Hot-starting problem

Our 1998 Peugeot 806 1.9TD has become increasingly difficult to start when hot after a 65-mile motorway run. It will turn over for maybe 20 seconds before starting. Despite having a tired battery, it starts first time on even the coldest day, but after driving the 65 miles to work, if you stop the car and try to restart it will turn over and over before starting. In all other respects, the car runs fine considering its age and 140,000 mileage. It has no excessive smoke and pulls OK for a heavy car with a smallish engine.

The clues I have are that the fuel consumption has increased from 40mpg to 37mpg and the car’s temperature seems to run cool just under 80°C even at the end of a 65-mile motorway run. It only hits 90°C on a hill climb – 90°C is at the top of the temp gauge and where I’d expect the needle to sit.

The car has new fuel, air and oil filters annually. Last year, the glow plugs were changed, the fuel tank was dropped and cleaned, and a new temperature sensor was fitted.

I have read online that it could possibly be the crankshaft sensor. What is your opinion? Roger K

As you have already changed the CTS, which is the most likely culprit, the next test I would try is to attempt a hot start with the CTS disconnected. If this makes a difference and the engine starts quickly with the sensor disconnected then the problem may be the ECU mapping.

The other possibilities is that the

CTS fitted is faulty or that the engine is running cooler than it should.

In this case, it would be worth checking the thermostat to ensure that it is not opening too early or is stuck partially open. If possible, check the actual running temperature of the engine with an infrared thermometer, such as this unit: https://bit.ly/cm4vdtz. If the engine is running cool, this may also explains the higher fuel consumption.

The crankshaft sensor may be faulty, as you suspect, and could be suffering when hot. If removing the CTS plug when hot makes no difference, it may be worth replacing the crank sensor.