Question about Spark Plugs' colour

Dear All,

Recently, my friend's 1.5L Civic EK had slight hesitation on acceralation,
some consumption of engine oil and decrease in mileage (increase gasoline
consumption). I had the air-cleaner and spark plug for him. The air-cleaner
looks satisfactory but the colour of the spark plugs are a bit strange -- it
is purple around the point gap. Any idea of the problem and what is causing
the purple colour. Thanks in advance.

Perpetuus

 

For the oil consumption and decrease in mileage, I'd replace the PCV valve
first. A clogged or malfunctioning PCV valve can cause (1) an increase in
pressure in the crankcase, forcing oil past seals it ordinarily wouldn't get
past. and (2) the ECU to be fooled so that it causes the engine's combustion to
run rich.

See how it runs then. If the slight hesitation is still present, I'd start with
general tuneup type things, starting with a new fuel filter and new plugs. If
these don't fix the problem, then try also new ignition wires, distributor cap,
and maybe distributor rotor. Lastly, check the timing, adjusting the distributor
housing as necessary.

I was curious about your purple spark plugs and so googled for {"spark plug"
purple} got a few hits right away. E.g.:

"Red to purple deposits on one side of the core nose are an indication of a fuel
additive. While many of these deposits are non-conductive and do not contribute
to lack of performance, some fuel additives contain octane boosters that leave
conductive deposits on the core nose. Care should be taken to select fuel
additives which are compatible with ignition systems and do not contain
conductive materials such as octane boosters."
http://www.nightrider.com/biketech/spkplghnbook.htm

http://www.circletrack.com/techarticles/71898/ said this is a symptom of
overheating (but why?)

Only use a brand of spark plugs recommended by the owner's manual.

The year and mileage on a vehicle is often helpful to discussion here. Maybe you
could provide these in your next post.

 

Caroline,

First of all, thanks a lot for the information. They are very useful.
Second, my friend's civic is a 1997 car with approximately 70000+ km. I have
suggested him to change the air filter and spark plugs first. Now, I need to
check with him whether he had add anything into his gasoline. Thanks.

Perpetuus

 

1. The crankcase is not a sealed system. A clogged PCV will only
result in NO POSITIVE crankcase ventilation. The blowby gases will be
vented out to the cars intake (before the TB). - No increased
pressure in the crankcase.

2. The ECU may be able to trim the fuel at part throttle using the O2
sensor. I have no idead how much air the PCV flows, so the amount of
fuel trimming available may not be enough. Ofcourse whenever the O2
sensor output is not used by the ECU, you are right, the engine will
run richer.

Bye,
Leon

 

Interesting. Through what aperature?

 

I don't know what you mean. For one, I call the oil pan gasket a seal that may
be compromised because of excessive crankcase pressure.

Numerous authorities beg to differ. E.g.

"A restricted PCV valve can cause this excess pressure to find new avenues to
vent, and an oil gasket or seal is usually "blown out" to let this pressure
escape." http://www.trustmymechanic.com/valve_cover_leak.htm

"Engine is using more oil than normal. Oil puddles under the car when parked...
The PCV system is not working properly: Replace PCV valve."
http://autorepair.about.com/cs/troubleshooting/a/bl303a_3.htm

These are merely the very first two hits of a Google search for {"PCV Valve"
"oil leak"}.

And here's the Car Talk guys on the subject:
-----
RAY: Blow-by occurs when combustion gasses slip by old, worn-out piston rings
and end up in the crankcase, where they don't belong. Actually, a small amount
of blow-by is normal and is easily expunged by the crankcase ventilation system.
But on old heaps (i.e., yours), worn-out rings can let so much stuff into the
crankcase that the ventilation system just can't handle it.

TOM: So the pressure in the crankcase builds up until gasses and oil try to
escape any way they can. And we often see air-filter housings full of oil, seals
blown out or leaking, and the occasional dribbling dipstick.

RAY: The solution is an engine rebuild, which would include a ring job. But
before you consider that route, or ditch the truck, I've got two other things
for you to try.

TOM: If you've lived a really good, clean life, your problem might just be a
plugged crankcase ventilation system. So have your mechanic check out your PCV
valve and the hose it's attached to. ...
-----
http://lang.motorway.com/home/articles/qandaoilydip.asp

The fact is that a clogged PCV valve results in one less possible avenue through
which blowby gases may escape. The average pressure in the crankcase of course
will tend to be higher as a result.

Also, you might want to consider that how serious oil leakage may be when a PCV
valve is clogged will likely vary from one car design to another.

According to my reading, it's very ambiguous as to whether a malfunctioning PCV
valve may affect correct combustion in open loop, closed loop, or both.

It may depend on the specific car design. There is quite a lot of minor
variation from one PCV system to another.

 

It's not sealed but as discussed umpteen times here recently a PCV valve,
as implemented by Honda, is a metered air leak through the crankcase. The
blow-by gases plus the leaked air is *sucked* into the inlet manifold
through the valve, therefore there must be a reduced pressure vs. no PCV
valve. If the valve is clogged, yes the blow-by gases will pass through
the breather tube, to upstream of the throttle valve, but there is nothing
sucking them there... i.e. higher pressures in the crankcase.... which are
pulsed in all but a few rare V8 configs.

Rgds, George Macdonald

"Just because they're paranoid doesn't mean you're not psychotic" - Who, me??

 

He's talking about, for example, the breather hose on various 1990s Civics and
other Hondas. It connects the region contained by the valve cover to the air
intake just upstream of the throttle body.

For a schematic and drawings of this, see
http://www.honda.co.uk/owner/CivicManual/pdf/11-109.pdf

A lot of web sites that discuss crankcase ventilation have a similar schematic.

But merely having an "alternate" escape route is not enough to maintain the same
crankcase pressure that would be present were the PCV valve operating correctly.

 

Sorry, I meant a clogged PCV *valve*. Then the blowby would go
through the little tube from the top of the valve cover to the intake,
before the TB.

Bye,
Leon

 

There is a little breather tube that goes from the top of the valve
cover to the intake, before the TB. This is part of the crankcase
ventilation system and if it's not clogged the crankcase pressure will
never blow out any seals.

So, there are some inaccuracies. I should have said: "a clogged PCV
*valve*..." and trustmymechanic should read: A restricted PCV
*system* can...

If an engine is producing so much blowby that the breather tube has
trouble venting out, blown seals is the least of one's worry. A new /
rebuilt engine is in order.

I agree with that a "clogged PCV valve results in one less possible
avenue through which blowby gases may escape." That does not mean
that the crankcase pressure (which is pulsing as the NG's guru George
explains) will be significantly higher.

A clogged PCV valve results in just that: no positive crankcase
ventilation. The crankcase gases will just vent out the tube on top
of the valve cover, which is not a small orifice and will not increase
the crankcase's pressure . A PCV system is the equivalent of having a
fan sitting on your house window venting out the stale air. The fan
does not significantly decrease the air pressure inside the house
because there is "another window" (the breather tube) open. That's
all a PCV valve does, vents out the stale air.

Bye,
Leon

 

Yup. That's one of several avenues for blowby gases to escape through.

I want to be precise here. I know what you mean by "blow out," but I think this
is too ambiguous for the layperson.

I'm saying a seal exposed to higher crankcase pressures than is usual will not
hold as well.

More below.

snip my citations for conciseness. One may also wish to groups.google for
anecdotal reports of oil leakage and how replacing the PCV valve fixed this

I certainly agree about the pulsing. That's why I'm using phrases like "average
crankcase pressure."

Or, if you prefer, "average peak crankcase pressure."

I, and many authorities, disagree with you about whether the buildup of pressure
may be significant enough to cause seals exposed to crankcase pressure to be
compromised such that oil leaks.

Again, my impression is that how serious the problem may become with a fully
plugged PCV hose or valve depends on the particular car design.

For some car designs it may very well be insignificant.

But out of concern for causing (in no particular order) premature failure of oil
seals, oil loss, reduced gas mileage, and dirtier sooner engine oil, I sure as
heck wouldn't experiment with neglecting the PCV valve on any car.

("Dirtier sooner" engine oil is also an indication of higher average crankcase
pressure, BTW, and you'll see this mentioned at web sites, too.)

 

OK, if authorities believe that a clogged PCV valve produces
significant crankcase pressure buildup to cause seals to leak, I have
a vacuum/pressure gage that will shed some light on this. I will run
the test over the weekend.

I agree, neglecting the PCV valve is foolish. One should always check
to see if it clicks, every time the car is serviced. In the days of
carbureted V8s it was standard practice to change the PCV valve on
every tuneup.

Bye,
Leon

 

I'm always game for an experiment, even if it's only one data point on one car
design.

But, say, can you attach your gage to the PCV hose and drive the car under load?
You know, say 55 mph up a hill for a mile or so?

Crankcase pressure is, of course, highest when the car is under load.

I'd be interested in what port you use to measure the crankcase pressure with
and without a plugged PCV valve, too.

Lastly for today, maybe you already know this, but I thought this paragraph
helpful to anyone wondering what kind of pressure/vaccum to maybe expect in the
crankcase, should they be able to hook up a gage and run the engine under load:

"When a PCV system is working right there will always be a vacuum (suction)
inside the engine's crankcase. But, when the PCV system isn't working, vacuum
becomes pressure. That's a problem because engine seals and gaskets are
designed to work under vacuum, therefore when vacuum turns to pressure it can
cause oil to be forced past seals. In severe cases, crankcase pressure causes
seals and gaskets to literally be pushed out of the engine resulting in an oil
hemorrhage."

http://www.patgosscarworld.com/pcv.htm

Indeed. See my posts on not changing nor checking my (fuel injected) car's
original PCV valve for approx. 140k miles, 12 years. My 91 Civic's fuel mileage
shot up after replacing it.

 

Easy way to check crankcase pressure: Remove the dipstick and fit
vacuum/pressure hose. I'll record the readings then get a pair of
vice-grips and disable the PCV valve.

BTW, was the PCV valve you replaced clicking when tested?

Bye,
Leon

 

I didn't know enough at the time to test it in position.

It was chock full of carbon-waxy buildup; completely covered at a depth of maybe
1/16 to 1/8 inch.. I have no doubt that it was not operating correctly.

 

Hi! Sorry to interrup your discussion. I had changed my friend's spark plugs
and asked him to drive a few miles. Then let's see what colour it got.
By the way, my 94 1.5vti civic had never changed the PCV valve. Is it a must
to change it? I always take it for granted that an aged machine (198000km)
had a small amount of engine oil leak is normal.

 

Checking crankcase pressure.

According to my vacuum / pressure gauge, the crankcase pressure is
ZERO with the engine off, ZERO with the engine on and PCV valve hose
crimped or not (as expected). The only difference between a running
engine and not is that the needle is vibrating (+/- 0.2 in Hg). What
else would one expect after having the valve cover venting out through
the breather hose.

All "authorities" that claim negative crankcase pressure with a
working PCV valve and positive crankcase pressure with a clogged PCV
valve are selling snake oil.

Procedure:

I hooked the vacuum gauge at the dipstick hole and started up the car.
The needle was still at zero vibrating both at idle and at higher RPM.
Did not load the engine but I don't that would make a difference. I
then crimped the hose going to the PCV valve (the valve clicked
loudly) but there was absolutely no change at the gauge measuring the
crankcase pressure. This was both at idle and at higher RPM.

Taking the gauge off the dipstick hole and hooking it up on engine
vacuum (idling) was close to 21" Hg. Crimping the PCV valve hose
results in higher engine vacuum momentarily (+0.5" Hg) then the needle
returns to where it was before. The opposite happens when the PCV
valve resumes operation. The PCV valve was clicking loudly when
crimping the hose and looked like it was operating normally,
"consuming" some engine vacuum. Introducing a major vacuum leak (like
removing the PCV valve) made the engine run really rough for a few
seconds before stalling and setting a 01 code - oxygen content. (This
whole thing involved a lot of sweat because it is hot and very humid
outside - should have gone swimming instead.)

The PCV system cleans the stale air inside the crankcase keeping
engine oil clean and improving engine longevity. It does not reduce
or increase crankcase pressure (unless someone stuffs a rag inside the
breather hose). A malfunctioning PCV valve certainly upsets the A/F
ratio (don't know how much though).

Hope this clears up things regarding crankcase pressure and the PCV
system.

Bye,
Leon

 

Units?

Are you saying the crankcase pressure is atmospheric (= approx. 14.7 psia) under
all these conditions?

snip

Do you realize that the PCV valve is near shut at idle then, as load increases,
opens more? On many cars, the PCV valve is open to its maximum (for normal
operations) at high load?

What does this tell you?

Higher RPM at standstill does not equate to higher torque.

I can't reconcile this with your statement above that crankcase pressure is
zero.

Folks can read the citations on the web, as well as many anecdotal reports at
groups.google.com, and make up their own minds about whether replacing the PCV
valve might improve an oil leakage situation, particularly when fuel efficiency
is also observed to have decreased.

Maybe you should call Tom and Ray with your "discovery." ;-)

 

Uh-huh.

It might.

 

People can go through life fine believing their crankcase is under
vacuum because of PCV, but they are wrong.

Bye,
Leon