I was driving up steap mountain passes in Colorado today and my oil buzzer would come on when I was driving under 3,000 RPM. I checked the oil level and it looks good. Is there any relation to the steep inclines and the oil buzzer coming on? When I pick up the RPM's to over 3,000 the buzzer goes off.
If it is the oil pump how involved is the replacement?
The hard part is getting the oil pan off. The bolts next to the transmission are hard to get to. You need a 1/4" drive socket and extension to reach them.
My guess is that the oil gets really hot and very thin so you lose pressure (sign that then engine's internals are worn). Since your car is an 85, it has a 30mm oil pump. Being turbo I recommend you replace it with the 36mm unit from 88 and later TDs (or a 1.9TD unit). That's what I did on my 87 TD and it fixed the low pressure problem when the engine was hot. The 36mm pump is a bolt on thing but you need the longer bolts.