compression test? worth doing?

BeenThroughItAll

londonTiger wrote: »

the american car youtubers seem to be all about their compression ratios and compression testing

Oh, well if the Americans are talking about it on YouTube, get your wallet out. They're bound to be right.

EdGasket

A compression test has to be done right otherwise you will get confused and incorrect information. Roughly speaking I think the procedure is:
1) Engine hot
2) All Spark plugs out
3) Disconnect fuel injectors (so you don't wash the cylinder walls with raw fuel while testing other cylinders)
4) Disconnect ECU (take out fuse) so it won't damage the coil packs while plugs are out
5) Connect gauge to each plug in turn and crank for about 5 seconds per cylinder with throttle wide open to take readings.

Many people miss out step 3 and think they have a cylinder low on compression when in fact all you have done is washed the oil away from the rings.

If there are no symptoms like burning oil or rough running, then I wouldn't bother testing it tbh.

There are further tests you can do if you get low compression such as inecting some oil in the plug hole to determine if the low compression is rings or a burnt valve.

forgotmyname

Curious if the OP knows what a good and bad reading is for their engine?

EdGasket

forgotmyname wrote: »

Curious if the OP knows what a good and bad reading is for their engine?

Plus a £30 gauge is probably not calibrated so only good for comparing one cylinder to the next.

WellKnownSid

londonTiger wrote: »

wouldn't think twice about using it to drive from london to leeds, and back again same day, which I did last october.

I think that's the issue.

Last year I took my 30 year old E-class - which had been sat on the drive for a year - for its annual service and MoT. Passed no advisories. Two days later I didn't think twice about driving it to the South of France and back (handy because it's LHD) - covering over 2,500 miles.

Meanwhile a friend of mine took their almost 100 year old Ford model whatever to Eastern Europe and back - probably covering closer to 4,000 miles.

You have a modern car, it'll happily cope with a quick trip up the M1!

Don't over think it... by all means keep an eye on levels and signs of obvious problems like a leak, but don't go looking for problems in a 13 year old car because you'll end up worrying unnecessarily...