Cooling vacuum fill - vacuum loss question

[MQTGN]

I'm in the process of filling the cooling system on my new engine - system is currently bone dry. I have a AirLift vacuum fill system to make easy work of the task and ensure all the air bubbles get removed.

When I pull vacuum on the system I easily reach ~24 psi (instructions say to get the vacuum between 24 and 26 psi). I let the system set for about 10 minutes under vacuum to see how much vac I lose in this time. The system seems to loose about 4-psi in 10 minutes. Is this normal or acceptable? This is my first time using a vacuum fill system so I'm not certain if this loss of vacuum indicates a possible cooling system leak?

Thanks,

Paul

 

[turbodave231]

If you continue to loose vacuum, you might have a leak somewhere. If the vacuum drops initially and then levels off, I wouldn't worry too much about it.

I have and use a vacuum fill system. It helped me find a head gasket that was on the verge of being fully blown on my S2 racecar. Same scenario as you describe.

Last fall I developed a leak in the water pump on my 87 White T. I replaced the pump/hoses and used the vacuum to fill the system. It would not hold vacuum very long. I checked the connections......all was OK. Found a pinhole leak in the radiator header.

 

[MQTGN]

If you continue to loose vacuum, you might have a leak somewhere. If the vacuum drops initially and then levels off, I wouldn't worry too much about it.

I have and use a vacuum fill system. It helped me find a head gasket that was on the verge of being fully blown on my S2 racecar. Same scenario as you describe.

Last fall I developed a leak in the water pump on my 87 White T. I replaced the pump/hoses and used the vacuum to fill the system. It would not hold vacuum very long. I checked the connections......all was OK. Found a pinhole leak in the radiator header.

It doesn't seem to level off, and contInues to loose vacuum, but it is slow. After 20 minutes I was down around 19 psi (starting around 24 or so). I'm also not able pull anymore than 24 psi of vac? Are you able to reach 26 or higher? Engine is new, all hoses are new, double checked all my connections. stumped. Guess I might look at the radiator next.

I'm assuming should be some some small loss present, or should it hold vacuum for long lengths of time?

Thanks for the help.

 

[turbodave231]

A small drop is normal and it should hold vacuum for a long period of time (2-3 hours). You might have a small leak. I can usually get to 25-26" on my gauge. Your deepest vacuum level depends on your elevation and local barometric pressure. (It will change slightly from day to day). I am about 50' above sea level.

If you want to see the "Best" vacuum you can achieve, pull a vacuum on a container that you know can't leak. (like a glass bottle). Watch the decay in vacuum too.


If you cant find a leak, fill and pressurize the system to 15-16 psi. You might be able to find the leak that way.

Dave

 

[MQTGN]

A small drop is normal and it should hold vacuum for a long period of time (2-3 hours). You might have a small leak. I can usually get to 25-26" on my gauge. Your deepest vacuum level depends on your elevation and local barometric pressure. (It will change slightly from day to day). I am about 50' above sea level.

If you want to see the "Best" vacuum you can achieve, pull a vacuum on a container that you know can't leak. (like a glass bottle). Watch the decay in vacuum too.


If you cant find a leak, fill and pressurize the system to 15-16 psi. You might be able to find the leak that way.

Dave

Dave,

Thanks - I noticed my S-hose is not sucking down so I have a look at the connections. If that isn't it, I think I'll fill it, pressurize and starting looking for leaks.

Thanks

Paul