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1G Car overheats when sitting still

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SnowmanFD

Proven Member
142
8
Dec 11, 2021
North Seattle, Washington
Title basically explains it, when im sitting still for an extended period of time, for example in the drive thru my car will overheat and start to shoot coolant out of my overflow im thinking the fans either aren't turning on or dont work but i wanted to double check before buying new fans or trying to fix them
 
If the car is getting hot enough to lose fluid out of the overflow tank and the fans aren't coming on, you have a problem. The trouble isn't likely to be the fans because there are two of them; it also isn't likely to be the relays because there are two of those, also.

If your A/C is working you can check both the fans and the relays by turning it on: when the compressor is cranking (cold air is coming out) the fans are turned on and much of that circuit is separate from the engine temperature circuitry.

Most likely this is an issue with the coolant temperature sensor though it might be the wiring or connector rather than the sensor itself.

This problem should be fixed before you do hot weather driving ... an engine with no working fan can overheat enough to be damaged.
 
On a 1G the radiator coolant fan is controlled by a thermoswitch in the lower passenger corner of the radiator. It grounds the relay coil to activate the fan when the coolant in the radiator reaches the temp. For testing you can short the pins and see if the fan comes on.

The AC fan should turn on when you push the AC switch on.

Check them both and report back.

The radiator cap controls the pressure in the system. It needs to seal well in the thermostat housing or coolant will boil over into the overflow tank.

The thermostat controls the flow rate of the coolant into the radiator.
 
I second fwdmaster. Replace the thermostat. It's pretty cheap and easy. Basically, when the motor is cool, all of the coolant recirculates inside the motor bypassing the radiator, letting the motor warm up as fast as possible. The thermostat is a gate that, when things get warm enough, redirects the coolant so that it goes through the radiator, adding extra cooling. So when your engine finally gets warm, the thermostat opens and redirects coolant to the radiator to regulate the motor temperature. If the radiator can't keep up (usually when you're stopped, in traffic, etc.), the radiator fan turns on. I forget the exact number, but our cars have (I think) a 190F thermostat - it sends coolant to the radiator when the coolant reaches (I think) 190F. Also, IIRC, the fans turn on at about 210F. On your temp gauge on the instrument panel, that's a bit above horizontal. So between 190F and 210F, the car relies strictly on cooling from the radiator. If the temperature gets hotter than this, the fan turns on to help pull air through the radiator. If the fan turns on but the temp keeps climbing, I'd say that it's the thermostat. If the thermostat "fails closed" then it won't send coolant to the radiator, so neither the radiator nor the fans on the radiator can help because no coolant is being sent to the radiator (thermostat is blocking this circulation). The thermostat is on the passenger side of the head, pretty easy to get at and replace. Google how to change it. It's maybe $10 and an hour or less of your time.
 
If the car is getting hot enough to lose fluid out of the overflow tank and the fans aren't coming on, you have a problem. The trouble isn't likely to be the fans because there are two of them; it also isn't likely to be the relays because there are two of those, also.

If your A/C is working you can check both the fans and the relays by turning it on: when the compressor is cranking (cold air is coming out) the fans are turned on and much of that circuit is separate from the engine temperature circuitry.

Most likely this is an issue with the coolant temperature sensor though it might be the wiring or connector rather than the sensor itself.

This problem should be fixed before you do hot weather driving ... an engine with no working fan can overheat enough to be damaged.
I just replaced my coolant temp sensor about a month ago because my car wasnt starting and it fixed it
 
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