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Questions and Answers

Chevy S-10 Cooling System Bleeding

Q. Vince: I have a 1994 Chevrolet S-10 extended cab pickup, with a 4.3 liter VORTEC central port injector (VIN W) engine. The truck has 135,000 miles and is 4-speed automatic (overdrive). It has front ABS, PS, A/C and cruise control. The problem started when I replaced the thermostat, upper and lower radiator hoses.

Chevy S-10 Cooling System Bleeding

The thermostat was an AC Delco #131-115, a 195° thermostat. I have since had the radiator and fan clutch replaced along with the temperature switch. When I first start out, the temperature gauge will come up to about ¾ scale, the "check gauges" light will illuminate, but then the temperature gauge will return to half scale or about 195°, the normal reading for this thermostat.

This process may repeat several times until it finally settles down to the half scale reading. Please note that at NO time is the engine actual overheating! I have been told that the cooling system has an air pocket and this is causing the gauge to misread. I have attempted to purge the system by allowing the engine to come up to operating temperature with the radiator cap removed.

My thought was that air is lighter than water (or antifreeze) and the air escape. Needless to say, nothing has worked. I should point out that I did not have this problem prior to changing the thermostat and hoses. Can you help me?



The sensor for the temperature gauge is in the drivers side cylinder head between the front two spark plugs. If there is any air trapped inside the cylinder head at this location, it may be the problem. Find a steep incline and park with the front facing up and do the open cap thing, Maybe that will allow any air to escape.

Did you happen to have the serpentine belt off and wrap it the wrong direction? This would make the water pump spin the wrong way. Just a thought. Also check the wire from sending unit to make sure it's not lying on the exhaust manifold and grounding out intermittently.

Additional Information provided courtesy of ALLDATA

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