B6 1.8 longer start when outside is hot

[caldy315]

My B6 cranks a little longer when the ambient temperature is considerably warm. I only experience this in the summer months and it seems to be most noticeable when the car is in the sun. I was reading some other posts and they were mentioning when the car engine was hot as if it was just shut off that it would crank a while before starting. Their resolution was to prime the pump by turning the key to accessory for a few seconds before cranking. I've tried this and it doesn't seem to change anything. What are typical places to look? I've scanned it within the last month without any codes.

[chad99]

It sounds like rear coolant sensor might be a problem

[caldy315]

Is that right above the coolant flange that goes bad? I've replaced this once with an Audi part because my coolant temp sensor was bad and causing chaos with the gauge. Same sensor?

[chad99]

Yep thats the one, if you have replaced it with new OEM before then I would be hesitant to replace it again, maybe the crank position sensor could be going out?
When my crank sensor was on its way out, I would have hard starts with both hot and cold temps but not all the time.
When my rear coolant sensor was on its way out I would only have trouble starting when hot.

One of my B6s requires the pump to be fully primed before every start, but thats only because the fuel check valve is not keeping the pressure up and it doesn't matter if its hot or cold.

[caldy315]

From my mental recollection and testing it only appears to be an issue when the sun is out beating down on it and consequently ambient air is hotter than normal. Otherwise it's not bad at all warm or cold engine

[Gin+]

I would consider maybe a weak relay like the fuel pump relay or something along those lines. Considering the interior of the car can get to deadly temps in the summer with the windows closed. Just my .02