Overheating Problem

S

scottwinter_uk

Member
 Markfield, Leicestershire
Hi everyone,

Since Friday I have been the proud owner of a Z4C and haven't stopped smiling since! Actually that's a lie, I stop smiling twice. The first time was when the air con stopped working mid drive and started blowing out warm air, the second was when the temperature gague beeped when it hit red after being stuck in traffic. When the overheat happened it was about 27 degrees celcius outside, again the air con wasn't working, and once I started moving and turned the heaters onto full heat and maximum blow, the engine temperature came down very quickly. Once I stopped again though it would start to creep back up, and I can't recall the auxiliary fan coming on.

Once I got it home and let it cool down, I checked the coolant levels which were full and the oil filler cap was free of oily mayo substance. So definitely no leak of water and the gasket is fine. I then started it up and left it at idle, waited for the engine to come up to temperature with the needle point straight up, after 10 miuntes of idling the temperature stayed perfectly normal without the auxiliary fan coming on, by now the air temperature was much cooler.

My question is, has anyone had any experience of this before? I am leaning towards something intermittently wrong with the operation of the auxiliary fan as I know for the air con to work the fan must be turning, but I have also read that people with overheating problems had the problem fixed by replacing the water pump. With the symptoms given above, does anyone have any suggestions as to what the problem may be?

Any help would be greatly appreciated....
 
Welcome to the forum Scott.

One of the guys will be along to answer your question soon.

But :worthless:
Also you should have bought a roadster, you wouldn't need air con in this weather! :D
 
It seems most overheating problems were either due to thermostat or electric water pump. I'll add my vote to the thermostat, but pump problems are more common than you'd think. Since the thermostat is quite expensive, you'd want to confirm which is at fault before changing out parts. This can be difficult if the problem is intermittent. You can test the thermostat in hot water on a stovetop, but it's a 103 C thermostat, so you'll need to heat it in a coolant mixture.

FYI, the wiring to the thermostat allows the ECU to lower the effective opening temperature under high heat conditions. Otherwise it works like any other automotive thermostat in the last century. You'll find the thermostat, wiring, and housing is all one single part, partly explaining the high cost.
 
I had indentical symptoms to you in my Z4M R..

It was the electric fan on the radiator...It wouldnt work to cool the engine or when the AC was engaged..

Any decent indy will have diagnostics to force activate the fan for testing or diag to read fault codes..

The parts alone are £480 from the dealers.. :o
 
The thermostats on the n52 engine also have an electronic element that melts wax thus opening the stat.

Mine packed up on my old n52 car but with the stat in the open position.
 
Hi all,

Thanks for the replies. I'm not massively technically minded so any help is appreciated. Interesting to hear your thoughts on the thermostat, I'm guessing that has a part to play in regulating the switching on and off of the radiator fan? When the car is travelling and so with wind keeping it cool, the temperature is always smack in the middle of the gauge so no need for the fan to come on for engine cooling anyway.

I had another look at it last night and have figured that the car only overheats when stationary and the fan won't turn on. Sometimes it does come on and all is fine when stationary, but even though I can't hear it coming on and off due to the goregeous sound of the straight six growling away, I know when the fan is deciding to work as the AC works, and I know when it's not on as the AC isn't working so at least I'm ready blast the heating on full or even turn the engine off if I ever have to stop at lights etc...

Again thanks for the input, not an ideal start to the life of a Z4 owner, but hey ho it could be worse!
 
The fan is controlled by the engine control unit (ECU, or DME in German). The thermostat is not directly related, rather it's just by coolant temp. The thermostat normally opens on it's own with no outside control, except under high heat conditions, where the ECU melts the wax element srhutch mentioned, so it opens at a lower temperature.

The ECU simply turns on the fan when the coolant temp reaches a certain level. The actual temperature probably depends on several factors. It also turns on when the A/C compressor is on. Sounds like the ECU is also calling for the A/C to be shut down when the coolant temp gets too high. Not surprising, actually.

With your bits of additional information, you and Z4M-2006 are probably right, the fan itself is on it's way out. Once again, it's not cheap, so some sort of confirming sign or symptom should be found. You might also check the electrical connections, just in case.

Your attitude towards 'new' car problems is refreshing. Once this is behind you, you'll have a fun, reliable car!
 
Thanks for the response bcworkz,

A little bit more information from some diagnostics last night:

Immediately once you turn the car on with the air con on, the fan spins for around 3 seconds and then starts to slow down. My dad is a bit of an electronics wizz so tested the fan with an ampmeter/voltmeter and conculded it was fine. He then put an osciloscope over the green wire (apparently this is the wire that 'tells' the fan when to operate and how quickly to spin.), and saw that once the car is turned on with the air con light on, the fan is told to spin for around 3 seconds, after that it changes so about 1/2 a volt is being told to go to the fan which is no where near enough to make it actually spin!

With your information from you previous post bcworkz, would I be right in assuming that as this information is passed down this green wire from the ECU, and re-programme of the ECU may solve the problem? Or could there be something else which is effecting the turning on and off of the fan from the ECU?
 
Yes the black/green wire is how the ECU controls the fan. Not sure of the communication protocol, on a 'scope, would have been obvious if it was digital, sounds more like analogue if it dropped to 1/2 volt steady. It is certainly possible it's an ECU problem and a reprogramme could fix the problem, but seems unlikely an ECU issue would only manifest itself this one way.

Check the resistance/continuity of the wire from fan to ECU. It comes out at the ECU in the connector farthest forward and offside (RHD). It may have been damaged and is leaking to ground or partly open. Check the connector pins for any debris or damage. Even though the fan is fine, I wonder if there's an internal short in the fan control that is pulling the signal voltage down, maybe only doing so once the fan spins a bit, warming things up? If you know the proper activation signal profile from the 'scope, maybe substitute an artificial low current signal and see if that runs the fan OK. Alternately, what does the ECU signal do if it's not connected to the fan? I'm assuming the previous testing was done with everything connected.

You should try to eliminate any other possibilities via testing before resorting to messing with the ECU.

BTW, having an oscilloscope is a great resource! As well as having your dad. I'm jealous!
 
Im fairly sure the green wire is a pulsed digital signal from the ecu..

When the AC is engaged the fan should spin slowly,increasing in speed if needed by external conditions and if the system pressure rises..

Have you tested the fan to see if it will achieve full speed?

An actuation test with a diag machine is the easiest way to diagnose the problem... The fan will actually throw a diag code if faulty.You then need to force actuate the fan whilst testing the 3 wires at the fan controller..

If you have 12v+ and earth at the 2 large wires,and signal from the ECU is recieved at the green wire,then fan control unit is faulty..
 
bcworkz - Sorry I didn't make it 100% clear, a pulse lasting 0.2 miliseconds was received every 5 miliseconds - I just calculated that to be an average of around 1/2 a volt over a full second - but is a digital signal being received, the pulse for the first 3 seconds lasts much longer than the 0.2 milisecond pulse there after. Without taking the fan out, and purely from the oscilioscope and mutlimeter readings of the fan/green wire, it seems that the fan is run by a number of FET's which are turned on and off by the pulses, coupled with a large capacitor to stop massive amounts of interference (the voltage across the fan when disconnected dropped steadily).

The previous testing was done with the fan disconnected so it wouldn't appear that an internal short in the fan pulling the voltage down would be the problem. However, I will get the old man to check the resitance/continuity from of the wire from the ECU to the fan and see what comes up.

A bit more info from the weekend, not sure if this will help to diagnose the issue or not, but I went for a spin on Saturday, temperature gauge sitting nicely in the middle throughout, parked it up on the drive and turned the engine off. Went into the house for a minute, came back and the fan was running. I can't recall hearing the fan running immediately after I turned the engine off (that's not to say it wasn't), but I popped the bonnet and turned the engine on, as soon as I did the fan stopped turning. I tried turning the engine and A/C on and off again but again it wouldn't start turning.

Z4M-2006 - I believe the fan was running at full or near to full speed when the engine was turned off after a run this weekend. There is 12v and earth at the large wires at the plug, but the signal from the green wire doesn’t show enough of a pulse to run the fan even with the A/C turned on. I had a friend plug his code reader into the car at the weekend, but not codes were being held by the ECU. Do you know where the fan control unit is located? I don't believe it is that, but it certainly won't hurt to get a multimeter across the components.

bcworkz and Z4M-2006, again thanks for your help with this, it's really appreciated.
 
Hate to sound obvious as it seems like you're having a blast trying to suss this out, but have you tried taking the car back to the dealer assuming you bought that route?
Obviously if you bought privately then it's moot, but if you bought from a dealer and the fan/ECU/Thermo is on the way out then they should be stumping up the money tbh. :wink:
 
The fan control unit is part of the fan itself...

The green wire that you are testing is the control wire for the fan control unit..

Edit....

Your friends code reader may not be good enough to pull the codes,quite a lot of the generic ones arent. You need somethhing that can interogate the main DME properly..

By the way,i have a dead fan,control unit and shroud off my Z4M here...If you want it feel free to ask,you may be able to cobble a good one out of yours and this one..
 
Hi Georgio,

I bought privately I'm afraid to say, and the guy who sold it to me lives 300 miles away! I'm not overly fussed as I believe if you're buying 2nd hand from a private seller then you almost have to expect a little something that needs doing. Other than this the car is absolutely immaculate so I'm dying to get it sorted and have a car I've wanted to own for the past 7 years to be running perfectly!

Also I shall be going back to him once the problem is sorted to try and get some re-imbursement (if you don't ask you don't get!), and my thinking is that I'm likely to get for example 50% of the cost from him if I spend the time identifying and using the expertise of board members to fix the actual problem alone, rather than 50% of the cost of changing a load of parts to find the problem.

So long as I'm not stuck in traffic for too long, I am loving the car and it brings a huge grin to my face every time I start her up! I don't know why I didn't buy one earlier!
 
I've previously read that a magnet in the motor can come loose and jamming or restricting the rotation of the motor, a jammed motor can get hot, potentially very hot. There was a very upsetting clip on youtube of a Z4 burning out apparently as a result but it seems to have gone now :cry: .
 
Did anyone manage to resolve this issue? I'm having exactly the same troubles with my Z4C

http://www.z4-forum.com/forum/viewtopic.php?f=3&t=51104
 
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