Mechanics

MY M IS OVER HEATED AND IS RUNNING HOT

1999 Chrysler 300 • 134,372 miles

My 300 m has been running fine but one day ran hot all of a sudden and the temperature gauge started rising past half and even more but turned it off. Won't start from being hot but let cool and tried once more, it stared but check engine light was on and no hot air. Had it tested and radiator fan high and low relays tested bad, so I put new ones in. Still ran hot, gauge stayed at half and sometimes began to rise even more. So I did a compression test on all 6 cylinders and they all held at 180 pounds. Then I remove the thermostat and tested in boiling water about 6 times at 212 degrees fahrenheit seemed to open up just fine. And put back together. Same problem as before. I have a new radiator and hoses new thermostat fans turn on and seem to work just fine. They turn on at about below the half mark on the temperature gauge. I even took the top radiator hose off and with the car running put water in the hose and took it just fine. Why is my car still over heating and running hot? PLEASE HELP ME!
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JMANN
April 22, 2012.



I'd start with a test for a leaking head gasket. If combustion gases are sneaking into the cooling system, it can pool under the thermostat and prevent it from opening. Thermostats open in response to hot liquid, not hot air.

Another clue is you might see air bubbles in the reservoir when the engine is running. The leak test involves drawing air from the radiator through a glass cylinder with two chambers partially filled with a special dark blue liquid. If combustion gases are present, the liquid will turn bright yellow.


Caradiodoc
Apr 22, 2012.
Ok do you have an idea why I don't have hot air all of a sudden ever since it got hot that day it has only got hot once and I was driving. And where can I get this combustion gas tester?


Tiny
JMANN
Apr 23, 2012.
Auto parts stores sell them. There cheap and work well. Thay might call it a block test kit


Djcl
Apr 24, 2012.
If the thermostat is closed, no coolant circulates so no hot liquid enters the heater core.

You can borrow the head gasket tester from an auto parts store that borrows or rent tools but they will make you buy the special liquid. The liquid will become contaminated if you accidentally suck up coolant during the test, then it must be replaced. To insure you don't get a tester contaminated by the last person to use it, they make everyone buy their own liquid. Since you're buying way more than you need, it's less expensive to just have a mechanic who already owns this tool do the test. It only takes a few minutes.


Caradiodoc
Apr 24, 2012.
Can I pressure up the cylinder with air and look for bubbles in the tank? Or will the air get trapped in a high or low spot?


Tiny
JMANN
Apr 24, 2012.
Yes you can but you have to remember that some leaks only show up when the engine is hot and cracks expand, and some only show up when the engine is cold. There is a tester called a "cylinder leakage tester" or "cylinder leak down tester" that does just what you're asking. You must put each cylinder, one at a time, at top dead center on the compression stroke, then compressed air is supplied to the tool, and air pressure regulated to around 30 psi is forced into the spark plug hole.

You look for the results of any leakage in four places. If you hear hissing at the throttle body or carburetor, you have a leaking intake valve. At the tail pipe; a leaking exhaust valve. Leakage past the rings will show up at the oil cap or dipstick tube. A cracked head or leaking head gasket will cause bubbles to show up in the radiator. With relatively small leaks, the air will sail right past the thermostat and be forced into the reservoir by normal cooling system pressure and you might not even know there's a problem. It's the larger leaks that can cause the thermostat to close.

Many thermostats have a small bleed hole to help hot coolant get from where it became hot to the thermostat where it will be sensed and cause the thermostat to open. During the leakage test, air from the combustion chamber sneaks through that bleed hole and goes to the radiator. For thermostats without that bleed hole, air must find another way, usually through the heater core, so it can take a while to show up where you can see the bubbles. You can watch to see if the coolant level is rising in the radiator, but the tester also has a gauge to show the percentage of leakage. Typically anything under 10 percent is acceptable. If you find much more than that in one cylinder but no other hissing is noticed, give that one plenty of time for the bubbles to show up. The air has to be going somewhere. Also listen at the spark plug holes for adjacent cylinders. A head gasket can leak between cylinders, but that isn't what your symptoms suggest.


Caradiodoc
Apr 24, 2012.
If I have pulled the thermostat and have it at operating temperatures should I not still get hot air from my heater? I ran it for 20 mins and it was running lower then normal. The next time I had it at idle it over heated. And I'm getting small amounts of water out the exhaust.


Tiny
JMANN
May 6, 2012.
Removing the thermostat is counter-productive. The coolant moves way too fast and doesn't stay in the engine long enough to get hot, therefore you'll get cold air from the heater. Running too cold also promotes sludge formation in the oil and accelerated engine wear from parts that haven't fully expanded to fit properly, mainly pistons.

In some instances the opposite can happen. The hot coolant won't remain in the radiator long enough to give up its heat so hotter than normal coolant goes back into the engine.

Some water dripping from the tail pipe is normal. That is one byproduct of a working catalytic converter. If you suspect it might be coolant you're seeing, you can add a bottle of dye in the radiator, then search a day or two later with a black light. The dye will show up as a bright yellow stain. If you see that at the inside of the tail pipe, coolant is indeed going there.


Caradiodoc
May 6, 2012.
Well I pulled the thermostat out to see if I can tell if the water pump is working. I started the car and squeezed the upper radiator hose and could not feel any flow at all I even kinked the hose to feel for flow but nothing.


Tiny
JMANN
May 6, 2012.
I never tried that so I don't know what results to feel or expect.


Caradiodoc
May 6, 2012.
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