Hey all. So I recently got a 2003 Silverado 3500 with 330,000 km. And I've only put about 1000 more km on. And I've noticed the oil pressure going down when the engines been warmed up and revving at about 2500 rpm. I figured it had probably been a while since the oil had been changed since I didn't know how the previous owner maintained it. The crank case was over full, so I dropped it, and noticed it was extremely thin (watery) but didnt smell like gas, and wasn't milky as if there was coolant in there. So I refilled it to spec, but after another few hundred km of driving noticed it was overfull again and thin. But again didn't smell like gas, and wasn't milky. The oil pressure stays decent until I hit 2800 rpm. then it drops fast and starts making valve train noise. If I decel the pressure rises back up. Anyone ever had problems like this?

 

Thats a problem with high mile used vehicles. You might want to send an oil sample in to be tested. At 200,000 miles a vehicle that hasn't been taken care of will have all manner of troubles coming down the pike. Few oil changes, lousy fuel and oil and no coolant changes will destroy an engine. The transmission probably needs a look at too.

 

The real concerning part is that it's somehow getting overfilled.

You've got either gas or coolant going into it, thinning it out enough to drop pressure.

Best case would be headgaskets. Worst case something is cracked be it the head or block or cylinder.