Tommycourt

I have an 88 vert. I just took a 1200K trip to Ca and back to Az. My speed on the highway was @76 mph and my oil pressure was 45-47 lbs.
I am running Mobil high mileage 15W-40. The car has right at 100k miles presently. My water temp. ran 195-198. At certain times the pressure would escalate to 61-63 lbs. for about 30 minutes and then back to the 45-47 lbs. The terrain was fairly flat and the ambient temp. was around 85-90 degrees. All fluids including engine, trans, differential were changed prior to my trip. After my trip I checked the oil and it used approx. 1/4 qt. of oil. I was running about the 300 mile mark when my oil pressure would jump to the 60 lbs. level. I checked the oil upon completion of my trip and did not notice anything in the oil. Prior to my trip I was running 5W-30 but due to the mileage and since it has a 100k on it, I decided upon speaking to my Vette service man to change the weight of the oil. Can someone enlighten me on the surge of my oil pressure? When hot and at idle the pressure stays around 26lbs. Car ran good with no hiccups but I don't understand the surging of the oil pressure. Any advise is greatly appreciated.
Thanks to all,
Tommy
P. S. I checked the oil temp and it ran @215 degrees.

Patsgarage

Just my opinion, but 5/30 to 15/40 is a pretty big jump. If you are concerned about the higher mileage why not 10/30 ? How good was the old oil drained ? Maybe some was left and the large difference in viscosities led to the pressure surge. If I remember my 89 runs high 50's on the highway, 80k, 10/30 oil. The oil temp seems a little on the high side, mine normally mirrors the water temp pretty closely. If you DIY I would get the oil nice and warm, drain it completely, and go back to the 5/30. Then take a nice ride and see what the pressures and temps do.

WW7

When my oil sending unit started going bad the first sign was the oil pressure fluctuated on the gauge as I drove at a constant speed..I would drive at 65 mph and my oil pressure would be at around 50 psi , then it would slowly go down to around 42 , then go back up to around 50 again....I would suspect the oil sending unit...You can pick them up for aroud $35.00 to $45.00...There are 2 ways oil sending units go bad, either the way yours is acting , or they peg to 80 psi and stay there....WW
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Tommycourt

I am going to drive it around town, which will include some freeway driving also and see what it does. It has only happened once and that was a long drive. Possibly as one has already stated I may have to change oil and then see how it does. Perhaps going to a 10/30 might be a better choice but I will also watch. I think you may be on the right track though with the oil sending unit starting to go bad. Sure appreciate the help from you guys as this is the first Vette I have ever owned and it has proven to be a good highway car, especially for long trips. One thing is I never abuse my vehicles and take pleasure in their appearance and want them to run as good as they look. Thanks again guys!!!
Tommy

dvoeltz

Where would you recommend getting the sending unit?

WW7

http://www.ebay.com/itm/Chevrolet-GM-OEM-1988-Corvette-Oil-Pressure-Sending-Unit-25036936-/151262863568?pt=Motors_Car_Truck_Parts_Accessories&hash=item2337f820d0&vxp=mtr#ht_914wt_1206
Rockauto.com has the same switch for $13.96, but you pay shipping , both are AC Delco..WW