Now that I have everything open and accessible I think it's a good idea to replace some of the freeze plugs on the psg side (4 total), they are rusty and have traces of coolant underneath them. It looks like a straightforward job, but like to hear some input from people who have done this job. The Mercedes Service Manual tells to use a sealant, is this really necessary? Anything else I have to be aware off?

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

Jorn, I've changed freeze plugs but not specifically on a 103 and I don't recall changing them on a Benz at all for that matter. Yes sealer is a good idea to prevent leaks since new plugs often leak/weep. They may stop leaking after numerous heat cycles.

Clean the bore sealing edge as much as possible and keep the new plugs in the freezer at least overnight to contract them some and don't take them out of the freezer until seconds before the install.

Try to block the water jacket with a rag to prevent the old plug from falling in and getting lodged.

I'd try to use OE plugs to increase the chance of getting the correct size and material.

Did you get a new hose to go from the water pump/t-stat to the head? Remember to put that on the water pump and slide it as far on the pump as possible BEFORE putting installing the head. Use the highest quality hose you can get.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Thanks again! I installed the water pump yesterday, with the head off it’s not that hard of a job after the lowest bolts are off and I did install the short hose (new) immediately. Would be a nightmare forgetting that one!

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

Do that rear most freeze plug that's threaded while you're at it. I just did mine it was a pain.

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"It's what non-car people don't get. They see all cars as just ton-and-a-half, two tons of wires, glass, metal and rubber. That's all they see. People like you or I know, we have an unshakable belief that cars are living entities..... You can develop a relationship with a car, and that’s just what non-car people don't get."
-Jeremy Clarkson

You want to torture me? Did you get the plug from the dealer and did you use sealant?

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

Yes sealant on them all .The threaded one is for the block heater .And it can be a problem to replace it . And the idea of keeping the welsh plug in the cooler is a good tip . You knock the old plug in on one side, so it turns to enable you to pull it out with pump pliers .A very good wire brush on the dremel or drill and clean out the slot in the block that the plug sits in .Good luck

What sealant to use?

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

I didn't use sealant on the threaded plug. It has an oring on it to seal. I did put a little bit of teflon tape on the threads though.

__________________
"It's what non-car people don't get. They see all cars as just ton-and-a-half, two tons of wires, glass, metal and rubber. That's all they see. People like you or I know, we have an unshakable belief that cars are living entities..... You can develop a relationship with a car, and that’s just what non-car people don't get."
-Jeremy Clarkson