E91/N52 running hot

[323i E30]

Hi all,

Not being all that familiar my wife her 2007 325i automatic touring, and being 2000km from home with very poor internet connection for research; I hope someone can explain what’s going on here.

We got the yellow coolant light with the message to ‘drive moderately, engine running hot’ warning when we left home after 30 minutes of flat highway driving.
We got off the highway to go for breakfast and let the car cool down.
Afterwards I checked the coolant level, which was half a liter low. Bought coolant, filled her up to level and hoped for the best.
We then drove ~1800km (mostly on the highway) without issues, so the car seemed happy again.

Now in the hills the car comes up with the same warning again every now and then, when driving uphill.
I checked the ‘secret menu’ for live coolant temp readings and saw the coolant rise to around 115/118 degrees Celsius (239-244F) before dropping back down to 95/100C (203-212F) in a matter of seconds every time.
When it touches 120C (248F) it’ll display the warning, but coolant temp will drop to 95/100C right away.
This is usually with speeds between 60-90km/h. It’s an automatic and rpms stay low as we’re not driving it hard at all there. We have two kids with sensitive stomachs in the backseat

Is this usual process to have the coolant rise to roughly 115C and then drop by 20 degrees in 2 or 3 seconds?

We have no record of when the waterpump was replaced for the last time.
The car seems to be doing fine at idle.

I’m a hobbyist wrencher on my E30, but am not familiar at all with electronic waterpumps and whatever comes with it, so I have little idea how that thing works.

Thanks for reading and please excuse my metric lingo!

[328 Power 04]

How many km and how old is the electric water pump on that car? Those have a definite lifespan, and can indicate a full failure coming soon. (Edit, I saw that's unknown.)

As to why the temp drop happens, that's interesting. It seems to suggest there may be air bubbles or failing thermostats just as well?

[323i E30]

Thank you for your reply Abel.
The car has driven 188k km total so far.
Air bubbles was what my gut feeling said, but the cooling system has not been opened recently.

Is it possible for the thermostat to fail intermittently?
It would explain having a fresh load of colder coolant being introduced at once from the radiator every time, dropping the temp like that.
Is the thermostat managed electronically?

[328 Power 04]

I'm not certain of the N52 itself, but BMW has been using a semi-electrically controlled thermostat since the late 90s with a wax core to influence opening temperatures, while still allowing a safe mode that will open under emergency.

It does sound like this thermostat may be malfunctioning, if the cooling is that immediate when it throws warnings. I think Chris may suggest more here.

Or it can be an intermittently failing water pump.

[02Pilot]

If it were my car, I'd simply replace the water pump and thermostat preemptively. That was the first job I did when I got my 128i, even though everything was working fine. 100k miles is where it was when I got it, and I didn't want the risk. I'll do it again when I hit 200k miles.

[323i E30]

Thank you both.
Throwing a thermostat and waterpump at it is probably a good idea indeed.
My wife is planning on keeping this car for a long while, so it’ll have to be done some day anyway.
I’ll just hope the car will get us home tomorrow again without troubles.

[bmwdirtracer]

Hi my friend,

Codes in the DME? Usually, when either a water pump or a thermostat fails, it sets codes.

Does the electric fan come on full blast? Usually it does, when there is a cooling system failure that the DME can detect.

Certainly, a water pump and thermostat are maintenance items, but you also should consider that the coolant temp sensor is bad, since you've got that sudden temp drop.

[323i E30]

Hi Chris!
We’re in France at the moment, so getting a german read out with matching equipment + a proper conversation about it is going to be difficult. People only drive and service Renault, Peugeot and Citroen here.
We’ll get it read out as soon as we’re home!
There is no message about any issue in the menu on the dashboard.

I’m not sure if the electric fan comes on on full blast at that moment as it hasn’t happened at idle, so hard to hear.
We’ve heard the fan spinning at full blast twice now when parking the car, which it didn’t use to do.

Good point. I hope it’s as simple as a faulty sensor..!

Even though my wife is set on keeping this car dealer maintained (even though we have a really good independant BMW focused shop here) I’ll need to read up on this car..! I probably won’t be touching it though.

Thanks!!

[323i E30]

So.. Still far from home here.
The engine was getting too hot again.
I didn’t see is manage to get home with a healthy engine like this, so we took a hotel and got the car towed to a shop.
They diagnosed it, and concluded the water pump is indeed failing intermittently. I’ve asked them to replace the thermostat as well while they’re at it.

Driving a rental Renault now, and extending the vacation for a couple of days..!
Thank you all for your help!

[shadowpuck]

good call.....

hey - rental car - fastest car on the planet!

[323i E30]

[bmwdirtracer]

Yep, good call. Where in France are you? Hope it's somewhere nice! Parlez-vous Francais?

[323i E30]

We’re 200km south of Paris now, in a small city.
It’s ok, but many shops are closed and there isn’t much to do for the kids. Many restaurants and other food options open by 7pm which is late for our kids as they are used to having dinner at 6pm, and be in bed between 7:30 and 8pm. Makes them grumpy to sleep too little, which doesn’t help.
There are worse problems in the world though.

I speak French yes, but poorly
If not Dutch I’d really prefer English or even German. Most French people don’t speak any English at all though, so it’ll have to do!

[bmwdirtracer]

A few French friends let me in on a secret, many years ago: Of the French people who DO speak English, fully half of them pretend they don't. This latest study shows that 57% of French people "have reasonable proficiency in English.":

https://www.thelocal.fr/20191105/why...aking-english/

[323i E30]

Haha yeah I know many will simply refuse to.
57% being able to speak a bit of English is way more than I expected though..!
It feels more like 5.7%

French people usually seem to expect me to be completely fluent in French when engaging in a conversation about anything, while there is not a hair on my head that expects a tourist in The Netherlands to know anything about our language.
Such a different mindset it seems.

[323i E30]

Just to close this thread; the car is fine again with the new waterpump & thermostat.
We drove home without any issues.
Cheers!

[bmwdirtracer]

Good to hear! And, um, what are you paying for fuel there, out of curiosity?

[323i E30]

That was roughly €1.85 per liter.
Much better than here..!