Overpressurizing Coolant System?

Asked by Jan 10, 2016 at 10:02 AM about the 2001 Dodge Neon 4 dr Highline ES

Question type: Maintenance & Repair

First off: there is a (known to me) minor leak in the top of the radiator. A few
faint wisps of white smoke coming off the engine after running is normal for
me by this point, but the coolant loss isn't extreme and I just haven't had
time to replace the radiator yet.

Here's what's happening besides:
The leak in the top of the radiator is something like a blown seam. I have:
Flushed the radiator, burped the system, checked upper and lower
hoses(good), replaced the overflow reservoir and the hose leading from
it(because, perhaps unrelatedly, they were torn up pretty badly. What you
get for buying a used car).

I do not have coolant in my oil. I do not have water in my tailpipe. I do not
have white smoke coming from anywhere(except slight wisps from under
the hood, due to the leak in the top of the radiator, as stated above). I do
not have the smell of burning coolant(but have the occasional smell of
burning oil). I do not have power loss. My heat works like a champ. My
temp gauge never rises above the 1/4 mark.

The further or faster I drive the car, the more rapidly my coolant depletes
through the 'seam' in the top of the radiator. Sealing it shut resulted in the
seal being blown through.

Several months ago(during the summer) I drove the car cross country, and
was having overheating issues with it. I'd drive a few hours, and hit the 3/4
mark on the temp gauge and then park for a few hours to let it cool down.
Chalked it up to summer heat and, as it didn't seem to be getting any
worse, forgot about it. Car ran fine as an around-town delivery car after
that.

My best guess, is that the coolant system isn't flowing properly, resulting in
a buildup of pressure. That being the case, I don't want to drop a new
radiator in until I find, and repair, the issue causing over-pressurization. I'm
fairly certain the Temp Sending Unit is shot, as I should definitely see a
reading above 1/4 at some point. So assume that my temp gauge is full of
crap. What I'd like to know is: where do I need to go from here? I'm thinking
water pump and/or thermostat is faulty and in need of replacement, but I'd
like some advice from somebody a bit more knowledgeable.

Thanks in advance!

7 Answers

274,605

The cooling system is pressurized, so a small leak in your radiator might be the issue. Perform a pressure test on the car to determine if all is good. You can also perform a cylinder pressure test too to determine if the head gasket is good.

60,665

Head gaskets are an issue on those cars. A small combustion leak can over-pressure the cooling system causing it to leak. You need to eliminate the head gasket as the cause. A bad head gasket doesn't always put coolant into the oil or cause water to run out of the tailpipe. It all depends on exactly where the gasket is leaking.

95,715

The seam in the radiator is leaking. Install a new radiator and a new radiator cap. No mystery here.

60,665

The mystery may or may not be why is the radiator seam leaking. Certainly could be just a bad radiator or could be overpressuring due to combustion gases getting into the coolant.

95,715

Radiators often separate where the core meets the tank which is what is happening as far as I can tell.

95,715

A new radiator cap with the proper pressure rating will stop high pressures.

60,665

Full_of, you may be correct. I was just supplying an alternate answer to the problem if the radiator does not fix it. Those engines had lots of head gasket issues.

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