Vacuum Coolant Fill Advice

[JACKAL]

So I recently had my supercharger off and when I put everything back together, I went to use my vacuum filler to purge air and add coolant. Now its been almost 2 years since I last did it so my memory isn't great, but I thought previously I was able to pull and maintain a vacuum reading of close to 25" Hg. For some reason, I was only able to get about 15" Hg on the gauge this time and even letting the compressed air run through the venturi for over a minute, this was the reading the gauge stabilized at so I shut the valves and watched. It did not bleed down even after 2+ minutes so it doesn't seem that there is a leak but I'm not sure why I couldn't pull more vacuum.

Any thoughts on this? I should mention my overflow reservoir did have a fair amount of coolant in it when I did this.

[430hps4]

If it didn't bleed off, I wouldn't stress. Goes to show everything was sealed up, nice N tight.

[Austin88]

Literally just happened to me yesterday. Same exact scenario and I figured out what it was. How many gallons is your compressor? I had to close valves at 15psi, then wait for my cheap 3 gallon compressor to refill, then open valves for it to finish climbing to 25 or 26 psi which is where it actually stops. In other words compressor ran out of pressure which is why it stopped at 15 psi. Don’t worry about coolant in the overflow tank just re-do it, make sure heater is turned up full blast when you do, and you may suck out some additional air this time by going to full 25 or 26 psi. Not a big deal though system self bleeds pretty well.

[Jk79]

It should read around the 23-25 mark. A vacuum filler should really only be used on an empty system. In order for the fill to work the negative vacuum needs to be created throughout and then replaced with the fluid. Did the volume of fluid you added match the approx capacity? I would at least bleed to make sure there aren’t air pockets.

[djn876]

Did the system pull the coolant level up to the fill area, it may have just become water sealed if it did.

You have to bleed it anyway so I wouldn't worry too much about it. Just finish up the normal bleed procedure and keep an eye on level as you drive for a little.

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[JACKAL]

Thanks everyone. Just to close the loop here, the issue was that I didn't evacuate my expansion tank fully. I went back today and pulled as much fluid out as possible, then gave it another shot. Pulled to just past 25" and held solid.