Compression and Leak Down Testing

shauncr91 · 6 Apr 2015 at 16:22

Hi,

My car has a problem with burning oil and I want to get it diagnosed to find out if it's rings or top end (I have a feeling it's a valve guide/seal but want to confirm before spending money replacing these).

I'm led to believe that someone should be able to diagnosed if it's piston rings or not by doing the above testing methods but how much should I expect to pay for this service on my engine? (2.0 Ford Duratec)

sigma · 6 Apr 2015 at 18:10

No idea if this is a decent bit of kit but perhaps you could do it yourself:

http://www.screwfix.com/p/laser-engine-compression-tester-piece-set/16856

Or just Google for the right size that you need.

pepsilol · 6 Apr 2015 at 18:14

That's definitely something you can do yourself as didn't you replace your spark plugs not that long ago?

I wouldn't pay a penny towards it as it's something so easy to do yourself, bordering I'd let you come to my place and I'll give you a hand to do it it's that easy.

shauncr91 · 6 Apr 2015 at 18:21

I gather that the compression test should be rather straight forward but what about a leak down test? I'm led to believe that this is a bit more complex as you need a constant supply of air going into the combustion chamber?

pepsilol if you would be prepared to help me out on this I'd be extremely grateful

pepsilol · 6 Apr 2015 at 19:06

Ah forget you wanted a leak test aswell. Should still be straightforward, hook up air supply and compare whats going in to whats coming out.

tl45 · 7 Apr 2015 at 18:11

For the leakdown test you'll need a compressor or similar so you rig up an air supply to the kit - around 120psi from memory?

My brother uses leakdown test mainly on the stuff he works on - not sure of all the differences but you can do leakdown on a static engine whereas the comp test needs engine to be installed and turn-overable

Also the leakdown test will give you more guidance as to where any problem lies. If you've got a cylinder (or more ) not holding pressure when at tdc, where the air vents out will identify what sort of problem there is.

i.e. venting out of inlet ports or exhaust port points towards valve sealing problems, whereas if pressure is escaping through the crankcases then it's bores, piston rings.

Bear in mind the leakdown test won't always show up faults like leaking head gaskets or cracks in cylinders as the pressure applied is not anywhere near that experienced during combustion.

shauncr91 · 7 Apr 2015 at 18:27

tl45 said:
For the leakdown test you'll need a compressor or similar so you rig up an air supply to the kit - around 120psi from memory?

My brother uses leakdown test mainly on the stuff he works on - not sure of all the differences but you can do leakdown on a static engine whereas the comp test needs engine to be installed and turn-overable

Also the leakdown test will give you more guidance as to where any problem lies. If you've got a cylinder (or more ) not holding pressure when at tdc, where the air vents out will identify what sort of problem there is.

i.e. venting out of inlet ports or exhaust port points towards valve sealing problems, whereas if pressure is escaping through the crankcases then it's bores, piston rings.

Bear in mind the leakdown test won't always show up faults like leaking head gaskets or cracks in cylinders as the pressure applied is not anywhere near that experienced during combustion.

Any idea how much I should expect to pay for this service?

Gibbo · 7 Apr 2015 at 18:34

Hi there

A leakdown test is something I keep meaning to get done on M3, compression test all six cylinders healthy and as car is making great power I have never performed a leak down test.

Still think its something I should get done though as car has passed 100k miles now and is still on original HG, so good idea as precaution I think.