Oil Pressure Falls at Idle

Hey Guys,
I have a 1996 Olds Aurora V8 and I’m having a number of problems, but we shall focus on the most “critical”. My oil pressure bell/lamp is going off at idle when the weather is hot, it’s been up to 113 here recently, and 100 consistently. It ONLY goes off when it’s very hot outside and I’ve been driving a few miles (lots of hills in my area). When I accelerate even a little, it stops. At idle it can get down to 5-6 psi (10-11 is normal). I will tell you I have an oil leak from the gasket, so I have to top-off every few weeks. I recently had to replace my intake manifold. The miles are about 120K and I rarely drive more than 30 miles from home, daily I only drive 10 or so. I have a bunch of electrical problems, my gas gauge just moves all over the place then stops (sending unit I guessed), my driver side electric seat doesn’t move, my cruise control was intermittent for a month then went out completely. This car has never been driven hard and I’ve always maintained lubricants, so please don’t be lazy and tell me the engine is shot. I will add it seems to run pretty hot when the oil pressure falls, but Auroras are notorious for running hot. Topping off seems to make the pressure rise and the bell stops. I hope this is adequate info. I am on permanent disability so a rebuild is out of the question. Where do I begin? I forgot, the car runs great and I hear no knocking, even when the pressure supposedly drops, it is slamming into gear out of low sometimes, but that’s tranny work I’m 100% sure. Thanks Guys, please help a Dad who can’t afford costly repairs or a new car…not after the intake manifold last month.

Have somebody hook up a mechanical oil pressure gauge and report the results to us


I’ll do that, thanks. What can I expect to pay for that test? I should also say I have no gas or coolant in my oil, no “frothing”, but I am having to top off my coolant periodically, and I am tossing in the cheapest, blank label 30 weight since I’m leaking it anyway…but is it bad to use generic oil all the same?

and thanks or the prompt reply, I hate poor-mouthing when I ask for advice, but I’m sure you guys realize disability isn’t exactly my former salary, so I have to be frugal…

If the pressure is confirmed to be low it’s a sign of worn bearings.
Replacing just the bearings would be a frugal repair.
You can get some short term relief by switching to a higher viscosity oil.
Given the hot weather I’d go to 15W-40.
Perhaps 5W-40 in the winter if it gets below freezing, but that’s synthetic, which can get costly with it leaking out.

I don’t know how easy it is to hook up a mechanical oil pressure gauge on your particular car, but if it’s not too difficult, you might expect to pay 1 hour shop time

As for that disability, I won’t ask for any more details, as that’s none of my business. As a matter of fact, I have a disability myself, although it’s currently not affecting my ability to work, and I didn’t even get diagnosed until a few years ago, by which time I’d already been at my current job for some time.

Is the oil pan gasket leaking, or is it something else?

You aren’t waiting for the oil pressure light to come on before you top off the oil are you? That will surely kill an engine. You have to keep the oil no more than a quart low or fix the gasket.

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Well where do I start? I had a 95. Nice car but lots of gremlins. What oil are you using, 10-30? Right from new that car had a discrepancy in the oil capacity. What the book said and what it took was a quart off so mine took 8 1/2 quarts to fill, not 7 1/2. Are you using an OEM filter? You cannot fix oil leaks on this car due to the engine being put together in two pieces. You can also not do head gasket problems with this car. To clean the EGR passages requires taking the transmission out and changing the serpentine belt is an hour long process requiring the factory service manual.

I don’t know though if you are getting low oil pressure at idle, most likely it is getting a little worn so just start thinking about replacing it at some point and don’t put any more money into it. The trans shifting may be related to the solenoid packs which were a problem. Cost me about $300 for new ones when it went to 2nd gear default on the freeway. The electrical issues could be wires or could be one of the computers going south. May be able to still find used parts which would be the way to go. I have the factory service manual yet if you have specific issues to deal with, but nice car but very expensive when stuff starts going wrong.

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Either the oil pressure is actually low, or it is normal and the gauge is reading wrong. So testing with a shop gauge is the first step as mentioned above. Hopefully the shop gauge will show the old pressure measures ok. Then you can just make a mental recalibration adjustment when you look at your dash gauge, b/c you know it reads low.

If the test confirms the oil pressure is low, since you are already using 30 weight , your car probably has some engine wear and that’s causing the low oil pressure. Not an emergency probably, but eventually you’ll have to do something about it. In the meantime you could try a thicker weight oil, maybe an oil additive for this problem. In my teenage driving years I couldn’t go a day without hearing or seeing an advertisement for a product called STP for this problem, but I don’t know if that product is still available.

I’ve always used the same name branded oil in my vehicles, change oil and filter about every 5000 miles, and never run into this problem. I don’t recommend using off brands or generic engine oils. Likewise for oil filters. To control the cost of brand name oil I buy by the case at the parts store when it is on sale, sometimes for close to 50% off the normal price. I’m not implying this is the cause for your problem, just saying what works for me.

My gut feeling . . .

Once the mechanical oil pressure gauge is hooked up, it will confirm that the actual oil pressure is in fact very low

Here’s why I feel that way . . . when an oil pressure sensor/switch fails, a common result is that the the oil pressure gauge reads either 0 or 80 (or whatever the maximum is)

The bargain basement oil can cause a serious problem if you don’t already have one. How much oil is leaking and how much is being consumed? The engine is a variation of the Cadillac Northstar that had a few problems built in. Have the heads been off the engine?

And automobile problems are never pro-rated relative to income.

As mentioned, you need to have an oil pressure check performed with an external mechanical gauge.

"so please don’t be lazy and tell me the engine is shot"
Unfortunately, the odds of this being true are quite high. And yes, an engine with excessive oil clearances on the crank bearings can run just fine.

You state the intake manifold gaskets were changed. I’m not familiar with the layout of this engine but it can be common for some engines to dilute the motor oil with engine coolant when an intake gasket leaks. That in turn can wash out crank bearings and other components; leading to lowered oil pressure.

And 10-11 PSI of oil pressure is NOT normal. Ten to eleven is bad news…

96 4.0 northstar. My 96 sts with 4.6 northstar had plastic intake. They do sometimes warp. I replaced mine with a used one. $25 at boneyard. The over pressurization port silicone seal leaked air. The northstar has a touchy oil pressure sender that does fail. The oil pump loses prime and you fix it by overfilling crankcase with 4+ qts oil and it solves issue. Than u drain xtra oil out. Unscrew oil sender and install oil pressure gauge. Easy. But messy. It’s next to filter.

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OK, you hit the nail on the head, I just replaced the intake manifold with a clean used one about 2 months ago, problems ever since. Did my mechanic do a poor install? Cavell, I’m permanently disabled, serious motorcycle wreck so I can’t do engine work, only minor electrical (and I was never good at engine work anyway). Can you tell me what to have done by a mechanic to resolve this? I can buy any parts you suggest at a Pick A Part or Ebay and pay to have the labor done. I did find that over-filling the oil made it less problematic, why does It only drop below normal on hot days. It was 75 this morning and never dipped below 8 psi (bell goes off at 5). I also noted my engine is running very hot for 10 miles of driving under 50 mph on a cool day. Please advise, it’s clear you know exactly what I’m dealing with and we can’t afford major engine work now after the intake. Thanks my new friend. Tommy

I planned to have the oil changed anyway, are you saying have the sending unit pulled and replacing it permanently with an oil pressure gauge in it’s place, or will both be installed simultaneously, I’m sorry I’m so inexperienced with engine stuff…

I understand your point clearly Rod, I’m just telling you what I can do versus what we literally can’t afford to do (engine rebuild = no mortgage). No, the biggest work this car has had was the intake manifold being replaced about 2 months ago with a junkyard pull, but it was in very “clean” shape (came from a low mileage Aurora)). To answer your other question, the leak is enough to stain the street, but you can’t see any “drip”, it must happen slowly overnight. It’s going through a quart every few weeks. If it helps you, this issue is far less prevalent when the weather is cool, and if I “over-fill” by half a quart or so, the idiot light/gauge doesn’t drop to the warning level (which is 5-6 psi). I will switch to a quality oil meanwhile…and have the pressure tested. Thanks for your patience

Hey OK. I meant to ask, what oil should I be using to help, straight 30? I’m sure we want a very high viscosity (it never gets cold here) but I don’t know what oil is a high viscosity. I do understand I don’t want like a 10/40 since I don’t need the variable…but that’s the extent of my understanding. Thanks again

That is all very helpful, thanks. I recall STP, we must be the same age (-;/

My F150 was doing the same thing it was a crack in the sending unit a new unit solved the problem it was spraying out going down the road with very small stain when it was parked. new unit stopped the leak & also had better pressure.

Hey DB, thanks for responding, my “gauge” is actually a digital readout of the pressure in psi, it’s not just an “idiot light”. The light goes off and the warning sound blares at 5-6 psi, only on very hot days, and only at idle. Do you happen to know a reasonable price for this test? I haven’t a clue, so I know not to go have it done blind…Thanks much