nice day out. lets do leakdown!
 

So I was going to do an oil change and I thought HEY I smell coolant under hard acceleration! I should call Braineack and tell him to come over with his leakdown tester just so I can sleep at night and not feel like I wasted an oil change.

we used the crappy compressor he stole got from work back in the day. It tripped my circuit breaker twice. But it provided pressure and that's what matters, RIGHT?

Popped the hood on the pollen-colored miata and spent some time watching Brainy tell me I had 99% leakdown in #1 before he realized he was not at #1 TDC Compression, but TDC Exhaust. i.e. valves open.

Once he swapped the hose to #4 which was at TDCC, we took readings:

cyl# pressure in/pressure held (leakdown %)
#1 80/77 (3.7%)
#2 100/96 (4.0%)
#3 60/59 (1.7%)
#4 80/77 (3.7%)

my motor is a stock 2001 with about 100k and about 2/3 of those miles turbocharged.


results: me, happy.
now I gotta pressure test my cooling system...

you can rent those testers at advance auto.

how long do you wait between pressurizing and reading?

constant air supply to the regulators from the tank. ideally the air source (compressor) should provide a steady 120 psi for your 100 psi setting on your inlet regulator.

instantly. once the clyinder was ready, I just started turning up the knob and pressurizing the chamber. How else would you do it?

btw, my compressor only holds 100psi max and the power outlet was being shared by y8s's wife at the time, so thats why the readings are all over the place for reference pressure.

but still, they were holding fine. I was consistently seeing 12% leakdown on my motor with the same gauge and method.

you haven't seen my bike pump adapter hose have you

oh yeah i have, but its not as good. :)

Cant wait to pull the head off my 00 motor today and see why it had 100% on cyc 1 and opening the throttle blade sounded like a BOV!

I think TurboTim meant how long after pressurizing and shutting off the air supply do you wait to take the second leakdown reading. (how much it's leaked down to)

still don't quite understand. you don't ever stop feeding it pressure, it's a constant supply of X pressure, and a constant reading of Y in the second gauge (which reads the clyinder).



thread now has a pic!

https://www.miataturbo.net/attachmen...1&d=1333383617

a leak is a constant source of pressure loss. so you have to provide a constant pressure to maintain the starting psi value.

the idea is to find out how big that leak is by measuring the pressure before a calibrated "leak" orafice and then before your engine's leaky sealing surfaces.

imagine filling a bicycle tire with your compressor. but the tire has a hole in it.

the leak down tester has two gauges, a... wait I will google a picture.

https://www.miataturbo.net/attachmen...ine=1333387239

the orafice maintains a limited flow rate between the two gauges to keep the inlet pressure up and allow the engine's leaking to determine the second gauge pressure reading. if there are no engine seal leaks, both gauges read identical numbers. realistically, even the tightest engine will read some nominal leakdown but get very close to 100%.

I find the term "leakdown" to be misleading.

why?


if you are supplying 100psi and the cylinder is leaking 20psi of it...you can then track it down :)

Based on that term, it seems like you have to take two readings, but I now see that its a continuous process.

Yeah me too, thanks fellas. I've never done a leakdown test, only compression test.

ah okay.

here:

https://www.miataturbo.net/attachmen...ine=1333388420


75psi is going in, but only holding 65psi. IIRc 20% is borderline, mine was consistent on all four so I'm not concerned.

Props to the Y8smeister.... and Brainey.

Such a nice man sized compressor housing <3

that picture does not do my engine bay justice.

What the hell have you been doing to that poor valve cover? Beating it will not make it run better.