My coolant tank never registered more than about an inch below the reference mark at the seam: hot or cold, for about 3 years. Coolant (I use G-05) temp gauge acted normally, as far as I was concerned, never moving above 110 (or so) except in summer traffic. I was advised by a knowledgeable MB mechanic to "just add a quart, or so..." & I put in a quart of pre-mix and the level hadn't moved the next time I checked it.

Added yet another quart and the level had moved up about an inch (in the clear tank) : now the temp gauge stays right at the 9:00 position once the car is warmed up.

What this indicates to me is that there is a pretty good FUDGE-factor as far as coolant level in the radiator is concerned. It is, after all, a 4 gallon system...

Cheers!

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'91 420 SEL @ 199K, '92 SVX @ 181K, '93 SC400 @ 86K, '93 Kaw ZX-11 @ 30K, '87 F250 @ 181K , 2001 Valkyrie Interstate @ 6K, Y2K Honda NightHawk 250 with 1.5K, '88 420SEL I.@ 179K & the 2nd latest, an '88 420SEL II.@ 210K runnin' parts car, '85 F150 300/NP435