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Discussion Starter · #1 ·
Just going to put out there in case someone has experienced this before, I have a 2008 civic hybrid, 340k miles, over the last few months it has been overheating, mostly when I go over 50mph, but cools down after I slow down, at idle it's fine, had it on for over an hour and the temp stayed good. I replaced the cluster because it started to fluctuate, on temp it would behave like the mpg does, they share the same line so I figured it wasn't overheating, the activity was based on the mpg I was getting going up when I cruised and drop when accelerated, the cluster has a diagnostic mode and after doing it it had error displayed, after cluster replacement it got better, weeks later it kept showing hot, just not erratic like before, I replaced the water pump, thermostat, dumped the thermo in boiling water and it opens, rated at 192 degrees, flushed the radiator, flushed the heater core, then bypassed the heater core to eliminate that altogether, replaced both sensors, radiator and engine sensor with oem type, pressure tested the radiator and held, tested the radiator with chemical to see if the head was leaking into the cooling system and no color change, replaced relays and fuses, nothing, still overheats, monitored the temp on scanner while driving and the temp on the dash matches the temp on the scanner, then noticed the fans weren't turning on when it showed hot, so I plugged both direct to battery unplugging from pcm connectors and they both turn on high, but when on the road at high speeds it shows overheating still, slowing down brings it down but the fans staying on does absolutely nothing to help cool it down, my thought is maybe the pcm is f**** up, please someone point me in the right direction, I can tear this car with my eyes closed now, I've done everything, hybrid battery replacement, tranny oil change, catalytic replacement, water pump etc, I need help with this, thinking of getting the pcm flashed or buying a junk yard pcm and getting it flashed, and help is highly appreciated
 

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Did you figure out the problem? On my 2007 hch it does the same. When my civic overheat the top radiator hose is very hot hot the bottom hose is cold. It’s like the thermostat never open, but I tested it over boiling water it opens. It’s either air pocket behind the thermostat preventing it from the hot coolant or the water pump has fail on the inside. I’ll be taking off the water pump this next week after I receive it from rockauto.
 

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Discussion Starter · #3 ·
I don't think it's your pump, if the top is hot and bottom is cold it means the thermo is opening and letting the hot water go to the radiator and is cooling down going back to the engine, had to take it in and they said I had air in the system, they burped it with a machine, it got better but I just too it back yesterday because it stl overheats after driving An hour, it doesn't do it like before but it stl goes up, I don't think they removed all the air, did you seal the thermo housing with gasket maker? I don't like how they didn't make grooves, it's metal to metal on the right side of the housing that can leak if not sealed properly, if you turn on the heater full blast does temp go down? Is it getting hot and staying hot or is it fluctuating to the driving speeds? I'll update when I get my car back today or Monday, this little problem really made me pull my hairs out, there has to be a legit way to burp the air out without a machine, I tried using the bleeder valve above the thermostat housing until water came out and kept adding water till bubbles stopped but I don't think this car behaves like other cars
 

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Hello,

I am experiencing more or less the same problem with my HCH 2007 FD3 European specs.

Initial problem :
City driving the car behaves very well with the temp,it can control it
While going on the highway I noticed at 120Km/h and when slight uphill the car overtemperatures.
When I reduced the speed to 100km/h the temp went down very quick.The car could travel on
the highway at 100Km/h or 110Km/h without overtemp

Action 1 :
I service my car at the dealership all this years so I went there and presented the problem with
all the symptoms etc etc.Without touching the car they advised replacing the water pump (belt,coolant) because
from the records it hasnt been changed in 11 years I take the car there.Also they advised to replace the
radiator.I didnt accept the radiator solution because it was replaced in 2017 .The car was bought second hand
and it looks it was involved in an accident,both radiators were bent inwards and from 2009 I got the car to 2017 there was no problem.Due to wearing out some bushes or whatever the two radiators started touching each other resulting in both leaking so they were both replaced in 2017

After getting the car from the dealership (water pump,belt,coolant replaced) the car became worse.It can no
longer travel on the highway without overheating at ANY speed.In the city the car still behaves

I replaced my self what is called ECT2 (aftermarket part) but the problem still exists.
I also replaced the radiator cap with no luck
I have found wiring schematics ans troubleshooting data and tested my self relays and
their sockets that they provide the voltage or ground according to troubleshooting data and they
were correct
I realised while testing on highway that my fans do not come on and the temp was on the red limit
The car has two fans located behind the radiator side by side.One for engine cooling one
for a/c cooling and the two fans have two speed settings. I used 12v directly to each fan and they work.
When you turn on A/C they both run at low speed , like they should according to info sourced from internet
I now though(still not sure) I had an electric problem

Action 2 :
I went to a car electrician and after working on the car he said he raplaced the ECT#1.
I tested the car on the highway,but still has the same problem

Actiona 3 :
I went to a second electrician shop and presented the problem.
When the car is overheated the technician touches the radiator hoses and also with infrared thermometer
and realizes the hoses have normal temp so the shop believes its an indication problem.

The car is also converted to LPG and they bypassed everything in order to make thhe car full factory.
This means the eliminated connections with water hoses and also the LPG controller.
Problem still exists

Replaced the second cluster that has the temp gauge but problem still exists

Next action is to change the PCM (engine controller) and see if anything happens



I will post when I have results
 

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Just going to put out there in case someone has experienced this before, I have a 2008 civic hybrid, 340k miles, over the last few months it has been overheating, mostly when I go over 50mph, but cools down after I slow down, at idle it's fine, had it on for over an hour and the temp stayed good. I replaced the cluster because it started to fluctuate, on temp it would behave like the mpg does, they share the same line so I figured it wasn't overheating, the activity was based on the mpg I was getting going up when I cruised and drop when accelerated, the cluster has a diagnostic mode and after doing it it had error displayed, after cluster replacement it got better, weeks later it kept showing hot, just not erratic like before, I replaced the water pump, thermostat, dumped the thermo in boiling water and it opens, rated at 192 degrees, flushed the radiator, flushed the heater core, then bypassed the heater core to eliminate that altogether, replaced both sensors, radiator and engine sensor with oem type, pressure tested the radiator and held, tested the radiator with chemical to see if the head was leaking into the cooling system and no color change, replaced relays and fuses, nothing, still overheats, monitored the temp on scanner while driving and the temp on the dash matches the temp on the scanner, then noticed the fans weren't turning on when it showed hot, so I plugged both direct to battery unplugging from pcm connectors and they both turn on high, but when on the road at high speeds it shows overheating still, slowing down brings it down but the fans staying on does absolutely nothing to help cool it down, my thought is maybe the pcm is f**** up, please someone point me in the right direction, I can tear this car with my eyes closed now, I've done everything, hybrid battery replacement, tranny oil change, catalytic replacement, water pump etc, I need help with this, thinking of getting the pcm flashed or buying a junk yard pcm and getting it flashed, and help is highly appreciated
Hello ,

I have a similar problem.Did you find your problem?


Thank you in advance
 

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Did you figure out the problem? On my 2007 hch it does the same. When my civic overheat the top radiator hose is very hot hot the bottom hose is cold. It’s like the thermostat never open, but I tested it over boiling water it opens. It’s either air pocket behind the thermostat preventing it from the hot coolant or the water pump has fail on the inside. I’ll be taking off the water pump this next week after I receive it from rockauto.
Hello, how did it go with your car? DId you fix it?
 
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