Many thanks for the valuable advice, hopefully not much damage caused.

You will not do any harm changing the oil and it is probably a good idea to do so, a good 20/50 will be fine. Many members of this forum use supermarket oil with no apparent issues, do a search there are plenty of threads here on the subject, although with the myriad of advice offered it is easy for the uninitiated to become confused. What have you used in the past? I assume you change the oil regularly! remember this is an unfiltered system so modern oil change intervals do not apply.

Location: NZ

Just to clarify, the reason for not putting modern oils into an unknown engine was based on experience. The modern oil contains cleaners , some older engines rely heavily on carbon deposits to help compression which I found out to my expense.

Location: Oakley , hants

Accumulation of water was certainly damaging with original oils but am surprised modern goes grey due only condensation. Esp to the extent of being evident on the dipstick. Are you using a classic oil of mere API SB rating or suchlike?

The habit of starting cars just to move in and out of the garage is best avoided. I still push family cars to avoid a cold short starts.

On sleeve valve cars it used to be reckoned that these improved with mileage and carbon build up but usually undesirable. Clogged oil rings were a feature of engines years ago.

Oil companies often claim that modern oils will prevent deposits but not substantially remove, but many consider modern oil will release sediment accumulated in the oilways, the usual reason for avoiding. I suspect a long hot run will likely do this anyway.

Location: Auckland, NZ