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Radiator Outlet Temperature Sensor Replacement
 
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Pelican Technical Article:

Radiator Outlet Temperature Sensor Replacement

Nick Czerula

Time:

1 hour1 hr

Tab:

$45

Talent:

*

Tools:

Flathead screwdriver, Coolant drain pan

Applicable Models:

BMW 323Ci Coupe/Conv (1999-00)
BMW 323i Sedan/Wagon (1999-00)
BMW 325Ci Coupe/Conv (2001-06)
BMW 325i/xi Sedan/Wagon (2001-06)
BMW 328Ci Coupe (1999-00)
BMW 328i Sedan (1999-00)
BMW 330Ci Coupe/Conv (2001-06)
BMW 330i/xi Sedan (2001-06)

Parts Required:

Radiator outlet Temperature sensor, lower radiator hose

Hot Tip:

Work with a cool engine

Performance Gain:

Cooling fan operates normally

Complementary Modification:

Lower radiator hose replacement

BMW E46 cooling system components include:

  • Radiator and coolant overflow tank
  • Belt driven coolant pump bolted to the front of the engine block
  • Electric cooling fan attached to rear of radiator -- the cooling fan is controlled by the engine control module (ECM) via an output final stage
  • Automatic transmission models: Belt driven fan attached to front of coolant pump -- viscous clutch controls fan speed based on engine compartment temperature and rpms
  • Electrically heated ECM-controlled thermostat
  • Automatic transmission cooler (heat exchanger)
  • Heater valve and heater core (for climate control)
  • Coolant level sensor inside expansion tank
  • Coolant temperature sensor at cylinder head
  • Radiator outlet temperature sensor
  • Coolant hoses and lines

The radiator outlet temperature sensor is located in the right side radiator hose. It monitors the coolant temperature as it leaves the radiator. The sensor reading is used by the engine management system (DME) to determine when the electric cooling fan is activated. The DME uses other inputs as well to control cooling fan operation and speed: coolant temperature at the cylinder head and AC operation.

If the radiator outlet temperature sensor fails electrically, a fault code is stored and the MIL (malfunction indicator lamp) is illuminated. The sensor can also leak coolant from the sensor sealing O-ring. I have replaced this sensor and soon after found a leak at the lower radiator hose. If it's in your budget, replace the lower radiator hose also as preventative maintenance.

Replacing the E46 radiator outlet temperature sensor is a snap and can be done working above the engine on the right side of your radiator. The sensor can be serviced from below also. You will have to raise and support the front of the vehicle on jack stands to do this.

Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches. 

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you're working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Do not work on your vehicle if you feel the task is beyond your ability. 

Vehicle models change and evolve, as they grow older, so the vehicle shown in our illustrations may vary slightly from yours. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

Drain cooling system. See our Pelican Parts Technical Article on Flushing Your Coolant. While working in the engine compartment at lower right side of the radiator, clean the area around your E46 radiator outlet temperature sensor.

If you are looking for more Technical Articles to diagnose or repair cooling issues please visit our E46 page.

Disconnect the radiator outlet temperature sensor electrical connector, (green arrow) (Radiator fan and shroud shown removed for clarity).
Figure 1

Disconnect the radiator outlet temperature sensor electrical connector, (green arrow) (Radiator fan and shroud shown removed for clarity).

On the side of the sensor, there are two tabs you squeeze to release it from the lower radiator hose (green arrows).
Figure 2

On the side of the sensor, there are two tabs you squeeze to release it from the lower radiator hose (green arrows).

Squeeze sensor release tabs and remove it from lower radiator hose.
Figure 3

Squeeze sensor release tabs and remove it from lower radiator hose.

When removing, check that the sealing o-ring does not remain in lower radiator hose (green arrow).
Figure 4

When removing, check that the sealing o-ring does not remain in lower radiator hose (green arrow). If the o-ring remains in the lower hose, the new sensor will not seal and you will have a coolant leak.

Before installing a new sensor, clean the sealing area inside the lower radiator hose using a lint-free cloth. Leaving dirt behind can lead to sealing issues. A leak may develop after replacing the sensor. If a leak around the sensor develops after replacing the sensor, replace the lower radiator hose. Install the new sensor into the lower radiator hose. Listen for an audible click to confirm each locking tab properly seats. Connect the electrical connector, fill and bleed the cooling system, and check the sensor area for leaks.

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Comments and Suggestions:
Crashx2 Comments: Hi - I have a 325i 2001 with overheating issues. First the Expansion Coolant Tank exploted, I replaced it and since electric Fan was not turning on when requiredwas the thought I replaced the Coolant Sensor. The FAN was activated if A/C is on, sometimes A/C was no cold, therefore FAN was not moving. I was using A/C Auto. I did a scan, and seems that the onboard computer sent the signal to the FAN, but the module does not do anything, same day after the scan the upper hose explote too. So I replace the electric FAN and upper hose. The lower hose is cold and the upper hose is extremely hot after 15 minutes, but the FAN still no moving. This time I did not use A/C Auto, this time I selected one position and FAN moves within a 30 seconds timeframe. But without the A/C the FAN is not moving. Should this be related to bad thermostat? Since lower hose is cold the coolant sensor does not detect FAN needs to move? Any idea? Suggestions?
November 29, 2016
  Followup from the Pelican Staff: Sounds like the thermostat is not opening. Before replacing it, pressure test the cooling system to be sure it is properly sealed. if so, replace the thermostat. Give The Pelican Parts parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
Douth Comments: AC not cooling, have replaced fan, checked fuses, fan does not start at all. Compressor clutch kicks in when hot wired. Ambient temp reads ok. Any clues on where else to look? Have cleaned every connection I can find.Not many hairs left to pull out. I am in Australia and it is hot!BMW E39 2001 525i
November 22, 2016
  Followup from the Pelican Staff: If a/c charge is correct and the compressor or fan does not kick on, it may be due to an incorrect pressure reading. Check the pressure sensor value when the a/c is commanded on. - Nick at Pelican Parts  
Clay Comments: 2003 325xi, Aux cooling fan stays on Run's - never turns off after engine stops. Replaced Temperature Sensor, Fan will not stop running until it drains battery. What controls turning the aux fan off after coolant temp decreases? How can this issue be isolated to relay or fan? Thx's.
November 4, 2016
  Followup from the Pelican Staff: The aux fan runs with either the A/C or when the DME requests it due to engine temp. monitor the signal (small wire) to fan, I recall the DME grounds this wire to activate fan. Confirm wiring using a wiring diagram for your vehicle. - Nick at Pelican Parts  
kct Comments: please help. where is the fan switch on the 2008 x3 bmw. The vehicle runs hot when the sitting still with the ac on. Advise to replace the fan switch but can not locate it
October 27, 2016
  Followup from the Pelican Staff: Does the fan come on when the a/c is on? - Nick at Pelican Parts  
lennox Comments: I have a 2003 318i touring with 174 000 miles that starts fine when cold but starts hard cranks about 5-10 seconds when hot. If i start it in the morning it starts immideately. When at operating temp after driving to work, if i turn it off and then try to restart, it will start right up. How ever if i let it sit for 30 minutes to a couple of hours it takes some cranking to fire up will sometimes kick when cranking but takes much longer than is normal When it runing it runs, it runs fine, smooth, good power. No lights lit on dash Check engine etc Spark plugs, air filter, petrol filter, crank sensor, petrol pump and all coils were replaced recently
Im all out of ideas. Any help would be greatly appreciated.
September 27, 2016
  Followup from the Pelican Staff: One of the items you state is good has to b e faulty. When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and fuel pressure, volume, quality and engine compression. Are there any fault codes? Once you figure out what is missing, it will be easier to diagnose.- Nick at Pelican Parts  
Gatsi Comments: I have got a bmw 318i E46 2003 model. If i drive it for a long distance and stop for a while,it doesnt start easily, it only cranks but after it cools for about 30 minutes it starts moving without any problem. I replaced the crank sensor and still nothing was solved.
Please help me
September 26, 2016
  Followup from the Pelican Staff: I can't help without knowing what is missing from the system when you are trying to start it. When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and fuel pressure, volume, quality and engine compression. Are there any fault codes? Once you figure out what is missing, it will be easier to diagnose.
- Nick at Pelican Parts
 
Jmj Comments: 2003 bmw 525i code 11 -i have changed the radiator, fan, thermostat and housing with also new sensor, have also replaced the radiator outlet sensor. Been through all fuses. car runs great seem to cool just fine and still the car is throwing this code 11 any ideas
September 22, 2016
  Followup from the Pelican Staff: What is the definition for code 11? On 2003 models P-codes or BMW FC-codes are displayed. - Nick at Pelican Parts  
dandi Comments: Any idea where the wires from radiator outlet sensor goes. Are they go straight to ecu or somewhere else becouse i connect sensor straight to ecu and its showing same -48 degrees. BMW e46 325ci 2001.
August 18, 2016
  Followup from the Pelican Staff: The should go directly to the DME.
I would grab a repair manual. It will have the wiring.

Give our parts specialists a call at 1-888-280-7799.- Nick at Pelican Parts
 
BKcarrera Comments: 2006 E46 330Ci Convertible. 110K miles. For maintenance I replaced the radiator, cap, exp. tank., brackets, rad. hoses, w/p, and temp. sensor in lower hose. I resealed the oil pan gasket and valve cover also. After the work, I got the check eng. light on with code P0128. It comes on after 2 days each time I reset it. I replaced the thermostat, but the light still comes on after 2 days each time I reset it. Do you think it's a bad temp. sensor or another idea? No BMW tech I have talked to has had this same symptom after the cooling system work. Any thoughts? And thank you for your excellent tech. procedures and pictures.
July 30, 2016
  Followup from the Pelican Staff: It's possible the connector for the thermostat is damaged. Check the DME data stream to check what the displayed temp is. If it reads open circuit, the wiring is faulty. - Nick at Pelican Parts  
Jake Comments: @Pelican Staff

The fan wouldn't turn once the engine reached operating temp. I bought a new sensor and measured the resistance.

New: 2000 ohms
Old: 7 kohms

That's how I figured out how to test it. The old sensor was written and not working based on the resistance in assuming.
July 24, 2016
  Followup from the Pelican Staff: if the fan won't turn on, it may be faulty. Especially if you can see correct temp on gauge. I would try to activate it using a BMW scan tool, if low speed does not work, it is likely faulty. - Nick at Pelican Parts  
Jake Comments: How do you test to see if this sensor is failing?
Symptoms:
1. Fan does not at engine start or Key "ON"
2. At shutdown, fan does not turn on after operating temperature is reached.
3. Fan does not turn on when the plug to the lower coolant switch is removed.
4. However, fan DOES turn on with A/C on Max.

So would this be the coolant switch failing or the fan with the noted symptoms above?
July 19, 2016
  Followup from the Pelican Staff: What are you trying to fix? A fan not turning on? Usually a fault fan will still run at high speed if available. - Nick at Pelican Parts  
welshmen Comments: I have a 2005 325i, manual. I had just replaced the coolant expansion tank. I had no problems with over-heating even when the old cracked tank was leaking. Now that I've replaced the tank, the first "test" drive it started over heating. I had the fan tested and that works, but doesn't kick on, ever. If I disconnect the radiator outlet temperature sensor electrical connector, the fan will turn on, but doesn't work properly
June 28, 2016
  Followup from the Pelican Staff: I bet you have air trapped in the cooling system. I would try bleeding it before you go too far. - Nick at Pelican Parts  
seth Comments: the green arrow thats pointing to the silver clips in the first picture where can i get one? i lost mine
June 25, 2016
  Followup from the Pelican Staff: From Pelican Parts.

Give The Pelican Parts parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
Vic Comments: I have a 2000 328i, the fan stays on and is very loud when the car is running, gets louder as the rpms rise, is that a bad temp sensor? Also after about 30 seconds of running it starts to misfire, when turned off and back on its goes away for about 30seconds again...
May 3, 2016
  Followup from the Pelican Staff: Either a bad temp sensor or fan. - Nick at Pelican Parts Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
 
Simba Comments: Mng I have a BMW 318I 2003,it failed to start after it ran with a leaking radiator causing it to have a temperature rise subsequently stopping.I need a solutions on how I can solve this problem please help?
March 24, 2016
  Followup from the Pelican Staff: The problem may be related to a bad head gasket. Check if the spark plugs are covered in oil or coolant. When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and fuel pressure, volume, quality and engine compression. Are there any fault codes? Once you figure out what is missing, it will be easier to diagnose. - Nick at Pelican Parts  
my325xi Comments: Answer for Dandi. Your issue may be the external/Ambient Temperature sensor located in the front wheel well. Assuming when you say ECU that you are looking at the temp setting on the instrument cluster.
March 13, 2016
  Followup from the Pelican Staff: Thanks for the input on this one. We appreciate the help.
- Nick at Pelican Parts
 
Dandi Comments: Hi I have BMW e46 325ci 2001 I replaced radiator outlet sensor but still ecu shows -48 celcius.when I disconnect plug from sensor the error code come up when I connect back and clear foulty code its disappeared but ecu still show -48 celcius.any idea what that can be.
March 5, 2016
  Followup from the Pelican Staff: The circuit is open. Check the wiring for the sensor. - Nick at Pelican Parts  
FreeBird Comments: I have a 2005 BMW 325ci, that over heats. I have replaced the pump/thermostat /fan /fan clutch/ the car still overheats.
I removed the thermostat housing and took out the thermostat.
Still overheats and the lower radiator hose never gets hot.
What do I do next?
thanks
Freebird
March 4, 2016
  Followup from the Pelican Staff: I would pressure test the cooling system. If the system will not hold pressure and there are no external leaks the head gasket may be faulty.- Nick at Pelican Parts  
e46boy Comments: If my temp gauge shows close to overheating and fans not on does that mean my fan switch not working?
February 22, 2016
  Followup from the Pelican Staff: That or the fan if faulty. - Nick at Pelican Parts  
Mark Comments: 2002 Bmw 745i "No heat" Replaced thermostat w sensor and coolant flush. Electric fan does not come on but I figured ambient temp around 10-15f degrees so there is no need. I am totally stumped but I know it's something minor. Oh also added a leak stop chemical and prior to heat worked. Lower radiator hose is cold to touch upper hose is hot. Low coolant warning comes on but level is at max. Tried to burp system through overflow being I have a closed system and remove as much air as I could. Auxiliary pump is working fine hot at the outlet as well as all hoses to and from heater control valve. At idle I can get the supply temp to 85f degrees but when I drive the temp drops drastically. Is my heater core plugged? What is my problem please help!
January 5, 2016
  Followup from the Pelican Staff: If you have hot hoses going into the heater core, and cold coming out, there is likely a restriction. If you have hot hoses in and out of the heater core, there may be a flap issue inside the heater housing. You can test flap function using a BMW scan tool. - Nick at Pelican Parts  
Acquaviva Comments: Good Morning, I need your help. I have a E46 325i 2006, but the engine don´t work correctly untill the temp increase more than 1/4. Untill this, i need start and accelerate a lot of times to pass this temp, because after start and accelerate the engine shutdown. After this, the motor work so better, without problems and not shutdown more.
December 1, 2015
  Followup from the Pelican Staff: Could be an issue with the fuel pump. I would perform a fuel delivery system test. Check fuel pressure, volume and quality.
- Nick at Pelican Parts
 
javizzz Comments: hi.......

do you know the switch point temperature of this sensor?????? do you know if the are other compatible sensors whit other operating point??????? thanks.......!!!!!!!!
July 26, 2015
  Followup from the Pelican Staff: I don't have that info, the radiator fan on and off temps for your model may be helpful. You didn't mention what vehicle you are working on.

No other sensor I know of that matches. - Nick at Pelican Parts
 
Larry Comments: Nick, thanks for the tutorial. My 2001 325XIT sounds like a vacuum cleaner upon startup even from a cold engine. Sounds like a vacuum cleaner.

It has been pretty hot here in Chicago the last few days, so I did expect the fan to be working overtime, but just this morning it threw a P1111 code. Also, the digital MPG readout sticking at around 17-20 MPG, though the analog gauge seems to be functioning fine.

I've checked the coolant level which is fine, and the engine temp seems to be stable dead center of the gauge. I'm going to start out by replacing the lower coolant sensor again, thanks for the tutorial, as I'm new to BMWs and see where that takes me.

My question is this - I know it's recommended, but is it absolutely necessary to replace the lower radiator hose when replacing the coolant sensor? The hose seems to be in excellent shape. Also, I'm also looking to check the coolant, and maybe doing a coolant flush - are there any regularly obtainable coolants read: ones I can pick up at Autozone that are up to BMW specs? Last, if the code fails to clear, what's my next step?
July 20, 2015
  Followup from the Pelican Staff: You don't have to replace the lower hose, it depends on the condition and if it seals again after the sensor is replaced.

I don;t know hat autozone sells, so I can;t offer advice there. If the code clears, you will have to trust there is no fault.

- Nick at Pelican Parts
 
Zambian Comments: Hi nick,
What is the optimum engine operating temperature in degrees celcius. Talking of a Bmw 318i E46 engine. I ve noticed my engine temperature on a warm day fluctuates between 105 to 108 degrees celcius. Is this normal.
July 14, 2015
  Followup from the Pelican Staff: 105 is about right, somewhere below 203°f. - Nick at Pelican Parts  
B Comments: Is there another coolant temperature sensor located behind the engine?
February 11, 2015
  Followup from the Pelican Staff: There is the engine coolant temp sensor, located under the intake manifold, mounted in the engine. - Nick at Pelican Parts  
Martin Comments: Answer to Kori - your problem, if the car is a 320d or 330d, is usually caused by the camshaft sensor.
February 2, 2015
  Followup from the Pelican Staff: Thanks for the input on this one. We appreciate the help.
- Nick at Pelican Parts
 
kori Comments: I have changed spark plugs, fuel pressure fine and the volume is half tank. When the coolant temperature sensor electrically fails, then the sensor starting to malfunction, what are the MOST likely effect to the engine starts especially when the engine is hot? Because what i am experiencing is NOT the engine failing to start but an instant auto-shut down of engine a minute i start the engine when it is hot.it start fine but auto-shut down instantly and at that time fuel pedal doesnt give the engine power when i press it. Could this be a failing fuel pump,coolant temperature sensor or what?
December 27, 2014
  Followup from the Pelican Staff: When the engine stalls, something has to be failing. One of the items I mentioned earlier is not present when the engine stalls. You have to identify that item. Once you locate the failing item, check if it is losing power, ground or the signal to activate. - Nick at Pelican Parts  
kori Comments: when the engine is hot somtimes my e46 model 2000 after pulling over and shut the engine,when i start the engine it would just do fine but suddenly shuts off the engine.i keep starting it successfully and it shuts off the engine until i have to leave it to cool to until be temperature gauge indicator points blue area. It is then it will start and engine run continuously. I have just changed spark plugs,fuel filter,coolant. Haved coolant leakage in the engine block
December 22, 2014
  Followup from the Pelican Staff: I can't help without knowing what is missing from the system when you are trying to start it. When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and fuel pressure, volume and quality. Are there any fault codes? Once you figure out what is missing, it will be easier to diagnose.
- Nick at Pelican Parts
 
messymitts Comments: Hi I have a BMW 320d 2008 I got a warning lamp coming up on my dash of a its a symbol of coolant on min it yellow then it goes to red then engine goes into limp mode then goes back to normal running the fan is constantly on I've changed the thermostat cos the top hose is hot but the bottom is cold I'm not overheating I've been told there are 2 coolant sensors if so can you tell me where or can you explain on the problem is I don't have any engine man lamps on dash so diagnosis machine is not picking any thing up.many thanks terry.
November 13, 2014
  Followup from the Pelican Staff: There will be one in the radiator hose and the engine (I think). As we do not have your engine here in the US. I would start by checking the DME for fault codes. If the system is not working properly, a fault code will be set. This will be your best bet when diagnosing.
- Nick at Pelican Parts
 
Jesus Comments: Will this sensor cause my radiator to not work properly and blow my expansion tank
October 27, 2014
  Followup from the Pelican Staff: No, it should not cause that. - Nick at Pelican Parts  

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Page last updated: Fri 12/9/2016 02:19:58 AM