An oil pressure gauge can give you an excellent indication of the health of various systems in your engine. The key is to establish baseline readings when your engine is healthy, and then be aware of any changes you see over time. The Lubrication System
The oil pump takes in oil from the sump (oil pan), and forces it through the engine under pressure. Since the oil pump is driven (indirectly) by the crankshaft, oil pressure is to some extent determined by engine RPM. Pressure is kept from rising too high by a relief valve. Typically, this is a spring-loaded ball, where a predetermined amount of pressure lifts the ball off its seat to allow oil to return to the oil pan without circulating through the engine.
The oil is pumped through drillings in the block and head, lubricating the bearings and also helping cool the engine. After it emerges from the drillings in the crankshaft and other parts, it drains back (with virtually no pressure) into the sump to be re-circulated. A filter in the circuit keeps dirt and metal filings from scratching the bearings or damaging the oil pump.
What Determines Oil Pressure?
At lower engine speeds, oil pressure is limited by the clearances between the various bearings and journals. For example, as the space between the crankshaft bearing journals and its bearings increases through wear, oil pressure will be lower because oil can flow out of the space more easily. The same is true for the journals on the big ends of the connecting rods. Thus, everything else being equal, low oil pressure can indicate worn bearings.
There are other factors that affect oil pressure, though. When the oil is colder, it has a higher viscosity (it's thicker), which means it cannot slip through the bearing clearances as easily. You'll notice that oil pressure at idle is quite a bit higher when the engine is first started up. On some cars (Fiats, for example), low oil pressure at idle when the engine is hot is quite normal. Oil flow may be perfectly adequate, even though the pressure is low.
It stands to reason that thinner (lower-weight) oil will indicate lower oil pressure than a thicker oil, at least at idle and moderate engine speeds. Lower pressure caused by changing to a lower-viscosity oil may not indicate a problem, provided it is not being overheated. If the oil is thinner because it is breaking down, too hot, or diluted with gasoline from an over-rich mixture or worn rings, you should change oil at once and correct the problem.
Potential Causes of Low Oil Pressure:
[COLOR="Blue"]Low Oil Level - You may first notice your oil pressure dip during a hard corner or under sharp braking. Stop at once and top up the oil, or you can seriously damage your engine!
[COLOR="blue"]Diluted or Worn-Out Oil - (see above).
[COLOR="blue"]Damaged Oil Pan or Pickup Tube - Have you scraped or banged your oil pan? Stop at once!
[COLOR="blue"]High Oil Temperature - Generally not a big factor, but if you're pulling a trailer or running flat out in really hot weather, your oil can run well over 250 degrees F., and oil pressure will be lower.
[COLOR="blue"]Worn Engine Bearings - (see above). A further indication can be a heavy knocking under engine load (main bearings) or a lighter knocking (connecting rod bearings).
[COLOR="blue"]Worn Oil Pump - This could be anything from a slight reduction all the way to catastrophic failure (which is rare unless the pump has ingested bits of metal from some other failure).
[COLOR="blue"]Dropped Crankshaft Plug(s) - This is not terribly uncommon in 4-cylinder Alfa Romeo engines. These metal plugs fill the holes where the factory drilled oil passages in the crankshaft. If one falls out, oil pressure will suddenly drop across the board. You can still drive (slowly) to get home, but the plug(s) will need to be replaced.
What About High Oil Pressure?
High oil pressure is not generally a concern, but if pressure suddenly increases, there may be a problem with the pressure relief valve. Switching to a higher-viscosity oil will also show higher readings. In choosing oil weight, it's best to follow the manufacturer's recommendations for the season and type of driving.
Re: Oil Pressure Gauge
Thanks for the informative article FGVILLEGAS!
I shoulda checked my oil pressure after the engine was overhauled to record baseline readings, sayang!
Otherwise i do monitor my oil pressure from time to time during every drive and compare it against the factory specs (but of course factoring in that i dont have a brand new engine). I am attentive to oil and oil filter changes as well as checking my oil level once a wk. and whatever possible leaks from the engine.
Re: Oil Pressure Gauge
Thanks for the informative article FGVILLEGAS!
I shoulda checked my oil pressure after the engine was overhauled to record baseline readings, sayang!
Otherwise i do monitor my oil pressure from time to time during every drive and compare it against the factory specs (but of course factoring in that i dont have a brand new engine). I am attentive to oil and oil filter changes as well as checking my oil level once a wk. and whatever possible leaks from the engine.
you're welcome! 🙂
it's not too late. you could still use the pressure reading after your next oil change. it should not vary that much if you're using the same oil as recommended by the manufacturer (which is usually mineral based). if you switched to synthetic, then the difference will be a little bigger.
if your oil pressuer is below 8 psi and your oil temp is just normal, check the level of your oil. if it is in a normal level, have your engine check for possible problems.
i'm currently using synthetic oil (5w40) and my normal reading once the engine has warmed-up is about 12psi.
Re: Oil Pressure Gauge
In 1970's, Mercedes-Benz put oil coolers in their engines mostly diesels because of geographic locations, such as Germany, Austria and Switzerland thus lots of driving mountain roads thus increasing oil temperature as they climb uphill. MB engineers solved the problem by equipping the engines with oil coolers which located left side of the radiator.
My 1966 200, I installed an oil cooler just an insurance policy also, I sometimes drive to the mountains in Cebu! (going to Toledo City via Manipis, Naga City, I once tried transcentral highway going to Balamban but I was anxious about the road's condition especially during rains). After I arrived in Cebu City, oil pressure dropped a bit (30 PSI) at engine's temp at about 90C the oil was Bardahl 15W40 Diesel engine oil.
Re: Oil Pressure Gauge
That was quite cold for the engine especially running a 15W oil inside. Glad to hear you've finished well.
Re: Oil Pressure Gauge
Even I warmed it up for 10 minutes the oil pressure dropped a little bit at idle, 15W is thick oil because older engines and high mileage engines required this pero pwede 'ring 10W as long as I don't go below this.
I drive up to Balamban with my uncle, I took this photo 4 years ago, you notice the car's paint is fading
engine bay with oil cooler beside the radiator:
Re: Oil Pressure Gauge
Just to understand it well, do you mean that your reading at idle is 30 psi? If so, I think this is normal. For synthetic oil users, idle reading is between 20 to 30 psi or even a little lower.
I know you posted some pictures but I can't see it in my office computer because of some safety settings made by our tech guys. 🙁
Re: Oil Pressure Gauge
Just to understand it well, do you mean that your reading at idle is 30 psi? If so, I think this is normal. For synthetic oil users, idle reading is between 20 to 30 psi or even a little lower.
Yes sir, about 30 PSI at idle after that trip using 15W40 BARDAHL mineral-based diesel engine oil. Before, it was below 20 PSI w/o the oil cooler. Syn oils are thinner (0W,5W,10W) thus lower oil pressure reading, older cars do not recommend filling with syn oils. By the time when my MB project is finished, I wanna drive it up there again with 3-tubed radiator installed. I prepped (fully equipped) my car for my planned long trip to my father's hometown in Tuguegarao City, Cagayan from here (Cebu City) using central Nautical Highway (CEBU-MASBATE-SORSOGON) route maybe no typhoon season.
Why I used diesel engine oil? because of ZDDP (Zinc Dialkyl-Dithio-Phosphate) it's an anti-wear additive to prolong engine life especially reducing valvetrain wear. I plan to use Mobil DELVAC (too expensive) I settle for BARDAHL instead.
