Today, I got curious to see how accurate my PFS gauge is versus my MityVac pump. I pumped 25 in/hg (on my MityVac), then checked my PFS gauge. The PFS gauge read ~24in/hg, which is pretty accurate if you take into account that the MityVac also has a certain range of error.

Now, I left it for ~15min to see how much vaccum will be lost in that time. After I came back to check on it, 1in/hg was lost (from 25in/hg to 24in/hg). Have any of you guys who have done a similar test found that you lost some vaccum after a short amount of time? Keep in mind that my car was cold when this test was performed, so the sealing may not be as well as it would be when it is warm.

 

Anyone?

 

you already figured it out. The engine is now warm which means the compression/seal is less. Remember cold things exand and hot things contract which is why you should always warm up your engine when doing a compression test.

 

sounds normal to me. i do notice that it changes after u have been driving and when u first start in the morning.

 

Wait, what are you measuring the vaccuum of, again?

From your first paragraph, it sounds like maybe you just connected the Mityvac directly up to the boost gauge (and to nothing else) and pumped it. Then you mention the engine temp; so are you really talking about the vaccuum chamber test, or maybe measuring the intake vaccum on a running engine?

 

Isn't Heat Expand and Cold Contract?

BC

 

Question

Expansion and Contraction : Why does heat and cold make things expand and contract ? Also why do some metals expand more than others?

Asked by: Marcus Mckean

Answer

Recall that all materials are made up of atoms. At any temperature above absolute zero (-273 degrees celsius) the atoms will be moving. In a solid they will be vibrating in fixed positions, in a liquid thy will be jostling past each other and in a gas they will be whizzing past each other at very high speeds. When a material is heated, the kinetic energy of that material increases and it's atoms and molecules move about more. This means that each atom will take up more space due to it's movement so the material will expand. When it is cold the kinetic energy decreases, so the atoms take up less space and the material contracts.

Some metals expand more than others due to differences in the forces between the atoms / molecules. In metals such as iron the forces between the atoms are stronger so it is more difficult for the atoms to move around . In brass the forces are a little weaker so the atoms are free to move about more. These differences in contraction are used in a bimetallic strip, which is composed of a strip of brass laid along side strip of Iron. When the strip is heated the brass expands more than the iron so the strip beds. It is used in devics such as fire alarms and circuit breakers to either make or break contacts in an electric circuit.

The differences in expansion and contraction are even more visible in different states, again due to the amount of force holding the atoms together. A gas will expand the most as its atoms are free from each other so are free to increase in speed the most.

Answered by: Sara Al-Assam, Student, Tiffin Girls' School, Kingston

OOPs Well forget that theory hehe

 

I tested the vaccum of the entire motor by hooking up a vaccum pump to a nipple off the UIM. I also then tested my boost gauge.