does nothing, clean it up and return it. Run a 180 thermostat. The cooling system, as you know, is a pretty simple setup. If you are not getting flow, then you have a blockage somewhere in your system (radiator itself, the block, the thermostat, the water pump).