Sounds a bit of a strange one this. It must be frustrating for you. Let’s look at it logically: Cold starts being alright means that, when cold at least, fuel is getting through, the pre-heater plugs are working, (not that you really need them when the engine is hot!) and presumably the engine is turning over at a decent speed, otherwise you would have mentioned it. But you don’t mention whether you are getting any smoke when it eventually starts up. Lots of white smoke would be expected if fuel was going in all the time that the engine was not starting, as all that fuel would need to be ejected when it eventually starts. So if there’s no white smoke, then it seems possible that fuel is not getting through, and possibly other things required for starting hot are not correctly operating. But why problems when hot, but not when cold? There are two possibilities to me, both quite possible. First, there could be a temperature sensor that is indicating a cold engine, even when the engine is hot, and thus setting the start-up conditions for a cold engine, which would make starting difficult. More likely, I would feel, is a relay that supplies power to a good number of items in the ECU/fuel pump circuit (it used to be called Relay 109, but may have changed number) that always tends to fail only when hot. This is a pretty good bet, but you’ll probably need to go to a SEAT (or other Volkswagen Group) dealer, who may confirm the diagnosis, although they may have problems replicating the failure conditions – not that it should be difficult, if your problems are very frequent, but Sods Law will no doubt operate when you take the car in. If it were an engine (coolant) temperature sensor, I believe that if the sensor were disconnected (rear of the engine, I believe) it will enable hot starts. I really hope this leads you to a solution, which should not be too expensive. In fact, come to think of it, if you’ve a good diesel specialist in your area, it might be a bit cheaper getting it sorted there rather than at a dealer. As a PS, I think, and hope, that the DSG unit should have no influence on things, but you never know if there is some kind of transmission sensor/interlock that might just be causing the problem, although I’m afraid I can’t offer any detail on this. Hope this helps.
My news to date is that the local garage who services the car has told me that the clutch and or DMF (Dual Mass Flywheel) is causing the problem, along with a quote for €2,800 to fix it! I have booked it into our local SEAT dealer (50 kilometres away) on Monday, as that was the first day they can provide a courtesy car. I am going to mention to them the Relay 109, and hope that their diagnosis is more friendly to my wallet. When I think of the (literally) hundreds of thousands of virtually trouble free miles in my previous Citroën XM and BX turbo diesels, I must say that if the worst scenario is indeed the case, it does not impress me after just 60,000 miles, but I guess that’s progress! Will keep you posted,
Doc D replied:
I am not at all happy with this diagnosis. If you have DMF problems, you should be noticing clattering noises on start-up/shut-down, and your actual hot starting problems (but no cold starting problems) are not really compatible with this diagnosis. €2,800 (£2,200 plus) seems very steep anyway for clutch/DMF replacement. It may be what a SEAT dealer charges, but you could halve that price elsewhere at a Volkswagen engine specialist, I feel. If they do confirm the clutch/DMF diagnosis, I would only go ahead on a no solution/no pay basis. I think they are possibly suggesting that the DMF is so shot that the starter teeth are not engaging properly – but why does this happen only when the engine is hot, and why no nasty shaking and rattling noises? No really, this does not make sense to me at all. It really could just be something as simple as a faulty temperature sensor, as I originally said. Be very wary about paying out this sort of money Barry. I’m not convinced, and if it was my body, I would be going to get a second opinion from another consultant! I’m not sure where you are geographically, with your SEAT dealer 50 kilometres away, but a Volkswagen, Audi, or Skoda dealer could give a second opinion on this problem. Please keep me posted.
Latest news was that the SEAT dealer, as opposed to the local garage that quoted the enormous repair cost, thought that it was probably the starter motor at fault, which indeed it turned out to be.
Postscript from Barry:
The replacement starter motor cost me €626 all in, including all other diagnostics etc. The starter motor itself was €289+VAT (it was listed at €170 including VAT at auto-pieces Oscaro, a French firm similar to EuroCarParts), but of course the SEAT dealer was not interested in that. They did not detail what was wrong with the original starter, except that it was “tres ancienne” (seven years old). Incidentally, the first and only other time that I’ve had to change a starter motor was in 1966, on a Ford 100E, on the street outside my mum’s house, and the exchange unit then cost me £9! Although as an apprentice tiler, that was nearly getting on for two weeks wages at the time!