First post and sorry to be asking for help out of the gate but I am stumped and in desperate need of guidance. I have a 98 civic EX coupe. Original owner and it has 160k on it. Current temperature outside is 0 degrees.

The problem:
Car is overheating randomly. It is also throwing cold air when I slow down and hot air only at speeds above 50 mph. My temp gauge will randomly fluctuate from normal temp all the way up to almost red. It does not always go all the way up and often just fluctuates around the normal temp area. It is throwing a 0117 error code which I have done some research on. This might be part of my problem but does not seem to be the whole fix. I am ordering an ECT today. The fuses are good and I swapped the radiator fan relay with the AC compressor relay just to narrow. I did unplug the two prong plug on the ECT and ran a jumper to see if the fans came on. They did not come on when the key was in accessory or when the car was started. I have seen the fans run but I have also seen the temp gauge reading hot and no fans were on. At one point I noticed the overflow tube had come off the radiator and so it was unable to pull from the reservoir which I am sure introduced some air into the system but I have driven the car for a while with it on and would figure most of the air would have came out in the reservoir. I have not verified that all air is out of the system. The water pump was changed at 110k with the timing belt so it should be good. I am not seeing any leaks of antifreeze or low levels. I have no reason to suspect a head gasket.

So my current thought is that there might be an air bubble in the system causing the car to blow cool at low speed and possibly the ECT is going bad? I could really use another opinion on this. Any ideas would be great? Thanks for any and all help

JT

 

1) Top off the radiator and reservoir with coolant and thoroughly bleed the cooling system. This may take 20-30 minutes:

i) Park the car on an inclined driveway with the front end higher than the rear.

ii) Push the dash heater lever/**** to MAX heat.

iii) Follow the directions in the diagram below





2) P0117 has nothing to do with the overheating, though you still need to fix it. The 2-wire ECT sensor under the distributor only sends signals to the ECU. It does not control the radiator fan, which is instead controlled by the 2-wire ECT switch located on the thermostat housing. Jump the 2-wire connector for this switch and the fan should always run with the key in ON(II).

 

Thank you for the help. I will try it out when I get home and report back. Thanks again!

 

Just a tip, since the first time I did this (waaaay back) it took a long time and thought something was wrong: I hold the throttle open a little to get the revs up and warm the engine faster. You can do that while still watching the level in the radiator.

 

my eg coupe did that but its cause my fan wasnt turning on check if your fan turns on by keeping the car running with the hood popped and just wait it should turn on within 20 to 30 minutes

 

Took about 45 min to get all the air out but you were right. I drove it last night and this morning and it is rock solid like old times. Thanks for the help on this one.

I did have a follow-up question on the P0117. Reader says "engine coolant temp circuit low input" Would the air in the system cause that fault or do you think the actual sender is failing? Also I thought the sender is the single wire unit under the distributor and the fan control is the two wire coming off the bottom of the thermostat? Thanks again for the help. Feels good to not worry about ordering a new head/gasket.

 

P0117 is for the 2-wire ECT sensor that is forward of the 1-wire sender under the distributor. You need to measure resistance across the two terminals of the sensor when the engine id fully warmed up. The air in the cooling system wold not have thrown this code, but you should reset the ECU to see whether the code returns.