Use nitrogen for leakdown test?

Hi Norman,

I have always used air from a compressor, through a pressure regulator (down to recommended pressure), so can only wonder why you would want to use Nitrogen??

Time to buy a compressor.

It’s an academic conversation for sure, but nitrogen would probably yield the same results as compressed air.  Air is composed of 78% nitrogen, 21 percent oxygen, 1% trace gasses, and the molecule size of nitrogen and oxygen is only 3% different.

Thanks for the replies. I have nitrogen in my hangar already for my tires. I get it at no cost. I will be sharing a hangar with my son in a year or so so this may be my last leakdown check before then. He has an air compressor already.  So I can borrow one from the guy in the hangar next to me or use nitrogen. I was more curious than anything else. I could even do a side by side comparison this time around to see if there is a difference. Of course my engine is young and last time around the worst cylinder was 78/80 so with that small amount of leakdown it would tend to show less difference if there is any. Thanks to all!

100% Nitrogen is about 2.5% Less Viscous than Standard Air.
So with a 78/80 reading in Air, you might expect a 77.95/80 reading with Nitrogen.
Add to that, that you are Not controlling for the temperatures of the gases it will make little difference until the readings are well into what would be considered massive failures anyway.

40/80 air would become 39/80 Nitrogen.  Does it really matter?
As Jeff stated, it is really just academic.

Use it if you got it!