Freeze plug - use sealant?

[JC220]

Posted in off topics as this relates to my 190E 2.5-16

The car has one freeze plug pushed out slightly on the rear of the cylinder head near cylinder 4 exhaust port.

I will proceed to remove the exhaust manifold to get access to the old plug.

For the new plug installation, I will use a close fitting socket and gently tap it home to the same depth as the others.

But should I use some sort of sealant or retaining compound? Or would that be a bad idea and may stop the plug from doing its job in the future albeit ill always have correct antifreeze in the car unlike previous owner.

 

[gerryvz]

I have never replaced a freeze plug myself, but I have heard in the past that one should use a light coating of aviation or automotive gasket sealer, Loctite sealant or other appropriate sealer on the edge of the freeze plug. Generally though, it should be a very tight "press fit" into the hole.

 

[500AMM]

I've never done any freeze plugs, but to my understanding it is meant to be a metal to metal sealing without any sealant. I'm sure that works fine on a new assembly, but the second time I would use sealant. I saw somewhere that Permatex 81160 High-Temp Red RTV was recommended.

 

[JC220]

I've never done any freeze plugs, but to my understanding it is meant to be a metal to metal sealing without any sealant. I'm sure that works fine on a new assembly, but the second time I would use sealant. I saw somewhere that Permatex 81160 High-Temp Red RTV was recommended.

View attachment 221611

Thank you, I asked a large core plug specialist also and they advised I should use Dirko sealant on replacement plugs so I have a tube of that anyway.

 

[JC220]

I eventually got to removing the 2.5-16 exhaust manifold. Bit of a nightmare job to be honest as the space was super tight, it took around 5 hours to remove but got there in the end.



The bad freeze plug:



Just one of them was half hanging out so the old girl must have frozen at some point:



Removed and gentle cleaning of the 'ole with 600 grit:



I had purchased an aftermarket but "upgraded" 19mm stainless steel freeze plug. EPC said 19mm freeze plugs. As @gerryvz mentioned above they should be an interference fit. So the spec sheet said 19.37mm for interference fit on this new plug:





I added a light smear of Dirko and used a deep socket that fitted nicely but not too tight to drive it home. However, the new plug would not drive all the way in. I was using a fairly heavy copper hammer and it was bouncing off the socket and freeze plug stopped the last 2 or 3mm. I stopped for fear of cracking the head or something bad, it felt wrong. Too tight.

I did leave it there and test the water jacket and it was holding as was the (unknown to me) engine block and head

So I removed the new malfitting plug to be safe. A die grinder was required to weaken it and a punch to start an edge on it. I removed it successfully with zero damage to the head.

Tomorrow I will phone my MB dealer and see if I can order all 5x or 6x of them as it was so difficult to remove the headers I want to replace them all now and be done with it. I'll make sure this one goes to plan before punching out any of the other old freeze plugs behind the exhaust manifold.

To remove you use a pointed sharp punch and hit one point on the edge. It will spin in the hole so you can grab an edge and pull it out. These do seem to corrode so approaching 40 years old now we may start seeing freeze plug failures if antifreeze isnt changed regularly.

 

[JC220]

My MB dealer advised this morning that the 19mm freeze / core plugs are NLA

I have ordered a set of 5x 19mm core plugs from a different supplier this time in the hope ill have better luck fitment wise than the last stainless one I tried. The plan is still the same, to first ensure I can get a good fitting and sealed plug in the open location at the moment. If it goes to plan then I will still consider proactively replacing the others.

 

[JC220]

Update - I received the new core plugs today, much faster than expected! This one fitted well so I was right to stop with the other first one it was clearly too large than spec.



Pressure tested and zero leaks. So I am going to renew the other plugs here one by one before refitting the exhaust manifold.

I also found a leak at the thermostat housing and traced that to no stat or seal fitted! A bolt snapped too.



I removed the old broken bolt and cleaned all threads with a tap. I had new bolts and stat on the shelf so sorted that.



Then the old radiator is also leaking so Ill order a new radiator and go from there. Possible heater core leak also which aparantly is common on the W201 chassis. May be an O ring if I am lucky ill check that first.

Lots of leaks but its still progress anyway.

For posterity here are the freeze plug measurements I took and the first one of 5x fitted fine.