half the time reserve tanks don't work. it's more of an overflow, instead of puking it on the ground. You really can't fill the system with it. as the system pressurizes the rad cap will relive some of the pressure if system is over pressurized. coolant will flow out of the overflow tube till the pressure drops and then it closes hard to get coolant back into the rad.

 

I have a 2004 Dodge Durango that's doing exactly the same thing, just started. I have no idea where or why, but after a week or maybe even two, it starts running hot. Coolant is low. Then repeat. I know this isn't help, but thought I would share that I am having the same/similar issue.

 

This is getting really strange. My truck would over heat...i'd check the coolant, it'd be low and i'd fill it. That would last for a week then the cycle would start again. That happened for 3 weeks in a row then all of a sudden stopped...its no longer leaking....?Its been 2-3 weeks without overheating.

 

Same here. You know what I did two days ago? I went out to check the coolant level, opened the rad cap and there was still a lot of pressure in there from the day before, it sprayed coolant from the drivers-side somewhere behind the grill. I looked inside and it was a bit low but I didn't top it up or anything... just put the cap back on, wiped the coolant off the front bumper and drove away.

Since then, it has not been heating up, but it will start again. Here is some history:

A couple months ago, I changed the rad hoses, top and bottom, myself. I did not change the thermostat. This is when the heating-up started. I asked the dealership service manager about it when I had it in for maint. He said "yup, that can happen if it wasn't flushed and there is an air pocket in the system somewhere".

Sooo... I am now thinking I will take it to them and have the system flushed along with the thermostat changed.

 

was it hot when you opened it up if it was cold my guess is you released the air pocket by doing that it shouldn't be pressurized after sitting for a couple days

 

On the 4.7 the top hose has a bleed screw to get the air out of the system.

 

It was not hot when I opened it. It was the next morning before going to work. I did this a few weeks ago prior and thought it got rid of any air pocket. Then a few weeks later, started heating up again, which brings us to when I made this post.

The fact that it was pressurized still the next day, I realized, there couldn't be a leak somewhere cause it would have lost the pressure overnight then. So this was kind of a relief. Someone put an aftermarket cap on the rad as well. I'm gonna replace it with the original Dodge cap as suggested by the service manager/mechanic.

 

Seriously! I did not know this. I'll look. How would you use this bleed screw? When it's hot, warm, cold?

I'm gonna look through the service manual Thanks!

 

OK, I have had a look at the service manual and discovered something interesting:



This could mean, theoretically, if the cap is not operating properly, the coolant can heat up, the temp sensor would report high temp but because pressure is constantly leaving the cap (it's not sealing), the system does not circulate properly and therefor the coolant stays above normal temp. Because the cap is malfunctioning (maybe), this would explain why the problem is intermittent.

This is just a theory of mine based on what the manual was explaining.

 

as the pressure rises in the system the boiling point of the coolant and water rises as well if the cap is leaking pressure cannot build in the system causing coolant to boil into steam with steam in the system it can act like an air lock