As I am mentally preping to do the head gasket on the 89 300SE, Should I use the loctite 5900 on the block & head, as well as the timing cover & seals?

NO! The OE gaskets have sealant around all needed areas!

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Is there a "rule of thumb" when to use and when not to use the Black MB gasket sealant or Loctite 5900? I never use any sealant on rubber gaskets such as rubber transmission pan gaskets or rubber valve cover gaskets - only torque to spec; but what about other areas?

I however did use sealant on the upper timing covers and around the camshaft position solenoids on my M119 engine.

Should the sealant be used on other gaskets such as water pump gaskets, oil pan gaskets, etc and like?

I'm not a mechanic by trade, but I attempt many DIY projects.

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Russell McMahon
Tulsa, OK
2001 CLK 320
1992 400se
1993 400e
2000 320ML

My thinking is to use the loctite on the exterior edges of the block and head.
This is where the gasket has a tendency to fail and leak continually.......???
Anyone else done this????

Ken, I am thinking the same thing. I am wondering if I can do it as a quick fix.
Where can I buy loctite 5900? Thanks.

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89 300 CE

The sealant is only used for parts that have no gasket, such as the front cover on the M103. Don't use it on the head gasket.

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Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.

I agree with most of you. It is used to seal the metal-to-metal surfaces and gasket corners (or triple points).

I wouldn't use it anywhere on the head gasket. There is always a difference of expansion between the iron and aluminum surfaces, and the gasket has to take up this micro-movement.

I've also seen people use it in addition to elastomer gaskets, such as o-rings. This is a no-no. Again, this interferes with the micro-movement of the gasket, which may need to move while under pressure for a good seal.

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95 E320 Cabriolet, 169K

Never use any sealant on a head gasket, it will cause premature failure. Proper sealant is already on it where needed (also don't buy one and let it sit around with the plastic seal sheet removed for long periods of time -- the sealant will set and cause failures. Leave the gasket sealed until installed).

Never use ANY sealant on rubber seals of any kind. The rubber is the seal, and the cure for a leak is to replace the seal. Valve cover gaskets have a limited life (three years or so, usually), and should always be replaced if the valve cover is removed. Proper installation is critical, else they leak instantly.

More than one engine has been destroyed by excess sealant getting into the oil passages and causing a lubrication failure (ditto for paper towling used to wipe off the oil filter fittings!).

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I have been looking at the StarTuned Magazine and the FACTORY SERVICE BULLETINS posted in PDFs and came across this one last night regarding Loctite 5900 sealant:

Haasman

Attached Files

Oil leakage at front upper seal.pdf (35.0 KB, 324 views)

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