Just today my car started overheating, and so far I've done the following:

- Verified thermostat is working
- Verified no air trapped in cooling system (done this many times actually, using bleeder screws)
- Verified fans are turning on/off

My next step was making sure the cooling system is maintaining pressure. I haven't had the cap pressure tested yet, but is it normal to hear the overflow tank swishing around when you squeeze on either of the two radiator hoses coming to/from the water pump when the motor is only slightly warm? Wouldn't this indicate that the radiator cap is bleeding pressure into the overflow and most likely the cause of my overheating problem?

Thanks in advance for your input!

 

Does your car sound any louder? You might have an exhaust manifold leak which would make your engine hotter. How hot is it actually getting? what's the outside temp? The fan relay, fan motor, or fuses could also be dead or shorted.

 

Uh, no, not any louder, entire motor is 100% stock right down to the iron manifolds. Car has 91k miles and original water pump, thermo, etc. Again, never overheated until today. Thermostat appears to be working as water starts churning in the rad about 180-200 degress, which means the water pump must be working to some extent. Without the car running and at a warm (but not hot) temp, I SHOULD NOT be able to squeeze a radiator hose and hear gurgling/swishing through the vent holes in overflow tank cap, right? A working radiator cap would prevent this unless the pressure exceeds the 18lb rating, right?

 

yes, it shouldn't be flowing back into the overflow tank that quick. When you refil it you have the engine running right? when it starts to overheat, check to make sure the fan is going on.

 

I called autozone and it's $2.99 for a radiator cap, so I'm going to try that tonight. I've done all refilling with the car running and it continues to overheat (240+ degrees) with both fans on high-speed. I really think it's loosing pressure. Hopefully replacing the cap will fix it...if it does, this will be the cheapest repair yet!

BTW, I really inspected my old radiator cap and noticed that the inner-valve assembly (that opens to pull anti-freeze back into the radiator from the overflow) is fairly loose and doesn't maintain a seal against the outer valve flange surface (if that makes sense any sense at all... ). This would be a bad cap, right?

 

I don't really think so unless you were losing water because of it. I had the same problem and I used that cap till it broke.

 

Well, I figured it out. The thermostat was only opening about 1/4 of the way when it reached 180. I removed it and bolted things back together and the car wouldn't even register a temperature going down the road. So I put in a 160 degree unit and now the car just crosses 170 degrees during highway travel. Good thing is the water pump is still strong and not leaking at 91k (knock on wood)!

Thanks for all your help!