Long-term update – M5 part two

Another instalment of project M5. It's been an expensive month...

By Tim Kendall | 26th May 2012

Garage Log

  • Model: BMW M5 (E39)
  • Date Purchased: March 2012
  • Total Mileage: 88,212
  • Mileage Since Last Report: 1,400
  • Cost Since Last Report: £1,500 (see text)
  • Economy: 21 mpg
  • Read previous garage update for this car

Time for an update on ‘project M5’. I’d prefer not to be referring to it as such, but with a list of things that need doing it’s fitting.

So I bought an E39 M5 through BCA’s online car auction system. Yes, buying an aging lump of M-Car on a mouse click is daft, but when it comes to bagging a performance ‘bargain’ my glass is always half full. Tellingly though, my wallet is half empty.

Buying online meant I hadn’t been in the auction hall to do the sheepskin coat routine – checking for weird noises, warning lights or any other ‘run for the hills’ warning signs. Instead, I relied on BCA’s grading system and the fact it was a historied BMW main dealer part-ex, in ostensibly good nick. The sense of excitement as I clicked my way to a suspiciously attractive hammer price some £1,700 below the trade book value was palpable. As was a mounting sense of doom, which crystallised as my shiny M5 backed off the transporter in a cacophony of shagged engine noise (I thank the engine gods I chose not to drive it back from BCA’s Bridgwater branch, instead opting for transporter delivery).

Shutting off the engine straight away fearing further damage, I fired up the Google machine and honed in on the noise issue – big end bearings. It seems the S62 motor fitted to the E39 M5, whilst reckoned by most corners of the motoring press to be bulletproof, actually isn’t. It’s known to suffer from worn big-end shells which can spin on the crankshaft, a problem with the potential to cause all manner of internal destruction.

Having sounded out the very useful M5board forum to find a decent M5 specialist, I picked up the phone to CPC Performance Engineering in Bucks. They listened to a sound clip of the engine knocking and tentatively diagnosed the issue as rod bearing failure. Reassuringly, they mentioned that 90% of the time, it results in minimal internal damage. The best case scenario was that I’d need to replace the big end shells and rod bolts – at £1,200-ish. And the worst case scenario? Bent rods, scored crank and a £6k engine rebuild.

M5 E39 engine

The heart of project money pit

To be frank, 90% of the time the prospect of £6k engine rebuilds scare the sh*t out of me 100% of the time. So after watching it depart in the direction of CPC on the back of a trailer, I spent the next 24hrs on a knife edge until they had stripped the stricken beast down.

But when the phone call came the news was good – No.2 big end shell had spun causing the death rattle – but the crank and conrods were all good. So with all rod bolts and shells replaced, a fresh fill of pricey 10w 60 and a new MOT – M50 AWT was ready to monster some more autobahns. I’ve never really got over my old C43 expensively lunching a gearbox, so it was a relief to feel like the M5 had shown me some mercy. Relatively speaking.

Digging through the history I’ve noticed that it’s also had several £k spent at BMW main dealers just weeks before I bought it – including a brand new VANOS unit. Following CPC’s work on the rod bearings, the net result is a rather fit sounding V8 with all 400 horses very much present and correct. A bit of a result under the circumstances. But be under no illusion, whatever the buying guides might tell you, these are not cheap cars to run.

So, all sorted? Not quite – I mentioned there was a list of things and whilst the obvious engine issue was number one priority, there’s been other stuff to attend to.

BMW E39 M5

The M5 is finally on the road

When the car was hooked up to the diagnostics at CPC they pointed out an O2 sensor fault, which is a simple but important fix. The M5 has four O2 sensors – two pre-cat and two post-cat. The bank 1 pre-cat sensor was past its best – meaning the fuel air mixture was probably out of kilter. Aside from the fault codes this registers on the ECU, a strong petrol smell on start-up was the other tell-tale sign – it was clearly running rich.

Dodgy lambda probes not only hit you in the wallet by throwing out the mpg, there’s the possibility of damaging the cats and causing other nasties like bore wash if left unattended to. So at around £70 for an OEM Bosch part and another £30 for local dealer, Dick Lovett in Hungerford, to fit it, it was a bit of a no-brainer and relatively speaking, a cheap fix.

Next on the list is a wheel refurbishment as the original shadow chrome finish is bubbling in places and past its best. Then there’s the brake judder – front control arms, bushings and brakes being the likely culprits. All common issues – the M5 is a heavy car and although nimble for its size, that weight gives the suspension a workout. It’s not a sign of poor maintenance – mine’s just at the kind of mileage where it would benefit from a suspension refresh.

M5 E39 wheels

Scabby alloys are on the lengthy ‘to do’ list

So there’s still loads to do and it’s no longer a £5k M5. Regrets? I’ve had a few, but this car isn’t one of them – yet. Thing is, I’d rather buy a good base to start with and then bring it up to scratch than shell out for a £9k M5, only to end up with these bills further down the line. Better the devil you know with ageing performance cars, I reckon.

By Tim Kendall
26th May 2012

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