Low Oil Pressure

[Guest]

On my 90 coupe with almost 59,000 miles my oil gage shows straight up at idle and at road speeds for the first several minutes. Then at idle the gage shows 3 segments and straight up at road speeds. I've been using 10W30 Quaker State and changing at 3000 mile intervals both oil and filter. The oil level is ok,looks ok and smells ok. It's now do for an oil change should I go to 5W30? What should be the steps to define the problem?

[Guest]

I dont think I would use 5w30 in the summer. In the winter in very cold climates Yes but not now. I think I would try 2 things. First off I believe in the 90's You can call up the oil pressure directly out of the ECM. I would verify that it is high. If it shows high then You might try putting a new oil pressure sending unit in it. I am not a great fan of Quaker State oil. It will not hurt it in the least to try valvoline or penzoil or one of the others and see if its viscosity is a bit less when it is cool.

[padgett]

what problem ? Sounds normal to me. Keep in mind that the GM oil pressure sender of that period is notorious for being not quite accurate. <P>The most serious failure (and GM issued a bulletin about it - see earlier postings) is a sender that reads 6-11 psi with no oil pressure (engine off).<P>Personally, I use 10W-30 all of the time but then live in Florida. Have also been known to use strauight weight racing oil but not in my 3800s. If you car is garaged in the winter, there is no reason not to use 10W-30 all year long. Have known some people to use 20W-50 all year long but do not go to that extreme.<P>Believe the 5W-30 is primarily an attempt to help meet EPA standards for MPG and not to make the engine last longer.<P>I too use only premium (Quaker State, Penzoil, Valvoline) oil and change the filter at each change but usually at 3,000 miles or before and after a long trip.<P>The GM spec for the '90 3800 (from Bonneville FSM) is 40 psi at 1875 rpm fully warmed up but might mention that it does not seem to need a lot. A few years ago my wife had her car in Indiana in the middle of winter and dropped the two center cam bearings (found later in the bottom of the oil pan).<P>She called saying oil pressure light was coming on at idle and was only reading 20 psi at speed. I flew up with a new sender but reading did not change. Took to dealer who said guage was rong & everything was fine (still have receipt). Changed oil and filter just in case. Drove 1200 miles to Florida pushing the speed limit & reading under 20 psi the whole way. Got home with no trouble.<P>Got home and connected mechanical guage - same-same. Pulled pan and found two mangled cam bearings in bottom but everything else as new and in spec. Figure the low drag roller lifers in an engine designed in early '60s had something to do with it.

[padgett]

Oh, and just as a data point, my '88 with new sender is reading 53-56 psi cold idle and 48 psi hot idle/53 psi at 60 mph with 10W-30 Valvoline. '90 Bonne indicates 40 psi hot idle/ 50 psi road. <P>Think anything over 30 psi idle/40 psi on road is probably fine. Probably wouldn't change idle but think the relief is set higher in 92 and later 3800s with a stronger spring. <P>Would not be concerned by 60 psi on road though the georotor oil pump used in the 3800s does not seem to vary much with rpm.<P>Note: have not looked at '90 Reatta guages but generally the midpoint (12 oclock ?) is 40 psi and the max is 80. Unlike temperature guages, oil pressure is usually pretty linear.<P>Key is really "some".

[Guest]

These 3800's hold good oil pressure dont they? Mine holds about the same as Padgetts. By the way Padgett have You ever heard of "Millenieum Electric"? My Son used to Own it in Orlando. He has since moved near Jensen Beach? My First visit down to see Him was where I learned about "no see ums" I fine bug I might add. Especially when You are trying to fish. I couldnt understand why no one was fishing in shorts but Me. I soon learned and then I noticed everyone had bog repellant. My Son loved it!

[Guest]

I forgot to mention that the engine sounds fine at idle and road speeds. Also, if I increase idle to 900 rpm with gas pedal the oil pressure goes straight up.<P>What do you think of the new blends with part synthetic?<P>Thanks for the comments guys.

[padgett]

a) keep in mind that even the service manual does not trust the panel gage - on complaint they say to connect a mechanical one.<P>"straight up" (suspect that is supposed to be 40 psi) at 900 rpm hot sounds fine.<P> have used synthetics in race cars where every little bit is nore important than cost. For street cars I use either Valvoline, Quaker State, or Penzoil (whatever is on sale when I get low) and change oil and AC filter at appox. 3,000 miles or when I see a little drop in hot psi (2-3 psi).<P>Do prefer the AC-52 to AC-47 filter when I have room which is marginal in the Reatta.