Having an issue with my 2004 Neon, is going through coolant rapidly. I bypassed the heater core as it was giving of strong coolant smell when running heater or defroster. But it is still losing coolant, in this past week it has gone through almost a gallon. No smoke from tailpipe, or coolant in oil. I have looked all over under the hood closely and I found no leaks. Not overheating, temp gauge never getting above the mark shown in attached photo. What am I looking at, head gasket issue? car has just shy of 149k on it.

 

Any thoughts on this???

 

Is the cooling system holding pressure? Most auto parts stores have a tester to check it out. Smelling coolant from the AC / Heater is a good clue, so look to see if one of the hoses coming through the firewall is dripping onto the hot exhaust pipe & being evaporated away.
Good idea to bypass the heater core as a trouble shooting step.
Did the problem come about suddenly after some event???

 

The heater core was suspect whenever I used the heater or defroster. A few days ago I put a 90% fitting in to bypass it completely, and capped off the heater core outlet tubes. I do have a pressure release type radiator cap, after a drive yesterday I just pulled it up for a second or 2, and I could hear the surge into the overflow tank but I could have it pressure tested. I do not see any leaks, no puddles when car is parked. Have to add some coolant every morning, no idea where it's going.

The heater core job alone is a costly repair

 

Aside from the heater core, I would replace all the hoses, make sure the radiator is not leaking, replace the thermostat and then go from there. If I remember correctly, the Neon had an issue with blown head gasket but I'm not sure what years/models.

 

You may have more than one problem, so rig a pressure check of the heater core too, as its still on the suspect list, because you said you could smell coolant coming from the vents when heat, or AC was used.

Year models before 2000 had head gasket problems but that doesn't mean we couldn't have a problem too, especially if the cooling system hasn't been cared for.

Check the oil level & condition. Remove the oil fill cap & look for a chocolate milkshake looking mess inside the cam cover, or on the oil dipstick.

With the engine at cold & hot idle, does the exhaust smell sorta sweet like coolant ?

A couple of years ago we developed a Intermittent coolant use problem, I looked everywhere never could find it. Had the scheduled 90K service done, including completely reworking the cooling system with replacing the water pump while they were in there replacing the timing belt, guess what, the water pump bearing was going out & it was dripping coolant out there.

A couple of years later it started again, this time it was the plastic tank atop the radiator, I had noticed it had slowly turned from glossy black to a dull brownish color over the years & had developed a stress crack along a cold flow knit line about midway, that didn't knit very well when the part was molded. Looked like the vendor didn't have good control of mold temp, or plastic temp, or maybe it was just a faulty mold design, anyway where the flow lines met it developed a tiny crack that would open up under pressure, blow out & evaporate, leaving no coolant puddles on the engine or ground. I topped up the radiator, started the engine & as pressure was building I spotted it bubbling out the stress crack & that's how I spotted it. Replaced the radiator & now that puppy has been leak tight for years.

I've also heard of the recovery tank developing leaks where the hose attaches. More thoughts for consideration, Have the system pressure tested, including the heater core, in case you have more than one problem & Murphys Law is messing with you as it did with me on the water pump & later with the plastic tank atop the radiator. Let us know what you find.

 

Another thought in case all the above comes to naught, most auto parts stores carry a fluorescent dye pack & black light combo like this https://shop.advanceautoparts.com/p/...8Pvw&gclsrc=ds in which we add the dye to the coolant & after it mixes & leaks some, use the black light to spot the leak source glowing at the highest point on the engine, or cooling system. Small leaks are better seen after dark if the leak is small & the glowing dye is minimum at the leak source.

More thoughts for consideration.

 

I changed the oil and filter a week ago, was not milky looking. New oil looks fine. Underside of oil filler cap and cam cover had no milkshake looking substance. Yes, I do recall a coolant like smell from the exhaust,but not seeing any white smoke. Hoses are all in good condition, I also saw nothing leaking from radiator.

Am facing the fact that it is going to cost me way more than I have in it to fix it, will have to see what a pressure test shows

 

Ok good to hear it doesn't seem to be getting into the oil bad enough to cause the milkshake scenario. Sweet smell in the exhaust sorta says maybe the head gasket belongs on the suspect list. If it fails the pressure test & you come to believe the head gasket belongs higher up on the suspect list, consider trying to retorque the head, to see if maybe one of the head bolts has lost some of its clamping force.
If you come to perform the dye / black light test, also include pulling the plugs & expose them to the black light & maybe be able to narrow down the leak suspect list some.

 

I removed valve cover, to check head bolts, they were torqued good, I could not budge them at all. Inside of valve cover, and cylinder head were very clean.
Used a half gallon of coolant yesterday for a road trip, totaling 180 miles. I will get a pressure test to see what it shows, as I am not seeing any external leaks. But I can smell coolant sometimes when it is idling