I was just wondering about this today. Say you start up your car in the morning after it has been sitting for a while. The oil has drained into the oil pan. How long would it take for the oil from your pan to get circulated throughout the engine? Now, what if you were driving around and your engine was hot, and then you turned it off for, say, an hour, and started it up again. How long would it take to circulate then? The same, less? (Let’s just say it’s 5w-20, and 50 degrees outside, for our purposes)
My oil pressure warning light goes off even as the engine is cranking. The oil does not drain back into the pan, the oil system has an anti-drainback check valve that prevents it from happening. The bearing journals do not go dry, oil stays in the clearance space because of surface tension (capillary effect).
I have disassembled engines that have sat for months and it is difficult to pull the rod and main bearings off the crankshaft due to the suction created by the oil in the bearing.
The oil is circulating in seconds, even in very cold temps. If your question is how long to wait before driving, start driving after you start the car, put your seat belt on, adjust your mirror and then put the car in drive and go. Drive moderatly for 5 minutes or so, but you can start driving almost immedieatly.
With 5W20 and 50F the oil will circulate adequately in about 15 seconds. HOWEVER, I have an old EXXON tape called The Cold War" where at -30F and 10W30 mineral oil, it can take 3 minutes or more for oil to even reach the valve gear. The test was done with a SOHC Ford Escort and the effect was dramatic and scary. After seeing it in the late 70s I switched to 0W30 (Shell Synarctic) synthetic for the winter months since I could not always plug in my block heater.
Today’s oil and tight engines allow 0W20 synthetic to circulate quickly, so 20 seconds is all you need in most cases. However if you go skiing in Colorado and start up the engine early in the morning, let it run for a while to at least clear the windows…
Moments. The oil that ran down into the pan was headed there anyway. The oil necessary to protect the engine on startup was captured when you shut the engine off between the bearing and wear surfaces and by the “honing” in the cylinders. Unless, of course, the car has been sitting for a long time.
It does take a minute (more in cold weather) for the pump to refill all the passages and bring the system up to pressure, but that does not mean the engine is totally unprotected.
The oil pickup tube is pretty much the only thing that needs to be re-filled with oil at startup. Oil is clinging or trapped everywhere else. A few turns of the pump and oil is sucked up into the tube to feed the oil pump and the rest of the system on most cars.
My race car has a mechanical oil pressure gauge. It will show adequate pressure to run the engine during cranking (40-60 psi) and it has pretty wide bearing clearances and a huge oil cooler and lines.
With all dues respect to @Docknick. Get out your old analog watch and see it count off 15-20 seconds. That’s a really long time. Even after an oil change that drains oil away from places it normally would hold - oil filter, passages to and from the filter, ect. - pressure builds faster than 15 seconds.
There is a big difference between -30 and +50. But I have adjusted the valves on a small block Chevy engine in cool temperatures and it only takes a second or two for even straight 30HD to start spraying all over the place from the rockers. Of course the engine was already warmed up to do the adjustment.
Kia oil filters have an anti-drainback check valve. My oil pressure and other lights turn off in about 2 seconds with the exception of air bag and seatbelt which take about 5-6 seconds. I’m guessing they have a longer self test. I fasten my seat belt prior to starting to avoid the (purposely) annoying dinging. Of course my brake warning light stays on until I release the parking brake.
keith: I’ve adjusted vintage small block Chevy solid lifters far to many times. What a mess! I guess it’s the “gravy ladle” shape of the stud mounted rockers. I was too young and dumb to think of goggles!
I think most all spin on oil filters have a one-way valve that prevents drainback when the engine is shut off.
This is a cut apart used filter from a motorcycle. The blue rubber ring to the left of the picture is the anti-drainback valve. It lets oil flow into the ring of small holes into the filter body but not back the other way.
This picture shows it in its normal position.
I like to prefill the oil filter with new oil before mounting it on the engine so that it doesn’t take so long for the oil light to go off after an oil and filter change, but in order to fill that filter, I have to defeat the anti-drainback valve. It won’t let air out of the filter housing and that prevents me from filling the filter completely with oil. I just stick a toothpick in one of the small holes to lift the lip of that rubber flap off the seat, allowing air to escape.
Doing this has the oil light off in one or two seconds after an oil and filter change instead of the 10 or more seconds it would take if I just installed the filter dry.
A lot of modern engines have overhead cams and the camshaft bearings get pressurized oil just like the mains do. Some OHC engines, those that use a single cam and rocker arms are designed so a small “bathtub” sits under the cam lobes, these tubs trap a small amount of oil for the cam lobes to dip into ensuring oil on the cam lobes right at startup. Others have cross drilled camshafts with oiling holes on the base circle of the lobes, essentially as soon as the engine starts, there is oil on the valve train parts.
10 seconds plus?? Wow, worst case for me ever was a couple of seconds and I install mine dry. Usually off almost immediately upon start. If I had one like that, I would definitely pre-fill too…
Just for the sake of making a comparison, after assembling all the pieces to rebuild a domestic V-8 engine and attaching a drill to the oil pump drive shaft and spinning it to prime the engine it takes about 10 to 20 seconds to fill the filter and then another 10 seconds for oil to begin pumping up the lifters. When primed and installed if the ignition is disabled and the engine cranked oil pressure will be immediately indicated on a gauge. Of course most recent engine design doesn’t allow spinning the pump to prime the oil but when installed prior to starting the engine can be cranked with the spark plugs removed to prevent compression and oil pressure will be evident within seconds if the filter is pre-filled.
Not to change the subject but still oil related. My Acura V6 takes 0-20 so before changing oil yesterday I got the manual out again to look for the actual SAE requirements. I noticed that the Acura V6 with the all wheel drive called for 5-20 and not 0-20. They are the same engine and 6 speed transmission as far as I can tell. I wonder if the all wheel drive puts more strain on the engine so they stepped it up to the 5-20 weight?
I am still of the opinion that the 0-20/5-20 requirement is more a political issue than it is lubrication. It could be that your car was among the last that had the 5-20 manual installed and a few hours later the 0-20 manuals were opened and thrown in mentioning how critical it was to use the ZERO-20 grade. The owners manual of a 2015 Rav-4 specifies oil changes at 5,000 miles but the dealership insists that isn’t true and specifies 10,000 mile intervals, insisting that the manual was out of date when placed in the glove box.
