[SerratedFrond]

Greetings!
I'm new around here, I hope someone can help me.

I recently purchased an '82 rabbit diesel (4spd manual) It was sold to me with 15w40 oil in the motor, with instructions to keep it that way. The oil was over 3k miles old so I decided to get it changed. Here is where the story begins.

They swapped out the oil and filter, and replaced with 5w30. This really wouldn't be a concern (since I live in Midwest and a thinner oil would be nice for cold start), but the thinnest oil the manual recommends is 10w30.

Another reason this new oil is a concern is; ever since I got the car back the oil light will go on when the engine is at low RPM. Essentially whenever I am coasting (clutch pushed in) or stopped at a light. ALSO this only starts happening once Ive driven the car for 3 or 4 miles (warmed up)

What leads me to believe the thin oil caused this is twofold. 1. it didn't happen before it was changed
2. with the 15w40 oil the light will go on at a HIGH rpm UNTIL the car is warmed up. (the exact opposite right?)

Anyway I took the car back to get the oil changed, I had them put in 10w40. HOWEVER, the light is still coming on in the same manner. What could be the problem?!

I have a hunch they may not have changed the oil . . Because they were trying very hard to talk their way out of doing the rechange. Is there a way to test motor oil to check what type it is?

Thanks for any help! = ]