E85 3.0si manual transmission and diff fluid change: do I HAVE to get new plugs?

EintrachtAdler · 12-13-2023, 08:57 AM

I’ve been doing my research to prepare for this job and cannot find anything definitive. I have 2 unopened Redline MTL bottles and 2 unopened Redline diff fluid bottles from a prior car that I want to swap in but would love to not buy the drain plugs if I don’t have to. They’re about $20 per plug right now. What is the consensus on reusing the plugs? I know the ones on the trans have the green seal. Could I avoid any issues with changing the plugs if I just suck the oil out of the fill plug and fill from there so the drain plug was never touched? And for the diff, do the plugs there even have any gaskets that would require new plugs?

For anyone that has reused the plugs, have you had any issues or leaks?

Thanks!

pungo · 12-13-2023, 09:48 AM

The worst thing you could do is suck the oil out of the trans through the fill plug since you want to flush stuff in the bottom of the trans out by draining from the drain plug

.
Plus, do it when it's hot so the fluid is thinner and flows out better.

I've reused the plugs in a pinch without issue, though I usually change them. The seal gets flattened over time as well as they're soft so unless it comes out easily, the hex may get a little worn.

My records show they were ~$10 for OEM plugs a few years back, you don't have to get them from the dealer.

If you reuse them, use some brake clean to clean the seal, then apply a thin film of RTV over the seal and let it dry while changing the fluid.

bosstones · 12-14-2023, 08:32 AM

Not sure which version or transmission type you have but a quick, arbitrary look shows anywhere from $6 to $19 for a drain plug for a 3.0si and M, respectively.

For $20, I'd change it for the gasket. Overpriced, perhaps, but $20? That is cheap insurance to know I have a good seal. It's up to you if you want try to re-use or make up your own solution. For << $20, that's a no-brainer.

Like Pungo indicated, why would you not drain the crap out of the pan? Unless you you need the added....viscosity.

wdb · 12-14-2023, 04:50 PM

I didn't like Redline trans fluid in my Z4MC. I don't see any reason not to replace at least the drain plugs; you only do the job once every 30K miles or so, seems silly not to do it well.

belcom · 12-15-2023, 11:04 AM

Quote:

Originally Posted by wdb

I didn't like Redline trans fluid in my Z4MC

Why? What happened?

3798j · 12-15-2023, 11:40 AM

RedlineOils isn't recommending their MTL. Their website lists D4 ATF for Z4 6spd manuals ...(D4 ATF for the M).

wdb · 12-15-2023, 12:37 PM

Quote:

Originally Posted by belcom

Why? What happened?

Quote:

Originally Posted by 3798j

RedlineOils isn't recommending their MTL. Their website lists D4 ATF for Z4 6spd manuals ...(D4 ATF for the M).

Yep, and that's what my car had in it from the PO. It didn't shift well cold and the infamous 3-2 downshift was nasty. I went with Royal Purple and both improved.

belcom · 12-15-2023, 01:51 PM

Quote:

Originally Posted by wdb

Yep, and that's what my car had in it from the PO. It didn't shift well cold and the infamous 3-2 downshift was nasty. I went with Royal Purple and both improved.

I got purple in the transmission as well. Seems it works well for me too. But what do you think about Red Line 75w140 gear oil for the M diff? Got purple in there now but its been a while and will be changing diff fluid in spring time. Already have Red Line on the shelf for that based on a recommendation from a buddy.

wdb · 12-15-2023, 04:25 PM

Quote:

Originally Posted by belcom

I got purple in the transmission as well. Seems it works well for me too. But what do you think about Red Line 75w140 gear oil for the M diff? Got purple in there now but its been a while and will be changing diff fluid in spring time. Already have Red Line on the shelf for that based on a recommendation from a buddy.

I used BMW oil in the differential. Wanted to treat the LSD properly.

GuidoK · 12-16-2023, 01:46 AM

Quote:

Originally Posted by EintrachtAdler

For anyone that has reused the plugs, have you had any issues or leaks?

Thanks!

I've reused the plugs on both the gearbox and the different (multiple times on that one even) and had no issues.

GuidoK · 12-16-2023, 01:47 AM

Quote:

Originally Posted by wdb

I used BMW oil in the differential. Wanted to treat the LSD properly.

But BMW doesn't make oil 😉

tomjonesBT33 · 12-16-2023, 03:02 PM

I agree that it’s best to spend the money and change the plugs. Cheap insurance.

I use Redline in both my Z4MR trans and rear diff and have been very happy with the results. To each their own I suppose

cbpip · 12-17-2023, 08:55 AM

Plugs are relatively inexpensive, why not replace. Reusable absolutely.

Using the Ford Fluid, works great allows synchros to mesh as they should. Tried the Redline stuff, too thin synchros didn't like it. Not a fan of RP products due to inaccurate sheer strengths.

https://www.amazon.com/gp/aw/d/B000N...b_b_asin_title

Efthreeoh · 12-25-2023, 02:35 PM

Over one million miles driving 5 different BMWs 400K, 250K, 197K, 135K, and 120K. Multiple diff and trans changes on each. I've never replaced a drain or fill plug. Waste of money and internet myth they need to be replaced.

My advice is make sure you have the tools on hand to reach and can remove the fill plug FIRST before opening the drain plug.

12-13-2023, 08:57 AM	#1
EintrachtAdler Registered 0 Rep 4 Posts Drives: E85 Join Date: Oct 2023 Location: Montana iTrader: (0)	E85 3.0si manual transmission and diff fluid change: do I HAVE to get new plugs? I’ve been doing my research to prepare for this job and cannot find anything definitive. I have 2 unopened Redline MTL bottles and 2 unopened Redline diff fluid bottles from a prior car that I want to swap in but would love to not buy the drain plugs if I don’t have to. They’re about $20 per plug right now. What is the consensus on reusing the plugs? I know the ones on the trans have the green seal. Could I avoid any issues with changing the plugs if I just suck the oil out of the fill plug and fill from there so the drain plug was never touched? And for the diff, do the plugs there even have any gaskets that would require new plugs? For anyone that has reused the plugs, have you had any issues or leaks? Thanks!
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12-13-2023, 09:48 AM	#2
pungo Colonel 880 Rep 2,547 Posts Drives: Z4MC-X3-35i-525i, Corrado G60 Join Date: Nov 2007 Location: MD iTrader: (5) Garage List 2011 BMW X3 x35i [0.00] 2001 BMW 525i [0.00] 2007 BMW Z4 M Coupe [8.76]	The worst thing you could do is suck the oil out of the trans through the fill plug since you want to flush stuff in the bottom of the trans out by draining from the drain plug . Plus, do it when it's hot so the fluid is thinner and flows out better. I've reused the plugs in a pinch without issue, though I usually change them. The seal gets flattened over time as well as they're soft so unless it comes out easily, the hex may get a little worn. My records show they were ~$10 for OEM plugs a few years back, you don't have to get them from the dealer. If you reuse them, use some brake clean to clean the seal, then apply a thin film of RTV over the seal and let it dry while changing the fluid.
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12-14-2023, 08:32 AM	#3
bosstones Lieutenant Colonel 1154 Rep 1,543 Posts Drives: o_0 Join Date: Mar 2008 Location: Suburbia iTrader: (0)	Not sure which version or transmission type you have but a quick, arbitrary look shows anywhere from $6 to $19 for a drain plug for a 3.0si and M, respectively. For $20, I'd change it for the gasket. Overpriced, perhaps, but $20? That is cheap insurance to know I have a good seal. It's up to you if you want try to re-use or make up your own solution. For << $20, that's a no-brainer. Like Pungo indicated, why would you not drain the crap out of the pan? Unless you you need the added....viscosity. __________________ - Jeff bosstones' flickr
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12-14-2023, 04:50 PM	#4
wdb dances with roads 4732 Rep 4,096 Posts Drives: '07 E86, '02 996, '95 Seven Join Date: Jul 2015 Location: the perimeter iTrader: (4)	I didn't like Redline trans fluid in my Z4MC. I don't see any reason not to replace at least the drain plugs; you only do the job once every 30K miles or so, seems silly not to do it well.
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12-15-2023, 11:40 AM	#6
3798j Lieutenant Colonel 11424 Rep 1,795 Posts Drives: E86 3.0si Join Date: Oct 2011 Location: Susquehanna Valley iTrader: (0) Garage List '55 Ford F100 [0.00] '08 Z4 3.0SI [8.50] '66 Triumph TR4A [0.00] '85 Corvette [0.00] '64 Corvette [0.00] '68 Triumph GT6 [0.00] '19 VW Golf "R ... [0.00]	RedlineOils isn't recommending their MTL. Their website lists D4 ATF for Z4 6spd manuals ...(D4 ATF for the M).
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12-16-2023, 03:02 PM	#12
tomjonesBT33 Second Lieutenant 177 Rep 267 Posts Drives: 2006 Z4 M Roadster Join Date: Oct 2019 Location: VA iTrader: (0) Garage List 2012 BMW X5M [0.00] 2006 BMW Z4 M Roadster [0.00]	I agree that it’s best to spend the money and change the plugs. Cheap insurance. I use Redline in both my Z4MR trans and rear diff and have been very happy with the results. To each their own I suppose __________________ 2006 Z4 M Roadster - Silver Grey Metallic 2011 X3 xDrive28i - Deep Sea Blue Metallic 2012 X5 M - Monte Carlo Blue Metallic 2017 X1 xDrive28i - Alpine White
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12-17-2023, 08:55 AM	#13
cbpip Private First Class 151 Rep 198 Posts Drives: BMW Z4C 3.0si 3 pedal Join Date: Nov 2020 Location: MD iTrader: (0) Garage List 2007 BMW E86C [0.00]	Plugs are relatively inexpensive, why not replace. Reusable absolutely. Using the Ford Fluid, works great allows synchros to mesh as they should. Tried the Redline stuff, too thin synchros didn't like it. Not a fan of RP products due to inaccurate sheer strengths. https://www.amazon.com/gp/aw/d/B000N...b_b_asin_title
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12-25-2023, 02:35 PM	#14
Efthreeoh General 17317 Rep 18,740 Posts Drives: The E90 + Z4 Coupe & Z3 R'ster Join Date: May 2012 Location: Virginia iTrader: (0)	Over one million miles driving 5 different BMWs 400K, 250K, 197K, 135K, and 120K. Multiple diff and trans changes on each. I've never replaced a drain or fill plug. Waste of money and internet myth they need to be replaced. My advice is make sure you have the tools on hand to reach and can remove the fill plug FIRST before opening the drain plug. __________________ A manual transmission can be set to "comfort", "sport", and "track" modes simply by the technique and speed at which you shift it; it doesn't need "modes", modes are for manumatics that try to behave like a real 3-pedal manual transmission. If you can money-shift it, it's a manual transmission. "Yeah, but NO ONE puts an automatic trans shift knob on a manual transmission." Last edited by Efthreeoh; 12-25-2023 at 02:41 PM..
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