coolant overflow

[jrrsmith18]

i have a 2001 catera and from just idleing from start the temp on the car will reach the line right above the half mark. when it reaches that point coolant starts pulsing out of the overflow bottle. just replaced thermostat with no luck, any suggestions?

[JRomano]

Comes from the cap?? I would try getting a new >$10 cap to rule that out before digging in too far. Is there any mayo-like substance on the bottom of the oil fill cap and or dipstick? Any brown oily residue in the coolant tank? Does the car smoke at all when idling? If so what color?

[jrrsmith18]

yeah there is some mayo like stuff on the fill cap but not on the fill stick. there is none of that stuff in the coolant bottle. i'll try getting a new cap and see if it does anything.

[investor74]

Just another possibility in addition to the coolant cap. I thought I had the same problem on my other car. Turned out I was over-filling it and the liquid expansion caused it to come out the overflow pipe.

Also, when I had the radiator flushed out, I found it dropped the temperature. I rarely go above the half way point now, except on very hot days in the summer.