2014 bmw 520d overcooling even with new thermostat

honda boi

Hi all

Have a 2014 bmw f11 520d (N47 engine) that has me scratching my head.

Not long after picking it up, it caught my eye that the oil temp gauge in the dash was increasing near middle point but then decreasing back to the 1/4 with no change in driving style.

So hooked up the obd and saw the coolant was rising and falling and not getting past 75 degrees.

So I picked up an aftermarket thermostat, stuck it in, bled it.

Drove it for a few days. Noticed the same issue was happening but it wasn't dropping as low.

Would sometimes get up to 90-95 degrees but would still drop down majority of the time to 70 degrees.

Read online that OEM is best so I bit the bullet and bought one from BMW (€100!)

Fitted it, bled it.

Drove it the next day and it seemed to run right, got up to 87-90 degrees. Happy days I thought.

Nope, turned car off for 15mins.

Drove again and the temp dropped and stayed between 69-80 for over 30mins. It would get to 85 if I redline and drive hard but as soon as I go back to normal speed/rpm it would drop.

Left it overnight, next day first drive it drove correctly. But same thing , left car for an hour and the temperature stayed around 69-80.

It has a brand new radiator cap also.

Tested the aftermarket thermostat in a pot of boiling water and it opens after 88 degrees.

I'm stumped as to what could be causing this.

Any ideas?

I know most people wouldn't notice this as the oil temp eventually stays at the mid point, 100 degrees. But to me when winter comes and I use the heating I don't want the temp never to reach optimum temperature for the dpf .

mikeecho

I would guess, that it's the water pump.

Especially if you've already changed the thermostat & radiator cap.

But that's a guess.

honda boi

https://www.boards.ie/discussion/comment/122536035#Comment_122536035

Wouldn't it overheat if the water pump was bad?

I'm assuming the coolant wouldn't flow around so it would just boil over?

greasepalm

Waterpumps when they go on normal cars they overheat.

How is engine cooled by fan and is it running soon after start up and not allowing car to warm up?

On some cars with window down you can hear fan coming on and going off.

honda boi

https://www.boards.ie/discussion/comment/122536058#Comment_122536058

I thought myself maybe the fan is kicking in too early at times and maybe it's cooling it down when it's not needed.

I have seen it running when temp is about 80 degrees, but come to think of it maybe it was on because the AC was on.

I wonder if I disconnected the fan and drove it and see if the temp will go up and stay around 90?

Another thing I found quite odd, is if I'm stationary and I just rev the car the coolant temp will drop from high 80s to high 70s in a matter of 5 seconds, then it takes long for it to eventually get up to high 80s again.

Oh and I do get heat inside the car.

greasepalm

Getting good heat inside car suggests waterpump is working correctly.

Switch off AC as its drinking fuel and second fan would be running.

80 sounds very low for fan to kick in as 90+ is operating temp and would imagine fan might cut in at 95.

Wonder if a coolant temp sensor or fan sensor and issue as 80 - 70 is a big drop in 5 seconds.

When car is at operating temp have bonnet open and note when it comes on or goes off as we would do that so you see + hear when things happen.

Chippy01

What type and concentration of coolant are you using?
It might make a difference to alter the concentration or even the type? Maybe?

Dirty Nails

https://www.boards.ie/discussion/comment/122536086#Comment_122536086

Multiple fast gauge fluctuations might suggest voltage. Watch voltage on your scanner as well as temp to see if they vary together. If you have a jump lead handy connect it between engine & body. It'll rule out dirty body earths.

honda boi

https://www.boards.ie/discussion/comment/122536125#Comment_122536125

Ok so a bit of a quick update.

Took it for a 20min drive with no AC or inside fans on, engine coolant was at 50 degrees before I took off so wasnt cold.

After 10mins it was fluctuating to 70-80-70 degrees, with the same driving style, cruise control on etc. ( very odd this I think)

Pulled over and the radiator fans were not on so I guess I can rule that as not the issue.

Checked the radiator hoses. Top hose was hot , bottom one with the thermostat was cold.

The next 10mins I drove it harder, got it up to 88 degrees. Pulled over , checked fan again and it wasn't on. Same thing with the hoses, top was very hot, bottom cold.

Drove home easy, and when I was coasting the temp was dropping.

Got home checked hoses again, top was hot and bottom had gotten hot. Also opened the coolant tank and used a meat thermometer to see how hot the coolant was and it was pretty close to what the sensor was reading.

So this to me means the thermostat is working as it should as if this 2nd stat was failed open the bottom hose would be hot after the first 10mins?

honda boi

https://www.boards.ie/discussion/comment/122536294#Comment_122536294

The one I got was a G11 coolant from febi bilstein, it's a greenish blue. . Was told it was the correct one.

Mixed it about 50/50 with water.

honda boi

https://www.boards.ie/discussion/comment/122536487#Comment_122536487

So I recorded my 20min drive on bimmerlink app monitoring battery voltage, speed, engine rpm, coolant temp and fan rpm.

Just looked back over it and the battery voltage stayed at 14.6-14.7 the entire drive.

The only car I had with rapid temp fluctuating was a car with a blown head gasket, where water was pouring out the expansion tank as you drove so the sensor was picking up air at times. But that was reading from cold to hot in an instant.

greasepalm

20min drive i would have thought temp would be normal running temp around 90??

Thermostat should have got up to temp to open and close and have bottom hose warm.

kirving

Is the gauge on your car for oil temperature, or coolant temperature? There will be hysteresis (lag) between the two.

Do you have the engine cover still in place or is it missing?

Was it remapped?

Is the outside temperature sensor working on the car? Engine management systems will pull as much data as possible, not just a single coolant/oil temperature sensor to manage fuel efficiency. Some cars will use an Intake Air Temperature sensor, along with charged air temperature sensor, or may pull data from the ambient sensor.

Why is this a problem? Is there low compression, loss of power? Could it cause more soot buildup maybe?

My 330e (B48 petrol) always rans on the cool side, versus the middle of the gauge. Is it is really just the workings of a modern ECU doing its thing?

https://www.boards.ie/discussion/comment/122536487#Comment_122536487

Could be the case, but there should be voltage regulators for anything critical I would think.

honda boi

https://www.boards.ie/discussion/comment/122536687#Comment_122536687

My thoughts exactly.

Every other car I have owned the temp gauge would always keep going up till it hit it's optimum temp, which is usually 90 degrees or bang centre of the temp gauge. Never have I seen it move up then down for no apparent reason, with no change is driving style, cabin fans etc.

Bottom hose only got hot at the very end of my drive.

Stayed cold/luke warm after hard driving and when temp was at 88 degrees.

It seemed to me like this engine is super efficient at dissipating heat without the need of a thermostat or radiator 😂

honda boi

https://www.boards.ie/discussion/comment/122536695#Comment_122536695

On this car it is an oil temp gauge.

But I was getting my coolant readings from the obd and at times the hidden menu on the cluster.

From reading about this car online I think there is no actual oil temp sensor, it just takes info from other sensors such as the oil pressure and other ones, like you say.

Ambient temp sensor working fine.

Car is bog standard, no remaps.

Engine cover still there.

At the minute it is not an issue. I don't seem to have any power loss or issues.

I only picked this up on June and it's my first "powerful" car so to me it pulls like a train.

I'm more concerned that once the weather shifts and it becomes a lot colder will I start to have issues with the dpf not doing a regen because the coolant temp remains too low. Or will I have no cabin heat with colder temps.

From a bit of research this car should sit at about 90 degrees.

If the thermostat is set to open at 87 degrees, to me this is around the optimum temperature.

John.G

Just a general comment on coolent temperature indication. For years now (on VWs anyhow) the temperature indication will read correctly up to 75C, between 75C and 107C, it will indicate a rock steady 90C, if, for whatever reason, the temperature exceeds 107C then the indication will again be correct, these were known originally as comfort gauges.

Again, these would be fairly typical settings for the thermostat and cooling fan speeds.

Thermostat begins opening at 84C. Fully Open at 98C.

Fan Speed 1 ON at 91C to 97C. OFF at 91 to 84C.

Fan Speed 2 ON at 99C to 105C. OFF at 98 to 91C.

colm reilly

All the signs of a failing water pump

kirving

https://www.boards.ie/discussion/comment/122536991#Comment_122536991

Why so? I would have expected that a failing water pump would cause an increase in temperature?

User1998

https://www.boards.ie/discussion/comment/122537761#Comment_122537761

I’ve had failing water pumps that didn’t cause overheating

kirving

Fair, bad bearings wouldn't necessarily cause overheatingz but why would a failing pump cause excessive cooling?

https://www.boards.ie/discussion/comment/122537849#Comment_122537849

User1998

https://www.boards.ie/discussion/comment/122537866#Comment_122537866

I’m honestly not sure, but wouldn’t a failing waterpump be obvious to spot. Aren’t they usually noisy when they start to fail?

blackbox

If your bottom hose is cold, the whole system hasn't heated up yet. The engine may be up to temperature as the thermostat has reduced the coolant circulation, but the rest of the coolant hasn't heated up yet.

The next time you have been driving for 20 minutes or so, leave the car idling until the radiator fan comes on and see if the temperature changes much ( AC off as it can bring on a fan independently of coolant temp).

It's also possible that the oil temperature sensor or associated wiring is faulty but unlikely if coolant temperature matches it.

honda boi

https://www.boards.ie/discussion/comment/122537889#Comment_122537889

I always assumed a failing mechanical water pump would either start leaking coolant, be noisey or cause overheating as it doesn't circulate coolant?

honda boi

https://www.boards.ie/discussion/comment/122537943#Comment_122537943

Ye it's very strange.

I cant understand how the temp can fluctuate from 70-80-70 with the bottom hose cold.

It seems like there is something else cooling the system besides the thermostat, which from my understanding there isn't anything else.

Will check the fan and temp later when I go out and report back.

I have checked the coolant temp and oil temp when the car is cold and they both read close enough to ambient temperature and both gradually increase so I think this would mean they are at least operating correctly.

User1998

https://www.boards.ie/discussion/comment/122538151#Comment_122538151

Yeah I’ve replaced a few waterpumps and its always been one or more of those symptoms. But I’m no mechanic so maybe someone else can advise better

greasepalm

Impellers on water pumps are like blades that move the water around and they can erode off or like VWS come away from the shaft , when car is cold can you remove rad cap and when starting up the engine see water movement in the rad ?

I have kept away from BMW as been a pain in the arse.

Does this car actually have a coolant / water temp gauge or is it just a light ?

landmarkjohn

I have watched the coolant temp in the diag display on my E65 N52 engine. Can't remember exactly but it ticks up to about 100-102 and then ticks back down again maybe 10º and then back up again and so on.

If it's not overheating I wouldn't worry about it.

Shawnee Poole

Drove home easy, and when I was coasting the temperature was dropping.

Its a headscratcher as the thermostat has been replaced twice.

Maybe this is some help in solving your problem, if a coasting test is possible.

I drove a '93 honda accord petrol for 11 years 2003-2014 and the engine only needed a thermostat replacement during that time.

On one of my normal routes was a steepish downhill road for about 2 miles and sometimes I used to slip the car into neutral until 1 day noticed the water temperature gauge was much lower than normal when near the bottom of the hill.

At the bottom when on level road I opened the bonnet and everything looked normal but for the top hose which felt cold with the engine still running, the car having travelled 8 miles by now.

I kept an eye on the temperature gauge and it returned to normal and remained that way until my next coasting trip downhill and the same drop in temperature occured. With the car in gear on the same downhill trip the temperature gauge used to read normal.

Replaced the thermostat and on the next coasting downhill trip the water temperature gauge contined to read normal.

As a test I put the old thermostat in boiling water and it opened but when it was taken out of the boiling water it didnt close fully.

I dont know anything about the newer BMW engines but have plenty experience of the older E21 6 cylinder units cylinder heads and gaskets and timing belts.

greasepalm

Its no good just putting in the stat into boiling water as you need a thermometer to check its opening correctly at that temp.

honda boi

https://www.boards.ie/discussion/comment/122538449#Comment_122538449

Yep those symptoms you have there would definitely shout out open stat to me.

But I've swapped my stat twice(1 aftermarket , then 1 OEM) and still no luck.

Yep tested the aftermarket market thermostat and it opened at the correct temperature.

Now I can't see it closing because I'm assuming the spring would put it back into the closed position when in the housing.

Not sure how I could replicate the thermostat closing myself. But the little needle/piston can be pushed back into position so the pressure of the spring should push it back into place.

John.G

Looks allright like a partially opened stat, cruising along with heater off you would expect the temp to be 4 to 8C higher than the stat opening temperature, I tested two of mine years ago with VCDS and both read 88/92C (stat opened at 84C) with heater on/off at normal cruising speeds.

honda boi

Drove it today for 40mins.

Got up to 87-89 and stayed there 95% of the time(all N roads, so steady 90kmh-100kmh) until I got into town when it dropped to 80 degrees.

Popped the bonnet quickly and saw the fan wasn't on so I can rule out the fan being the issue.

An hour later I had to drive it for 10mins and during that drive it went between 70-80-70 as always. But this time I pulled over again and checked the 2 hoses and both were hot!!!

Indicates thermostat must be opening early!!!!

2nd thermostat it seems!! And an OEM one as well.

When I get time I'm going to take it out and try make up a little contraption to simulate it opening and closing.

I hope if it is not working that bmw will give me a replacement part.

John.G

Just wondering are the stat and housing compatible, one would assume that the OEM one should be, there is a very strong spring on these keeping them closed, so difficult to imagine the stat opening and then sticking partially open.

greasepalm

I notice the pin in the stat and on VWS it would bust in the housing causing stat to fail . Was the housing replaced also or just the stat?

We always replaced both at same time due to heat and contraction and failure of components.

John.G

I'm not sure exactly how that stat is securely held but maybe there might/should be a slight gap between the housing cover and its seating before tightening up the bolts, some of these type (almost universal now) stats relied on the compression of a O ring to ensure this, so on that type it was essential to renew the O ring as well.

greasepalm

Housing contains the sealing ring as comes as one unit.

John.G

There to be two "different" types of stat offered here, so maybe the cover sealing ring is only to stop external leakage.

greasepalm

They look handy to hold stat into the plastic housing while fitting as so many keep falling out is a joke and time consuming.

John.G

The push pin will start extending when the coolant temp reaches 87C so where is the stat "seat" that allows water to flow into the top of the rad?, is it the cone shaped piece on the top of the left hand stat or/and the flat brass part on the right hand stat?.

greasepalm

The push pin cannot extend has its sitting in a seat , but the main stat top should move down to allow circulation.

John.G

OK, it extends downwards carrying the stat seat with it against the spring pressure, is it the conical part inside the outer rubber piece that moves downwards?, or does the whole rubber top move down?.

greasepalm

The whole top will move downwards as a unit and when looking at it open will see a longer pin on top

John.G

So, there should be a very slight cover clearance to ensure seat tightness when the cover bolts are tightened down?

honda boi

Small update, .

I didn't want to go ripping apart the thermostat housing and losing another €20 worth of coolant.

Took the hose off that connects to the thermostat. My thinking was If it's stuck open then a lot of coolant should pour out. Nope maybe 200ml coolant came out.

Used my phone to see if it's sitting correctly and looks fine.

Now when I squeezed the top radiator hose , a bit of coolant squirted out by the thermostat, it looks like it's coming out of the weep hole on the thermostat , I'm assuming this is normal?

Driving for a bit I've noticed It seems it will get to high 80's if I sit at 100/120kmh.

But as soon as I get into a town the temp will drop to as low as 69 and stay between 69-80, even revving at idle the temp drops until I get an open road and get up to a higher speed.(All these times with no AC or heating on)

When temp drops I go and check the radiator hoses. And the top hose is very hot while bottom is warm, so to me the stat isn't stuck open.

I'm out of ideas so it's booked in next week with the mechanic, hopefully he can spot something.

greasepalm

Usually stuck in traffic it heats up as no air flowing through the rad , then driving fast should cool rad and lower engine temp down slightly

John.G

https://www.boards.ie/discussion/comment/122555380#Comment_122555380

That weep hole in the stat is interesting, didn't realize they still had one, the older type, like below, had a jiggle pin and was supposed to be mounted at the 12 o'clock position on a horizontally mounted stat, if its just a hole then shouldn't be more than 1mm or so, I knew someone who drilled a 1/8" (~ 3mm) hole in a stat without a air vent hole and the coolant temp would fall well below the opening temperature while idling. Has the first replacement stat got a air vent hole in it?.

honda boi

https://www.boards.ie/discussion/comment/122555840#Comment_122555840

Ye exactly.

Mine seems to be doing the opposite.

https://www.boards.ie/discussion/comment/122557575#Comment_122557575

Yep this cars stat seems to have that kind of hole in your image, but it's plastic.

John.G

Here's one (Mick's Garage) that fits the 136 & 163 BHP engines, is this, and the first replacement, dimensionally the same as the original??

John.G

This might be worth a read, possible EGR stat the problem??

https://5series.net/forums/e60-discussion-2/bmw-e60-530d-not-heating-up-correctly-118696/page2/

John.G

Don't know if you have solved the problem but below is a trend from a Skoda Octavia, presume the horizontal (X scale) is in seconds and that the car was idling.

honda boi

https://www.boards.ie/discussion/comment/122558922#Comment_122558922

Hi John,

Sorry missed the last few posts.

Yep mine is that one alright.

https://www.boards.ie/discussion/comment/122571659#Comment_122571659

This was one of the first things that popped up when i first looked into this issue but it seems my car does not have an egr stat, only a main stat.

I had the car at the mechanics for an unrelated issue and he scanned the codes and found a code for the "thermal oil level sensor".

So I've ordered a new oil level sensor and will swap it out when it arrives. I'm not sure if it will sort out the issue but will swap it out and see.

Will update once it arrives and is swapped.