Head Gasket Bed in procedure(?)

[JC220]

Hi all,

I have replaced many a MB head gasket over the years - m119 included and thankfully have had no issues afterwards.

I am currently replacing the head gasket in my S320 m104. (But Subject matter applies to m119 and all MB engines of this era)

These composite head gaskets come with a red sealant pre applied to them. I believe this is heat activated.



My question here is there any thoughts on best practice regarding the first running of the engine?

Should you leave the radiator cap off so as to keep coolant system pressure down and get engine to operating temp and shut off? Does this risk air pockets in coolant system? (Probably yes but maybe using vacuum coolant filling tool would safeguard against that)

I typically have left rad cap on and burped the system as the car is on first warm up post head gasket replacement. And as soon as it reaches operating temperature I shut it off and gently loosen off the coolant cap in order to take pressure off the coolant system and allow the engine to cool off fully overnight before replacing rad cap.

Any thoughts or opinions appreciated. I may have asked and answered my own question here since I have never had issues before but just seeing if anyone else has considered this too.

 

[gsxr]

Joe, I believe the red stuff is silk-screened RTV-type stuff. I don't know if it's heat activated though. Maybe @Klink could pop in and let us know!

The FSM just says to not pressure test the cooling system until after the new head gasket has reached operating temp. I would fire it up and drive under light load, and after a while at operating temp, let it cool overnight. Top off coolant if needed and then drive more, ahem, vigorously. I wouldn't worry about keeping the system pressure near zero though, but I would try to keep the temps <90°C if possible.

 

[gerryvz]

Check out my procedure for the M104 Top-End rebuild.

Link to the relevant post is below.

HOW-TO: M104 / W124 Top-End Rebuild [Cylinder Head / Gasket] | "HOW-TO" Tutorial Articles

Re: M104 / W124 Top-End Rebuild :update: Today (Sunday) I worked in two different sessions, totaling around 7 hours. The good thing is that I made a lot of progress in terms of the "little" jobs that all add up to movement toward getting the job completed. I would say that I'm now 80-85%...

www.500eboard.co

 

[JC220]

Check out my procedure for the M104 Top-End rebuild.

Link to the relevant post is below.

HOW-TO: M104 / W124 Top-End Rebuild [Cylinder Head / Gasket] | "HOW-TO" Tutorial Articles

Re: M104 / W124 Top-End Rebuild :update: Today (Sunday) I worked in two different sessions, totaling around 7 hours. The good thing is that I made a lot of progress in terms of the "little" jobs that all add up to movement toward getting the job completed. I would say that I'm now 80-85%...

www.500eboard.co

Thanks Gerry and I see you had the same thoughts as myself try and keep the coolant pressure off the new gasket for first start up.

Good note Dave pointed out also ref no pressure testing. I would say it is a good idea to not just put coolant cap on and run as Is for first heat cycle to give the gasket the best chance.

 

[gerryvz]

There was some further discussion (and here too) about this topic in the posts following the one I linked in my M104 thread.

All of the M117 and M104 gaskets I've seen have the red bead on them.

 

[JC220]

Here is another opinion much the same: