Coolant temperature sensor

[Slootvreter]

My car's radiator fan is now on all the time. Had to bypass it because of an electronic fault. Doesn't really bother me, it's the same fan that runs when the aircon is on, which is almost always. But I've heard you get an aftermarket coolant sensor you attach to a bolt on your cylinder head somewhere that can send a signal to the fan to go on. Anyone else have some knowledge about this?

 

[DOOMIE61]

My car's radiator fan is now on all the time. Had to bypass it because of an electronic fault. Doesn't really bother me, it's the same fan that runs when the aircon is on, which is almost always. But I've heard you get an aftermarket coolant sensor you attach to a bolt on your cylinder head somewhere that can send a signal to the fan to go on. Anyone else have some knowledge about this?

What car? The temperature sensor that connects to your radiator pipe maybe faulty.. i wouldn't trust getting a sensor that sit's on your block would rather get a new sensor or get the electrical problem sorted..

 

[Slootvreter]

What car? The temperature sensor that connects to your radiator pipe maybe faulty.. i wouldn't trust getting a sensor that sit's on your block would rather get a new sensor or get the electrical problem sorted..

It's a BMW, no it's not just a matter of replacing a sensor. The problem lies with the computer. The sensor gives it a signal to switch on the fan, but it doesn't switch the fan on. This has caused me major damage.

 

[Claymore]

My car's radiator fan is now on all the time. Had to bypass it because of an electronic fault. Doesn't really bother me, it's the same fan that runs when the aircon is on, which is almost always. But I've heard you get an aftermarket coolant sensor you attach to a bolt on your cylinder head somewhere that can send a signal to the fan to go on. Anyone else have some knowledge about this?

They don't attach to the cylinder head, they attach to the radiator near the top (after all, you want the fan to come on when when the coolant in the radiator is hot). However, the sensors need to be properly mounted to the radiator, which means you'll probably need to have a radiator repair place remove it, drill the hole, and mount the sensor. Then it's just a matter of rigging up a simple relay linking the temp sensor to the fan.

You can buy temp sensors for various temp ranges; I know Gordon's Auto Spares in Randpark Ridge used to carry them, so must big spares places whould have them.

 

[.Froot.]

I have the same issue with my car... except that it is off when it should be on and on when it should be off (with "legal" overlaps too). Maybe have a look at your thermostat... it's a likely cause to your problem.

 

[Gnome]

Not sure how old the BMW is but newer cars mount the coolant temperature sensor on the head, the ECU monitors the temperature and turns on the fan when needed.

But what Claymore said will work, go to a Opel/VW scrapyard and get a temperature sensor from one of the older cars, not sure about VW models but I know the Opel Kadett/Astra A/F still used those fan switches. Basically you cut the radiator pipe on the intake side mount, reattach and wire the switch so it turns the fan on.

Are you sure the coolant temperature sensor on the head isn't broken? Car needs that to run optimally, not just for the sake of cooling.

@Froot: If it is the thermostat, then the fan would still switch on but the temperature wouldn't drop (regardless of if the fan switches on or not), if the coolant is cold the thermostat is closed to keep fluid in the engine alone (and speed up the heating process), when it heats up it opens to allow water to enter the radiator. Not matter what engine if the thermostat is stuck closed the engine will overheat, fan or no.

 

[Claymore]

@Froot: If it is the thermostat, then the fan would still switch on but the temperature wouldn't drop (regardless of if the fan switches on or not), if the coolant is cold the thermostat is closed to keep fluid in the engine alone (and speed up the heating process), when it heats up it opens to allow water to enter the radiator. Not matter what engine if the thermostat is stuck closed the engine will overheat, fan or no.

Heh. I have the opposite problem in my car: thermostat is stuck open, so the car takes 25 minutes to warm up even in peak traffic, and it runs cool. Sadly, the thermostat is not sold separately, so I have to buy the whole stupid housing for R1100.

 

[.Froot.]

@Froot: If it is the thermostat, then the fan would still switch on but the temperature wouldn't drop (regardless of if the fan switches on or not), if the coolant is cold the thermostat is closed to keep fluid in the engine alone (and speed up the heating process), when it heats up it opens to allow water to enter the radiator. Not matter what engine if the thermostat is stuck closed the engine will overheat, fan or no.

In my case the engine hovers on 100 if I drive in 60-70 zones, drops to 85 on the highway and runs to 110 (111 is red).... which clearly tells me the fan doesn't run when it should. It does however, when the car is turned off, turn on. This happens if I pull the car out of the garage or if I come back from a drive.

 

[Slootvreter]

Are you sure the coolant temperature sensor on the head isn't broken? Car needs that to run optimally, not just for the sake of cooling.

Yep, had an auto electrician test the signals. The fault lies with the ECU. It gets a signal from the sensor so switch the fan on, but it doesn't do that. I had them bypass the ECU so that the fan now always runs. It's the same fan that runs when A/C is on, which is always anyway.

 

[Gnome]

Heh. I have the opposite problem in my car: thermostat is stuck open, so the car takes 25 minutes to warm up even in peak traffic, and it runs cool. Sadly, the thermostat is not sold separately, so I have to buy the whole stupid housing for R1100.

Yeah at least it did stick in the wide open position, most times it does which just leads to less fuel efficiency but it happens that it gets stuck in the closed position, not cool, I've seen a Corsa that happened with and the person in question kept driving, end result: Cam cover melted along with everything attached to it, not cool.

In my case the engine hovers on 100 if I drive in 60-70 zones, drops to 85 on the highway and runs to 110 (111 is red).... which clearly tells me the fan doesn't run when it should. It does however, when the car is turned off, turn on. This happens if I pull the car out of the garage or if I come back from a drive.

Yeah that can't be the thermostat because the engine wouldn't lose heat at all but it's strange that the fan turns on when the car is off, modern cars don't do that (since there is no point), what kind of car is it if I may ask?

Either way it's a easy fix, any car can be retro fitted with a fan switch which will work too but what most newer cars do is the ECU turns the fan on at lower speeds to keep the engine in the exact temperature range instead of constantly switching on the fan at full speed then switching off. I think for the newer engines, especially ones with high compression this can be quite important since knock becomes a factor when a engine runs very hot.

Yep, had an auto electrician test the signals. The fault lies with the ECU. It gets a signal from the sensor so switch the fan on, but it doesn't do that. I had them bypass the ECU so that the fan now always runs. It's the same fan that runs when A/C is on, which is always anyway.

What kind of car is that if I may ask?

 

[Slootvreter]

What kind of car is that if I may ask?

2000 BMW E46 323i

 

[TestMate]

2000 BMW E46 323i

Right! now you'r talking.

Get the technician to check the Sensor resistance at terminals
D38 & D39 of the ECM.

@10deg. (cold) = 3.5 to 4 KOhm
@80deg. (hot) = 600 - 650 Ohms

You said it sends a signal...but ECM doesn't respond. (but it does when Ign. Key/Off) So the ECM is not at fault here.

The ECM monitors:
the ECT (engine coolant temperature sensor) C24 & C25
Oil temp. sensor C27 & C28
and the blower motor temp sensor (above)
Any of those may interfere (contradict) with proper operation.

Also have him check this:
@ A7, A8, A9 when Ign.Off must have 12v to earth.
@ D26 when Ign/On must have 12v to earth ( & it probably has couse it runs
A4, A5, E5 & E6 = Earth ECM terminals

Blower motor signal output @ D4 (black&green wire) This is Earth Out signal, so check that you have 12v when Ign/On on the Fan's 'other' wire. The ECM output is DC negative Pulse Width Modulated. i.e a waveform. String of 'square' pulses to the Fan. The ECM controls the Fan Speed by shortening the pulses. IF some idiot had shorthen the wire to +12v it's good by ECM Output. Best checked with a Osilloscope, but a 12v LED will do too or even a ordinary test light. bcose it's a power output.

AC Clutch Relay signal output @ D29 --- // ----- (also earth (constant negative out when AC on)
May conect it to operate the Fan through a relay. not perfect.

Have you 'read' the car with a code reader. Any known fault codes?

My 2 cents...right there

Edit: Forgot to mention those BMW's are notorious for faults in the bulk head harness connectors.

 

[Slootvreter]

Wow. Let me print that out!

 

[TestMate]

Right! now you'r talking.

The ECM controls the Fan Speed by shortening the pulses. IF some idiot had shorthen the wire to +12v it's good by ECM Output.

Sorry, just found a typo:

It should read good-bye ECM output

 

[Slootvreter]

Sorry, just found a typo:

It should read good-bye ECM output

What has happened, the ECM/ECU (or whatever you want to call it) has been bypassed completely. This fan now runs whenever the car is on, and it runs at full speed making the car sound like a jet.

I will have to go to a technician to check everything out, but obviously this cannot be done in my lunch hour Thanks for this post, hope it solves by problem! Will post feedback

 

[TestMate]

The ECM can be posibly repaired.
If you're lucky it will be a single MOSFET transistor.
If not, will be a block of them...
Good Luck & keep us posted

 

[Slootvreter]

The ECM can be posibly repaired.
If you're lucky it will be a single MOSFET transistor.
If not, will be a block of them...
Good Luck & keep us posted

I usually always fear the worst, and I am seldom wrong This little problem with the ECM has cost be a lot of money so far! Thanks for the info, I will certainly post next week!

 

[spacemanwayne]

E46 radiator fan running all the time

Hi guys

Great posting, more info than most places i have visited.
Hope this is an easy question. My fan on my 2000 E46 320D runs all the time, the radiator fan. Bmw said i need to spend R8500 to replace the fan shroud, oh and that includes R1000 labour to do a 10 minute job. Crazy! I went and searched around to see what the problem is and turns out it apparently is this silly Bosch component attached to the fan, i could be wrong. I tested the current going to the fan, its that main connector on the side of the fan housing, on the left if you are facing the car. I connected earth from the multi-meter to the brown cable of the connector and then the positive from the multi-meter to the red wire,and i get 12v. Then i connected the positive from the multi-meter to the black/green wire, it is the thinnest of the 3 on that connector. I got 5.6V on cold startup and then when the cars temperature reached the half way mark, it was 5.8V. Does this sound right at all to anyone? Should i measure in ohms? I am a bit of an ammateur at this so please excuse me.

Any help would really be appreciated.

Thanks guys
Wayne

 

[TestMate]

To Spacemanwayne

The little silly Bosch component is a Fan driver.
It's a kind of "softstart" Fan Speed regulator.
It's controled directly via the black/green wire from the ECU.

Cut the b/g wire and see if the fan stops.

CAUTION: DO NOT earth or apply positive (+12v) to the b/g wire (the part that goes to the ECU) you are warned.

Now: If the fan stops after you've cut the b/g wire...then the ECU applies constant signal to the Speed regulator. Question is why?

If it doesn't stop...replace the speed regulator. (or fix it...)

Note: the Red is +12v , brown is earth. Power for the regulator and (throught it) the Fan

Good luck

 

[spacemanwayne]

Hi Testmate

Thanks for the reply. I cut the b/g wire and the fan still runs at high speed so i guess i got to replace the whole fan shroud, BMW nor Bosch supply that regulator separately from the fan and i have looked around at scrap yards, they sell the whole thing complete. BMW wants R7500:erm:

You mentioned: "CAUTION: DO NOT earth or apply positive (+12v) to the b/g wire (the part that goes to the ECU) you are warned."

I went and connected the positive cable of the multi-meter to the b/g cable and the negative of the multi-meter to the brown cable and i get a voltage, do you think i broke something now? I did this before posting to this site so i missed your advise there. I did it again now just to see if anything is different but the voltage is the same so i am hoping nothing broke by doing this test of mines.

If i am in the clear here, i will go get a new fan.
Any advise on getting the pirate version of the fan shroud? I see there are a couple of spares shops around jhb that do supply these and they say the fans work fine.