Compression testing?
Discussion
take out all 4 spark plugs
remove fuel pump fuse (optional)
screw in compression gauge
throttle wide open, engage starter (try to start car)
repeat a number of times until gauge doesn't move anymore
repeat on other cylinders.
if you do get a low reading on all cylinders, a little oil down the spark plug hole and retest. If new test shows a higher reading it's likely your rings are leaking.
remove fuel pump fuse (optional)
screw in compression gauge
throttle wide open, engage starter (try to start car)
repeat a number of times until gauge doesn't move anymore
repeat on other cylinders.
if you do get a low reading on all cylinders, a little oil down the spark plug hole and retest. If new test shows a higher reading it's likely your rings are leaking.
It's losing coolant from wherever it decides it can leak from - opinion of the breakdown guy was that it's building excess pressure in the cooling system due to head gasket failure and venting through any slightly weak point in the 196k mile old cooling system.
Trying to verify (going to do a sniff test tomorrow if the gear arrives)
Trying to verify (going to do a sniff test tomorrow if the gear arrives)
Sounds like hg failure to me, take it to a garage and get it tested via the emissions machine, they will hover the tester over the expansion cap if the hc shot up then hg fault. What happens is the exhaust gas mixes in with the coolant via the blown hg depending on where it has blown.
For it to be low on all 4 suggest blown hg between 1-2 and 3-4.
For it to be low on all 4 suggest blown hg between 1-2 and 3-4.
If your hg has gone enough to be the cause of low compression you wouldn't need a compression test to tell you, you would be pissing water, oil and compressed gasses from very orifice. Sniff test will do the job. If you do have a compression problem it will only be through valves or ring/piston seals being poor. Unlikely that you'd get the same reading on all cylinders even if it was. I'd say you have a s
t tester or a leaking o-ring seal where it screws into the head.
Holding throttle open makes little difference to the final reading in my experience.
t tester or a leaking o-ring seal where it screws into the head. Holding throttle open makes little difference to the final reading in my experience.
Have you got another engine you can test your equipment and method on?
Most engine faults usually show up as being unequal cylinder pressures which you don't seem to have.
It doesn't matter whether the throttle is opened or not as long as you are consistent - think about it, if air couldn't get in when the throttle was closed the engine wouldn't run.
Most engine faults usually show up as being unequal cylinder pressures which you don't seem to have.
It doesn't matter whether the throttle is opened or not as long as you are consistent - think about it, if air couldn't get in when the throttle was closed the engine wouldn't run.
Notice this looks very similar http://www.amazon.co.uk/Am-Tech-Automotive-Compres...
and there's a review saying it only showed 50psi on all cylinders whereas a better tester worked properly.
and there's a review saying it only showed 50psi on all cylinders whereas a better tester worked properly.
Toaster Pilot said:
Notice this looks very similar http://www.amazon.co.uk/Am-Tech-Automotive-Compres...
and there's a review saying it only showed 50psi on all cylinders whereas a better tester worked properly.
well spotted... that's what I like about Amazon as opposed to Ebay... the feedback facility on Amazon is great compared to the blind buying on Ebay!and there's a review saying it only showed 50psi on all cylinders whereas a better tester worked properly.
its kind of why I have stopped buying cheap stuff... Spent hours a while ago diagnosing a fault after fitting 4 new coils to a Scenic... turns out that TWO of the new coils were faulty... Same with a Lambda sensor on a Ford, fitting a new one just introduced another intermittent fault...
Edited by buzzer on Thursday 3rd April 13:22
I'll go out and buy my own tester later - looking at either http://www.machinemart.co.uk/shop/product/details/... which I like the look of because it's got lots of adaptors for lots of different vehicles or
http://www.halfords.com/webapp/wcs/stores/servlet/...
I figure it's worth the extra £5 for the much increased flexibility.
http://www.halfords.com/webapp/wcs/stores/servlet/...
I figure it's worth the extra £5 for the much increased flexibility.
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