Okay. I've never encountered this before so there is a change of some kind. I just don't know if it's a problem. I've got a '91 N/A with 122, 000 miles. When I start it from cold, I always sit and let it idle for a minimum of two minutes. Then, when under way, I don't go past 3000rpm until the temp gauge says it's ready. The oil pressure gauge has always hovered at around 60psi while driving and around 30psi when I'm at a stop light or whatever. Recently, even though I've continued my start-up/warm-up protocol, the oil pressure drops to below 30psi when I'm on the freeway, but if I push in the clutch pedal and just cruise at idle for a few seconds the oil pressure goes right back up. Then, after it gets up to operating temp, the oil pressure behaves as normal..high revs, high oil pressure; low revs, lower oil pressure. It's weird...almost like reverse behavior for the first ten or fifteen minutes of driving. Any ideas?

 

First thing to start with is the oil pressure sender itself - that sounds like one of the sender's failure modes.

Dale