Check Oil light on during cold startup

[RobertHammen]

Hi folks,

First off, I don't own a Caddy, but I do own a 1998 Olds Aurora, with the 4.0L Aurora NorthStar. I'm posting here because I've heard that there are some Northstar experts on this site, and I'm looking for their input/suggestions/advice.

Late last winter, my Aurora began to show the "Check Oil" light only on cold (< 40 degree external temperature) startups, going off after 5-10 seconds. I was having my local Olds dealer do the oil changes, and I queried them about the weight of oil they had used at my last oil change - they told me they weren't sure, but probably used 10W30. I spec'd 5W30 at subsequent oil changes, and didn't see the light...

...until the last couple of weeks, as the temperature here in Wisconsin has plunged to under 40 degrees on a regular basis. Again, the light comes on for 5-10 seconds, only on a cold startup. I've tried leaving the car in the Run position for a few seconds before starting, and it doesn't make any difference. If the outside temp is above 40, the light doesn't come on. I can't hear any unusual engine/lifter noise, like it's being starved of oil.

I've got 89K on the Aurora, and generally have not had oil issues (changed every 3-4k), with the exception of the infamous "rear crankshaft seals" repair done almost 2 years ago ($1800, under extended warranty, thankfully). Otherwise, checking weekly or before trips, I haven't seen my car really use or leak oil (despite the Northstar's reputation), ever since I specified exactly 7 1/2 quarts (Olds dealer overfilled it once to 9 quarts - thankfully I checked before driving off).

Could this be a bad sending unit? Or could there be something more serious going on? It's due for another oil change and I'm thinking about putting 0W30 in just to see if it makes any difference.

Just wondering if any of the experts here could provide some suggestions or thoughts.

Thanks, in advance, for any assitance or suggestions that you could provide,

--Robert

[JasonA]

Robert, the "CHECK OIL LEVEL" message is really only valid, as you might imagine, if the car is sitting on a level surface. If you park on a hill, you can probably discount it right away. But in the morning, check the oil level on the dipstick and see where it's at. If it's low, that's your answer. If it's not, it's probably a bad sending unit.

The weight of the oil should not make a difference to the oil level sending unit. In fact, 10W-30 is the proper weight probably. If you live where it gets REAL cold in the winter, 5W-30 can provide easier starting, but generally, 10W-30 should suffice. My '97 manual recommends 10W-30 for all temperatures above 0*F.

[RobertHammen]

My driveway is very level (car is outside unfortunately :-(. Oil level is fine in the a.m. Oil pressures are fine/normal once at operating temps (50 lbs psi at highway speeds). I did suspect the sending unit, just not sure if one would fail under the temperature conditions of my post. I live in the Milwaukee metro area, and, while we are usually above zero most of the winter, we do get the occasional cold snap where the temps go to -10 or so.

I'm thinking I'll just have the sending unit changed and put in 5W30 (always try to use Castrol for dino oil as it's done me good in my other cars - except I use Mobil 1 in my 2004 GTO :-).

Thanks for the reply!

--Robert

[JasonA]

Hi Robert, is this an oil LEVEL message or an oil PRESSURE message?

[RobertHammen]

It's not a message on the DIC (I had the oil level one show up when the rear crankshaft seals were leaking), it's the "Oil" idiot light on the dashboard that comes on...