Spiffyjiff

i am neither buying nor selling, but track season is coming up so i will be doing pre-season maintenance: oil change, brake and trans fluid, etc. i can do myself, but will prob bite the bullet and go to dealer this one time because it's easier/i'm lazy.

my questions are: should i bother with getting a compression and leakdown? it's >$400 service. beyond that, should i even trust a dealer (as opposed to an indy race shop) to do this test? i.e. could they potentially screw anything up?

thanks.

Dervish

In my recent experience, compression is next to useless, leak down better at assessing if there is a problem. If you really want piece of mind get them to stick a camera up in cylinder 6, this is actually less labour than either test. The 3.6 and 3.8 engines are (more) prone to scoring which is what I'm assuming your checking for seeing as you track it...

I wouldn't let a dealer do it either, get an indy.

997_rich

Agreed and agreed. Leakdown and indy. Make sure it's a competent indy (someone who is pulling engines apart instead of just a place that changes tires and brakes).

If you've changed sparkplugs on this car before, then you're probably capable of doing yourself. If not I wouldn't attempt it. $400 will buy you quite a nice home use compressor and leakdown gauge.... and maybe even a boroscope.

Macster

If the engine is running ok neither is necessary.

The engine is fitted with a very sophisticated engine controller that among other things constantly monitors the acceleration imparted to the flywheel from every cylinder's power stroke. If the acceleration is too low (or too high) the engine controller will turn on the check engine light and probably log one or more misfire error codes.

If the check engine light bulb is not burned out and not on then the engine controller has not found anything amiss.

IOWs, the engine's fine and a compression test/leak down test is a waste of time and money. And everytime the engine is touched there's always a risk of something getting screwed up. A spark plug thread can be stripped for instance.

Sincerely,

Macster.

cbzzoom

This is true, however the built in tolerances in the computer before it fires a CEL are actually very high. If you're trying to maintain your car at peak condition, you won't be happy with how big that tolerance is.

Spiffyjiff

actually this was going to be my next question...

somewhere i've read that the comp/leak test possibly can indicate an IMS bearing issue (or other issues of course). but in all the talk/posts of IMS failures, i have not once read where a check engine light went on beforehand. and this is the reason i was considering getting the test i.e. could the test tell something is amiss or that conditions are deteriorating before the electronics are aware of it, or before the afflicted part/system has completely broken down, etc.

or...i could just shut up, stop worrying, and drive it flat out.

cbzzoom

Yeah, this is the best idea. Unless you have a weird noise or loss of power or for some other reason think something is wrong, no need to go digging around with leakdowns or borescopes.

An IMS failure is a bit like being struck by lightning. It's very rare, and there's not much you can do to prevent it. So just enjoy yourself and hope it doesn't happen!

mattyf

FYI leakdown test tools are not that expensive. Since you sound capable of doing your own fluid changes, if you really wanted too you could do a leakdown yourself... perhaps next time you need new plugs. Borescopes are a little more expensive, but still not out of the range of a DIYer.

997_rich

I don't believe you're going to see an IMS or RMS failure with a leakdown. You will see bad valve seats, scored cylinders, cracked or broken pistion rings, leaking head gasket etc. Basically anything that has to be "explosion-tight".

I guess you might see that the valves aren't completely closed in a leakdown at TDC if the IMS was so trashed that the valves were out of time. If that were the case, the engine would be running like **** anyway and you'd be throwing failure codes.

I'm not 100% sure that you need a compression test if the car is running well. Usually in a higher mileage car I'd do one to get a sense of how much life the cylinders and top end have left in them. I don't see that much harm in it though... if you're using someone who knows what they're doing (using a torque wrench to drive the plugs etc). If you have a monkey who's going to beat on the car I wouldn't do a leakdown but I wouldn't let that guy touch my car anyway.

You may need to buy a few exhaust bolts/clamps in the process because the tech will drop the secondary mufflers to get at the plugs (even on a young car the exhaust bolts are often rusted and it's nice to replace).