Panoramic Sunroof Grease Paste

256 Views 3 Replies 3 Participants Last post by BigJase88, 10 d ago

jcdenton

Discussion Starter · 11 d ago

My sunroof is making squeaky noises and it made me look into the infamous MB Synthetic Grease for over $100, or to be more specific into its alternatives because I'm not paying that much for synthetic grease. I have read numerous posts about what people use as alternative and all of them sound experience-based e.g. "I have used that and never had issues". While that might be true, I am still curious about MB Grease specifications and what makes it to special.
Working in the automotive industry I know that OEM's don't make stuff themselves; they write specifications and other companies make stuff for them according to the spec. One such supplier usually works for the whole automotive market and not just one OEM. Accordingly, for cost optimization one single product could meet several specs from different OEM's: same product used for Ford, GM, MB, BMW, VAG, etc.

Having said that, if we look closely at the Maintenance Instruction AP77.20-P-7732CW "Panoramic sliding roof - clean and lubricate guide mechanism" it refers to Synthetic grease, sliding roof 500 g, DB supply specification 6827.60.
A quick internet search leads me to the product called Klüber POLYLUB GLY 151 Special synthetic lubricating grease. I am sure there are more and I will look into it later, but for now let's have a close look at the composition and datasheet of this product:

The product series POLYLUB GLY 151 is based on a synthetic hydrocarbon oil, mineral oil and special lithium soap. It comprises three lubricating greases reducing friction and wear in plain bearings, slideways and small gears made of plastic.
The lubrication of plastics is special in a number of ways. As the behaviour of metals and plastics differs in many aspects, the lubricants' properties have to be adjusted to the plastic.
Compared to many metals, plastics are relatively soft. Solid lubricants, which may achieve a positive effect on many metal friction points, can have a negative or no effect at all on plastic lube points. With the formulation of POLYLUB GLY 151, Klüber Lubrication offers products which are free of solid lubricants, and offer good adhesion.
...
Approved by many renowned manufacturers and suppliers in the automotive industry, e.g. DBL 6827.60, VW TL 52147, Ford WSD-M1 C244-A, Brose Fettgruppe 11 and many more

Based on just this specification it is safe to assume that this is the correct alternative product for MB Grease. It does not contain silicone, so the recommendations to use silicone spray on your sunroof are sub-optimal.
Other products from Molycote with similar composition say that lithium soap is used as a binding agent, so it doesn't participate in lubrication. That leaves us with a mix of hydrocarbon and mineral oil that do the actual lubrication.

This post is not finished and I will try to make a list of compatible products, to be available for fellow MB owners, but let me know what you think guys!

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ans

· #2 · 10 d ago

just had my one done at dealer as part of a main service, but will be interested to here what other options are available

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jcdenton

Discussion Starter · #3 · 10 d ago

So far I've found out that Klüber POLYLUB seems to be the actual product sourced by MB. It is different from most other synthetic greases by being a mix of synthetic hydrocarbon and mineral oil, whereas similar products from Molykote are only synthetic hydrocarbon (PAO). The other difference is that it doesn't contain solids (e.g. PTFE). Some Molykote products recommended for sunroof applications do contain PTFE which can eventually erode the plastic, but it's mainly a question of thousands of opening / closing cycles of your sunroof. Personally I wouldn't care much about eroding my sunroof guides, I don't use it that much.
Silicone is definitely a no-go because it attracts dust. One of the requirements for sunroofs is water tightness, and having a contaminated interface means you get leaks. It also means that a buildup of contaminants can prevent the sunroof from closing fully, resulting in a broken drivetrain or more leaks.

I've compiled the table below to compare several greases for plastics - some of them are for sliding guides, some are for gears:

Property	DB 6827.60 / Klüber POLYLUB GLY 151	POLYLUB GLY 501	POLYLUB GLY 801	Molykote EM-50L	Molykote PG-75	Molykote G-1068	Molykote G-1057	Molykote G-1051	Molykote G-1033	Molykote G-1021
NLGI grade, DIN 51818	1	1	1	1	2
Chemical composition, type of oil	mineral oil	mineral oil	mineral oil	--	mineral oil	--	--	--	--	--
Chemical composition, type of oil	synthetic hydrocarbon oil	synthetic hydrocarbon oil	synthetic hydrocarbon oil	synthetic hydrocarbon oil	PAO	PAO	PAO	PAO	PAO	PAO
Chemical composition, thickener	special lithium soap	special lithium soap	special lithium soap	lithium soap	lithium soap	lithium soap	lithium soap	lithium soap	lithium soap	lithium soap
Chemical composition	UV additive	--	--	--	PTFE	additives	--	Additives	--	--
Lower service temperature	-50 °C / -58 °F	-40	-40	-40	-40	-40	-50	-50	-43	-55
Upper service temperature	150 °C / 302 °F	150	130	150	130	120	150	120	125	150
Color space	beige	beige	beige	white	beige		Semi- transparent	white	Off-white, beige (smooth, buttery)	white
Density at 20 °C	approx. 0.85 g/cm³	0.88	0.88	0.84	0.86
Worked penetration, DIN ISO 2137, 25 °C, lower limit value	310 x 0.1 mm	310	310		270			308	294	265
Worked penetration, DIN ISO 2137, 25 °C, upper limit value	340 x 0.1 mm	340	340		300	330	348	334	302	295
Kinematic viscosity of the base oil, DIN 51562 pt. 01/ASTM D-445/ASTM D 7042, 40 °C	approx. 150 mm²/s	500	730	1050	32				31.2
Kinematic viscosity of the base oil, DIN 51562 pt. 01/ASTM D-445/ASTM D 7042, 100 °C	approx. 18.5 mm²/s	40	60						6.1
Shear viscosity at 25 °C, shear rate 300 s-1, equipment: rotational viscometer, lower limit value	1 800 mPas	3000	4000
Shear viscosity at 25°C, shear rate 300 s-1, equipment: rotational viscometer, upper limit value	3 000 mPas	5000	8000
Corrosion inhibiting properties of lubricating greases, DIN51802, (SKF-EMCOR), test duration: 1 week, distilled water	<= 1 corrosion degree	<= 1 corrosion degree	<= 1 corrosion degree		1–2
Oil separation, ASTM D 6184 [FTMS 791 C 321], after 30h/100 °C	<= 6 % by weight	<= 4 % by weight	<= 4 % by weight
Drop point, DIN ISO 2176	>= 250 °C	>= 250 °C	>= 250 °C	195	190	193	234		210	213
Oxidation stability of lubricating greases, ASTM D942, 100 h/99 °C, pressure drop	<= 0.3 bar	<= 0.3 bar	<= 0.3 bar	0.2 bar
Water resistance, DIN 51807 pt. 01, 3 h/90 °C, rating	<= 1 - 90	<= 1 - 90	<= 1 - 90
Minimum packaging size	400 g or spray 400 ml	1 kg	1 kg can, 400g cartridge	1 kg	15 kg	16 kg	1 kg	16 kg	16 kg	17 kg
Manufacturer recommends for sunroof lubrication	Yes	Yes	Yes		Yes				Yes

This article explains how to interpret the parameters in the table.

A special purpose lubricant, damping greases are formulated with high-viscosity oils, which create a stickier grease with higher internal shear resistance. As parts move and shear the damping grease, higher internal shear resistance "damps" noise. It also controls how fast or slowly a part will move and ensures that when power stops the motion does too: no coasting or backlash. Heavier loads require higher viscosity oils to ensure enough lubricating oil film remains between two surfaces. <source>

I planned this as a scientific post and I apologize if you didn't find the answer which $20 replacement to use

Some people say using BMW or VW grease is cheaper and I will look into that.

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BigJase88

· #4 · 10 d ago

I used whatever was in the grease gun at work.

Cost nothing

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