The only reason I mentioned the coolant/water mixture is because of warmer weather if it was a high percentage of water and the outdoor temperature had risen several degrees recently from what it had been maybe that was having an effect. Another thing that I just thought of is the radiator cap. If it isn't holding enough pressure it would cause the car to overheat. Another thing you could do is run the car until the thermostat is open and remove the radiator cap with the car running and see if the water is circulating through the radiator good. It seems to me that it should run hot when sitting and idling more so than when being driven, because when it is being driven it is getting road draft through the radiator to help cool it.
What about all the "Never ever remove while hot!" warnings?
Check your coolant level with the engine cold, top it off if necessary.
Start the engine with the radiator cap off and let it warm up.
Look for the coolant to start moving when the temperature gets up to normal. You can also hold your hand on the top hose and feel it get hot as the coolant starts to circulate.
Look at the coolant all the time and see if there are any bubbles coming up to the radiator cap area, which would indicate a possible head gasket problem.
This is assuming you have the radiator completely full and there are no air bubbles "burping' out of the coolant when it is cold.
If the bubbles are coming up to the radiator neck when the engine is hot, look at them to see if they have any smoke or steam in the bubbles. that would indicate a head gasket.
You had the radiator replaced before. If the coolant was not properly filled (some systems need to be bled) then your problem could simply be low coolant level. Variations in temperature can be due to something as simple as the coolant level not being filled properly.
The recovery bottle should (if working properly) have a low level mark for engine cold, and a high level mark for engine hot.
If the recovery bottle is changing its level as described above, then you probably do not have an air pocket in your cooling system. In fact the best test is the recovery bottle level working the way it should.
If you have a bad hea gasket, you may be loosing coolant without any signs of a leak. Make sure the radiator is full and the recovery bottle is at its proper level. if after that you have coolant magically disappearing then the head gasket is suspect.
if you park in the same place make sure there are not leaks that are leaving anything on the ground.
Don't remove the cap if the car is running hot, but if the car is running at normal temperature the pressure won't be that high only about 14-16 lbs. of pressure. The pressure builds up after cutting the car off because the coolant is no longer circulating through the engine it is sitting still in the heat of the engine which makes it get hotter and build more pressure. Just use a heavy rag or towel and let it overlap the the radiator cap so nothing can spew on you and remove the cap slowly. Just open till it is loose but still locked onto the filler neck of the radiator until the pressure is off of the system. There will probably be a little bit of coolant come out, but if it is not running hot it won't be enough to amount to anything. Or if you don't feel comfortable taking the cap off while the car is running you can take the cap off and start the car and let it idle until the thermostat opens to see if it is circulating good or not. It will just take longer for the thermostat to open because the engine won't heat up as fast with the cooling system open.
Thanks for the advice, gary and Ford Man. I will try that on my lunch hour (yes, I drove the car to work this morning--that's how I know that the heater is sufficient to keep it cool, and that suggests to me that this isn't a total failure of the cooling system, but I'm no expert).
Originally Posted by landon
thornburg, was the A/C on when this was happening? Was the temp gage at or near red? Have you confirmed the operation of both cooling fans?
The A/C was running when I first noticed the rise in temp, but I have confirmed that problem occurs even when you don't use the A/C. I checked that both fans came on while the car was sitting idling w/the A/C running, but I haven't come up with any other way to check the fans. I may have to try the direct-wire method.
(Remember, I'm an engine newbie, so I don't know what "normal" is).
When I popped the cap off, the fluid was right up to the top. There was some grey-green sludge on the cap, maybe some kind of sealing grease? It did not look like corrosion or deposits. I started the car and let it run to get it up to temp, but it seemed to stop at about 45% of the gauge (normal operating temp in the past has been 50%). I don't know what I should see when it runs, but it appeared that small amounts of the fluid were going into the "overflow" tank. Very small amounts. I did not see any bubbles or steam. After several minutes at the 45% level without increase, I decided that maybe revving the engine a little bit would bring it up to temp. When I revved the engine (not real far, up to about 2000 for about 2 seconds and then up to about 2800 for about 1 second), the level in the fluid rose and it started to spill out the top. I decided that was bad and shut the engine off. The fluid sank back down. I restarted the engine to see if it was up to temp. Close, but not there. I let it idle and watched the fluid. It seemed to be the same as before, except now I saw some steam (I think) coming from the area of the cap. Not much, I really had to look close to see it. Still no bubbles. I watched the temp for another two minutes (and the very small amount of steam/water vapor) and then shut the engine off, came in here, and wrote this.
The fans did not come on during any of this. I have no idea how I would know if the thermostat opened up or not.
All help appreciated.
EDIT: Sorry for double post, but it seemed appropriate in this circumstance.
Revving the engine/water pump might have just created enough extra flow to cause it to spill out from the radiator since the top rad hose is likely next to the filler neck and the water pump would have been pumping coolant to that end of of the radiator faster than it could drain through the radiator.
It could be an intermittent problem with the fan controller or maybe an intermittent problem with the thermostat sticking closed.
As the others said, a bad head gasket will usually result in an overflowing overflow bottle and then a big air space in the radiator after it cools down (at least that's what happened to my engine when my head gasket went bad).
You might check to see that there isn't a bunch of dirt/dust built up on the front of the rad behind the AC condenser coils (shine alight through it to see how clean it is).
Start it and let it idle. Just leave it. Don't rev it or anything and leave the radiator cap on. Don't worry about it boiling over when you are doing this test as it takes way more than that to cause damage.
- If the engine temperature rises and the fans never come on, the fans are the issue(that's a given).
- If the fans come on and the engine still starts to get too hot then your thermostat is the issue unless you rev it up and see the symptom below. Usually the return line from the radiator is cold to the touch and the line to the radiator is hot.
- If the radiator is clogged, then when the fans are on and the car is getting hot you should be able to pop the revs up to 4000 or so and see the hot hose swell and the cold hose collapse(you'll definitely see this one). Since you aren't losing coolant this isn't as much of a possibility but might be still.
You aren't loosing coolant so the radiator cap is fine as is your head gasket.
Almost every car will spill water out when you rev it up with the cap off. The water pumps in cars create a lot of hydraulic pressure. It's enough to not only do that but force water past a thermostat that isn't opening to cool the engine as revs climb.
The temperature won't never get too hot with the radiator cap off as long as you keep water in the system. I have actually loosened the cap on cars before when they would run hot so I could drive them home to check them out. Be careful underneath the hood if the car is running hot. If the thermostat is stuck it could create enough pressure to bust a hose and hot coolant cover you. I had one bust on me for that reason once. I was lucky I had just pulled to the side of the road and was getting ready to pop the hood when the hose busted so I was still safely inside the car. I'm not trying to scare you I just want you to be aware.
On the Dodge Neon, I overheated once, and the problem was stupid:
the car would overheat, and I would hear bubbling, the overflow tank would go low.
Turned out the radiator cap was not sealing right, and needed to. Replaced it and all went back to normal. Couldn't tell by looking at it.
=> So it's not always a head gasket problem or a faulty thermostat
I suggest you find a forum for your car that looks technical, and search for the symptoms. It could be a known failure mode of your car. If one in a hundred cars hits it, people in the forum will know about it.