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I bought a second-hand 2005 Nissan Almera 1.5 just under 6 months ago, and apart from an early issue with the catalytic converter, seemed to be running okay.

However, a month or so ago, I was out running errands and the car refused to start again after my first stop. Battery and starter motor all checked out okay, and after 20 mins or so it started up fine, and drove like normal. However, after returning home I tried to start it again out of curiosity, and had the same issue. Again, it was fine after 20 mins or so.

After some experimentation, it seemed to start okay after short journeys, but not once the engine reaches full temperature.

I have since discovered that the engine fans only come on if I use the AC, so I'm assuming it is a temp sensor or relay somewhere playing up and underreporting engine temp, but I'm not sure where to look for it, or what to look for in a replacement.

Any help would be appreciated. I'm in the UK if that's relevant.

WolfieSmith
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There's a few things that come to mind which match hard starting when hot and a loss of fuel economy:

  1. Bad coolant temperature sensor: if your car's ECU (Engine Computer) doesn't know what temperature the engine is it will not know the correct air-fuel ratio to inject into the cylinders. This is where an OBD reader would com in very handy, you can read the temperatures the ECU is reporting and see if they look accurate. If they stay the same no matter whether the engine is warm or cold, or fluctuate in illogical ways then you probably need to replace the coolant sensor. They cost about 3 beers for the part, and usually are pretty easy to install
  2. Fuel pump: hard starts are one possible sign your fuel pump is on its way out, especially when it's hot. The way to diagnose this is to measure the fuel pressure using a gauge, and replace the pump if it's low. Note that low fuel pressure can also be from a clogged fuel filter, but if that was a problem you'd be getting a loss of power. Your fuel pump is almost certainly electric, and they are usually under £100 for the part, which is in the tank itself, usually accessed though a panel under the rear seat
  3. Faulty Exhaust Gas Recirculation (EGR) valve: The EGR valve is an emissions control measure which should stay closed when starting, if it gets stuck open you can have issues starting, reduced mileage and other performance problems. These valves can get clogged up over time, and in some cases can be cleaned to get them operating again. Given they cost about 35 quid most choose to replace them

This isn't a complete list by any means, just what seems most likely given your description.

GdD
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There were a ton of Hondas that had fuel pump relays on a circuit board that failed after a few years. And they would fail when it warmed up, so the first drive was fine, but a quick stop would leave the car not able to start.

No idea if Nissan had a similar problem, but relay should be relatively easy to test (or replace). Or if you have access to the fuel pump wiring while you start, see if you're getting power to it during the failures.

BowlOfRed
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