300 Tdi Oil Pressure At Start Up

[rxe]

Posting here on the off chance that someone knows the answer.

I have a Wolf 110 with a 300 Tdi engine. It seems to have a problem with oil drain down when it is left for a while, and I'm not sure why. Symptoms as follows:

1) The engine makes good power, no funny noises, no smoke and starts on the button. The oil light does not flicker on hot idle.
2) If I start the engine again if it has been running, the oil light goes out instantly.
3) If I start the engine the day after it has been running, the oil light goes out pretty much instantly
4) If I leave it a week, it takes a few seconds to go out, enough time to think "huh", then it goes out.
5) If I leave it 2 weeks or longer, there is a buttock clenching 10 seconds before it goes out.

I've changed the pressure sensor, no difference. I'm going to change the oil filter this weekend, as I understand there is a non return valve in there - though I am clutching at straws here, it is a pretty new genuine parts filter.

Having watched a video on the oil thermostat operation, I'm wondering if it has jammed open, and is getting the pump to refill the oil cooler before registering pressure.

Any ideas?

[camel_landy]

I leave mine in storage for long periods of time without any issues.

Genuine filter (ERR3340) & regular 10W-40 oil.

M