2000 GP GT Low Oil Pressure at Idle

[thrashette]

So my dad and I switched cars for a bit, and now I'm back with the Grand Prix. The low oil pressure light is appearing at idle/low RPM after being driven for about 20 minutes. It appears at stop signs, while coasting slowly, or just sitting idle. He says this has been happening since October (!!) Probably about 10k miles since then. There are no codes, no SES light, and the car seems to run and drive just fine. No hesitation, stalling, noise, etc. However, the idle speed does seem to be relatively low? I can't remember what's normal, but it's idling at about 700 RPM. It's 1000 RPM when first started, and when the nose is high on an incline. The only abnormality I can really observe is a very SLIGHT vibration that coincides with the light flickering on. You would never notice it if you weren't looking for it. Oil level is good, looks right and smells right, and was changed about 1000 miles ago with the manufacturer's recommended oil. No fluid leaks. Have a "LOW COOLANT" light, but coolant level and temperature are fine. Gave up after replacing the sensor a third time.

I'm not very mechanically inclined. I don't currently have an oil pressure gauge, but I could get one if they're not difficult to install (or get help if they are, I suppose.) Besides getting this gauge, what are some other things to look at? Any common failures that produce these symptoms?

Currently it's a bit above 230,000 mi on the original engine. I understand that this is generally an omen, and since it's been running like this for quite some time, it's baaaad. I'm a student in the process of building credit, so buying a car before the end of this year is not ideal.

[Fivefingerdeathpunch]

Maybe the sensors is at fault or it really does drop in pressure but it just never dies.

Hard to guess at it and the fact that it's been this way for a long long time makes it a weird issue.

You could always try a new sensor.

[thrashette]

Yeah, I figured something would have exploded or failed by now. Which sensor in particular would be faulty in this instance? Oil pressure sensor?

I showed it to a friend, and he guessed that that very slight vibration would be the engine giving a "breath of life" to keep running. You can also observe the needle moving very slightly, maybe like 10 RPM when this happens.

[FordMan77]

Idle speed doesn't sound that low. Might give the MAF and TB a good cleaning. Besides that, you need to get a REAL oil pressure gauge on it to see what it truly is. The light in the dash comes on when there is around 5psi of pressure, also known as the "change engine" light. If it was this low all this time I'd guess it would have given up by now.

To install a true gauge, you remove the oil pressure sending unit from the oil filter adapter (it is near the oil filter and points towards the firewall) and install the gauge sending unit in its place.

230K on the original motor isn't much as long as it's been maintained. My 00 GPGT just rolled 350K today and it sits around 48-50psi fully hot in gear/idle according to my Autometer gauge.

[thrashette]

Ugh, I've had to replace the MAF 3 times in the past 4 years. -_- Maybe there's something related to it that's gone bad and has caused all this drama? Pretty sure nothing in the engine bay but the dipstick has ever seen a rag, so maybe it'd give me an excuse to peek around.

Frankly, the mileage is an accomplishment for a salvage title... dumped on my father as a "temporary vehicle" and dumped on me, as my first car, also assumed to be temporary. 5 years later... I do my best to maintain it, but I don't get a lot of help from my "DRIVE IT AND FORGET IT" dad.

I'll definitely talk to my friend to help me with the oil pressure gauge and update after checking that and cleaning it.

[Dancing Bear]

After you've driven for 20 minutes, the engine's oil has heated up and thinned out. Naturally, when this happens the pressure will drop. Pressure will be lowest at idle, which is why you're seeing it at the times you described, when engine speeds are lowest. When you give it gas, pressure goes back up somewhat, shutting off the light. My Foxbody had 160k on the original engine, and my pressure at idle was starting to get low ~15psi at idle. Switched from 10w-30 to 10w-40 and it helped.

However, I'm not sure if running oil that thick on these engines is recommended.

[QUICKSILVER462]

I have seen this symptom on engines on high mileage engines that have sludge in the bottom of the oil pan. The sludge blocks the oil flow to the pick up screen and restricts the oil flow to the pump. Removing the oil pan and cleaning the sludge out of the bottom of the pan is the only proper way to fix the problem.

[BillBoost37]

I would suggest starting by pulling the connector off the oil pressure sensor and looking to see if it's wet with oil Often enough the seals go bad in these and they can read incorrectly when doing so.

At the same point, it's very possible that at low rpms and higher mileage (if it is high miles) that there is worn items and pressure is lacking at low rpm.

[thrashette]

I have seen this symptom on engines on high mileage engines that have sludge in the bottom of the oil pan. The sludge blocks the oil flow to the pick up screen and restricts the oil flow to the pump. Removing the oil pan and cleaning the sludge out of the bottom of the pan is the only proper way to fix the problem.

I'm buying this. Under my dad's care, the oil was never changed. I'll avoid disclosing the precise duration because it will make you cry. The procedure isn't something I feel comfortable performing in the least, but I've got friends with garages who will hopefully feel generous enough to help out.

[BillBoost37]

Or you could start changing it super often with cheap crap oil and that'll slowly remove the crud, the same way it got there.