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Does anyone vacuum fill their coolant in a system that's been completely drained? I've already got the tool and went to see if could find anyone doing this (more specifically a reason not to) and there is nothing out there on the topic?

I do this with my BMWs and it really makes refilling coolant from full empty a breeze.. I know I can do it the old fashioned way but is there really any reason not to? I've replaced every hose in the coolant system as part of the many rabbit holes I've gone down on my timing belt project.

Richey wrote: Wed May 13, 2026 6:28 pm Does anyone vacuum fill their coolant in a system that's been completely drained? I've already got the tool and went to see if could find anyone doing this (more specifically a reason not to) and there is nothing out there on the topic?

I do this with my BMWs and it really makes refilling coolant from full empty a breeze.. I know I can do it the old fashioned way but is there really any reason not to? I've replaced every hose in the coolant system as part of the many rabbit holes I've gone down on my timing belt project.

That’s the way I fill 86 turbo. Works perfect and very easy. Never even have to mess with the bleeder screw. I don’t know why more people don’t do it especially on these cars.

I think that's why I was second guessing it. I finally found one video but it was just an ASMR video of filling it with a vacuum.

Mscromer wrote: Wed May 13, 2026 6:39 pm

I don’t know why more people don’t do it especially on these cars.

Yes, I vacuum-fill everything I work on. It also doubles as a crude leak test---be sure to suck the system down to a vacuum for several minutes to purge, and then remove the shop air hose and keep the ball valve closed. The system should hold the vacuum---if it doesn't there is a sizable leak in the system.

If one does not have access to a vacuum-filling system, the next-best way to fill the 944 cooing system is to crack the bleeder screw open, make sure the heater valve is open, and slowly pour coolant into the reservoir. Each time the coolant reservoir is filled to the brim, use a coolant pressure tester to force the coolant through the system, which will purge most of the air via the bleeder hole. Rinse and repeat until there is a steady stream of liquid coolant from the bleeder. If done properly, there will be minimal bleeding needed with the engine running.

Very interested in this as well. Any risk of damage to anything with this method? Looking at this unit https://a.co/d/0buDvgfQ any recommendations or anyone use this one?

As long as your cooling system is in good shape then you won’t run into issues. That one will work fine as will the one from Harbor Freight. The Snap On and other tool truck brands are probably better but unless you do this daily that’s over kill.

I use the Hazet one out of a general preference to avoid made-in-China. A good bit more dear, though....