changing/draining coolant in 1970 280SL 4-speed

[Ferrolanoman]

I am about to change coolant (from the ordinary green stuff to the extended life orange version), so a couple of questions to those who've done it before.
1) where's the drain plug (s) for the engine block?
2) how do I drain the coolant from the heater core?
3) do I use distilled water for a 50% mix with the orange stuff or regular tap water or what do you recommend?

many thanks in advance
Ricardo

[Larry & Norma]

Don't think the extended life 'orange stuff' is suitable for older engines.
Read that somewhere

[Ferrolanoman]

Hummm, are you sure? I, on the other hand, have read that the green glycol promotes a galvanic action on the aluminum head leading to corrosion and head gasket problems--thus my reason for wanting to change over. Let's hope for more comments on this.

[jameshoward]

I think the colour is just a colour, ideally to allow one to differentiate between old and new, etc. What is important is that you make sure you have coolant designed to meet the requirements of aluminium. Many here will say that you should use MBs own brand coolant. BASF Glysantin is also suitable and has a type specifically designed for aluminium heads. I went down that route because it was vastly cheaper. I would have used MB's own brand if price weren't an issue, but a few changes of Glysantin over the years has done no visible harm.

There is plenty of info on this site about changing coolant. Tons of it. Read it. Personally, I wouldn't sweat trying to squeeze every ounce of old coolant out of the system. If you intend to flush it, that's different, but just doing a change will give you a good 90% solution (no pun intended). (There is some good info on the site on how to flush the engine if you've having problems with cooling,etc).

If you haven't done this before, or don't know when the coolant was last changed, I'd strongly recommend not using the radiator drain plug. They can become seized and corroded. Too much pressure will result in you tearing the plug and its thread off the rad. That's an expensive mistake to make (as I learnt years ago). A safer option is to remove the large hose jubilee clip at the bottom of the rad and drain it that way. You can't go wrong in that respect. It's how I do it even after an expensive repair.

If you open the heater core when draining the coolant, you'll get most of the coolant. Ensure it's open when you refill and allow the engine to warm up, open the thermostat and circulate into the core/rest of the engine, etc, then top up as necessary after the car has run for a bit. As I said, I wouldn't worry about every last drop of the old stuff. Expect to get in around 8.5 - 9 litres or so at best. (80-90% of capacity).

I'd shell out for distilled water rather than tap water. Tap water mineral content will vary enormously depending on where you reside.

Finally, pay attention to the info on the site about re-filling to avoid an air lock, which is unlikely but possible.

Have fun!

[ja17]

The Mercedes Dealers have pretty decent pricing on anti-freeze, and brake fluid. I also get my Mobil 1 from the Mercedes Dealer for my AMG.  With a discount at Mercedes, I cannot even buy the Mobil 1 oil cheaper at Walmart. The Anti-Freeze and brake fluid  containers have MB part numbers on them.  The anti-freeze is formulated by the Manufacturer for MB engines and is not just re-labeled. The anti-freeze is a little bit more but most likely worth it. Most people in-the-know feel distilled water is the way to go.  Its very inexpensive.

You'll sleep better at night knowing that, off-brand, acidic anti-freeze is not slowly eating away at your 3K aluminum cylinder head !

[Larry & Norma]

OAT, Organic Acid Technology based antifreeze should not be used where copper or brass may
be present in the system, usually applies to older engines.

[Jonny B]

If you take a look at the "General Discussion" forum there is a listing of Pagoda Notes issues, Volume 5 No 4 has a description of the draining and flushing process.

[Ferrolanoman]

thank you to all who've replied. I'll probably buy a couple of gallon of the M-B antifreeze and mix with distilled water. However, given the widespread use of aluminum and other alloys in the manufacture of today's engines (blocks and/or heads, radiators), I remain somewhat skeptical that Prestone DEX-COOL (with its touted 150,000 mi warranty), among other premium brands, is not good enough for our Pagoda engines. I fear we may be falling prey to the usual manufacturer's dire but baseless warnings. Other examples that come to mind are Porsche (as of late peddling oil of their own label for early cars) and Harley-Davidson who for decades has sold oils at risible prices.