I didn't get many responses to my requests for finding an affordable Mercedes coolant pressurizer so I built my own, adapting the idea from another car forum. I will be adding this to my routine for flushing coolant. This concept should be adaptable to nearly any car with an expansion tank, removing the need for an exact fit adapter for the expansion tank.

To start, I bought a bike tire inflater with a PSI gauge, some fuel hose and a plumbing barb.

I cut the fuel hose and shoved some spare bolts on the open side in order to block air and coolant from escaping.

Then, I removed both lines from the expansion tank and connected the fuel hose with the bolts.

For the line connecting into the radiator, I connected an air line with the barb and then connected the opposite side back into the air pump.

From there, pump the pressure to around 20 psi and let it sit for a few minutes. To release the air, remove the line on the pump side. This is best done on a cold engine with the car sitting overnight.

Dkr.

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Nice one.

Are you pressurising the expansion tank as well?

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

Yep, everything gets pressurized.

Dkr.

What is the intended purpose of this? You can buy or rent coolant system pressure tester at Autozone with a fitting that screws on the expansion tank. For coolant flushing, isn't a garden hose sufficient?

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

It does the same thing as the one you would get at AutoZone although it is cheaper and you don't have to worry about adapter compatibility. My kit did not have a W123 adapter.

Dkr.