The coolant is boiling when I shut off engine

Question

I have a 2000 Chrysler 300m. A few days ago out of the blue my car cut off on its own and I was unable to start it for a few hours. I left it sit in the grocery store parking lot. Went back 3 hours later and it start right up. Five miles down the road it started overheating bad. It started to stutter and had a loss of power. The next day I took it to shop and was told that the water pump was going bad, the hose need changing, and the timing belt. The price was crazy so I took it to another well known shop. They did the work for half the price. They had the car running for 2 hours and it was fine. I picked it up from the shop and drove maybe 50 miles that evening and it was fine. This morning I drove it 15 miles and when I turned it off, I heard the boiling sound. After it cooled off it needed 4 large cups of water. I drove it home and it was boiling again. The mechanic that did the work said the water was really nasty in the pump. I am so over not knowing if I will be able to get my kids to school. Thank you in advance for any responses.

Answer 1

tl;dr: this might be as simple as a bad radiator cap.

Funnily enough, I am currently experiencing similar issues with my (completely different) car. I smelled coolant, looked under the hood and saw this:

Even with new coolant, I noticed that it was boiling out of the overflow pipe.

So, what does this tell me? I'm almost certainly losing pressure somewhere in the system which, due to the ideal gas law, allows the coolant to reach boiling point even though the car isn't overheating.

What should you do? Get the car hot, open the hood and then listen carefully in various places over the engine (obviously it's hot, so watch out under there).

My suspicion is that you'll hear exactly what I do: hissing right at the radiator cap. The solution is pretty simple:

1. Buy the replacement cap for about $20 USD.
2. Wait for the car to cool off.
3. Replace old cap with new.
4. Top off coolant.
5. Drive around enough to get it hot.
6. Confirm no boiling and no hissing.
7. Go to the shop and have them flush the coolant. Tap water is not good for the cooling system. You should always use a proper mixture (and Home Depot Prestone is probably fine).
8. Come back here and brag about how you fixed it. :-)

Good luck. Many of us are parents and feel your pain!

Answer 2

Overheating can be caused by several things. First, make sure you are actually overheating, that is the temperature gauge tells you the coolant is too hot. (See Bob Cross's answer).

If it IS too hot, it could be caused by 1) bad thermostat stuck closed 2) bad/clogged radiator 3) bad water pump.

A bad thermostat will also cause a fairly rapid overheat, and usually a cold or cooler than normal heater.

A clogged radiator is more frustrating to diagnose because you do NOT want to open the radiator while it's hot. If it IS a bad radiator, get a NEW one, not a rebuilt one.

A bad water pump will usually be making a squeaking noise. You will also be able to see coolant leakage on or around the pump. Some water pumps are easier to change than others, and you don't necessarily need to change the timing belt. Depends on how much mileage the timing belt has on it. And DO NOT let a tire store or Wal-Mart do that work. Find a shop where they make their living doing mechanic work.

Finally, if you need to add fluid to the coolant system, use either pre-packaged 50/50 non-silicate antifreeze or a 50/50 mix of full strength and DISTILLED water (really cheap to get at the grocery store). Don't use tap water unless it's an emergency.

Answer 3

Are the cooling fans running when its overheating? I've seen plenty of Chryslers over heat from fan failure. Other possible cause would be the head gaskets. The water pump was probably leaking, but when it started to run rough and died you may have caused a leak in the head gaskets

Answer 4

So - I had exactly this problem on my 2003 Mazda Protege 5, 150K miles. I also happen to live in AZ where summers are 115F. When I would turn the car off after a bit of a drive, the temp gauge in the car was at medium. However, after about 30 seconds of being off, the coolant started to overflow and boil into the spare holding tank. And the boiling was vigorous in there.

I went to Autozone, got a $10 radiator cap, put it on, and the problem stopped.

Thus, my radiator cap was faulty - and was letting fluid out at too low a pressure (which happened to be less 16 psi per the rating on the cap).

Want to thank this forum for saving me a trip to the mechanic. Cheers!

Answer 5

I'll agree that coolant is boiling because there's probably not enough of it in the system. So if you fill/check it and know it's full, and drive a while and the boiling happens then the coolant is going someplace. Where it's going is what you need to find out.

Your original problem seemed to be a bad water pump, and that was replaced which seemed to fix the overheating, but don't rule out that the recent work you had done could have introduced a new problem. A poorly installed gasket for example could work fine for a while and then start leaking coolant.

I can't speak to the shops involved, but objectively if some place can do the same job for half the price, that can sometimes means a) the work they do isn't as good, b) the parts they use are probably cheaper, and maybe not as good, or c) they are cutting corners, like maybe not changing the coolant out or checking everything over as well.