Coolant bottle overflow

[old school]

What would be causing this to happen. The coolant bottle overflows after driving the vehicle. After it cools down, overflow bottle is empty. 1998 GMC Jimmy 2wd. Thermostat maybe?

[smilingjack]

Sounds like the thermostat is stuck closed and it overheats filling up the bottle.
When it cools down it refils the radiator from the bottle leaving it empty.

[lojo]

Yes the thermostat could be stuck closed as smiling jack says but there are also other considerations. One fans are not coming on if it has electric fans you can listen for them. If it is the clutch style you can have someone hold the fan start it and wait to see if it engages when the engine heats up. I do not advise this if you never have done it becouse as you can see serous injury can occur if not done right. Be sure your fluid is full as lack of coolant will cause it to heat up too much and expand to where it overflows. Finally check the radiator cap and test it to be sure it holds the correct pressure it is suppose to with a tester. You can rent them for free at the auto store. I just take mine with me and check it there. IF none of these when the engine is cool and fluid is full start the car with the cap off and look for air bubbles coming out of the radiator. If it is bubbling when cool then you could have a bad head gasket. You would most of the time get some fluid coming out the exhaust which will have a sweet smell to it and sometimes in your oil which will have a milky look on the dipstick. Make sure your water pump is not leaking it out becouse if so your pump is bad. If the vehicle sees a lot of dirt roads you may need to blow your radiator out with air and clean the fins up. Pretty much sums it up with overheat problems exept if your car is out of time which I would seriosly doubt.

[mopar611]

Go to your local radiator shop and have them do a pressure check on your system before you go buying and replacing everything. Its free, easy, and quick and they will tell you whats wrong in a couple of minutes.

I think its the cap????

Mopar

[ido]

Its probably a head gasket blowout. Compression from the cylinder(s) is forced into the water jacket where the gasket is blown away and goes to the sealed radiator through the top or bottom rad hose and then forces the liquid in the rad to overflow through the attached overflow bottle (the pressure has to go somewhere).

[old school]

I added coolant to the recovery bottle and topped off the radiator with coolant and water. Also bought a new radiator cap and replaced. All is good now. :) Thanks everyone, for the suggestions.

[Matisse]

it was the radiator cap..had the same thing happen to me....amazing what perceived problems a $7 cap will cure...aint it?