I'm stumped. I'll drive on interstate for 15-20 miles and get off onto a regular street...the oil light comes on and beeps, then goes away. I have enough oil...is there something wrong with the oil pump?
I use 15w-40 MOTUL in my 1994 GOLF and I don't show that kind of problems on my car, I drive my car for 12 miles from my house to my job on a high way with any problem and my home town is Santo Domingo, Dominican Rep. whem summer is like hell.
YA I SUGGEST 20W/50 I RUN AMSOIL RACE LUBRICANT IN MY 2.0 TURBO I STARTED RUNNING 20W/50 CAUSE I HAD A SLIGHT LIFTER TAP, BUT I AGREE WITH A PREVIOUS REPLY I THINK YOU ARE RUNNING TOO THIN OF OIL AND IT GETS TO HOT AND THIN, HENCE WHEN YOU GET OFF THE HIGHWAY YOUR OIL PRESSURE WILL DROP CAUSE OF YOUR LOW RPM, BUT WITH THE THINNER OIL IT WILL LEAVE THE HEAD FASTER AND YOU WILL LOSE LUBRICATION
You may also have sediment in your oil pan that is partially clogging the intake for your oil pump after it get's sucked up. Change your oil and filter and look for debris. Oh yeah, my car is much faster than yours.