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Car question for the mechanically informed....

Discussion in 'off topic' started by JTC, Mar 9, 2018.

  1. jay

    jay built for speed

    I would be surprised if either of those are the case. Is that something you’ve read somewhere? Would be interested in finding out more.
     
  2. Tony Lockhart

    Tony Lockhart pfm Member

    A lot of time and money went into developing starter motors that can go through ten times the stop/start cycles of a traditional starter.
     
  3. misterdog

    misterdog Not the canine kind

  4. jay

    jay built for speed

  5. davidsrsb

    davidsrsb pfm Member

    Tony Lockhart likes this.
  6. Rico

    Rico Bloody Colonials

    This vidjo should provide some perspective on the question of stop/start:

     
  7. Rico

    Rico Bloody Colonials

    Indeed, same here. The ZF 6 speed auto in my 545i is seriously good. Clever, quick to shift, smooth... and the change-ups at redline you cannot feel - only hear. I was playing 'lottery winner which car' recently, and had zeroed in on e92 M3. Found myself eliminating 'autoboxes' (in fact DCT) because "must be manual", it's a sportscar right? Then I thought, hey, much as I take pride in heel-and-toe double de-clutching, do I really need a clutch pedal? Conclusion: I'd have to drive them both; 6 speed manual, and the 7 speed M-DCT, in order to decide. ;)
     
  8. davidsrsb

    davidsrsb pfm Member

    The fuel penalty of autos has gone and modern manuals have proved to be a headache, dual mass flywheels anyone?
     
  9. stevec67

    stevec67 pfm Member

    Those and concentric clutch slave cylinders, don't get me started. You put a hydraulic cylinder in a nice hot bellhousing so that over time the heat cooks the seals and when it leaks it contaminates the clutch and the whole lot needs to come apart because you can't just unbolt it like you did on the old Minis. Goodbye £400+. Please will someone explain what was wrong with a cable clutch? When the cables wore out, typically after 100,000 miles or so, it was £30 and half an hour's labour. If necessary they could be repaired at the roadside.

    I am more relaxed about stop/start, I know the starters are now beefed up and preengaged solenoids have saved wear on ring gears. I'm relaxed about engine wear, modern engines will do 200k miles+, who here has taken a car beyond 100k miles? Not many. Still fewer beyond 150k, and I bet not 1% of UK drivers go beyond 200k miles in a car.
     
  10. JensenHealey

    JensenHealey pfm Member

    4 of our cars have gone over 100K, viz: 128K, 130K, 170K and 125K. None were scrapped either - all traded or sold. I am not sure we that unusual.

    I know of many high milers in regular use - even for business
     
  11. stevec67

    stevec67 pfm Member

    I am. You are very unusual. I know very few people who run cars beyond 100k and none beyond 150. Look round a breakers and see how many are over 150k. I run old bangers and most of them become uneconomic to repair around 120k. Most of my family and friends think I'm mad. My current Mondeo is nearly on 150, if it makes it it will only be the second car I have got this far. The point I'm making is that these days minor faults make cars BER, the engines last way beyond the rest of the thing. Few people will put a £400 clutch in a £300 car that needs an MoT in a few months.
     
  12. -alan-

    -alan- pfm Member

  13. Tony Lockhart

    Tony Lockhart pfm Member

    From the above linked article:

    "This is when most wear takes place. Fitting stop-start means the boundary condition (and metal-to-metal contact) could exist perhaps 500,000 times in the life of the engine instead of 50,000 and normal bearings would wear out long before that."

    Well, I really don't think the oil will disappear in the few seconds most engines stop for with this tech.

    I'm no fan of stop-start, but that's because I find it annoying. I reckon most crankshafts and big end bearings will last a million miles no problem now, without stop start. So, with it, in typical use, 200-500,000 miles? Most cars are in the tip by then! And, of course, well before then, we will all be in toy battery powered things.
     
  14. jay

    jay built for speed

    When we first got our car I would leave start/stop on and marvel at the fuel savings I was making....in my mind....

    Now it’s religiously turned off when I jump in.
     
  15. stevec67

    stevec67 pfm Member

    Nor do I. Start wear is when the oil is cold and has drained away from the surfaces overnight. In 30 seconds? No chance.

    And the rest. I doubt it takes anything significant off the big end bearing life in the real world. Far more significant is oil change frequency and how well the thing was screwed together in the first place. The days of the crappy 3 bearing flexomatic crank with wafer-thin bearing surfaces as fitted to crossflows are long gone, thank God. When did any of us last hear the lament "I think there may be a big end going on this car"? I had a little end go in an Alfa in about 2001, and a 20-year-old Spitfire drop a big end in 1993.

    Absolutely. The manufacturers know how long the cars need to last. Engines now typically outlast everything else. The bete noire of the modern motor car is ECU failure, or failure of some other electrical part. I chatted to a guy with a VW Transporter that had developed an ABS computer fault. New computer? £1400, fitted. He was pleased to tell me "I got it done for £900 in the end, so that wasn't too bad". Not too bad? That would send any of my last 5 cars to the breaker.
     
  16. James

    James Lord of the Erg\o/s

    My 2006 Subaru now has 240,000km / 150,000mi on the clock. It's still running well, but the engine is starting to use oil, there are rust spots developing and a few minor niggles here and there. I'd be lucky if it's worth more than the set of Michelin tyres I put on it six months ago. Safety trumps cost-saving in motor vehicle ownership. I can't understand folks who drive expensive cars and drive them with Ling Longs.
     
    Tony Lockhart likes this.
  17. Snufkin

    Snufkin pfm Member

    As we have shifted to stop/start, I think my main concern with this type of system is if you don't disable it on long runs. If you have been hammering, or cruising, along a motorway for a few hours and pull into a service area and then your engine shuts down you risk two potentially damaging scenarios.

    The first problem is the temperature differentials across cylinder heads which can, as I understand it, reach 70%/30% (exhaust/inlet). Suddenly stopping the engine does not allow time for the cooling process to even this temperature differential out which in turn must create stress across the cylinder head. Idling the engine for a short period should help reduce this.

    The second potential problem would be if you had a turbo charger. These get very hot at speed and use oil to both lubricate and cool. Shutting your engine down when very hot would a/ starve the turbo of lubricant/coolant and b/ possibly carbonise the lubricant left in contact with the turbo which gives the turbo a nice abrasive compound on start up.

    For these reasons I disable the stop/start on long runs and idle the engine for a minute or two if I have been pushing it on a motorway just to try and give the heads and turbo an easier life. I am hoping Rana will come along soon and correct me if I have got this wrong because at heart I am a bit of a dilettante where as he actually knows what he is talking about.
     
  18. jay

    jay built for speed

    Given you outline such an obvious and common use case I would be very surprised if these systems weren’t designed to cope appropriately. When I used stop start in my vehicle it wasn’t entirely predictable when the system would cut in.
     
  19. JTC

    JTC PFM Villager...

    Begone, evil thing! (I had to get this done on the car last year - all told, including clutch, DMF and fitting, came to the best part of a grand. And at that point it had only done around 78K miles. Though only 25K of those were ours, so who knows what muppet drove it before.... hopefully the new clutch and DMF will last for at least 100K miles...
     
  20. JensenHealey

    JensenHealey pfm Member

    There is a pretty complex computer system in one's modern car. In fact quite a lot of computer systems. One of the reasons that modern cars are so much more reliable than the previous few decades is the sheer number of sensors scattered around and the monitoring and adjustment that goes on. We have had several stop/start cars now, and as far as can tell they are pretty bullet proof. If the car does not switch off at a set of lights you can bet that there is a pretty good reason for it. Manufacturers go to HUGE lengths to avoid cars coming back to them with warranty issues, 'cos warranty work is stupidly costly to deal with.

    That said, as Honest John would say, cars are designed to last about 7 years. I mostly run ours to about 10 years, but it is clear that in the last 2 - 3 years the 'costs' and niggles rise in an unpredictable manner and you have to judge when it is right to pass it on to someone who perhaps either doesn't care about niggles and/or can do more of their own maintenance. My independent repairer has been quite good at saying ' er...you ought to think about changing this' ..even though for the next 3 years he will not see us until the new car is taken out of the dealer network.
     

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