1998 Honda Civic Temp Gauge Rises

HONDA CIVIC
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MECHANIX
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I have a ’98 Honda Civic EX. Recently my temperature gauge has been moving up to around three fourths mark. I’ve changed the thermostat and radiator cap. The radiator fan works, I jumped it, check voltage while the car was on, and I finally hear it today while I was sitting at a stop light. Here’s the weird part, my temp gauge will stay around normal when I have the heater controls on hot, heater off, and the temp gauge will jump up to three fourths when I move the heater gauge to cold, still have the heater off. Car doesn’t heat up when just sitting, just when I’m driving down the highway.
Jun 24, 2006 at 5:31 PM
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JOUGH626
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Faulty coolant temp sensors. Replace them both. Double check your fan relays.
Jun 25, 2006 at 10:38 AM
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MECHANIX
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[quote:6a8f2c9d4e="jough626"]Faulty coolant temp sensors. Replace them both. Double check your fan relays.[/quote:6a8f2c9d4e]

I changed the sensor at the thermostat, not sure where the other one would be located. Fan come's on, but car still warms up beyond the safe zone. Thanks again for the help.
Jul 6, 2006 at 1:44 PM
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BRUCE HUNT
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When you turn the heater on, even with no fan pushing the hot air, this provides another avenue for the hot liquid to flow and release its heat. When you shut of the heat you close that valve and thus the system becomes smaller and because of another problem the engine will run warmer and in your case much warmer and not good. I would check simple things like a collapsed hose. They can look good and still have blockage. Another is a radiator blockage.

Did you say that you replaced the engine thermostat or just the sensor located by the thermostat?
Jul 10, 2006 at 1:36 AM
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MECHANIX
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[quote:9687e6a233="Bruce Hunt"]When you turn the heater on, even with no fan pushing the hot air, this provides another avenue for the hot liquid to flow and release its heat. When you shut of the heat you close that valve and thus the system becomes smaller and because of another problem the engine will run warmer and in your case much warmer and not good. I would check simple things like a collapsed hose. They can look good and still have blockage. Another is a radiator blockage.

Did you say that you replaced the engine thermostat or just the sensor located by the thermostat?[/quote:9687e6a233]

I replaced the thermostat. The upper and lower radiator hoses are hot when the car has been running, I would guess that they are fine because liquid is flowing through them to cause them to heat up. I'm gonna do another flush tomorrow. Thanks for the reply.
Jul 10, 2006 at 2:57 PM
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Suggested Repair

Replace both coolant temperature sensors and recheck the fan relays. Also inspect for a collapsed radiator hose or radiator blockage, and flush the cooling system. Note that setting the heater to hot opens an extra coolant path and can mask restricted cooling.

Conversation Summary

A 1998 Honda Civic EX temperature gauge rises to about three-quarters while driving on the highway, especially when the heater control is set to cold, but stays nearer normal with the heater set to hot. It does not overheat while idling. The thermostat, radiator cap, and thermostat-area sensor were replaced, and the radiator fan operates. Experts suggested faulty coolant temperature sensors, fan-relay checks, a collapsed hose, or radiator blockage. The owner planned another coolant flush.

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