Mk 4 golf tdi 150 - Hot start issue

[Jester27]

Hi, I am a victim of the allusive "hot start problem" on my mk 4 golf tdi (150). The problem started 6 months ago and like many other people the symptoms were the same, started fine from cold but after running for 30 mins it would take several attempts to start, so took it to my local garage who ran a diagnosis and no errors came up, they checked glow plugs,battery etc and all fine, so then they replaced the CT sensor, and still had the same problem, I trust my local garage and there work has been great over the years but I decided to take it to a "VW specialist " hoping that they may shed some light on the problem, I didn't tell them about the previous checks I had done as I wanted them to start from fresh, my mistake when I collected the car they said they ran diagnostics and it was the temp sensor ! I got charged £130 and they also gave me a list of other things that needed doing, left the garage stopped at some shops and again the car took several turns to start, pretty miffed with this but thought I would give it a few days in the hope that maybe the new sensor needed time to bed in, very unlikely scenario but couldn't be done with taking it back and trying to prove that they did FA ! Anyway a couple of weeks later I put some redex through the engine as I had a bit of a flat spot through the revs, several days past and the car had started fine hot and cold had this fixed it ? I was very smug telling people how I had solved this problem with a £5 bottle of additive, unfortunately the smugness lasted 3 weeks and it started again !! So after reading more posts I took the car back to my local garage and got them to give the car a full service, replace starter motor, replace MAF sensor check everything in a bid to solve this headache ! Out come ? They found that when the temp sensor is unplugged the car starts fine from hot so they believe that it may be a signal from the ECU to the sensor ? Sorry for the essay but has anyone come across this problem before or does anyone have any other ideas ?
Thanks for your patience

[niall campbell]

Do you know what Coolant Temp sender unit they are fitting ? I would go to VW and buy it there. I would also ask if the CT has been updated

You can tell by its colour, alas I have forgotten if its green or black is the one to fit.

New parts can be faulty as you have found out, giving you a red herring.

I would also consider changing the Fuel Temp sender unit, or at least disconnect it to see if it makes a difference, disconnecting these things means the ECU diverts back to cold settings & so the car starts.

[Jester27]

Hi Niall, thanks for the reply the first cts was fitted by my local garage and the second was fitted by a VW specialist using genuine parts, both times it was not showing a fault code on either sensor, I believe the sensor is green.
I'm not very mechanically minded so not sure what you mean by updated CT ?
will have them check the fuel temp sender as it's going back in on Thursday for a MOT, will keep you posted.
thanks mark