Overheating Honda Civic, need some assistance.

[buck]

Well on my way to work today i was sitting in traffic and thank goodness i looked down and saw the temp gauge raising to H. I quickily pulled over and popped the hood to make sure i had fluid in there. I had not been using the AC btw. There was fluid in the resevoir and after waiting a few, there was fluid in the radiator. Some lawnmower guys were nearby and suggested that I crank the heat when i started it again and that might "reset the sensor". When i started the car, the needle started moving up, so i cranked the heat. It stopped rising and dropped back to about 1/3 (close to the cooler than the hot). On my way to work i left the heat on for a minute then stopped it, it stayed 1/3 the whole way to work.

My question is, WTF happened? I had fluid in there, was the sensor being stupid? I wasnt sitting in traffic for that long and its only 65F outside here. Thanks SOOOO much for any thoughts.

 

[Zenmervolt]

Cranking the heat allows coolant to flow through the heater core and the blower moves air across the heater core. The heater core is a small radiator that dissipates heat into the cabin. By turning on the heat, you are essentially using the heater core as an auxiliary radiator. There's no "resetting the sensor" involved.

What has happened here is probably that the thermoswitch for coolant temp has failed and the radiator fans are not coming on in low-speed driving. When you drive at speed, you force enough air over the radiator to keep it cool without fans, but in traffic the fans need to come on. If the fans don't come on, the temperature in traffic will increas very, very quickly, even in sub-freezing weather.

Let the car idle for a bit with the hood open and watch the guage, once it gets to about halfway, you should hear the fans come on. If they don't, you need to have the thermoswitch for the fans replaced.

ZV

 

[steppinthrax]

<div class="FTQUOTE"><begin quote>Originally posted by: buck
Well on my way to work today i was sitting in traffic and thank goodness i looked down and saw the temp gauge raising to H. I quickily pulled over and popped the hood to make sure i had fluid in there. I had not been using the AC btw. There was fluid in the resevoir and after waiting a few, there was fluid in the radiator. Some lawnmower guys were nearby and suggested that I crank the heat when i started it again and that might "reset the sensor". When i started the car, the needle started moving up, so i cranked the heat. It stopped rising and dropped back to about 1/3 (close to the cooler than the hot). On my way to work i left the heat on for a minute then stopped it, it stayed 1/3 the whole way to work.

My question is, WTF happened? I had fluid in there, was the sensor being stupid? I wasnt sitting in traffic for that long and its only 65F outside here. Thanks SOOOO much for any thoughts.</end quote></div>

Couple of possibilities. Not knowing the system of your car some cars have two temp sensors one for the fan which is a temp switch. It turns on the fan when the temp reaches a certain level. Another sensor for the actually ECM and/or gauge. Most cars I think have one sensor though.

Did you hear your fan turn on while it creped to hot?

1. Could be a bad sensor?
2. Most likely a bad thermostat. The thermostat diverts radiator fluid from the radiator to the block when it gets hot enough.
3. Could be a radiator blockage.
4. Bad head gasket (rare)
5. Cracked cylinder head (rare)

If it happens again the first thing I would do is drain and flush the radiator you can get some 15 min radiator flush at Wal-mart. I would then change the thermostat. If that dosen?t correct it I would then go to replacing the sensor.

 

[buck]

If it is a bad thermoswitch, whats the cheapest way to get this replaced? I am not very car savy obviously, but if its something easy, I can do it. Any chance that it was just a fluke and its fine? Thanks for all the responses.

 

[steppinthrax]

Originally posted by: buck
If it is a bad thermoswitch, whats the cheapest way to get this replaced? I am not very car savy obviously, but if its something easy, I can do it. Any chance that it was just a fluke and its fine? Thanks for all the responses.

Go to the library and get a chilton or hayes manual for your car model and year. It should give you a whole section on cooling. You will need a wrench to remove the sensor and replace the other one. It's essentially in the cylinder head or block. There should be two or 3 wires on it.

 

[ViviTheMage]

time for a new waterpump and timing belt!

 

[buck]

Originally posted by: ViviTheMage
time for a new waterpump and timing belt!

Could you explain more?




Also, I just had to go to the bank, i started it cold, it rose steadily to 1/3 of the way and stopped there for the rest of my ride to the bank and back..... No a/c or heat on.

 

[Zenmervolt]

Originally posted by: steppinthrax
1. Could be a bad sensor?

Thermoswitch. Not a sensor in the true sense.

Originally posted by: steppinthrax
2. Most likely a bad thermostat. The thermostat diverts radiator fluid from the radiator to the block when it gets hot enough.

No. If the thermostat were stuck, then while turning on the heater would help, the car would not cool down again with the heater off when not in traffic. The symptom described does not indicate a failed thermostat. (Note that for some cars the thermoswitch for the radiator fans is part of the thermostat, only in that sense could you say the thermostat has failed.)

Originally posted by: steppinthrax
3. Could be a radiator blockage.

Again, in this case the car would not cool down again once moving. It doesn't match the symptoms.

Originally posted by: steppinthrax
4. Bad head gasket (rare)

Again, doesn't match the symptoms.

Originally posted by: steppinthrax
5. Cracked cylinder head (rare)

Once again, doesn't match the symptoms.

Originally posted by: steppinthrax
If it happens again the first thing I would do is drain and flush the radiator you can get some 15 min radiator flush at Wal-mart. I would then change the thermostat. If that dosen?t correct it I would then go to replacing the sensor.

I would suggest replacing the thermoswitch first and fixing the problem rather than throwing money away on a radiator flush and a thermostat that aren't going to fix the issue.

ZV

 

[Zenmervolt]

OP, it's very easy to check to see if the fans are coming on. Do what I suggested in my first post. Also, turn on the A/C and see if the fans come on then as well. If the fans still don't come on when you turn the A/C on then the issue may be with the fans themselves or their wiring.

ZV

 

[AdamK47]

Originally posted by: ViviTheMage
time for a new waterpump and timing belt!

A water pump is designed to leak if it goes bad.

 

[exdeath]

Originally posted by: AdamK47

Originally posted by: ViviTheMage
time for a new waterpump and timing belt!

A water pump is designed to leak if it goes bad.

Not necessarily. Most often the pump is fine as far as coolant goes, but the bearings are shot or there is some shaft play making ticking or knocking noises or whatever. Some cars drive the water pump off the timing belt, and i that case, 99% of the same stuff has to come off for both. And since its only like $25 for a timing belt and $30 for a water pump, might as well get them both at the same time.

But yeah, as ZV said. Any kind of blockage or loss of coolant volume would result in persisting overheating that would not be resolved without service. Do all above to make sure fans are coming on. In addition to the thermal sensor, it could also be the fan relays.

But usually it's a good idea to replace or at least check the thermostat anyway; it's cheap, easily accessible, a part that fails and sticks often, and overheating problems tend to come in multiples and cascade and effect other things down the line once you heat it up one good time. Thermostats for example use a wax core that liquefies and pressurizes to open at the right temp. If you heat it up too much from some other problem, it could pressurize too much and squeeze out the wax making the thermostat useless.

Simplest way to check is just squeeze the upper hose when the engines at full operating temperature and running. It should be squishy and flow readily (you can hear and feel water flowing), not firm and plump, indicating pressure from blockage from a stuck thermostat.

 

[Zenmervolt]

Originally posted by: exdeath
Do all above to make sure fans are coming on. In addition to the thermal sensor, it could also be the fan relays.

Yeah, that's why I suggested turning on the A/C and seeing if the fans come on then. If they do, he knows that the wiring and relays are OK and it's just the switch.

Originally posted by: exdeath
But usually it's a good idea to replace or at least check the thermostat anyway; it's cheap, easily accessible, a part that fails and sticks often, and overheating problems tend to come in multiples and cascade and effect other things down the line once you heat it up one good time. Thermostats for example use a wax core that liquefies and pressurizes to open at the right temp. If you heat it up too much from some other problem, it could pressurize too much and squeeze out the wax making the thermostat useless.

It's pretty rare in my experience to ruin a thermostat. It can happen, but given that his is still working properly (as can be seen by the car's remaining cool at speed) I don't think it's necessary to replace it. It certainly can't hurt to do so though.

Originally posted by: exdeath
Simplest way to check is just squeeze the upper hose when the engines at full operating temperature and running. It should be squishy and flow readily (you can hear and feel water flowing), not firm and plump, indicating pressure from blockage from a stuck thermostat.

Upper hose should also be warm/slightly hot to the touch. If it's cold/cool the thermostat is sticking too.

ZV

 

[buck]

Well i leave work in 35 min, ill update when i get home. Thanks VERY much guys.

 

[buck]

That was fun.

Well I started the car, it was normal but no fan started as it was running for a few min. When i turned on the AC there was one of two fans that started. I started my way home and then it started heating up and rising. I pulled over and checked to see if fans were running. They were not. I cranked up the heat and it went down to 1/3 on the gauge(normal). I tried going to a service place but of course they were closing. I may just take it in since one of the two fans never started. Im happy i made it home though, good thing we have two cars.

 

[Zenmervolt]

Originally posted by: buck
That was fun.

Well I started the car, it was normal but no fan started as it was running for a few min. When i turned on the AC there was one of two fans that started. I started my way home and then it started heating up and rising. I pulled over and checked to see if fans were running. They were not. I cranked up the heat and it went down to 1/3 on the gauge(normal). I tried going to a service place but of course they were closing. I may just take it in since one of the two fans never started. Im happy i made it home though, good thing we have two cars.

If that's wired the same as my old '88 Accord was, then one fan is the low-speed fan and one fan is the high-speed fan. The A/C will force the high-speed to turn on, but without the A/C being on, just the low-speed fan will come on in traffic. I cannot remember if both fans should come on with the A/C though.

The good news is that this should not be an expensive fix. The pieces are easy to get to and not terribly expensive.

ZV

 

[natto fire]

ZV is right again at the first post. It appears the civic only has a thermoswitch in the top water outlet. see here

However, the second fan only turns on when the A/C is on, as it is mainly for the condenser. Do not listen to Steppinthrax that it might be the thermostat, this is not very likely. Also a Helm's manual is much better than a Chilton. Much more expensive, too.

 

[buck]

Thanks alot everyone! I got a guy to replace the thermostat for $30 plus $18 for parts on craigslist. All is well now, I REALLY appreciate the help.

 

[steppinthrax]

Originally posted by: buck
Thanks alot everyone! I got a guy to replace the thermostat for $30 plus $18 for parts on craigslist. All is well now, I REALLY appreciate the help.

So this was a bad thermostat right? Not a sensor.

 

[Ross996]

Unbelievable, I was sold that the problem was the sensor but in fact it turned out to be the thermostat.

I have same problem on a 2007 and the steps to replace the upper sensor #1 is also unbelievable. they start with remove coolant, air cleaner, but the ringer is the EGR valve, which starts with revealing the fuel presser, remove under dash relay box, remove PGM-F1 relay 2 for fuel pump, re-install fuse box, start car until stalls, remove fuel fill cap, disconnect neg battery, remove quick connect fitting cover, disconnect quick connect fitting, reconnect battery, enter audio codes, remove fuel line, disconnect hose, disconnect CMP sensor A, remove EGR valve 6P connector, remove EGR valve, disconnect CMP sensor A, remove harness cover, disconnect ECT sensor 1, remove ECT sensor. Install in reverse order.
wow
--Ross

Hello and welcome to AnandTech forums. You have replied to a thread from 2007. Replying to threads this old is generally considered to be very bad etiquette as it clutters the front page of the forums with outdated threads that are no longer helpful because the OP has long since either fixed his problem or stopped caring. Please feel free to stick around, but try to avoid replying to old threads going forward.

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