I have a 99 Dakota Sport with the 3.9L. I am losing about a gallon of antifreeze every 250 miles or so. There are no leaks that I can see. I've gone under after driving it to look for very small leaks or maybe one dripping on something hot and evaporating. It all appears dry. I checked my oil and it looks good (no milkiness). The only other thing I can think of is that I'm burning it. It's hard to tell by looking at the exhaust, if it's more white than normal. It doesn't smell overwhelmingly sweet, although again, it's hard to tell. I normally don't stick my nose in the exhaust and sniff so I don't have whole lot to compare it to. I got a block tester to check for combustion gasses in the radiator and the fluid didn't change color. I did the test with the truck running with the thermostat open. One time I just started it and let it warm up until the thermostat opened and the other time was right after I drove it for about 30 miles. Both times, no fluid color change. Could it still be entering the cylinder but not allowing combustion gasses back into the radiator? I'm really leaning toward it being a blown head gasket but I was expecting it to fail the block test, but it didn't! Any other ideas?

 

If there is a head gasket leak the combustion pressures will force any gases into the coolant.

Look very closely at the water pump and all hoses. Check the drain on the HVAC housing. Look at the radiator cap and reserve tank. Make sure there are no cracks in those lines.

You might also try getting a pressure tester so you can pressurize the system while you check for leaks.

 

Relax sounds like a bad/worn out rad cap to me. It could also be a leak that only happens when the engine is hot and as you drive. Check where the rad cap attaches they get hair line cracks at the rad cap spout its hard to see an very common same every hose mount they are all plastic and crack over time.


Be sure to buy a quality rad cap STANT.


I forgot look at the water pump weeper hole if the pump seals are worn it can pump coolant out the weeper hole.

 

Try pressure testing. I had a similar issue a while back but my loss was very small.


https://dodgeforum.com/forum/2nd-gen...loss-4-7l.html

 

I'll figure out how to do the pressure test. I failed to mention the first thing I did was get a new cap and the overflow tube and reservoir are dry.

 

New ok but a cheap cap or stant?


Cheap caps can allow coolant to get pumped out the cap bypassing the tank completely a good cap is a little hard to get on cheap caps are over easy to twist on.


Never think new I can mark that as the possible problem off the list as new parts are sometimes the problem.

 

The new cap is a Stant. I just did a pressure test and it lost pressure really slowly. Maybe 1 PSI after 5 minutes, if that. I wouldn't be surprised if air was sneaking out at the filler neck where the cap attaches.

 

Just a thought.
When the pressure cap releases(@ 17psi). The coolant goes into overflow.
What if the tube connected to that nipple wasn't tight and the coolant just ran to the ground.
Once the engine was cool there wouldn't / couldn't suck the coolant from the overflow jug back into the radiator.

May want to add a ziptie around the hose at the nipple and check the overflow hose and jug for cracks.

I had a small cut in the bottom radiator hose where the clamp held the hose to water pump.
May want to put soapy water on hose and connections. Do the pressure check again and look for bubbles.

Just a thought.

 

He can pull hose off from neck to bottle, stop up one end and blow with mouth to check if airtight.

Regarding pressure test. If pressure holds good for around twenty mins, it's probably okay with regards to a leak.

 

Thanks for all the input! I'll check all the lines really carefully. This has make me think about tiny leaks. After I drive with the engine up at operating temperature and then park, the system would still be pressurized. Wouldn't I then at least be able to see a drip coming from somewhere? I have looked everywhere and it all looks dry!