Hi Everyone, I have a 2001 Durango 4.7 Liter with 170k miles on it. Owned it since new. I recently began pushing coolant out past the radiator cap and into the coolant overflow reservoir. It takes about 100 miles for me to push about 1/2 gallon out of system and it will start to overheat. Suspected a faulty radiator cap and replaced it. Problem continued. I then thought it had to be a compression leak from one of the cylinders into the water jacket. So I pressurized the system to 20 pounds and let it sit overnight. It was still 20 pounds in the morning. So the overall integrity of the cooling system is still good. Plus I was looking to see if it would push coolant into a cylinder to reveal a blown head gasket. I took it to my local shop and had them run a hydrocarbon test on the cooling system while the engine is running and it comes up with nothing. I'm at a loss as to how the cooling system is exceeding the 20 pound cap pressure.


I also replaced the radiator and thermostat about a year ago. But this problem started a couple of months ago. The engine runs as smooth as the day it was new and as long as the coolant level is full, it runs cool as a cucumber.


Also, when I go out in the morning and pop the radiator cap, the system is still under mild pressure (4 or 5 pounds). So it never gets to a vacuum to pull the reservoir coolant back into the system.


What am I overlooking? Thanks. Ken

 

I am real curious where the pressure is coming from..... When the engine is stone cold, there shouldn't be any pressure..... Unless ambient temp has changed dramatically..... (50 or more degrees inside a couple hours....)

So, try this test: With the engine stone cold, relieve any pressure on the cooling system. (take the cap loose.) With the system sealed up, and cold, squeeze the top radiator hose, get feel for how much pressure you need to actually squeeze the hose. Start the engine, and see how long it takes for the upper radiator hose to start getting hard. As the engine warms up, it will normally build pressure in the system. If the hose starts getting hard right away, then you likely do have a headgasket leak somewhere. (though, one would expect the hydrocarbon test to show that......)

 

Thanks HeyYou. I think I'll use my cooling system pressure tester for that. If I connect it to a full radiator on a cold engine it will be at zero pounds. If pressure starts building within a few minutes, it has to be a gasket. Without a gasket leak, the coolant would not heat up enough in a couple of minutes to produce any significant pressure. If it does build significant pressure in a short period of time, I'm going to pick up an old-school chemical hydrocarbon tester. The shops now all use computers and sniffers. Not sure I truly trust that.

Might be a day or so before I can get to that, but will let everyone know.

 

Overheating could also be from a collapsed hose. Has the lower hose (the one the pump sucks on) ever been replaced?

 

Hey JeeperDon, Hoses are new when I replaced radiator a year ago. But I also think the 4.7 is a reverse flow engine. The thermostat is at the bottom of the engine and the top hose is the one with the anti-collapse spring in it. If memory serves me right the thermostat I installed a year ago was a 185 degree unit. I'm anxious to run my own chemical hydrocarbon test this weekend. Once I'm positive of those results then I'll have a better idea which way to go.

 

Hi Everyone, So I ran my own hydrocarbon test this morning and it does show signs of exhaust gas in the cooling system. It's very small and barely changed the color of the fluid in the tester. Plus, I can see bubbles periodically work their way to the top. My next step is to figure out how to resolve the problem. I've been reading up on chemical fixes for mild gasket leaks and think that might be the way to go at this time. Bar's Leak has a product designed just for this and it seems to have good reviews. Has anyone tried this before? https://barsleaks.com/product/head-gasket-fix/
Thanks
Ken

 

Don't use any any product that you pour into your coolant. No leave in products. It may clog your heater core and radiator. Use a product that mixes with water that you eventually drain out and allow to dry.

Search my threads and use the K&W product that I used. You'll want to isolate the heater core and remove the thermostat. Also, don't follow the instructions which tell you to idle for 20 min with the stuff. A slight HG won't seal that fast. You'll need to drive with it for 500 miles. I did it years ago and have been driving my truck daily ever since. I can still do the head gasket today if I wanted to, but the need is gone.

This is the stuff. Advance has it too... https://www.tractorsupply.com/tsc/pr...BoCoBIQAvD_BwE

 

Great advise. There's a Tractor Supply just a couple miles from me.