Carpokes

Meine44 wrote: Sun Mar 29, 2026 2:54 pm I received the new gauge for the coolant vacuum tool, and tested it on the car today. It will get to 15 in-Hg of vacuum pressure before coolant starts coming out of the venturi hose.

I left the system under 15 in-Hg of vacuum pressure for 10 minutes and the pressure didn't bleed off, so the system must be sealed. This gives me a fair bit of confidence that there are no leaks on the system. I will plan to bleed the system at the vent and top off with distilled water as needed before driving the car home from storage.

Like I was asking earlier, I think you may be mixing up some of your terms and measurements. Vacuum is the opposite of pressure. So are you sure you are pulling a vacuum, aka putting the system under negative pressure? In that case, you are not actually testing your coolant system properly. It needs to be under positive pressure, NOT a vacuum. However, any coolant test tool I'm aware of creates positive pressure, so I suspect you're just misusing the term "vacuum."

Also, 15 in-Hg is only about 7psi. If you ARE in fact pressurizing the system, then this is only about half of the pressure it needs to take. You need to pressurize it to 15psi/30in-hg (which is what your OE coolant blowoff cap should be). If you are experiencing leaks at 7psi/15in-hg (again, of *positive* pressure) then that is your problem - it will leak under normal operating coolant system pressures.

fasterfaster wrote: Sun Mar 29, 2026 9:10 pm

Meine44 wrote: Sun Mar 29, 2026 2:54 pm I received the new gauge for the coolant vacuum tool, and tested it on the car today. It will get to 15 in-Hg of vacuum pressure before coolant starts coming out of the venturi hose.

I left the system under 15 in-Hg of vacuum pressure for 10 minutes and the pressure didn't bleed off, so the system must be sealed. This gives me a fair bit of confidence that there are no leaks on the system. I will plan to bleed the system at the vent and top off with distilled water as needed before driving the car home from storage.

Like I was asking earlier, I think you may be mixing up some of your terms and measurements. Vacuum is the opposite of pressure. So are you sure you are pulling a vacuum, aka putting the system under negative pressure? In that case, you are not actually testing your coolant system properly. It needs to be under positive pressure, NOT a vacuum. However, any coolant test tool I'm aware of creates positive pressure, so I suspect you're just misusing the term "vacuum."

Also, 15 in-Hg is only about 7psi. If you ARE in fact pressurizing the system, then this is only about half of the pressure it needs to take. You need to pressurize it to 15psi/30in-hg (which is what your OE coolant blowoff cap should be). If you are experiencing leaks at 7psi/15in-hg (again, of *positive* pressure) then that is your problem - it will leak under normal operating coolant system pressures.

The tool I have is a vacuum tool; it is also used to fill the system with coolant under vacuum to eliminate air pockets in the system. The idea is to fill the system under vacuum instead of bleeding the system at the bleeder screw. Usually I do both: fill with the vacuum tool, THEN bleed the system at the bleeder screw.

The vacuum system can check for leaks, but it is more difficult to spot them with soapy water. The bubbles that show near a leak under vacuum are more difficult to spot than when the system is under positive pressure, but not impossible. The system should still hold a vacuum the same way it would hold positive pressure.

I think the major difference is that the system will NOT hold vacuum while the vacuum pump is still running because it is sending coolant out of the venturi hose. Once the valve is closed it holds vacuum, but won't build past 15 in-Hg once the coolant starts evacuating.

Ah, got it. You're using a vacuum bleeder AS your leak tester. Certainly a failed vacuum will also highlight a leak, but it is a different failure mode than a positive pressure leak. Not to mentioned harder to track down. It is entirely possible to have a system fully sealed under vacuum (which increases hose clamp/seal pressure) and still have leaks under positive pressure.

If you're still losing coolant after your next fill, I recommend dropping the $30 on a pressure testing kit.

I haven't been able to spend much time on the car lately due to my work schedule.

However, I did find a used coolant reservoir at a price that I couldn't pass up, and it was worth every penny!
Now the coolant level is clearly visible; no more guess work.


I will still bleed the system through the vent bolt and cycle the HVAC system to get air out of the heat exchanger etc. I do plan to invest in a pressure tester also at some point.

What are you pointing at?

danmartinic wrote: Wed Apr 15, 2026 1:24 pm What are you pointing at?

When I removed the coolant reservoir, I found a loose bolt in the engine bay. I don't know where it came from or how long it's been rattling around in there.

Hopefully it's not for something important.

I'm game

One of the bolts that attached the original AFM to the original air cleaner housing

My guess is one of the bolts for the water pump. If we win, do we get your old coolant tank as a prize?!