The past few weeks there has been a ton of post about peoples cars overheating, and what to do to fix it. I though I'd do a write up, so people wont have to ask so much and it will make it easier.
So if your car is overheating here are some tips to and things to look at.
1. The #1 cause of overheating, a unmaintained vehicle. The very first thing to check for is the coolant level, is there even coolant in there. Not enough coolant in the system it wont be able to cool down the engine with a low level.
The next thing old coolant, or coolant that is plugged up someplace in the cooling system.
Is the coolant anything but the color it is suppoused to be? Is it black or brown? If so time to flush it out. A shop usually charges around $80 for this. Some people will say to just drain the radiator. Wrong, it wont get it out of the block and head, and the heater core, and the lines from the heater core to block. It is time to suck it up and pay the $80 to have it flushed. A machine that shops use actually forces old coolant out as the new coolant is pushed in. Therefore getting about 98% of the old coolant out.
Sometimes if the coolant is plugged up enough the machine cant force it out. If this is the case the component that is plugged should be replaced.
#2 A stuck closed thermostat. A thermostat is placed from the block to the radiator. When the temp reaches X temp the wax pellet on the t-stat allows it open up. Therefore allowing coolant flow to the radiator to be cooled before going back to the block.
If it is stuck closed the car will overheat within a few miles of driving, the reason is the coolant is not having heat removed from it, and it cant remove heat from the engine.
A new thermostat is about $10 at the most. It is located on your engine going from the block to the radiator. Normally there is two or three bolts around its housing.
#3 A faulty water pump. If this is bad your car will overheat very very fast. Within 1/2 mile of driving. A water pump has an impeller inside it that spins. It receives coolant from the radiator and pushes it through the block to cool the block. If the impeller breaks, it will not be forcing coolant throught the block, therefore causing severe overheating. Driving with a bad water pump will destroy the block or the head.
Another way a water pump can fail is the weep hole on it will leak.
If this happnes it is time for a new one as well.
#4 The fan is not coming on.
Before continuing it is important to note a few things about the fan, and its operation.
The fan is NOT turned on at highway speeds. Instead the air flow on the radiator, and the air flow spinning the fan is enough to keep it cool.
The fan does NOT come on until the car has hit at least 195F.
The fan does operate ANYTIME the A/C is turned on, and the car has not been just started, so if you go outside it is 95F air temp, jump in the car flip on the A/C, the fan may not come on until 195F, in some cases it may come on right away, the computer decides it.
Okay so you have determined your fan is not coming on when it should.
Here are steps to diagnose the problem easily as possible following these steps will save you time and money of replacing the wrong part.
If your fan isn't coming on. The first thing to do is not to check the fuse, or the motor or this and that as people say the first thing to do is......
If the car is at operating temp, turn on your A/C. Does your fan come on then. If yes you have verified the fan, the motor, the wiring and the fuse are good for the fan.
If no. Then shut off the A/C. Check the fan fuse now. Then if that is not blown check the fan. Does the fan spin freely, if no. The fan is no good and must be replaced. Does the fan make a whirling sound when spun by hand, if so the bearing is trashed and the and should be replaced.
Now lets say you have verified the fan is good itself. But it isn't coming on. Few possibles left here, the motor is shot, the wiring is damaged or a faulty ECT sensor.
Lets start with the ECT sensor. The ECT sensor is an input to the PCM. It tells the PCM what the temp of the coolant, and the PCM uses this input to determine to operate the fan. It tells the temp of the car on a 5V scale, 0V being -40, and 5V being say 225F.
If your ECT sensor is reading 65F, but the car is actually 195F, the PCM will not command the fan on. The ECT when unplugged, will obviously not give a reading, and the PCM doesn't see a signal. So it goes to fail safe mode and it uses a subsatute value of -40F, yes -40F every car almost.
Heres how to test your ECT it done in a few simple steps, I just said above what it does when unplugged 0V. So what do you think it will do with 5V being sent to the PCM, read 225F, and bang the fan should come on. How do you apply 5V to it. The ECT is three wires, input to PCM, 5V reference, ground. Simply t pin the 5V reference, and t pin the input, use a paperclip the connect the t pins, fan the fan should then come on. If it comes on good, the wiring for the ECT is good, and PCM is good.
Now that was just part of it. Now using a voltmeter set it to DC 20V. You need to t pin the input from the PCM. It will read between 0-5V. Now if you t pin and say the car was hot at say 195F, but it is giving an input of 1.2V, the ECT is not working correctly.
I dont have the chart in front of me, but simply it should be giving X amount of volts at X temp. To low of volts and the fan will not come on, since the PCM uses volts as the temp value.
Also a final note the ECT input for the PCM is not the same one used as for the dash temp. It is a different sensor for that one, only one wire i believe, the ECT is three wires.
This is also reversed for the fan is staying on all the time.
Now if you have read this far, everything else is good but the wiring for the fan and the motor.
The first to check the fan relay, you need an ohmmeter. I dont have a spec chart in front of me, but to much resistance or not enough and the relay contacts will not operate correctly.
The next thing is, is the fuse blown. If yes you have a short circuit someplace. If no but the fan isnt working and everything is good, you have a open someplace.
Basically you need a voltmeter and with an open you simply use the last/lost procedure. The last place you had 12V, to the first place you lost 12V. There is your open.
With a short simply put the 12V is going ground before the load.
To test a fan motor, you need a amp clamp and a voltmeter. Now I know most people dont have one, I spent over $350 for my set of them. Thats why I saved it for last. Basically you looking for how much current is the motor drawing, clamp the amp clamp around the power wire of the motor. If it drawing a lot of current you have mechanical resistance inside the motor, it is drawing a little bit you have electrical resistance at the fan motor.
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- 2004 Cavalier - 124k, owned since new
lack of info^^^^needs more info
Travis C wrote:lack of info^^^^needs more info
Are you being sarcastic, or do you really think so?
- 2004 Cavalier - 124k, owned since new
^^^^ sarcastic.......
Its a good write up.... maybe moderators dont like it
I was thinking maybe a sticky?
- 2004 Cavalier - 124k, owned since new
Looks really good to me. Sticky or put in the library.
I had a water pump on a friends car that sheared right off, car ran fine but over heated. No leaking from anywhere.
The heater core is a coolant by pass, even with a blocked thermostat the car should be blowing heat inside, provided it has coolant in it. That was what gave it away for us, I shouldb have taken a picture of it. Basically what had happened was 1)poor maintence 2)it was -40c and her coolant froze 3) she started it up and it snapped the impeller off.
HP Tuners | Garrett T3/T04B | 2.5" Charge Pipes | 2.5" Downpipe | 650 Injectors | HO Manifold | Addco front/rear | Motor Mounts | HKS SSQV | Spec stage 3 | AEM UEGO Wideband | Team Green LSD | FMIC | 2.3 cams | 2.3 oil pump swap | 280WHP | Now ECOTECED
Quote:
The fan does NOT come on until the car has hit at least 195F.
That is sort of incorrect. The fan comes on when the temp is around 218, but can come on before 195 for other reasons.
Quote:
The fan does operate ANYTIME the A/C is turned on, and the car has not been just started, so if you go outside it is 95F air temp, jump in the car flip on the A/C, the fan may not come on until 195F, in some cases it may come on right away, the computer decides it.
this statement is incorrect. Anytime the A/C is on the fan is on. The A/C system uses the fan to cool. No matter what temp the car is at, if the A/C is on the fan should be as well.
FU Tuning
^^^ agreed, I checked my Hptuners file and the fan comes on at 218 or something like that,
HP Tuners | Garrett T3/T04B | 2.5" Charge Pipes | 2.5" Downpipe | 650 Injectors | HO Manifold | Addco front/rear | Motor Mounts | HKS SSQV | Spec stage 3 | AEM UEGO Wideband | Team Green LSD | FMIC | 2.3 cams | 2.3 oil pump swap | 280WHP | Now ECOTECED
My 04 temp gauge reads 195F for the center of the gauge. At that temp the fan does on.
- 2004 Cavalier - 124k, owned since new
