I read about the following technique at this site some time ago. I believe that Benzmac mentioned this approach.
Before you change coolant/hoses/etc. Go rent a cooling system pressure tester. These are easy to use and are great for finding coolant leaks anyway.
After you get your hoses on, tighten up the clamps a bit 'til they're fairly snug, but not too snug. Connect the tester to your overflow tank and pump up to about 15-17 lbs. The system is likely rated at 20 lbs, but I like to back off a bit from this so I don't blow the seal on the water pump.
Watch for leaks at the ends of the hoses and tigten gradually until the leakage stops. I like to see the system as a whole hold 15-17 lbs of pressure for at least 20 mins.
1991 300-SEL - Model 126
M103 - SOHC
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