Temp Gauge Fluctuation- 2006 Dodge Ram Mega Can 5.7L Hemi

[ArcherOfStardust]

Ok guys, any help would be greatly appreciated. I have a 2006 Dodge Ram Mega Cab 5.7L Hemi. I love my truck, I've had it for 6 years but man lately, it seems like I can't get it! Truck started over heating, maybe like a month ago, off and on. Took more antifreeze than usual. Eventually it over heated and wouldn't start. I had to have it towed home. When I got home and checked it out, the water pump was cracked, everything was just leaking out immediately. Replaced the water pump. It seems good for a few days but temp gauge kept fluctuating from cool to hot, back and forth, wouldn't stay at one level. So a couple days after water pump was changed my truck over heated pretty badly, smoke and everything. Pulled over immediately. Once it cooled, popped the hood, temp fix out some water in it to get to the mechanic down the street. Come to find out radiator had a crack in it. So more work, more money into my truck. Radiator, hose and thermostat was all replaced (radiator cap was replaced when water pump was). Truck seemed okay for a day before anything wonky. I've driven it to work the last to days, drive is about 40 mins each way. Gauge started fluctuating again, it goes to hot then back down to cool, then maintains in the middle then goes up hot where the check gauges light will pop on because the truck is reading as it's really hot. Then that will go back down. Sometimes it will seem like it's getting a little warm maybe but most of the time it when I've driven it the last couple days, it doesn't seem like it's getting hot to the point of over heating but I'm sure whatever is happening can't be good for my truck. Has anyone ever experienced this or know what is causing this?

 

[huntergreen]

Aftermarket thermostats can be defective right out of the box. Try a mopar.

 

[ArcherOfStardust]

I will definitely give that a try because I am at a complete loss.

 

[jws123]

If you got this thing hot enough that it says check guages you need to test your head gasket modern engines cant be overheated badly without damage not very forgiving with aluminum heads. Also make sure your using the correct coolant/mixture you cant run straight water im sure you know that but just putting it out there any ways.

 

[ArcherOfStardust]

The weird thing is it goes to Hot then right away goes back down and just fluctuates back and forth like that and never seems to actually be overheating. I will check the head gasket though. And yeah, I've only ran straight water in a couple emergency situations but typically always use the coolant mixture.

 

[jws123]

The weird thing is it goes to Hot then right away goes back down and just fluctuates back and forth like that and never seems to actually be overheating. I will check the head gasket though. And yeah, I've only ran straight water in a couple emergency situations but typically always use the coolant mixture.

it will overheat with just water it boils so make sure your coolant is good 50/50.

 

[Tank Guy]

Your temp sensor may have been damaged when the engine overheated. You can check it with a meter if you have one by attaching the meter leads to it and placing it in a pot of water on the stove, then heat the water. As the water temperature increases the resistance displayed on the meter should gradually change. If it begins to fluctuate your temp sensor is shot. This test can be done with a heat gun as well.

 

[HemiLonestar]

If the stat isn't defective it sounds like it's still trying to burp itself (purge air). Was the stat installed properly (bleed hole up)?

 

[FaceDeAce]

When mine was doing this, the problem was the thermostat had failed and actually fell apart in the hole. The bottom of the thermostat had separated. The second thermostat I put in was just a cheap motorad one that did not really open very much so the flow was marginal. After 4 thermostats I finally got one that works awesome. So the easiest place to start is with a new quality high flow thermostat. Make sure it also has the pin hole and the jiggle pin so it can remove vapor lock itself through normal running. The hemi also wants to run warm. Run the 203 F thermo. Avoid avoid avoid do not use any of those lower temp stats (160-180).

On the drives there will usually be some up/down on the gauge needle as the thermostat and the fan thermoclutch do their thing. The gauge should be in the middle but will not be firmly steady there. Expect it to go up or down a bit, as being normal.

Your op does not mention anything of checks or replacement of the fan thermo clutch. These are known to fail with age too. It may stick on full or not come on at all. So you might be due for a new fan clutch. A fan clutch that does not engage will definitely send the temperatures for yoyo as the vehicle speeds up and slows to stops. Exactly what you have described. Hayden or Four Seasons clutches work very well and last quite awhile.

Hope that helps!