Petrol engine oil in a diesel?

diesel engines use a little detergent in the oil to clean the insides I use it in my petrol so it doesn't do any harm

The message from "paul" contains these words:

Provided you're not swamping the existing oil and you don't skimp on oil changes there shouldn't be a problem.

Diesel oil differs from petrol oil in its ability to cope with acids from the combustion, amongst other things, but provided you're not adding half a gallon it should be OK.

Since acquiring my Astra diesel, I have religiously replaced the oil at regular intervals with Magnatec 10W40 diesel oil.

However within a day or so the oil has the consistency of black 'water' and therefore looks worryingly thin. Is this normal for diesel engines?

The message from "ivan" contains these words:

I've not known diesels thin the oil noticably.

Completely normal. The oil does not thin though. It is an illusion. A petrol engine oil would not dirty as quickly and does not have the ability to hold the dirt in suspension for as long as a proper diesel oil. This is why a petrol oil is not suitable for diesel engines except for the occasional top-up. The colour of the oil is not an indication that it should be changed. My BMW diesel is quite dirty but the oil is good for 12/15000 miles even though it looks like shit five minutes after a change.

If you are convinced that the oil thins though, check whether the oil level actually increases in the sump. If it does, you have diesel leaking into the sump from some source. This situation, however unlikely, would need sorting sharpish.

Huw

If I fill it up to the maximum level after an oil change, then it still remains on the exact level until I replace the oil at the next service (3 to

4000 miles) it has 125,000 miles on the clock and everything seems to run OK with no sign of any smoke.

Although like I said, after a day it looks nothing like oil and runs off the dipstick like water even when cold. I'm comparing it with my old Astra petrol engined car in which I used Magnatec for over160,000 miles without any trouble, that always looked like oil on the dipstick every time I checked.

Diesel oil contain additives which soak up the gunk that a diesel engine tends to produce. Therefore the oil actually thickens over time so if you are comparing before and after, it can look thinner.