I wanted to get some advice on why my 97 Civic DX is overheating. The problem started 2 weeks ago. I was driving for an hour on the freeway and when I exited I noticed that at the stop light the temp was getting above half way. When the light turned green and I started driving again the temp came down a little but still remained above half way and was overheating. The car has never overheated on the freeway and it seems as long as the car remains at speed (above 50 mph) it will never overheat with the temp at below half way. After this happened, I changed my Thermostat, radiator cap, and coolant (flushing with distilled water and “burping” the system for any air bubbles). But the problem has persisted. What I have noticed from my commute to work is that if the car is cold in the morning, you can drive it for at least 5 minutes through city streets to get to the freeway and the temp stays below halfway, once on the freeway the temp is good staying below halfway, but like clockwork once I exit the freeway it begins to overheat when I am sitting at a light. Last time it began to overheat I stopped to check the radiator fan and it was not running even though the car was overheating. The fan however is functional as it does turn on when I start the car up from cold and let it warm up in the driveway. Is it possible that the Engine Coolant Temperature (ECT) Switch is going bad causing the fan to not turn on when the car is hot? Or could the Cooling fan relay be bad?

Other notes:
-The cooling system has no leaks and is not loosing fluid
-The engine is not loosing oil and there is no coolant on the dipstick

Any advice would be greatly appreciated

 

TLDR: Water pump failing or air in the coolant system or t-stat getting stuck closed(not very likely). how new is your water pump t-belt all that stuff ?

 

Timing Belt and Water Pump were changed 7 years ago to the month and have 93k on them.

 

I would test the thermostat then and bleed the coolant system after.

 

I changed the thermostat and the problem stayed consistent so I was ruling that out? But I could test it. I don't believe there is bleed screw on this year honda so I ran it with the cap off to get the bubbles out. Is there a better way then this to bleed it?

 

Put car on ramps, leave cap off, run car til thermostat opens and it is bubble free.

 

or just jack it up on stands, if you just replaced it recently I'd say no it's probably ok then was it OEM Honda tho ?. starting to lean towards bad water pump.

 

What do you think about the fan not coming on while it is overheating. Shouldn't the fan run constantly if it was overheating? Also, if the water pump was going out would it still run cool on the freeway?

 

Any chance your fan isnt coming on? if it isnt you can test the wiring by unplugging the coolant temperature sensor and jumping the pins with a paper clip on the plug side no the sensor side (there are two sensors one is the on the thermostat housing and the other is above the tranny below the distributor if it is on the left side of the motor (not sure which one you should probably look it up but the ignition needs to be in the on position)

 

This^ is good info.


and may be the case but I would find it a bit strange as my fan never comes on at lights or after heavy driving(yes it works)and it never goes past just under half way. On the freeway you're probably around 4-5K rpms thus the coolant is flowing well/better then at idle so it's not 100% ruled out. try the fan switch(s) and bleed it.

 

Open the cap and let the car warm up and see if the fan comes on and if coolant flows through the radiator (verify fan and water pump). Anything blocking the airflow of the radiator? How do the radiator fins look?

 

While bleeding air the fan should come on twice.

 

Ok.... I bled the system again and checked for flow. The fluid level definitely rose and decreased when the thermostat opened up. The fan turned on multiple times when I was bleeding the system. Its strange that the fan comes on when the car is at normal operating temperature, BUT last time it overheated the fan was not running at all. SHOULDN'T THE FAN BE RUNNING CONSTANTLY WHEN IT IS OVERHEATING ? Is it possible that an engine temperature control switch could fail after the car is running a while or when it gets really hot?

The fins on the radiator look ok, I little white oxidation but from my limited knowledge it looks ok.

I was thinking of changing out the Engine Temperature Control Switch next and possibly getting the radiator chemically flushed at Jiffy Lube. Do you think this could solve the problem?


Again it only overheats when it has been on the freeway for a while and you exit into traffic.

 

dont pay someone to flush your rad, go to a car wash and flush it yourself...unless youre just not into doing stuff yourself.

 

flush a radiator at a car wash? people actually do that?

 

Ok, I will try flushing it myself.

But what do you guys think, shouldn't the fan be running constantly if the needle is past half way. If it is not, it would seem that there is some sort of fan issue, right?