We have two Diesel cars. Both have issues on starting after cold nights. This week we had about -10° to -16° C at 6.30 am, so in the night it was probably even colder. I am not able to start the cars, but my husband gets it done by trying to turn and hold the key again and again for maybe five minutes. What negative effects could this cause? Are there methods to prevent the cars from denying to start?

Unfortunately we have no garage anymore.

The cars:

  • BMW 525d (2002)

  • BMW X5 3.0d (2006)

  • Can you tell us a little about the cars; Year/Make/Model and how many miles are on the engines? These details help us give a more precise answer to your question.
    – CharlieRB
    Feb 27, 2018 at 16:08
  • the older has 300.000 km and the other 200.000 km on the engine.
    – Kinaeh
    Feb 27, 2018 at 16:22
  • At low temperatures diesel fuel turns to jelly in the fuel lines as it beings to solidify. Oct 23, 2018 at 13:37

5 Answers 5


-10°C should be no big deal for any car to start in, including diesels. Many diesel cars have glow plugs that are activated during cold weather before start (yellow spiral symbol light on dashboard). You have to allow sufficient time for them to preheat the engine: turn the ignition on and wait a few seconds for the yellow spiral symbol to disappear before starting the engine. The glow plugs also might have failed since they can wear out and fail.

Continuously and repeatedly cranking the engine is very bad for the battery and starter system.

  • yeah, it says 'pre-glowing' when I plug in the key, I did this several times but it doesn't help when it'S very cold outside. (at ~ -5°C there is no problem though)
    – Kinaeh
    Feb 27, 2018 at 16:14

The extended cranking is hard on the starting system, but should not hurt the engine.

From the information you have provided, including comments, it sounds like the glow plugs need to be replaced. It could also be fuel system and/or injector issues. OR a combination of them.

My suggestion is to have them serviced to ensure starting is as it should be.


I don't have a garage, but I have mounted a small 400W heater under the hood and a battery charger that come on from 4AM ready for 7.30AM _ car starts fine...

  • Yeah, I thought about that to, but we have no power access at our parking space. Are there wireless chargers?
    – Kinaeh
    Feb 27, 2018 at 16:15

Have your glow plugs and the corresponding ECU checked. Some of the 3 liter BMW diesels of that era are notorious for oil leaking from the intake manifold; the glow plugs' ECU is mounted below the intake manifold and gets destroyed by the oil dripping onto it.

First check should be to read the car's fault codes via OBD. If the fault codes indicate a failure of all six glow plugs, chances are the ECU is broken.

If only one or two glow plugs show faults it may be sufficient to have only the glow plugs replaced (all of them because the others are likely to go bad in the near future).

If the ECU is damaged by leaked oil from the intake manifold it should be replaced together with the intake manifold (and the glow plugs, while they're at it), to prevent having the same happen again too soon.


There are block heaters available operating on either electricity or fuel.

The electric ones are usually low-power (300-700W), the lowest-power of which (300W) just heat the block externally and the best of which (700W) heat the coolant and have a coolant circulator pump. These are ideally combined with an interior electric heater (1000-2000W). I have a 700W coolant heater and 0W/1100W/1900W interior heater in my 2016 Toyota RAV4 hybrid. I also have these connected to a battery charger, so the same cord provides battery charging, coolant heating and interior heating.

The fuel-operated block heaters (at least Eberspächer and Webasto are available in Finland, the country I live) are much more powerful, 4-5 kW, and can heat both the car interior and the engine. Unfortunately, the fuel-operated heaters require about one minute of driving for each minute of heating because they use up the battery charge. So, if you heat for 30 minutes, your trip should last 30 minutes or else your battery charge depletes in the long run. Of course, this can be solved by installing a battery charger, but then you need the cord and it's a good question whether it makes sense to have a fuel-operated block heater with battery charger cord or just go for the electric ones.

However, you may find that if your cars are old, nobody may have in stock the exact block heater parts needed for your cars. Usually, these devices are installed on new cars, not on old cars.

My advice for the next car purchase would be to select a gasoline model. Not only are diesels dirty, they also may likely be forbidden in the future in many densely populated places due to exhaust emissions, and diesel engines are less reliable and more expensive to fix than gasoline engines. Add these to the cold start problems of diesel engines and you have a loser. So, choose gasoline! And for good cold starting, choose a block heater for the gasoline car.

I have never experienced any cold start issues at -10C to -16C on any gasoline powered car. Heck, all of my cars even started up just fine at -20C even though I occasionally didn't bother to schedule the block heater use.

  • 1
    I think your line about diesel engines being less reliable and more expensive to fix is very opinionated and I would consider removing it. They certainly are proving to not be any cleaner than gasoline so the dirty comment is fair. Feb 28, 2018 at 17:37

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