How useful are oil pressure gauges?

I go back-and-forth on these a lot. I hear a lot of people saying that they are necessary. And while I agree it is a good thing to know your oil pressure, I don’t feel like the gauge would be useful to tell you that information when a failure occurs, simply because you won’t be looking at that gauge 24 seven. It seems like you would look at that gauge once the engine starts to make some strange noises, then see low oil pressure, and then begin cussing that you did not look at that gauge in time To shut down the engine. I could see it being useful for a new engine rebuild to make sure that you have proper oil pressure going. It just seems like instead of a gauge it should have a warning buzzer that annoys the hell out of you at the first drop of oil pressure

If its a British car, it's a good indication when you need a rebuild.  

I have found an analog gage that gives actual readings useful. Having one saved damage to a GMC I had when an oil cooler quick connect fitting disconnected going down the road  

While you may not directly look at it very often, there is a good chance that you’ll pick up on the needle being in a different spot when glancing at the tach or  speedometer. 

I prefer analog gages with the scale set so the needle points straight up (or close to it) under normal conditions. Easy to see at a glance if everything is normal, dropping, or rising.

The problem is fake gages. Some gages, like the oil pressure in late 90’s ford rangers, are really just a warning light with a needle. The pressure reading is very stable because the sending unit sends and on/off signal that makes the gage read 0 or Normal as long as it’s over some minimum pressure (5psi iirc). .

By the time the needle drops on a late 90’s ranger you have no oil pressure. 

I’ve had a gauge give me early warning of issues that I wouldn’t have known about unless I had it, mostly related to being low on oil when endurance racing. The pressure would go down from normal, but still high enough to not trigger a light.  

On my tow vehicle that has an actual OEM accurate oil gauge (not a light in disguise), it has indicated to me that the oil viscosity is breaking down a bit and I need an oil change.  

As I have blown a motor from a factory oil hose to a factory oil cooler coming off, and it was all over before I realized I had a problem, I personally find an oil gauge or small idiot light to be worthless.  The first indication I had of a problem was the motor being down on power.  The idiot light was this tiny little orange thing on the gauge cluster, as I drove into the sun with sunglasses on.  Useless.  For the locost, I have wired up a fuel pump kill to the oil pressure sender (idiot light sender), and the idiot light will be an 18 wheeler LED tail light.  Anything I build from now on will be that way.

Interesting, I ask because my 97 Miata has the faux gauge, and I am debating whether to go through the hassle of sourcing a real Miata pressure Gauge and swapping it in. 

Dr. Hess said:

As I have blown a motor from a factory oil hose to a factory oil cooler coming off, and it was all over before I realized I had a problem, I personally find an oil gauge or small idiot light to be worthless.  The first indication I had of a problem was the motor being down on power.  The idiot light was this tiny little orange thing on the gauge cluster, as I drove into the sun with sunglasses on.  Useless.  For the locost, I have wired up a fuel pump kill to the oil pressure sender (idiot light sender), and the idiot light will be an 18 wheeler LED tail light.  Anything I build from now on will be that way.

Lmao! That’s how to do it!

If you're going hard at HPDEs or racing, I think it is a good idea.  You need a gauge and a light, and I'd recommend a higher oil pressure light switch -- say 20 PSI?  Stock oil pressure lights come on a 'next-to-none.'  That way you have something that will grab your attention to look at the gauge.

I've had one save an engine before.  Lost an intake gasket on a long highway run and it started sucking down oil at a seriously alarming rate (like 2 quarts in 200 miles).  Right around what turned out to be the 2 quart low mark, I noticed the issue on one of my routine gauge scans.  "Hmm, 18 psi isn't normal for highway cruise, should be 30+, better stop and check on that".  Based on the slight pressure flickers when slowing down and pulling over, it wouldn't have been much longer before it lost almost all pressure.  Thanks to the gauge, I caught the issue before any identifiable damage occurred.  

I run both a warning light and a gauge. I scan the gauge on the straight along with the other gauges.  The warning light is mounted in the top of the gauge pod so it's very visible.

Wiring the fuel pump to the oil pressure will also prevent you from starting the car before oil pressure builds unless it's one of those cars that uses a little toilet bowl to dribble fuel into the intake manifold. That could be desirable, but you'd want to be aware.

spitfirebill said:

If its a British car, it's a good indication when you need a rebuild.  

On an air-cooled beetle, it's a good indication of how hot your motor is.

Large idiot lights (5W LED or bigger) in the heater vents. That way the driver knows to STOP when they are suddenly <20 PSI on track.

An analog gauge is good for measuring long-term engine health. An idiot light is good for winning the "PRESS X NOW TO SAVE ENGINE" quick-time event.

Another way to reduce wear on startup is to delay fuel when cranking, this gives the engine more time to build oil pressure before it fires:

https://grassrootsmotorsports.com/forum/grm/i-need-to-make-my-engine-start-slower-ms3-questions/137993/page1/

I've had 2 engines saved from low oil by idiot lights. My sister's old NB that she never did any maintenance on, and a replacement G13A in my Samurai that was losing oil with unexpected speed. A G13A's oiling system is so good that it will get down to 1/2qt before it starts to oil starve under heavy braking and on steep downhills.

I was climbing the entrance ramp to get on the highway, get a quick scan on my gauges, and actually saw the oil pressure gauge drop from 50 to 0.

I had just had the oil changed, and the drain pan plug was loose. The fact that I was looking at it at that moment saved my engine. 

I like the idea of a warning light that comes on at a higher pressure, in combination with an accurate gauge.

I've been considering adding an aftermarket temperature and oil pressure gauge set to my NB Miata.

Edit: it was decades before I had anyone else change the oil in one of my cars again.

aircooled said:

spitfirebill said:

If its a British car, it's a good indication when you need a rebuild.  

On an air-cooled beetle, it's a good indication of how hot your motor is.

On a Harley also.  'Course, I have both an oil temp and oil pressure gauge, plus an idiot light on my bike. 

Keith Tanner said:

Wiring the fuel pump to the oil pressure will also prevent you from starting the car before oil pressure builds unless it's one of those cars that uses a little toilet bowl to dribble fuel into the intake manifold. That could be desirable, but you'd want to be aware.

The locost has an accusump on it, and I also wired in a line from the starter control line to the fuel pump relay so that the fuel pump relay is energized if the starter is on.  You need a diode in that line to prevent feedback.

I have an  extra 1.6 miata oil pressure sender - I can send you one if you pay the (presumably) very small shipping charge.

A proper gauge is useful for determining long term health of the greasy bits, but is almost entirely useless on a race track, unless you have an in car camera.  Then, you can watch the gauge to determine whether you need an accusump. 

Big, shiny red light aimed at your eyeballs is the answer for sudden pressure loss.

I am also quite capable of driving a thousand miles and never noticing a gauge, which is why I have a "distance to empty" setting on the message center whenever I can.

I like to have both a gauge and a light.  The gauge gives you a good indicator of overall engine health.  If it's doing something different that you can figure out the root cause before things get expensive.  The light is nice for quickly notifying you of major issues when you might be distracted.

On the track I scan all the gages on every straight (At least officially.  I might forget if I'm setting up for a pass).  On the street I scan them every time I look at the speedometer.

In race cars I mount the gauges so that the needles should be more or less straight up and down during my scan, or, in the case of the tach at redline.  Below is a crappy picture of the gauge layout in my Camaro.  From the driver's seat the oil pressure gauge is front and center while the voltmeter and water temp are also easy to see.  The warning lights are just below the oil pressure gauge.  I can see the tach without taking my eyes off the track.  I can't read the numbers without refocusing but I can tell when the needle is almost vertical and/or see the shift light peripherally.

My oil pressure gauge saved my engine (EJ257). I had excess water and fuel content clogging my OEM oil filters from various vacuum/boost leaks from previous shops' work (in addition to my own attempts at fixing things).

My cold start and warm cruise oil pressures were significantly lower than normal once winter started. I sent an oil sample to Dyson Analysis to help me figure out what was going on, and that started the quest of cleaning up the engine bay. If I didn't have the aftermarket oil pressure gauge, I wouldn't have known I had an issue until I spun a bearing most likely.

Also, the stock oil pressure warning light Subaru gives you is useless. I see 70+ psi warm cruise regularly, and the light is designed to come on at 2.1 psi. Yes, two point one. A light designed to tell you when to replace the engine hah.

accordionfolder said:

I have an  extra 1.6 miata oil pressure sender - I can send you one if you pay the (presumably) very small shipping charge.

I might take you up on that. Does it need the sender too? 

I was discussing this with some fellow racers at a race once, and we all came to this conclusion:  On the dash, I only want a sequential shift light, bright blue light for low coolant pressure, bright red light for low oil pressure and a bright yellow/orange for high water temp. 

I'd like all real gauges, too, but not in my line of sight.  I don't want to have to look at gauges while racing, but if they're there, I can't help it.

I find them useful in a road car - if nothing else, it's nice to know when the oil is fully warmed and I can start having fun (obviously a temp gauge would do the same, but the pressure gauge effectively does two jobs here). I like them mounted up high; low mounted gauges are too easy to ignore or forget about. In my 2002 I pulled the seat belt warning pod off the top of the dash and mounted a pod up there. In fact I was just plotting how to add an oil pressure gauge (among others) to my hopefully-soon-to-arrive Saab 900 project - contemplating yanking the radio and mounting gauges in a DIN adapter, and getting the oil filter mount off a turbo to repurpose one of the oil cooler line bosses as a sending unit mount (blocking off the other, naturally).

We had both oil pressure gauge and light on my old LeMons car.  The light was a turn signal with an obnoxious LED bulb, mounted center of the column right above the steering wheel.  Ain't no missing that bad boy.

We also ran an oil temp gauge which proved to be interesting in telling us our oil cooler didn't do E36 M3.

On a street car, I'd still so both, just wire the light up to be only slightly less tacky.  Maybe a small, super visible LED somewhere I that the driver will always see.