m103 head gasket...use loctite 5900 on it?
 

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!

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.

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.

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.

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.

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

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