One guys say plug hole with finger while you do the swap.

BMW E90 Radiator Outlet Temperature Sensor Replacement | E91, E92, E93 | Pelican Parts DIY Maintenance Article

Coolant leak from your lower radiator hose? It might be the radiator outlet temperature sensor. Replace your radiator outlet temperature sensor quickly with this guide.

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Which coolant temp sensor? You will loose some coolant, but not a lot.

 

Hi Herb.

I'm replacing the one that's on the left-hand side of the rad (as you stand in front of the car looking into the engine bay).

I have an issue with my fan not coming on, but it can be triggered by ISTA so I don't think it's an issue with the fan itself. Googling the symptoms led me to various posts saying the coolant temp sensor may be faulty.

I figured for £20 it was worth a shot, but YouTube vids were saying the whole system needed to be drained down. 🙄

 

So, just an update in case anyone else is looking to replace that sensor...

Easily done without draining the whole system. I removed the fan first. Worth the 5 minutes effort just to ensure that the sensor is fully visible and easily accessible.

Pulled the old sensor and lost a tiny bit of coolant, but really not much. I was surprised at how little came out - and, actually, I'm now wondering if that is indicative of another problem as with the sensor replaced I'm still getting 'Engine Overheating' and the fan not being triggered.

I have noticed that there are signs of a coolant leak around the water pump, and a few times I've heard a rattling noise coming from that area, so starting to wonder if the pump is on it's way out. 🤷‍♂️

 

Now even more convinced it's my water pump.

Removed the resevoir cap - absolutely no pressure release whatsoever, despite the engine having been run up to operating temp 30 mins previous. If I start the engine with the cap removed, I can initially see a weak flow of coolant coming into the expansion tank, then after about 30 seconds, the flow stops completely.

I'm assuming that this is not normal.

 

Ah FFS. Now when I try and trigger the fan using ISTA it doesn't start

 

If you pressure test the cooling system, you can typically find any leaks pretty quick

 

If the lower coolant sensor does not sense any coolant flow, it will not activate the fan. Try putting your old sensor back in with a new o-ring, & see if the fan starts to work. There are 4 speeds on the fan, so check them all. This is the time of year that the fans start to fail. If you search the net very good, you might find the fan by itself at a much cheaper price. BMW only offers 2 years for their fan, but local auto parts stores can get the fan with a lifetime guarantee. As much as our fans fail, I would go that route. I am not a big fan of Dorman, but their warranty makes their fan a better choice.

 

Just dug the old sensor out of the bin. Will refit in the morning. I'm also trickle charging overnight just to rule out any voltage-related nonsense.

It really is a love/hate relationship with this car 😂

 

I just ran this for my car on O''reillys, & they are now showing just the fan also. I don't know if it has the correct module for our fan, but you have options. The good thing is the lifetime warranty on them.

https://www.oreillyauto.com/shop/b/accessories/truck--towing---jeep/trailer---towing/engine---transmission-coolers/cooling-fan-assembly/d27432abe1f0/v/a/18497/automotive-car-2005-bmw-645ci?q=cooling+fan+assembly

 

Thanks for that Herb - it may yet come to that. But I have a slight update...

Having trickle charged overnight, and leaving the new coolant sensor in place, I plugged the car in to the laptop today and I can trigger all 4 stages of the fan using ISTA. However, the fan still won't come on when the engine gets up to temp. Now, a few hours on, I can no longer trigger the fan using ISTA. 🤷‍♂️ I'm now getting fault code 279D showing up (which I didn't get yesterday). If I clear the fault and start the car, the fault returns.

I found this vid of a bloke that has the exact same symptoms as me (no fan, overheating, aircon blowing warm air) (

) - he goes to a level of diagnostics I can only dream about, but his conclusion was that there was a broken wire between the DME and the fan.

The only other thing I've checked has been the 60a fuse in the glove box - that looks fine to me. (Fuse no. 9 according to this: '04-'10 BMW 6 (E63, E64) Fuse Diagram)

I guess I'll try to trigger the fan again via ISTA tomorrow. And maybe order a new fan 🤷‍♂️

 

You could try & jump the wires going to the coolant sensor, to see if this will keep the fan on. If the fan starts to fail after it gets warm, it might be just a bad.

 

Another small update.

Drove the car to drop my lad off this evening. Usually the oil guage on the dash takes 10-15 mins to get to temp. On this journey it got up to temp in less than 5 mins, and the amber warning light for engine temp came on.

Car is not smoking, and I checked the oil today - so I'm not losing oil.

Waited 2 hours for the car to cool so I could nurse it home. Not gonna drive it any more. So something seems to have got worse quite quickly.

My gut feeling at this point is to order a water pump - but gut feeling isn't good enough. I think I may have to give in and have it towed to my local indie 🙄

 

Is it possible that no flow to the radiator is being caused by a defective thermostat?

 

The thermostat should throw a code. Have you tried turning the heater on high & filling the reservoir until it takes no more coolant. If the coolant bleed line does not have coolant coming back thru it, I would start thinking water pump. Our engines stay cool with air thru the grill while moving, but it will shoot up quickly sitting at a red light. 1st check the coolant bleed hole for flow, then check the radiator fan as soon as you get an engine hot warning. If the fan is not running at this point, it is bad. You can also leave ISTA or INPA running while driving, & watch the coolant temp. A OBD2 reader can also monitor the temp. There was problems some years ago with plastic water pump rotors that simply stopped turning. We need to discover what the problem is, without throwing money away eliminating items one by one.

 

Think I'm going to order a new fan. All manner of weirdness here.

So, this morning, I plugged the car in to see if the fan could trigger. When cold, I can trigger the fan via ISTA - but I don't think the 20% stage is kicking in. When I trigger the test, the fan doesn't start right away - only when the test moves to 40% does the fan come on.

I then started the engine, and reran the test multiple times as the car warmed up. For 5 mins or so, the test continued to run successfully. Then the final 100% stage of the test started to not kick in (the fan speed didn't increase). I then tried to trigger the fan via the DME module functions, and the fan kicked in. But when I tried a couple of minutes later, neither the service function test nor the DME module component trigger would start the fan.

Another thing I noticed is a rumbling sound coming from the center of the engine when the car starts to get hot (the oil temp needle just starts to leave the bottom of the dial). I tried to record it - I'll see if I can post it shortly. I couldn't discern whether the noise was mechanical, or - as someone suggested on another post regarding water pumps - if it was a bubbling/popping sound (coolant boiling?). The noise would disappear as soon as I gently feathered the throttle.

Can't for the life of me work out why the fan would fail to trigger as the car warms up. So I think I'll take a punt on a new fan.

 

its pretty easy to determine if your water pump is working. all I do is leave the reservoir cap off, start car, bring to temp, and watch the water exchange into the reservoir . its pretty obvious as the exchange occurs. that is how I bleed the cooling system.

 

When the fan fails, it will do it at random speeds. When the coolant gets hot, it will usually fail on stage 4. This is when you hear the expansion tank start to make popping & a crackling sound. The expansion tank want handle the rising coolant temp very much, & it will start to crack at the seams. If you look inside the expansion from the top, the red float will start to melt, then get shorter.

I really think your fan is the problem, but there could also be a problem with the water pump. The water pump is pretty easy to remove & inspect. If it looks good after inspecting & turning it, put a new gasket back on it, & eliminate this part from the troubleshooting. There is a way to enter the secret menu on the Kombi, & it will actually show the coolant temp. I don't use this very much, but it can help show you when the engine starts to overheat.

 

New fan ordered yesterday, Herb 👍. I'll let you know how it goes.

 

I think that will fix the problem!

 

New fan fitted. All appears to be working 👍

Thanks to everybody that contributed to the post - especially HerbP.

Cheers all, have a good weekend.

 

I have gone through 2 fans already with my car. When they fail, they can be hard to figure out what the problem is? Glad you got the problem fixed!

 

Hello. If anyone could help me with information on a 2016 BMW 650 I convertible coupe, I would appreciate it. I need video or easy instructions on changing temp coolant sensor. Iam a women so take it easy on me lol.

 

You are in the wrong forum, I will leave a link to the correct forum. There might be 2 sensors, which one seems to be the problem?

https://www.bimmerfest.com/forums/f12-f13-2012-2018.155/