Oil pressure - intermittent warning light - How concerned should I be?

mazda
mpv

#1

Intermittently, the oil pressure light flickers on when I’m driving.

Sometimes, it flickers on when the RPMs drop in the range of 500-600 at traffic light and other stops. Most of the time, it does not come on at all. Yesterday, for a short while (one 15 minute trip), the threshold seemed to be closer to 1,000 RPM. But, after that, it never came on again for that day. This has been happening intermittently for the last year or so, roughly 25,000 miles.

The oil level is in the nearly full range, with around 1,000 miles on the most recent oil change.

I asked my mechanic about this once a few months ago. He thought the idle control valve might be acting up. But, the thing that is bothering me is that flickering does not seem to be related to the idle speed.


#2

The problem might be caused by a faulty oil pressure switch.

That can cause flickering oil light.

These are inexpensive and easy to replace. They’re usually located next to the oil filter.

If replacing the switch doesn’t fix the problem, then you’re going to want to take the vehicle to a shop so an oil pressure gauge can be installed in place of the switch, and the real oil pressure can be determined.

Tester


#3

What year is the vehicle and how many miles?
These symptoms are typical of an engine with high mileage and/or lots of wear. The oil pump will have trouble keeping the pressure up as the spaces between the bearings and their corresponding surfaces grow.

No disrespect to tester, but I’d recommend testing the oil pressure before spending money on the switch.


#4

Well?

If you were to bring your vehicle to my shop to have the oil pressure tested, you’re looking at at least $50.00.

My shop time isn’t free.

Tester


#5

@tester’s suggestion is a good one.
in one of our cars, failing pressure switch (aka pressure sender) is a known problem that gives the same symptoms.
sometimes, unplugging the switch will reveal oil that has leaked through. pretty good confirmation of the problem


#6

No one’s shop time is free. But if the average labor charge to replace an oil pressure switch is $50, why not spend a few bucks more to find out if you’re actually going to fix the problem by replacing the switch.

Last week I had a car come in with the complaint of oil pressure gauge goes to 0 and warning light comes on at idle. Instead of just replacing the switch for $50 labor, I removed the switch, installed a gauge, ran the engine and verified good oil pressure, and then installed a new switch for $100 labor. I’d rather spend $100 and know for sure than spend $50 on a guess.


#7

If the guy is a DIYer, then replacing the switch first is a good idea. If he is relying on a mechanic to do everything, then let the mechanic guide him.

However to answer his question, be concerned, be very concerned. Oil is the lifeblood of your engine. Imagine if your blood pressure were to drop to say 20/10 instead of the normal 120/80, would you be concerned? This could be what is happening to your engine.


#8

OP doesn’t say the vintage of or mileage on the engine. If an older car and higher mileage, more likely this is caused just by the working parts of the lower engine starting to get worn out. Not suggesting that should be assumed, definitely further testing or parts replacement guessing is worthwhile, but I think with this symptom and a full crankcase, a worn out engine is the most likely explanation.

Your mechanic’s idea of the idle air control being the problem is a possibility if the idle rpm is dropping to the point the engine is nearly stalling out. 500-600 rpm at idle seems on the low side. 1,000 rpm should be more than enough to bring the oil pressure up to normal tho. I think my Corolla warm idles (by design) at 800 rpm in neutral. I’d guess your MPV would normally idle between 650 and 800, depending on the operating condition. Higher rpms would be associated with turning the steering wheel, AC on, headlights or coolant fans on. with no load at all, I’d guess around 700 rpm. So 500-600 Is a little on the low side. But if the oil pressure warning light still flickers at 1000 rpm, the idle air control is not the most likely explanation.


#9

With all due respect . . .

I think the fact that both of your vehicles are very old, is affecting your opinions

500-600 idle rpm is quite acceptable on a modern engine, and not on the verge of stalling

While your car might be designed to idle at 800rpm, your car is about 25 years old, and things have changed since then. Why idle at 800rpm and use more fuel, when the engine can idle just fine at 500-600rpm, and use less fuel?

I believe @asemaster and @Waterbuff summed it up quite nicely


#10

Whether the OP measures the pressure first or tries replacing the switch first, the goal is to get at the problem. I didn’t mean to imply that changing the switch wasn’t a good idea, only that I’d prefer to know the pressure first.

I hope my post wasn’t taken in a manner not intended, and if it was I apologize to tester. It was never intended as a criticism. Only as food for thought.

I do wish Tom would tell us the age and mileage of the vehicle. That might make a big difference.
Tom?


#11

Good point @db4690 … but no need to guess. The factory service manual or most any reputable shop can look up the manufacturer’s idle speed spec in their service data.


#12

Correct, it is an older, high miles car: 2005 with 220,000 miles.


#13

The idle speed is quite consistent at 500-600 (the idle control valve was replaced about 2-3 years ago). The thing that is not consistent is when the oil pressure light comes on. Since I posted this last week, it has not come on once. When it does, it is usually when at the idle level. Usually. That time last week, the threshold for turning back off was up closer to 900-1,000 RPM.


#14

You have reached 220000 miles so engine wear is not unusual. You could just use a high mileage oil a little heavier than what you use now and watch the oil level. Only you can decide if the vehicle is worth an engine rebuild at some point. No way to tell how much more use you can get.


#15

That’s expected. The oil pump’s rotational speed and the resultant oil pressure is related to the engine rpm. So the oil pressure will be tend to be lowest at the lowest engine rpm, which occurs at idle.


#16

Thanks for the input everyone. Took the car to my (new) mechanic. The problem was a leaky, failing sending unit; replaced. With the high mileage, I’m also going to shift to using a 20/50W oil. That said, when the pressure checked with a mechanical tester, it showed 85 lbs of pressure…not bad for 220,500 miles.


#17

It’s good to know the problem was a simple one. That same thing has been reported here quite a few times, not necessairly on Mazda’s, but in general those screw in oil pressure senders are a not uncommon failure item. I had to replace one on my prior VW Rabbit. One concern about your post, if you car’s engine has a feature called “variable valve timing”, unless you have a very good reason for doing otherwise, suggest to stick to an oil spec’d in the owner’s manual. Many of the VVT designs are very sensitive to oil specs, and using the wrong type of oil can result in expensive repairs.


#18

The 3.0 V6 in the Mazda is, I believe, a version of Ford’s 3.0 Duratec design from the early 2000’s, a time when they had a controlling interest in Mazda. It is a further development of the 2.5 liter version from the late 90’s. Don’t think any of them had VVT type implementations.


#19

Have you been using “high mileage” oil? If not, you might want to try that before changing the weight of the oil from original Toyota recommendation.