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Rmldaytona, Certified Technician
Category: Car
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Experience:  ASE Certified. 13 years Automotive Experience.
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1996 honda civic ex: it starts to overheat only when sitting still

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What is wrong with my car when it starts to overheat only when sitting still? i have a 1996 honda civic ex
Sounds like your radiator fans are not turning on. When your car is overheating, see if your fans are running. If not, check to see if you have power going to the fan. If you have power going to the fan and no fan operation, you have a bad fan motor. If you don't have power there, please let me know and I will give you further diagnostic information.
Customer: replied 9 years ago.
Reply to rmldaytona's Post: How do i check to see if there is power going to the fan? So if it was the fan motor, it is normal for it not to over heat when driving?

The radiator must have air moving through it to cool the colant. When your car is moving, you have air going through the radiator. When your car is still, the fans turn on when the temperature reaches a certain point to blow air through the radiator. If your fans don't blow, radiator is not cooled untill you move.

As for checking for power to the fans. Do you have a test light? Connect the ground strap of the testlight to a good ground (battery will do) and disconnect the fan plug. check for power at one terminal and then the other. One terminal is power and one is ground. If your light lights up at one of the posts, you have power. If you want specific diagrams, please give me the engine size and transmission (manual or automatic).

Customer: replied 9 years ago.
Reply to rmldaytona's Post: Okay I know the motor has power going to it because I have seen it work. Are you sure you think it is the fan motor,because the only times the car tend to overheat is when I have been driving it for a while then happen to have to stop (accident on the highway or runny errands and get stopped at a long light) but other than that it works fine. Also when I get out of the car you can smell the coolant in the air like the car has over heated, even when it hasnt. do you think this is related?
If your car is overheating ONLY at stops, I am 99% sure it is because a radiator fan is not turning on. However, why a radiator fan is not turning on is a different story. You must make sure you have 12V going to the fan before you can say it's defective. Yhere are other things that turn on the fan. Coolant temp sensors, relays and computers all turn the fan on and off as needed. So, it is crucial that you check to see if the fan has power going to it. Understand? If you have further questions, please let me know.
Customer: replied 9 years ago.
Reply to rmldaytona's Post: Will I still be able to ask you questions about this later if I go ahead and pay you? I don't have time right now to fix the issue so it will be soon in the future
If you pay me, you can still ask me questions related to this subject. However, I prefer that your problem is resolved and you are satesfied before I recieve any payment. In the end, it's up to you. Let me know what you want to do. Remember, anytime a car is overheating, engine damage is a possibility. So, it is in your best interest to get this straightened out sooner rather than later. Let me know. Rob.
Customer: replied 9 years ago.
Reply to rmldaytona's Post: I replaced the fan motor and it is still over heating...
Have you checked for power to the fan motor?
Customer: replied 9 years ago.
Reply to rmldaytona's Post: I have seen the fan work...i dont have any other tool to check it
To repair the car you must first locate the problem. Here's how this works... The coolant sensor on the engine turns the relay on for the fan. The relay turns on the fan. Your fan obviously works intermittantley because you are overheating at a stop. You could have a bad temp sensor (fan switch), a bad fan motor, a bad pcm, a bad fan relay, blown fuse, or a wiring problem. To find the problem you must test to see if you have power at the fan. Then, you test the relay and check your fuses. If the relal and fuses are good, you test the temps sensor (fan switch), and if that fails you are looking at a bad wire somewhere or a pcm. I can talk you through the diagnostic steps, but you would need a voltmeter. It is cheaper to locate the problem and repair it rather than guessing at what the problem might be.
Customer: replied 9 years ago.
If you can talk me through it i will get a voltmeter...

the fan motor has been replaced...i have seen it run on its own, but then there are times when its not running when i think it should be...

and the fuses were all fine last time i checked which was back in our first messages...

do you dont think it might be the thermostat?

no, not a thermostat. Let me know when you are ready

Customer: replied 9 years ago.
go ahead and type it and ill pick one up on my way home

I usually do this step by step with people, but I will give you this all in one. If you run into problem, please ask.

OK. Here's how you do this.

Warm up your car to operating temp (195deg)

Wait for your car to start overheating. (200+)

You must do this while the car is running and when fan should be on and isn't. Engine will be hot so be careful. Also, don;t let the car get too hot, keep the gage out of the red zone.

Check for power at the radiator fan motor for 12V. (red wire) If you have power, you have a bad motor.

If no power check power at relay. Remove the relay and see if you have 12V at terminal 1.



Got power, good. If not, check fuse 33 and 35 in under hood fuse box.

Check for power at terminal 3 for 12V. Got power, good. No power, check #13 fuse in dash fuse box.

Jump terminal 1 &2 with a suitable wire, paper clip, or anything that's metal. Fan should start.

remove jumper and Reinstall relay. Disconnect the temp switch. Engine coolant temperature (ECT) sensor. Jump the yellow/green to black wires together through the plug. if it fan turns on Replace the temp sensor.


If all fails, swap the radiator fan relay with the condenser fan relay and see if the fan works. If it does, you have a bad relay. If not, you have a wiring problem or a bad pcm.

If you have any questions, please let me know. Let me know with what you find.

Customer: replied 9 years ago.
Relist: I prefer a second opinion.
I dont think it is the fan motor or the wiring because the fan comes on...I also just replace the thermostat and gasket it is heating up above normal operating temperature but not hitting the red area...could it be a different temperature range in the new thermostat? and if so will that be ok for the engine?
If it is not getting to the red, it is not overheating. Where on the gage is it running. (1/4, 1/5. 3/4???) If your car is running warmer than usual, first thing I would suggest is a good radiator flush and a thermostat.
Customer: replied 9 years ago.
it was runny at 1/ with the new thermostat it is running at 3/4 until i slow down and it slows down 1/2 and when i start accelerating again it gets back up to 3/4
OK. Your car is running warmer when you move. Few reasons for that. First, your antifreeze needs to be 50% water and 50% coolant. Nothing more, nothing less. You may have an air pocket in the system. That would have come out by a few miles. A block in the cooling system. Possibly a defective thermostat. Or a waterpump that is not circulating coolant as it should (broken/rusted propeller, calcium build up, loose shaft).
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Customer: replied 9 years ago.
Reply to rmldaytona's Post: after driving it around for a while after replacing the thermostat....the air pocket has worked its way out and it is now running at normal operating temperature...thanks for your help through the matter
no problem
Customer: replied 9 years ago.
Reply to rmldaytona's Post: I know i told you it was fixed but of course it started running hot after i told you that...I have still be driving it b/c it has been overheating only slightly when driving. However last night it didn't over heat all the way but enough that there was steam in the cold air when i got home. With what we know from all the old conversations what could it be? Now I know that the lower hose is not heating after driving the car (possibly a thermostat or pump?) the top one however is almost to hot to touch. I took it to a family mechanic and they replaced the thermostat. and it didnt do anything different to to car except now i cant drive around and rely on the air to cool it off it will start running hot after 15-20 minutes...

I was just looking to get your advice one last time b/f I gave up and took it somewhere again
Has the car ever overheated to the point that it stalled, made "funny noises", or did the gage on the dash ever get to the red or higher?
Customer: replied 9 years ago.
no...the two or three times that it got to red i stopped and turned the car off

OK. Thanks.

First thing to do before you go any further is to do a compression test. This is to eliminate a blown head gasket. Test all 4 cylinders for 150 PSI. No cylinder can vary more than 15%. The lowest to highest cylinder can't be more than 25% off. You can also test for a blown head gasket with a chemical tester avaiable at most part stores.

Your thermostat is good, yet you have lack of flow. This can be because the thermostat is bad, the water pump is not cirulating, an air bubble in the system, or combustion gasess in the cooling system are building up. If your water pump would not be circulating, the overheating woult be more constant. An air bubble would have come out by now. That is why I would like you to test for a blown head.

Customer: replied 9 years ago.
Reply to rmldaytona's Post: Ok ill go test of a head. What causes this? I had to get rid of myy last car b/c of a blown head?
A cylinder block is cast iron. A cylinder head is aluminum. The head is bolted onto the block. Aluminum will warp at lower temperatures than iron. What happens when a car is overheated, the head warps (bends) on top of the block. When it warps, it no longer seals cylinder compression well, therefore, cylinder gases are blown into the cooling system. If a head warps enough, coolant mixes with oil, the car will not run at all. If the head is slightly warped, just to allow some exhaust gases to escape, the car will intermittently overheat. It only takes 1 thousandth of an inch warp to cause overheating.
Customer: replied 9 years ago.
just a you think that the head gasket would effect the flow of the coolant through the system?

also what is the difference b/w the thermostat and the thermostat gasket? b/c i was looking at my reciept and it says thermostat gasket is what he replaced.

Yes, a leaky cylinder head gasket will affect coolant flow. What happens is that combustion gasses will gather up at the top of the cylinder head and restrict coolant flow. It will cause the same effect as an air pocket in the system.

A thermostat is basically a coolant flow stop plug. What it does is restrict coolant flow when the car is cold to warm it up to operating temperature. (cars need to run at 195 deg for proper engine operation). When the engine heats up, the thermostat spring collapses due to the heat and opens the thermostat. A thermostat gasket is what seals the joint between the thermostat inlet and thermostat housing so no coolant leaks out. A good way to test the thermostat is to remove it, place it in hot boiling water and see if it opens. If it does, its good. If not, it needs to be replaced.


Customer: replied 9 years ago.
is that thermostat housing located where the lower hose connects to the block?
The thermostat is located at the rear of the engine, on the cylinder head.

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