Engineers/builders: Unsafe time for lack of oil?

[Raven]

Hi,

I have a question I have been pondering for some time now, and I figured if I had it in my head, someone else had it too.

The question is this: How long can a typical engine last (ignoring certain unusually robust ones) with no oil in the sump before engine damage starts to set in?

There is a certain amount of oil that is left on the bearings, journals, rings and valve guides that is left behind after the oil is drained. But how long will that remainder last before it becomes unsafe to continue running it?



As for a story, this question brewed out of an incident I had long ago, about 10 years ago. I just got off work for a 3 day weekend, and hit a side road on the way home. I punched the gas on my '88 BMW 325is (who wouldn't, it ran exceptionally well) and the oil pressure light came on. ???? went through my head. There were two possibilities: The voltage supply line to the oil pressure sensor wraps around the front of the block, and is hardly protected well, and it may have been severed. Or I had a serious mechanical failure of some kind.

The next day when it wasn't at night I examined the wire. It looked fine. So I started the engine for 5 seconds to see if it was a fluke. Nope. Okay, take off the oil filter, put a rag on the mounting plate, start it and run it for 5 seconds. Not wet. If there was oil, there would have been oil on the rag.

A small piece of metal about the size of your small finger nail had somehow gotten inside the oil pump and seized the gears. Of course the engine doesn't know anything about that and kept chugging on, and snapped the oil pump driveshaft. Total bill: About 750$.

 

[meep]

at light load my guess is 20 seconds is about as long as you could go until the film on the cylinder walls yields if a car is good and hot. Cold, with thick oil, a little longer? But maybe you could get away with a minute or two under light load. I've always guessed, though, that 20-30 seconds and then the carnage begins.

Unless of course you use Slick 50. (haha)

 

[dishdude]

Is the engine running at idle or WOT?

 

[crazyoildude]

Damage is done within seconds however the engine can run with no oil for a while... The longer it runs with no oil the more damage is done.

 

[AZjeff]

So what's the rest of the story? The only repair was the oil pump driveshaft or was the engine trashed? How long did you drive after the light came on?

Did you drive it for years after or dump it?

 

[AlaskaMike]

I lost oil pressure in my 2000 Dodge Ram 2500 pickup (5.9l diesel) several years ago. Thankfully I noticed it right when it happened. Conditions were cruising at about 45 mph on flat ground, and running empty.

I immediately threw it into neutral and coasted with engine at idle so I still had brakes and steering, into the nearest driveway and shut it down. It was probably close to 20 seconds or so. I haven't noticed any issues whatsoever in the 6 or 8 years since it happened.

I think in my case the turbo might be the first thing that would show damage, but I honestly don't know. To this day there's no significant radial or end play in the spinning parts of the turbo.

 

[Brybo86]

Originally Posted By: Raven

A small piece of metal about the size of your small finger nail had somehow gotten inside the oil pump and seized the gears. Of course the engine doesn't know anything about that and kept chugging on, and snapped the oil pump driveshaft. Total bill: About 750$.


Lemme guess you were running a K&N air filter and a Purolator? Basically zero filtering going on with that combo.

And I agreed with crazyoildude, the damage begins within a couple seconds of losing oil pressure. I would think only a couple revolutions and the "film" is gone.

 

[Cardenio327]

Originally Posted By: Brybo86
Originally Posted By: Raven

A small piece of metal about the size of your small finger nail had somehow gotten inside the oil pump and seized the gears. Of course the engine doesn't know anything about that and kept chugging on, and snapped the oil pump driveshaft. Total bill: About 750$.


Lemme guess you were running a K&N air filter and a Purolator? Basically zero filtering going on with that combo.

And I agreed with crazyoildude, the damage begins within a couple seconds of losing oil pressure. I would think only a couple revolutions and the "film" is gone.


I don't like K & N or Purolator any better than the next guy, but...

A K & N air filter wouldn't let a fingernail sized piece of metal into the crankcase, and...

Oil is filtered after it goes through the oil pump, not before. The pickup screen would have to be damaged or have fallen off for something that big to get into the pump. Or, it could have been some kind of casting flashing that broke free between the screen and the pump.

 

[bullwinkle]

Originally Posted By: AlaskaMike
I lost oil pressure in my 2000 Dodge Ram 2500 pickup (5.9l diesel) several years ago. Thankfully I noticed it right when it happened. Conditions were cruising at about 45 mph on flat ground, and running empty.

I immediately threw it into neutral and coasted with engine at idle so I still had brakes and steering, into the nearest driveway and shut it down. It was probably close to 20 seconds or so. I haven't noticed any issues whatsoever in the 6 or 8 years since it happened.

I think in my case the turbo might be the first thing that would show damage, but I honestly don't know. To this day there's no significant radial or end play in the spinning parts of the turbo.
What happened? Were you out of oil, or (like my '06 did) did your oil pressure sender (which apparently is just a switch) just go out? Scared me to death whem mine did it, but I still had oil pressure, gauge just went dead & warning lights all came on.

 

[A_Harman]

I know from sad experience how long an engine lasts at full power when the oil pump shaft shears. 3 seconds after the pressure dropped to zero, the engine started seizing up. Welded half the rod bearings to their crank journals.

 

[AlaskaMike]

Originally Posted By: bullwinkle
Originally Posted By: AlaskaMike
I lost oil pressure in my 2000 Dodge Ram 2500 pickup (5.9l diesel) several years ago. Thankfully I noticed it right when it happened. Conditions were cruising at about 45 mph on flat ground, and running empty.

I immediately threw it into neutral and coasted with engine at idle so I still had brakes and steering, into the nearest driveway and shut it down. It was probably close to 20 seconds or so. I haven't noticed any issues whatsoever in the 6 or 8 years since it happened.

I think in my case the turbo might be the first thing that would show damage, but I honestly don't know. To this day there's no significant radial or end play in the spinning parts of the turbo.
What happened? Were you out of oil, or (like my '06 did) did your oil pressure sender (which apparently is just a switch) just go out? Scared me to death whem mine did it, but I still had oil pressure, gauge just went dead & warning lights all came on.


I had just purchased an aftermarket turbo from a friend who had upgraded to a larger turbo. He had torqued town the bolts for the oil drain hose from the turbo after we installed it on my truck, and I stupidly failed to check them before I drove it home from his house.

The bolts backed out on my drive home, and I noticed the oil pressure slowly dropping before it finally dropped to zero.

 

[badtlc]

I feel like there was a synthetic oil commercial that covered this very topic.

 

[BrocLuno]

Not the same engine at all, but we sometimes have a car we try to blow up with no oil in it as a demo at the local car show. Last time was a Jeep Grand Cherokee V-6.

No oil, no coolant and 15+ minutes went by at 4,000 RPM and it was still running. Yeah, I'm sure it was damaged. But a seasoned engine will run a l-o-n-g time w/o oil unless it has serious mechanical issues.

Many engines in the old days were only lubed by hand pump occasionally and they ran for years on old oil formulas ...

With modern add-paks it seems they will run on the anti-wear films for quite a while ...

 

[eljefino]

I had a saturn s-series that lost prime in its oil pump and ran a minute with no pressure, but I only idled it/ got up to 10 MPH.

The "fix" was I removed the oil filter, drained it, and reinstalled it.

I can't explain it. Car ran fine after.

 

[Raven]

No particular consensus here, but I think that can be due to the variety of motors out there. Given the closer operating tolerances of 2005+ engines and so forth, particularly those with alloys not used in the past and the OW-20 requirements, it's still a good question though.

The question starts with the motor being at idle. I also wonder what is the weakest point (or the damage to occur first): crank journals, camshafts, turbos, or what not.

Any more input / experiences?



As for that 325is, it was towed to a shop (I didn't have a lift to drop the steering rack and the sump, otherwise I'd have done it myself) and repaired. It ran just fine thereafter and then someone lost control of their vehicle and hit mine which was parked. Sad, the motor was excellent. 191K miles on it and ran like it wanted to get out and love life. I didn't have a K&N filter, it was a paper air filter, and the filter was not a Purolater make. I think it was FRAM. The pickup screen was intact and undamaged. A baffling diagnostic case indeed.

 

[andyd]

A 528e with essentially the same engine, is a pretty robust engine. In 20 yrs of ownership, I've never have had a head off. If the 325is is similar to the 528e in setup. if the oil light was in the over head display. Thats a low level lite. I would have gone for used parts from an engine that ate a timing belt. or the whole lower end if the pistons weren't too bad. Slap the i head on it and drive.. My sister AKA Leadfoot, drove her '85 Grand Marquise for 60 miles on a siezed oil pump. Rick just R+R the pump etc, plus the valve seals which were the root cause. They drove the car for a few more yrs K miles. 10 yr old 302 V8.

 

[CBR.worm]

I had an oil filter failure near redline in top gear. The oil filter was safety wired in place, so after the threads failed, the filter hung around so we could see the damage.

Anyway, I smelled something, then the oil pressure light came on. I pulled in the clutch and turned off the ignition, coasting to a stop. I figure there was probably about 10 seconds WOT at ~14k RPM before everything registered and I killed it. People watching said it was smoke screen for 1/4 mile before I killed it.

The engine still ran 'fine', but when I tore it apart, significant damage was done to all the rod bearings and the crank was scored. I sent the crank out, replaced all the bearings and was back on the track pretty quickly.

So my experience is that at WOT for a few seconds will do a good bit of damage.

I was running M1 10w40 w/ a Fram filter.

 

[Raven]

The E28 and the E30 (except the early 316, 316i and 318i with the M10 mill) all had the ... forgot what it was ... Check Control system display.

This one when it came on was the one below the tachometer. Was definitely oil pressure light, not the cool retro red LED indicator above the mirror.

I wouldn't put an M20B25 head on a M20B27 motor though, unless you like a really low compression ratio. I had a 325e, so the 'B25 was definitely an upgrade. On the other hand the 'eta told me I was getting 50mpg at 45mph on a level road. Nice. Also slow. (Though my 'eta had the 2.79 LSD.)