Question on Radiator/Coolant Temp Sensor

[turbospeeder]

I have a brand new radiator temp sensor installed, but my fan still does not start accordingly.

The part number for the sensor is 61318363677.

Situation:

Some time ago my aux fan went out, and it also blew a fuse.

I have replaced the fuse and the fan, and afterwards, the fan would turn on when the A/C is on.

I have tried short-cutting the pins on the socket to the rad temp sensor, and both hi-speed and low-speed fan work.

So at this point, I know that the fuse is good, the fan is good, the relays are good as well.

I was wondering what else could possible go wrong that prevents my aux fan from running.

I will try to submerge the new temp sensor in hot boiling water tomorrow to see if it will trigger the fan.

Any inputs will be appreciated!

Thanks!

[SOLVED]

The cooling system has to be bled properly for the radiator temperature sensor to trigger the aux fan.

[flyfishvt]

That sensor only triggers the fan to come on if the engine overheats. It has nothing to do with the a/c being turned on. If your car never overheats then that temp sensor will never close and your aux fan will never come on unless you turn on the a/c. If the aux fan doesn't come on when you turn on the a/c then that's a very different problem that has nothing to do with the radiator temp sensor. If the aux fan isn't coming on with the a/c you need to diagnose the a/c system. Could be low refrigerant or a bad pressure switch

[turbospeeder]

That sensor only triggers the fan to come on if the engine overheats. It has nothing to do with the a/c being turned on. If your car never overheats then that temp sensor will never close and your aux fan will never come on unless you turn on the a/c. If the aux fan doesn't come on when you turn on the a/c then that's a very different problem that has nothing to do with the radiator temp sensor. If the aux fan isn't coming on with the a/c you need to diagnose the a/c system. Could be low refrigerant or a bad pressure switch

Thanks for your reply.

As I said, AC works fine. When AC is on, fan starts.

With the new temp switch, the aux fan doesn't turn on even when water temp is 108 degrees C.

Yes, my car is overheating because the fan does not turn on. In traffic, I always turn on my AC to force the aux fan to avoid overheating.

[blizzard424]

That sensor only triggers the fan to come on if the engine overheats. It has nothing to do with the a/c being turned on. If your car never overheats then that temp sensor will never close and your aux fan will never come on unless you turn on the a/c. If the aux fan doesn't come on when you turn on the a/c then that's a very different problem that has nothing to do with the radiator temp sensor. If the aux fan isn't coming on with the a/c you need to diagnose the a/c system. Could be low refrigerant or a bad pressure switch

The aux fan should come on when the engine gets up to operating temp, and will switch to high mode if things start to overheat.

[pbonsalb]

Make sure the switch is connected solidly to the harness. If using a 318i switch for its colder temp, the harness does not fit properly so you have to trim off a tab on the switch. Then the harness is not as secure on the switch. I have used a wide hose clamp around the switch/harness to hold them tightly together, but even this is not ideal though it works. Ideal is to salvage a 318i harness end and splice it in or to convert to an early big prong switch (also available in 80/88C) and salvage an early harness end or salvage a later aux fan harness end (fits the early switch) and splice that in.

If using this fan for primary cooling, you want the 80/88 switch not the hotter stock switch.

[KevinMullins]

Aside from the connector issues mentioned above...make sure the coolant system is absolutely bled correctly, otherwise that fan switch will never work.

[turbospeeder]

Make sure the switch is connected solidly to the harness. If using a 318i switch for its colder temp, the harness does not fit properly so you have to trim off a tab on the switch. Then the harness is not as secure on the switch. I have used a wide hose clamp around the switch/harness to hold them tightly together, but even this is not ideal though it works. Ideal is to salvage a 318i harness end and splice it in or to convert to an early big prong switch (also available in 80/88C) and salvage an early harness end or salvage a later aux fan harness end (fits the early switch) and splice that in. If using this fan for primary cooling, you want the 80/88 switch not the hotter stock switch.

Thanks for the input!

This morning I have submerged the new sensor in hot boiling water, and it triggers the fan.

So I believe the socket and the sensor are good.

I should have bought the 80/88 switch

[turbospeeder]

Aside from the connector issues mentioned above...make sure the coolant system is absolutely bled correctly, otherwise that fan switch will never work.

Thanks for the input.

I'll do a coolant flush and bleed the system ASAP!

[turbospeeder]

The aux fan should come on when the engine gets up to operating temp, and will switch to high mode if things start to overheat.

Thanks for the input!

Definitely Normal operating temp is definitely above 91 degrees C. So low speed should be on most of the time.

[flyfishvt]

The aux fan should come on when the engine gets up to operating temp, and will switch to high mode if things start to overheat.

This is not true unless you have a 318 with the factory electric cooling fan. If your car has a clutch fan and an aux fan the clutch dandies all of the normal cooling and the aux fan never comes on unless you turn on the a/c or if the engine overheats. The aux fan has 2 speeds. Turn on the a/c and it triggers the high speed. If the engine starts to overheat it triggers the low speed. If it continues to get hotter it triggers the high speed.

Keep in mind the location of that unit. It's in the top if the far side of the radiator. That means the engine has to overheat AND the coolant in the entire radiator has to overheat before that temp switch is triggered. It doesn't turn the fan on the instant the engine starts to overheat. There is a pretty big delay. If you have air in the system you'll have an air bubble at the top of the radiator and the temp switch won't be able to sense the correct temp because it's not emmersed in coolant.

[Nanniepoo]

Agreed with fly, the aux fan is back-up for cooling. Your aux fan supposedly not working is not the cause of your overheating. Something else is wrong.


As a side note, I was always taught to turn the heat on when the temp starts climbing. Air over the hot coolant helps cool it. Although turning on the AC turns on the aux fan, you're warming up the air from the condenser before it goes through the radiator, opposite of what you want.

[blizzard424]

This is not true unless you have a 318 with the factory electric cooling fan. If your car has a clutch fan and an aux fan the clutch dandies all of the normal cooling and the aux fan never comes on unless you turn on the a/c or if the engine overheats. The aux fan has 2 speeds. Turn on the a/c and it triggers the high speed. If the engine starts to overheat it triggers the low speed. If it continues to get hotter it triggers the high speed.

Not sure what you consider overheating, but the fan switches on low speed at 91c while the viscous engine fan does the rest, and high speed at 99c in extreme cases of high heat. I don't consider 91c to be overheating.

[Nanniepoo]

Not sure what you consider overheating, but the fan switches on low speed at 91c while the viscous engine fan does the rest, and high speed at 99c in extreme cases of high heat. I don't consider 91c to be overheating.

Location matters a lot. That's on the outlet of the radiator. Generally you want coolant temp near the cylinders to determine if you're overheating or not.

[turbospeeder]

Update:

Yesterday morning, I have submerged the new sensor in boiling hot water, and it triggered the aux fan.
Hence the new sensor is working properly.

Then, I did a complete flush on the cooling system. Now the car drives fine and the temp sensor triggers the aux fan normally.

KevinMullins is right! The cooling system has to be bled properly for the sensor to work. Now I have proven that.


Facts:
The aux fan will kick in when water temp in radiator reaches above 91/99 degrees Celsius.

For those who says engine fan is good enough for cooling, the answer is no.

It is only enough when the car is moving so that fresh air is going into the engine bay.

When the car is in stop-n-go traffic or idling, you definitely need to aux fan, no matter where on this planet.

As a matter of fact, all engines overheat, you just need something to cool it down.

[Midnighte36]

Make sure the switch is connected solidly to the harness. If using a 318i switch for its colder temp, the harness does not fit properly so you have to trim off a tab on the switch. Then the harness is not as secure on the switch. I have used a wide hose clamp around the switch/harness to hold them tightly together, but even this is not ideal though it works. Ideal is to salvage a 318i harness end and splice it in or to convert to an early big prong switch (also available in 80/88C) and salvage an early harness end or salvage a later aux fan harness end (fits the early switch) and splice that in.

If using this fan for primary cooling, you want the 80/88 switch not the hotter stock switch.

Which year 318 i should i get the electircal harness from ?