Audi 4.2 oil pressure / running engine with diesel

[TROOPER88]

Hi Guys
I have been given a car from a work colleague.

It is a 1998 Audi A8 4.2.

I had a look at it recently as he said the red oil light / oil can started flashing and beeping in red. I understand that this is most likely to be the sump strainer / oil pickup clogged up with oil/gunk.

I will try replacing the oil pressure switch but think this is most likely not the cause. The car has plenty of oil in it.

Rather than scrapping the car or paying a garage to remove the sump and clean all of the components, is it worth draining the oil completely and running the car with just diesel in it instead?

If so would you advise pure diesel or mixing the diesel with some cheap oil?
How long should the engine then be run for and do you think this would clean all the internals??

Cheers in advance

[Locknut]

That's an old trick and I'm not sure you should use it in something as sophisticated as an Audi. I did it once or twice back in the days of Escorts and Fiestas with Kent OHV engines. I used a 50/50 mix of diesel and old lube oil but I can't remember if it did any good. I think you should drop the sump to make sure it's not an oil pump problem.

[Pumaracing]

TROOPER88 said:

If so would you advise pure diesel or mixing the diesel with some cheap oil?
How long should the engine then be run for and do you think this would clean all the internals??

Cheers in advance

Don't even think about doing it. Modern oils, especially fully synthetics, have very good detergent properties and don't create much in the way of deposits. If something like the strainer has blocked it'll be with deposits that resist mild solvents anyway and will need physically cleaning or a proper carbon solvent. If it's crank bearing or pump wear then you'll also achieve nothing obviously. In either case you risk destroying the engine.

You might try half filling the sump just enough to cover the pickup with a strong solvent like paint thinners, leaving it overnight and then draining it again before refilling with proper oil.