Battery Nightmare

R

rj-ph

Member
 Buckinghamshire
Car is parked on driveway so dusted the snow off on Tuesday and went into my local town 3 miles away. Car would not start for return journey. When ignition key moved to second position all the warning lights went out. I was a little surprised to have a flat battery as the previous weekend I had driven to Paris and back. For some reason the car started and I got home with no clock and ABS + Brake warning light on and put the battery on charge. Twenty four hours later - nothing. Total flat with only 10 volts on voltmeter. Booked it in for today to have a new battery installed by my local independent specialist. Yesterday put jump leads on to see if it would start and after a few attempts and letting the slave car run for some time it started (still with the above warning lights). Voltage at the terminals with engine running was 14.5V. Did the same this morning and it would not start until eventually I put a jump lead on the starter cable instead of the battery terminal (I know about the terminals in the engine compartment but nothing seemed to happen with them).

Took the car in and told the reception that I would leave it running until they knew were they wanted it and was told that the would probably look at it very shortly. Later in day had a phone call to say that they had left it running for about 20 minutes then there was a bang and it dumped its coolant on the ground. Jumped in the other car to go see and the mechanic said that "probably with no battery there was no fan and some cars have an electronic thermostat and that probably would not be working". When it had cooled down they were going to refill it and see if it was just the pressure cap that had blown or something else. It was something else. The expansion bottle had blown a hole and I would need a new one which as it comes with a "leveling sensor" would be a cool £175.

I am in a slight discussion about how this cost should be spread but this will have to wait until the bottle is back in, the new battery is installed and we can see if the flat battery theory is the only fault. basically I wonder of anyone can shed any light on the original problem and if the overheating was related to this or not.

It has been a bad week with the other car a BMW 5 series Tourer failing the MOT with a broken spring!
 
Ok, firstly I'd find another garage... If the engine was running and you were seeing 14.5v, then regardless of the battery condition the fan would work..

I'll type more later when I've a min.

Mike
 
What do they mean “no battery”??? I suspect the problem with the very fast battery discharge is that the electric water pump was running continuously.

Faulty waterpump also caused overheating and caused expansion tank to crack (although the cap is supposed to be a pressure relief valve).

Time for new waterpump perhaps. It’s a very common failure on the N52
 
Thanks PH001, Seems to add up perfectly. They have got the car until they can get parts on Monday so I will put this to them then. Richard
 
Sequel - New battery and expansion bottle were fitted and coolant added. Start up showed no problems, no leaks. Talking to garage it could not be established that the car had ever overheated and that maybe the expansion bottle failure was a coincidence. They do fail as they age and the car has done 94,000 miles. They paid the labour because they felt that I had had some hassle and I paid the parts. Have done a 200 mile journey yesterday and all well although the return journey at night in the rain makes me think I have to look at the headlamps!
Thanks for the comments and help.
 
Sounds like a fairly good outcome OP. :thumbsup:

But with the water-pump being electric I suppose it could have a fault one day yet be working another day - I'd keep a close eye on the temperature gauge anyway!

Do you know if it has had a new pump before? Only my 1st Z4C had it's pump die at just 9 years and 60K miles.
 
No I don't know. The car has a good service history but no invoices so can't tell. After this experience have a very beady eye on the temperature gauge!
 
You never guess what, I've had the exact same issue with my car (E86) last month. I knew my battery was in poor condition and I also don't drive it much. So, after a long winter with the car sat idle I had to drive to a wedding on a beautiful spring day. Car washed, tyres checked, fluids good and I'm on my way 3-piece suite and the Ray-bans on!! I turn the key and it just about starts, clocks reset and ABS light is on, seen this before so I ignore it and go to fill up the tank with some good stuff. Start the car a 2nd time after filing up and ABS light is off now and the clock is keeping time, all good now!! Drive for 10 mins and approach traffic, slowly making my way to the dual carriage way and the temp gauge shoots to red followed by a beep sound, my asshole tightens up!! I'm just about to pull over and bang!! Bonnet thumps up and steam everywhere!!

The expansion tank has a long split down the edge and bonnet skin has separated from the brace when the pressure was released. I replaced the tank and will change the battery. The water pump is working fine verified by coolant venting procedure. The fan and thermostat are also working fine so only theory I have is the battery was too weak to either run the fan or water pump, I'll have see if there were any fault codes coming from water pump.
 
I wasn't at the garage when my tank split but the phone call telling me that it had dumped its coolant and they were waiting for it to cool down before they checked the damage made me clench too. The split was the same as yours and then you read it is not uncommon which doesn't help much. No damage done fortunately. Cars eh! Just been told that wiring loom to tailgate on my 5 Series 3.0 Tourer 2009 is damaged and replacement including labour is £600. Still can open it from button on fob annd in footwell so will just accept that the car at 146,000 miles is getting old like me.
 
When I inspected the broken expansion tank the plastic was still in very good condition, it wasn't brittle or faded. I even left it in the sun and smashed it with a hammer a few times and it didn't shatter. I'm hesitant to believe the tank just split because of age.
 
They do crack though - it's well reported on here. What doesn't quite add up is the connection with a battery in poor condition. With the engine running the alternator provides all the power required to both charge the battery AND run all the electrical ancillaries. I think it's rated around 100A or so, so more than capable.

When the battery gets sulphated (which they do very quickly if left to go <11.5V for a few weeks) it essentially goes high impedance (or high resistance if you like) and it won't absorb charge current. Similarly, when you try and take current from it, the terminal voltage drops. So even though it might measure 12.5V on the terminals off load, as soon as you take demand from it; that falls rapidly.

If it gets to the point where the battery gets very sulphated, it acts almost like it isn't there, and this can play havoc with the system electrics as the alternator needs the battery to absorb voltage spikes and create the smooth DC needed to run the car electronics. This is why you will always be advised never to disconnect the battery from a running car.

I'm wondering if the sulphated battery caused one or more of the ECU's to lock up in some way which led to the overheating (electronic thermostat, water pump or radiator fan function perhaps)??? Sounds fairly unlikely to me though.
 
Thought I'd update this thread with the reason to why my coolant tank cracked. After thorough investigation I figured out the radiator fan stopped working over the winter due to corrosion forming in the fan signal wire near the fan connector. This meant the fan wasn't getting a clean PWM signal to turn on when coolant temperature increased and subsequently led to coolant overheating and finally boom.
 
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