I have a 1994 EX sedan 4-cyl VTEC automatic transmission. As soon as I started for work today, the temp guage began rising quickly. This is after cold-crank first thing in the morning and the car had been sitting for 10 hours. Within 5 minutes of driving 30MPH, the temp guage was pegged at the top. Every other morning that I've driven this car to work, the temp needle would have still been in the blue at this stage of the trip. I pulled off the road, let the car cool for an hour just to be safe, removed the thermostat (Honda OEM approx 18 months old), re-filled with coolant, checked the radiator for coolant flow, and began the return trip back home. The temp guage pegged again within 60 seconds, so I pulled off the road to try to judge actual engine temp. I had just been working on it with my hands in the coolant when I removed the T-stat, so I knew it couldn't get that hot within 60 seconds. Sure enough, it didn't seem hot, so I drove it back home with the temp guage pegged at the top and took another car to work.

Any ideas which sensor might be malfunctioning and causing the temp guage to top out?

 

you got most likely a bad gauge or a bad coolant sending unit switch..

 

Or it could be wiring to the coolant temp sending unit. Find the coolant temp sending unit (it should be around the thermostat) and there will be some wires sticking out of it. Start the car and find the voltage between the two wires going to the sending unit. The voltage should be pretty low. Also, you can disconnect the connector that is going to the sender and start up your car. If the temp shoots up again, the wires prolly shorted somewhere and are sending the PCM a 5v signal which is the signal for a really high temp. If you disconnect the sensor and the temp does not move or stays at the cold position, then the problem is either the sending unit or the gauge like desert said.

 

AGENT ,, the reason why i do not think that it is the wiring shorted to ground , is that , it would take less than 10 seconds to go all the way to hot as soon as he turn the key on,,

he mentioned it took about 60 seconds ,, but i guess wire could be not a full short to ground ,, so yeah ok ,, it is possible .

and by the way there is only 1 wire yellow/green to the ECTSU ( engine coolant temp sending unit ) ,, it is located below the distr ,,

 

Your right about the shorting to ground thing, but it takes 30 sec to do so your not really losing anything. I didn't look up the wiring diagram for that car, so sorry about the 2 wire CTSU thing. I think the easiest way to tell if the sending unit is bad or if the guage is bad is to disconnect the sending unit.