Oil bolt confusion?

[khigh]

Hi all.

Loaned my 2000 OBS Z71 5.7 to a friend and asked him to change the oil. He lost the oil pan bolt outdoors.

He went to the auto parts store, got one, and it went in, but the threads were wrong. It was too loose and it leaked.

I told him to go back and tell them it was a 99. They gave him a different oil bolt. It will start but it won't thread in. The threads are much finer.

Is there some science to getting the right bolt?

Any suggestions? Were there different oil pans used? Anyone have a good part number to try?

Thanks for looking.

 

[Doubeleive]

since the wrong bolt was used you will need to re-tap the bolt hole to the correct thread, you may be able to rent a tap & die set from your autoparts store.

 

[swathdiver]

Seems to me the first one was english and not metric threads, pitch was different causing the leak.

Plug your VIN in over at ACDelco's or GMPartsGiant's website and see what comes up. Take Wes' advice and run a tap through there once you know the correct threads to straighten them out again.

 

[adriver]

I was thinking your friend was a complete fool, but...…2,000 was a split year. They made both 2000 NBS and OBS body style tahoes. I'm guessing they use different drain plugs and your friend didn't know which one, nor did the auto parts store know if they asked them. That at least COULD explain the second one. Not sure how the first replacement bolt could go in correctly and still leak, unless they didn't tighten it enough.

 

[khigh]

Well we got it sorted.

There were two possible oil plugs. Metric or standard, and it was the two he tried.

The one that went in loose was M12-1.75. We theorized maybe it had already been re-tapped to a different size and that we'd have to try various hardware bolts to spec it.

Fortunately there was one called "M12-1.75 Oversize". That seems counterintuitive to me, but we gave it a shot and it was the right one.

No need to retap because the first one wasn't forced. It went all the way in finger tight.

You really do learn something every day.

 

[Doubeleive]

Well we got it sorted.

There were two possible oil plugs. Metric or standard, and it was the two he tried.

The one that went in loose was M12-1.75. We theorized maybe it had already been re-tapped to a different size and that we'd have to try various hardware bolts to spec it.

Fortunately there was one called "M12-1.75 Oversize". That seems counterintuitive to me, but we gave it a shot and it was the right one.

No need to retap because the first one wasn't forced. It went all the way in finger tight.

You really do learn something every day.

YA I had a 00 nbs, you have to be sure to specify that when ordering parts or shopping online it can be a real pain sometimes because even the parts guys have no clue.
my solution was to just shop 2001 and that usually sorted it out pretty well because the parts are the same and by then GM had stopped the OBS confusion..

 

[adriver]

Well we got it sorted.

There were two possible oil plugs. Metric or standard, and it was the two he tried.

The one that went in loose was M12-1.75. We theorized maybe it had already been re-tapped to a different size and that we'd have to try various hardware bolts to spec it.

Fortunately there was one called "M12-1.75 Oversize". That seems counterintuitive to me, but we gave it a shot and it was the right one.

No need to retap because the first one wasn't forced. It went all the way in finger tight.

You really do learn something every day.

I've never heard of an "oversize" bolt. I weigh 180lbs with an oversized belly. I can bench 750lbs, undersized. Looked it up on rockauto for a 99 5.7 Tahoe, and shows M12-1.75. I was curious so I looked it up for a 2001 Tahoe 5.3, that is ALSO a M12-1.75. This is DEFINITELY NOT adding up..... What's the chance your friend tried something else? What's the chance they tried some other bolt before going to the auto parts store

 

[HiHoeSilver]

I replaced the one on my OBS 2000 Z71 once. Iirc, it was a Dorman from the HELP section right of the rack. Easy peasy.
I almost always shopped '99 parts for that truck or they would be wrong.

 

[TJ Baker]

I've never heard of an "oversize" bolt.

https://www.napaonline.com/en/p/NDP7041359

 

[adriver]

Oil change is such a simple and quick job to do. What oil did they use, how much, what weight. What would inspire you to have this friend do it, who ended up having this much trouble with a drain plug?

 

[915_Tahoe]

GM#11562588
PLUG, OIL PAN DRN (M12X1.75X25) (W/SEAL) (EXC MAGNET) (W/HEX HEAD)

 

[khigh]

I had him do it because I put Seafoam in it and it needed to go 100 miles.

The oil was full synthetic. The filter was a Wix Gold. Got too much in it for a cheap oil and filter.

The prevailing theory is that the neighborhood loose nuisance dog made off with the bolt wrapped in a paper towel while it was draining. It's really the only thing that satisfies Occam's Razor.

I'm not 100% sure it came from the factory with the "oversize" designation. It could have been rethreaded, but it was absolutely the correct bolt.