Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Coolant vacuum tool

Got a new coolant vacuum tool for refilling the cooling system and have a question. If the coolant system has a pressure relief of 16lbs what would be the equivalent stress on components using vacuum? I see all the repair videos running a full vacuum on the system to over 25 inches. So if high pressure could blow a hole in a radiator what amount of vacuum would do the same damage but in opposite direction. My question boils down to the force applied with16lbs of pressure is equal to how many inches of vacuum?

IIRC 30 inches of mercury = 15 pounds per square inch.

Google will convert it for you too. Type 'Convert 30 inches of mercury to psi" into the Google search bar.

1 Like

Thanks, I tried googling but just couldn’t find the right words to describe what I wanted. So I believe pulling a vacuum with this tool will do no adverse harm on a normal 15-16 lbs system.

Actually more like 47 psi. Air pressure at seal level is 14.7 psi and 760 mm of mercury. Do the math, and this equates to 46.4 inches of mercury at sea level.

that amount scares me a little

How does this work? Why would it pull a full vacuum?

Why would vacuum be applied to a closed cooling system to purge air? To burp air the radiator should be filled and kept filled with the cap off while vacuum is applied to the highest accessible point in the cooling system. As soon as coolant reaches the vacuum point the radiator cap should be installed and the opening where vacuum was applied closed. It is impossible to draw water up and out through a column of air that will become a dry vacuum.

1 Like

Design for pressure or vacuum is different. For example, a thin plastic sphere that will hold 16 psig pressure could crumple under full vacuum. “In another life” we used the rule of thumb that a vessel that needed to take full vacuum must be rated at a minimum of 60 psig pressure.

1 Like

Cooling system exchange units that operate with vacuum have been common for the last 20 years with no harm to the cooling system. You don’t need to draw a full vacuum on the cooling system to yet most of the air out.

I saw this riddle a few days ago and this thread reminded me of it

gimmicks annoy me and while I recognized the blockage to #4 the others got by me.

760 mm = 30 inches appx
Or did I misunderstand your comment above?