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We had an oil change done at a quick lube type shop. After nearly 3 months and 3,000 miles driven, the oil drain plug fell out, resulting in blowing up the entire engine. There was no oil leakage or any sign of trouble up to the point where the plug came out; no oil in the driveway, or parking spot at place of employment.

We have gone through the process of filing a complaint with the oil change shop, and both their owner and insurance company have denied liability, even though they were the last to have touched the oil drain plug.

What could cause the oil plug to just come out, if not for that company's possible negligence or shoddy workmanship? Have we just driven the car too many miles to assign blame to any party?

  • Note that the question title and the last sentence are asking different things, and I'm not sure if we can effectively answer the legal aspect... Interesting question on the loose oil plug tho. – JPhi1618 May 5 '16 at 18:08
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    a little off topic, but I'm surprised manufacturers haven't implemented an engine kill when the oil pressure drops below a certain threshold. – rpmerf May 5 '16 at 20:01
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    Fix Or Repair Daily – Autistic May 6 '16 at 11:02
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    "resulting in blowing up the entire engine" - How long/far did you drive after the red oil pressure warning light turned on?! – JimmyB May 6 '16 at 12:35
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    Don't make the assumption it was actually your oil plug, and not the one from the car on the next ramp which was bigger than yours, fitted with the correct torque, but with only a quarter turn of threads engaged. That probably wouldn't leak until something shook it loose and it fell out. – alephzero May 6 '16 at 14:42
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It definitely could have worked it's way (the drain bolt) over the three month period from the previous change.

The cause would be an improperly torqued oil drain bolt. It wouldn't be the first time.

Getting together evidence that it IS their fault is impossible.

So, to clearly answer this question

What could cause the oil plug to just come out, if not for that company's possible negligence or shoddy workmanship?

Oil drain plug was not tightened properly upon its last placement.

Regarding the negligence. It's impossible to say.

Your other question

Have we just driven the car too many miles to assign blame to any party?

Can't be answered. This seems more legal. You can probably read some legal verbiage associated with your work order, if you still have it, and determine the answer to that question.

  • How quickly would the plug work loose? Would it go from no drips to falling out in one trip? – JPhi1618 May 5 '16 at 18:32
  • I have no idea. It would seem to depend on high tightly the plug was installed. If it's hand tight, how long will it stay in the oil pan? I don't know. – DucatiKiller May 5 '16 at 18:35
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    @JPhi1618 They fact they the OP says there were no leaks noted does not mean there were no leaks. The pan is hidden under a plastic shroud and probably dripped a little after a bit. Anyhow, this is more common than thought because these shops tighten the oil pan bolts with power tools. The OP is basically SOL because it is very very hard to prove as a mistake on the shop's part. The resources spent on lawyers are more than an used engine from the junk yard. Either way they are out about $2500. – race fever May 5 '16 at 21:50
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    @JPhi1618: when I change the oil in my Sienna, oil doesn't drip until the plug is on the last thread. So I can certainly imagine that if it was loose it may not drip at all until the last two turns are undone while driving. – Martin Argerami May 6 '16 at 5:38
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    @MartinArgerami How many times have you let it site on the last few threads? It will leak oil all day slowly if you do it. Drop by drop. – DucatiKiller May 6 '16 at 5:54
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I had exactly the same experience with a chain oil change shop. It's one of the reasons I stopped using any outside mechanic for anything short of things I can't handle due to specialized tools or time required.

In my case it was also thousands of miles before the problem showed up. I did have droplets of oil on the driveway, but I can easily imagine scenarios where you wouldn't see any drops depending on how the oil pan is placed, and how loose the screw was.

Bottom line, I found it before the drain plug fell out and dropped all the oil on the road. The cause in my case was that the shop did not bother to torque it properly when they put it on. It's unknown if they even put a wrench on it, or just hand tightened it.

I cannot address the legal aspects of your questions, but, I can confirm that it will go thousands of miles driven before that bolt works itself out enough to release the oil. With a car as young as yours I can't think of any other cause for that bolt to just drop out. In an older car with some kind of crush washer behind the drain bolt, perhaps it was too old and needed replacement. For a car that new, I am stumped as to what else it could be besides the incompetence of the shop.

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I don't have enough reputation to comment, so I will post here.

If the low oil pressure light, or similar indicator, did not light up, or was not noticed, it could be that the oil pan plug or bolt fell out during a longer trip and prior to the 3000 miles when the condition was noticed.

If the plug did not leak (much) before falling out, the small amount of oil could be trapped by the plastic shroud, as mentioned by race fever.

If the plug finally fell out on a longer trip (rough guess based on my oil changes: maybe as little as 20-30 minutes), almost all of the oil could drain out on the road before parking it at home or work, where you would have the possibility of noticing it.

After that, if the indicator still is not enabled or noticed, it is possible to drive around for a while.

How long? It depends on many factors, but maybe as much 50-100+ miles (80-160km) before the engine "blows up." Note that shorter trips, where the engine does not get too hot for too long, could delay the "blow up."

I had a co-worker experience this a few months ago on a much older car (13 years old, >200k miles). The co-worker's lack of awareness and automobile experience resulted in at least 3-4 trips of about 5-10 miles (8-16 km) after the no oil (and no oil plug) condition was noticed. The engine never seized and fortunately the quickie lube business (a large national US chain) paid out the claim. In this case, the condition occurred only 2-3 weeks after the oil change.

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I had an oil squirter come loose inside my engine and destroy a piston about 10 years after a rebuild. Sometimes stuff just comes loose and it's no one's fault.

My feeling is that it it was probably an improperly torqued plug, but it wasn't so far out of spec that it would count as negligence in the minds of most judges or juries. It held in there for 3 months and 3k miles so it was at least somewhat tight. (I'm a lawyer and I wouldn't feel like this is anything like a slam dunk).

You wouldn't notice any leak before it came out. Once it came loose enough to leak, the plug would soon fall out and all the oil would very quickly leave out the bottom of the engine. Some time shortly after that your oil pressure would bottom out, warning lights would come on and shortly thereafter you will suffer bearing and cam journal damage. You can rebuild an engine after this sort of mishap, but it basically means taking the whole thing apart so you can replace or machine all the lubricated moving parts (bearings, cams, anything touching the cam journals). It's a huge pain.

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