This thread is more about the "Use Once and Replace" drain plug on the oil tank, but before that - Today I did an interim oil change on my CPO 2017 AMG GT that I purchased in October. Car has less than 21000 miles, and I am NOT one who dumps oil every 3000 miles, but since I had no history with this car, I thought I'd do one oil change even though the onboard service clock has a lot of time left before the next service. This creates a benchmark for me.

Now to the drain plug. There has been some conversation in the past, on a couple of threads about reusing the plug vs. replacing it each use per the MB spec. Originally, when I thought the plug was a traditional threaded plug, I fell into the camp that the only reason MB called for a replacement each time was because "engineering practice" calls for O-Ring seals to be "one use" replace each use and since the O-Ring is not sold as a separate part, MB specs the entire plug be replaced.

Based on that, I was in the camp that a person with reasonable technical skills/knowledge could examine the O-Ring and "make a call" to reuse it (no harm, no foul). However, now that I've been able to look at other parts of the plug design, there is a second, maybe a more serious reason to change the plug (renew) after a one time use. That concern lies in the cam lock design of this PLASTIC plug.

The cam lock (quarter turn) uses a detent lock to secure the plug in place. This can be felt when installing a new plug. It is the last 1/64th of the turn that feels like a slight resistance, then the plug seats. The issue that caught my attention was the detent. Since the plug is a molded plastic, including the detent, it becomes deformed after it is installed and then removed at the next oil change. So, the NEW concern for me is whether the detent can secure the plug if used a second time, as well as a brand new plug. Add this to the O-Ring and one needs to consider two possible failures when reusing the plug.




In the pic above, the old drain plug is on the left, brand new, unused plug on the right. Take note and compare the detents (old one on left, new one on right). On the used plug the detent is noticeably deformed. If I reused the old plug (and I was paying attention) the resistance I should feel the last 1/64th of a turn will be a lot less than with a new plug. This means the old plug will not necessarily lock with the same resistance and could possibly (probably extreme circumstances) vibrate past the detent. If that happens, the 1/4 turn plug would fall out in an instant.

To mitigate that possibility, there is a second lock. Notice that the mating pin that rides in the cam groove will cause a little bit of a secondary lock when the pin is in its final resting place. It's not very much of a secondary notch, but it is something, and heat/pressures in the tank will want to force the plug down and seat the pin more into that final stop.

Conclusion - I'm now at the place that for $12, I'd rather just replace this plug new each time. If you decide to reuse it, please make two inspections now -

Make sure the O-Ring is good,
Make sure the Detent meets your satisfaction it can hold the plug in place. This can be tested two ways - Visually, and by feel of the resistance in the last 1/64th turn when it locks. If the plug is used a third/ fourth time or more, my assumption is that with each reuse, the detent will be further and further deformed.

 

Excellent explanation!

 

Thank you sir...hopefully it helps some other DIYers....

 

Yes good write up. Even when new still feels sloppy. My c7 z06 with sump tank has regular m12 thread which is reassuring to not leak or fall out prematurely. I changed oil on my gts and now the gtr and never replaced it. As long as o ring was in good shape, back in. Never a drip or worry, prolly pick one up next time tho.

 

Nice photo. No way would I re-use a plug like that. O-rings degrade over time, and the plastic plug is analogous to a torque-to-yield bolt. The plastic notch can be seen deformed in the photo.

The plug costs $xx. The engine costs $yy. $yy >> $xx.

Even if a leak is experienced, and engine failure is avoided, how much is your time worth to pull the leaking plug that should have been replaced with new, drain at least some of the oil, install a new plug, and pour in some or all of the oil? Then you have the missus upset because there is oil on the garage floor or driveway.

My time alone is worth far more than the cost of the plug. Avoiding an upset missus is priceless.

 

Ha haa...You made me laugh! I have one of those Missuses too!!

 

Great information, I will definitely be using a new plug for each oil change, I had also assumed it was threaded and would replace a crush washer, but knowing its a cam lock and o-ring, I will always change it.

Years ago I did a timing belt and balance shaft removal on a 4g63T (my car) and put it back together re-using a couple of o-rings. After I was done I had an oil leak from the oil pump castle nut, which took 4 hours to get back into to replace a $2 o ring, I had to redo the belt tension, re-align the cams, take half the top of the darn motor off. I should have used a new 0-ring it the first time...

 

Good info.

 

I apologize for asking such trivial questions. I have looked at the pdf’s in “Let’s talk Maintenance” and I have searched FCP Euro, Pelican Parts, AutoHauz, ECS Tuning, MB Parts and more. I thought I had it figured out, ordered the part from OEMMBparts and it’s the wrong part.

What is the part number of the one-time-use reservoir drain plug? And, where may I purchase a few?

Thank you in advance.

I have my Schedule 40 PVC 1&1/2” pipe cut down on a lathe and ready to go.

DaveM

 

Only one left here...everyone has been buying them by the "twos"

These copper washer kits MIGHT have a washer that fits:


Or this one if you want even more copper:

UPDATE/EDIT - I want to add a disclaimer, after some discussion, and since I have not purchased either of the above variety packs of copper washers, the washers closest to the 14 mm washer size might or might not fit BC of a taper that appears at the base of the threads on the drain plug and before the landing where the copper washer fits. I've only used the factory washers in my personal experience and happened to notice the taper on the last change I did. Unfortunately, I didn't measure the washer (ID/OD) nor did I measure the base of the taper. So, just a Caveat Emptor.

 

Thank you so much. Parts ordered!

 

You're welcome, my pleasure!

 

These are cheaper... and bonus I find them in the bathroom, sofa cushions and just about everywhere else I look in my house!

 

Hello.

For your information, in France, the part number is not available from the 1780140300 , but using the 0009909518 , you can find the FEBI 48401 or ELRING 233.451
https://www.piecesauto.fr/febi-bilstein-9797499.html
https://www.piecesauto24.com/elring/7924064

I just ordered the Elring, hope it could be the same.

Many thanks for this topic really clear and helpful

 

I just vacuum the oil out of the tank. Dont have to touch the plug.

 

How many litres come out when you vacuum the tank, and then how much comes out the sump drain plug just to know how much to put back in. Do you warm up the oil first to the specified temperature for the coolant?

 

The complete is around 7 L to begin to start. Make the appoint after the temp is higher than 100°C if the gauge is too low.

 

Descarts I get out about the same amount that I got out when I would use the drain plug in the first two oil changes. Yes I do it when the engine is fully warmed up, and yes I remove the sump plug and get about a quart out of the sump. The refill is like said above, around 6.5 quarts to 7 quarts.

 

Thank you, Sir.

For the Copper Washer, is the 14mm for the Inner, or Outer Diameter?

 

Hi MBNRG,

Inner for the washer - 14 mm is the diameter of the drain plug. The actual washer ID might be a little larger than that as there is a slight taper after the thread ends and before the flat where the washer seats against the head of the drain plug.

Best,

 

Hi,

metric washers are normally 0.5 mm larger than the associated thread.

Best regards

Stenzel

 

Hi Stenzel,

Yes I agree that with any standard sized "dimensional" washers whether metric or not, they are "nominal" IDs sized to match a given standard thread size and will be larger than the nominal thread dimension.

However, what I was conveying to MBNRG, the drain plug is 14 mm, but there is a "taper" past the 14 mm thread and before the washer landing that would make the ID of the copper washer larger than 14mm (or better said, non-standard).

Here is a pic of the drain plug and washer. If the threads are 14mm, (even nominal), the washer will likely have a non-standard ID and more than a standard 14mm washer.

 

TY. And the Outer Diameter should be 18mm, not the 20mm that is included in certain kits, correct?

 

Hi MBNRG,

In all the times I've changed oil on this platform I've always had the factory washer. I don't have first hand experience how closely the washers in the variety packs would be a perfect match. I also cannot verify the OD. I don't have access to a new or used one right now. On a soft crush washer, the OD would only be a problem if it was larger than the drain plug head as it wouldn't seat in the recess.

 

Just for kicks. I measured a brand new oem sealing ring. ID = 14.35mm and OD = 19.83mm