I have a 1998 civic ex i bought back in october 2022 that at first was having overheating issues, so i bought a mishimoto radiator, fans, and thermostat. I also replaced the waterpump. Turned out to be the heater core, so i just did a bypass. The car runs good now but the temp gauge stays at a 1/4 and at night a little bit under a 1/4. Im thinking it might be the thermostat is stuck open or its opening up at a much lower temperature than oem, but im not sure and i wanna ask a for a second opinion since im still new to cars and this is my first car.

 

Is it a Genuine OE Honda thermostat ? If your thermostat is stuck open, the temperature will come up to the normal position when warmed up if you simply let the car idle in your driveway. Once it comes up, get in the car and drive. If the gauge goes back down, you know that the thermostat is stuck open.

 

Have you looked at the OBD2 data to see if the temperature that the ecu is getting more or less agrees with the gauge on the dash?

 

Its a mishimoto thermostat. When i let the car idle in the driveway it stays at a quarter and doesnt drop or go up more. When I drive it stays at a quarter. The fans turn on everything so the temp switch is working. My fuel gauge also reads low so im also thinking i have bad gauges

 

i have not i will look into that thank you. I think it might be the gauge because my fuel gauge also reads lower than it is

 

If the car is running normally it's more likely to be an issue with the gauge sender circuit. That wire runs mostly unbroken back to the gauge cluster, except for a single connection at the driver's side shock tower connector. If there is increased resistance in the circuit it will read low - similar to the documentation for the ECT sensor:



Key on/engine off but with a warm engine (better if it's not so hot that you're uncomfortable reaching up under the distributor and around hit coolant hoses), move/bend the connector at the gauge sender around while someone watches the gauge for you. See if you can affect the gauge reading. It's just a push-on type connector, pull it off and give it a gentle squeeze with a pair of pliers to tighten it up a little. Insepct the pole of the sender for corrosion. Polish it a little with a Scotchbrite pad. See if it's more stable afterwards.

If it was a thermostat stuck open, I'd expect to see the engine take really long to get up to temp and then for the temp to fluctuate quite a bit as you go driving around. If the fan is coming on, it's almost definitely an issue with the gauge circuit only.

Make sure you've thoroughly bled the system as well. Air pockets can get stuck near the sensors and cause issues.

If none of that gets you anywhere, the next step is to sub in a known good cluster to see if it's the gauge itself.

 

I will look into that thank you for advice i really appreciate it man