Help please:
What would cause the oil pressure light to come on at idle, AFTER city driving for 20 minutes. Oil temp shows 80°C, and the oil feels like 80°C but the dipstick and rocker covers feel very hot. Could this be a blocked fan shroud? A blocked oil cooler? Idle speed is good, after say 30mins of city driving the oil light comes on before the generator light.

I would get a propper pressure gauge on it or at least another sensor. Could be a dud sensor.

If not i would be suggesting bearings.
What is the endplay like?

What sort of motor is this? 1600? 1776?

Its a fairly new (8000mile) 1641. I have changed the oil pressure sender (old one had a leak) but I don't think it would be that as the engine stalls shortly after the oil light comes on.
It has been suggested that I could have used the wrong seals to refit the oil cooler and therefore resrict the oil flow, but they looked exactly the same (little spaceships)

If it's stalling as well, is the temp correct? Both (low oil pressure and stalling) can be symptoms of being too hot. If the fan or oil cooler are not doing their job the temp will go up.
What type of sender do you have? Location?
Also what oil do you run? (or have you changed brand or type recently)

I have always used shell helix semi syntetic 15/50. the temp gauge is tapped into the back of the case and I have verified the reading with a dipstick sender and verified the dipstick sender with boiling water. I have changed the fan shroud to the early 36hp type But I have been told that this will not make any difference.

What's the engine RPM when this happens?
A very low idle will also give low oil pressure.
Otherwise a weak spring on the relief??

RPM is a standard to high rpm, oil light comes on before generator light. Could it be a bad oil cooler restricting the oil flow?

Or could it get that hot from air leaks at the bottom of the fan shroud?

I don't really think is a over heating problem, more of an oil flow issue.

I did too much work in one hit, now its hard to find the fault.

1 changed oil cooler.
2 fitted new seals for oil cooler.
3 changed oil pressure sender.
4 changed fan shroud.
5 changed rocker covers (alloy bolt ons).
6 maybe changed timing.
7 changed clutch cable.
8 did change carbies for a while (back to original 30 pict now)
9 and did an oil change.

I really didn't want to pull the engine again!

59 Bus

side issue here - i just went back and checked your picture in the carb post.

You say above that you are running a 36hp shroud - ie non dog house

The carb picture shows you are running a 009.

A 009 doesnt have the 3 degrees retard on number 3. A standard vac dizzy does. VW did this because the oil cooler was in the way and got #3 hot.
You might want to check up on this and make sure all is ok

I was running the 009 and a non doghouse cooler before this problem, i could try the vac dizzy, but I think I have the 009 retarded as is (big flatspot).

Could there be a problem with the oil pick up? is it a rubber hose or metal pipe?

The oil pick up is the metal tube/umbrella thingy above the oil strainer

That "can" come loose - even fall out

I did do a quick oil change before the problem started. but if the tube fell off I should get a low pressure light when she first fires up, wouldn't I ?!?

Is it possible to squash the oil cooler seals, enough to resrict the oil flow?

Getting tricky now!!
The oil pump is positive displacement, so any restriction will only increase pressure, unless there is a bypass relief on the pump itself. (unlikely) So a restriction here 'shouldn't' drop oil pressure down stream of the cooler.
Also all things being equal (bearing condition etc) the only way oil pressure will drop is with a lower viscosity (ie getting hot).
Your point on the suction side is worth investigating though.

One from out there. The oil light wire isnt shorting on other wires in the engine bay? Like the coil wire. If it was it would cause the light to come on and engine to stop.

wouldnt do it after 20 mins of running though.

Sorry - i am still betting on bearings