Cooling problem with 1999 Cutlass Supreme going.

RGRIFFIN087

MEMBER
1999 OLDSMOBILE CUTLASS
130,000 MILES

Cooling problem with 1999 Cutlass Supreme going unsolved. I have replaced the thermostat (correctly), the waterpump and coolant reservior and cap. I have checked the coolant for exhaust gases as well as the oil for the milky substance for indications of a bad head all passed. So my problem, when my car is driven at a slow speed the tempature begins to rise but as long as I stay at a slow speed once it gets to 3/4 mark it seems as if the thermostat opens and the car goes back to normal. Now when I get to highway speeds to quickly the gauge continues to climb and reaches the red until I stop sit for a minute, turn the car off then back on then it reaches normal tempatures. Once the tempature is leveled out it will run fine for hours. Also when it gets hot it will push all of the coolant out of the reservior hose. I have checked for leaks and done a pressure test and didnt find any leaks. This also seems to be related somewhat to the heat, when the heat works (which is only some of the time, the tempature is fine). If you could give me any direction on this please.

1 Reply

CARADIODOC

MECHANIC
33,737 POSTS

You need a tiny bleed hole in the thermostat. The high temperature is making its way to the gauge's sending unit but not the thermostat. The bleed hole will allow the coolant to flow enough so the heat gets to the thermostat sooner so it can open. The same thing happened on my '88 Grand Caravan after the thermostat was five years old. Had a student drill a 1/16 hole in it and it's still working fine many years later.