Why does my Citroen Xsara sometimes (but not consistently) refuse to start?

[MyNightWithMaud]

Our car has developed a fault, whereby it will always start from cold but, if the engine is hot, it won't. So, if the car stalls, we have to wait 20 minutes before it will restart. We recently had the ignition coil replaced, but that hasn't fixed it. The garage seems completely clueless - they say if the car failed completely, then they might have some idea - so I'm hoping MN can suggest some things I can ask them to investigate.

Have you had the starter motor checked? When the starter motor starts to fail the car will sometimes start and sometimes it won't but eventually it will fail altogether and won't start at all.
Is the fan still running when you switch the engine off? Some very modern diesel cars do this as normal but older cars which do it might have a problem with the head gasket and be overheating. You can check the head gasket by looking at your oil ; if the oil has a white foamy layer on it then your head gasket has failed and it will cost £££££ to fix.

Hopefully somebody with more knowledge of cars will come along and give some more targeted advice than I can.

Thank you! We paid for two hours of diagnostic work, during which they allegedly looked at the starter motor, but I'll ask them to look again. The fan does tend to run on after long journeys - it always has - so I'll add the head gasket to the list of suspects.

Mine did this last year. The AA came and rescued me one day and he unlocked the steering wheel adjuster bit thumped It up and down and it started.
It was the ignition cable but it was a loose connection rather than needing replaced.
He says it is a common fault. It started every time doing that until the weekend when Dp fixed it.
Never did it from cold only after I'd driven somewhere.

We had that and needed a new battery - we were both convinced it was the starter motor, but the mechanic said battery, changed it, and it's been fine ever since!

Thanks for the further suggestions. They're all things that the garage ought to have checked last time round, surely, but I shall be very assertive this time!

Is the fan still running when you switch the engine off? Some very modern diesel cars do this as normal

No, perfectly normal on older cars as well.

You can check the head gasket by looking at your oil ; if the oil has a white foamy layer on it then your head gasket has failed and it will cost £££££ to fix.

More crap advice. It can be perfectly normal to see some white mayo type stuff especially on a car used for short journeys, this is caused by condensation. Also not all head gasket failures will cause oil to mix with water. To diagnose correctly a sniff test of the coolant and a compression test are required.

OP - does the engine spin over and just not catch? If the engine is spinning over normally then the starter motor is not your issue, my bet would be something electrical breaking down when hot and put under load when starting. Could even be a dry joint in a relay of some kind. If the engine is not spinning over then the fault is likely with the starter motor or its control systems. If a mechanic can replicate the fault then it should be fairly easy to find out whether the problem is fuel, spark or compression related.

No, when the key is turned (when the engine is hot) there is just a loud mechanical click from under the bonnet and nothing further happens.

Something electrical is breaking down under load when it's hot and that something is part of the starting system. My first thought would be the starter motor but it could also be the heavy gauge wiring for the starter motor. The mechanical click sounds like the starter solenoid is working. A competent mechanic should be able to diagnose this. Starter motors can do funny things. Is the battery in the engine bay? Failing batteries can also do strange things.

Yes, that's exactly my concern. I can't believe mine is the first car they've seen with this problem, and yet two hours of investigation produced no conclusion. Thank you for your advice - if they fail to fix it this week, I'll draw my own conclusions about their competence!

When I had my loose connection the solenoid was definitely working as well. Can't remember why the AA man said it only happened when engine was hot always started first time in the morning always wouldn't start after I'd already dropped the dc off at school and needed to be somewhere else