so let me start by saying i am a certified motorcycle mechanic and i know my way around engines pretty well, so here goes,
next i have a 2001 cavalier z24 with a 2.4l twin cam motor in it.
in january my cavalier suddenly overheated and started pinging really bad, and i put water in it, i drove about 10 miles and it did it again, i thought i had a blown head gasket because i was losing coolant so rapidly. since it was raining at the time i could not tell if there was any coolant leaking anywhere, but i couldn't see any, also it did not look like any water was coming out of the pipe.
so i have been riding my motorcycle since jan, and i decided to start tearing into my car to find the problem, and here is what i have found, clean spark plugs, with no white residue like they are burning water, no visible leaks and no water in the oil... so i do not know where my water is going.

so today i put just straight water in the motor and fired it up to check for leaks so i wouldnt waste coolant and i have the following,
motor runs great,
no water coming out exhaust,
no visible leaks,
no water in the oil,
the water i put in the overflow bottle is staying as cold as it came out of the jug,
the top radiator hose is getting to hot to touch, but doesn't seem to have pressure, (it feels soft when i squeeze it)
bottom radiator hose staying pretty cool,also soft no pressure
heater works, (i did not find any water in the floorboard like i have a broken heater core,
car doesnt seem to over heat, only got to about 200 deg F after about 20 min of idling.

and here is the questions i have
my thermostat is working or the top hose would not be getting hot?
i think maybe the radiator might be clogged because the overflow and lower hose are not getting hot?
i might have a bad water pump but i dont have direct radiator access so how do i test that?
if you have run into this problem or have suggestions please let me know,
thanks,
mike

Sounds like a bad radiator cap. Had the same thing happen to me. I even went as far as replacing all the hoses, water pump, and radiator just to find out that it was the $7 radiator cap the whole time!

It is worth replacing the cap anyway. The first thing I would check when my car is hotter than normal is if the cooling fan is going on and off as it should.Once I had to replace the fan motor about 2 years ago and last time it was the connector.

I was just about to mention (like Jason)- Radiator cap.

If the coolant heats up, but there's no preasure in the hoses, that expanded coolant must be going somewhere. The broken radiator cap, which regulates preasure, could be allowing steam to escape. That would explain overheating (while driving), no problems while idleing (less demand on your cooling system), and where you coolant is going despite no leaks.

i dont see why starting a whole new thread when i am having the same problems... ok

Is a 2.2l 97 5spd 7200 miles
*stays cold when started takes about 5 min of idiling to get to normal temp
*randomly overheats when driving
*water reservoir Boils once overheating has begain
*


Things i have checked

*hoses no visible leaks (could have missed something)
*changed thermostat
* flushed radiator

what am i looking for to see if cap is bad? and how can you tell the water pump is operating properly?

Ps... FIRST POST
Pss.

As far as I know, there is no good way to look at/test if your radiator cap is good or not. However, the symptoms you describe suggest this to me (I.e your coolant isn't operating at the correct preasure).

As noted, it is a cheap part, so the best way to check it is to buy the part ($7-15) and see if the problem is fixed. I would want to eliminate the radiator cap as a problem before I head to the water pump. Make sure the basics of the system are functioning first.

i have the same problem with mine. I replaced the cap and the problem was fixed. Once I got on it and reved the car up to 6500 rpms the cap poped again. is there a chance the thermostat is bad, or is there a higher psi cap we can get?

just to throw this out in the air... my 96 2.2ohv cavi would over heat after 5 minutes of driving time. the coolent would disappear but did not show signs of being in the oil. turned out it was being burnt away in my cylinders, also causing misfires in cylinder 3 and 4