Black is poorly burnt fuel- almost always a result of a too rich mixture-
such as an engine on choke when it doesnt need it, or another fuelling
fault. Its bad for the engine- the excess fuel results in bore wash.
White smoke is either normal condensation from the exhaust system, or if it
persists and the coolant is vanishing- then you have an internal leak into
the combustion chamber(s)- be it a failed headgasket, cracked block or head,
Are you sure its not just residual soot in the exhaust system that is being
blown out when the gas speed is high- i.e. high revs?
Poor compression due to bore wear / oil control problems will be sky blue
or dark blue in coloour. Poor compression caused by poor valve sealing will
just give poor engine performance- not smoke.
Well you could be right. My mechanic could be wanting to cheat my
money. How do I tell whether it's because of black soot or not?
but I think my mechanic feels it's due to poor valve sealing because
the guy took out the air filter and looked into the carb.. there
seemed to be fuel residue coz the intake valve doesn't close properly
anyway what's the process to fix valve sealing problems?
White smoke is steam and usually means the head gasket is letting coolant in.
You get some white smoke as water is a by product of petrol combustion, but
it's usually mixed with black smoke resulting in grey and the odd drip from the
As to how easy it is to fix the valves, that depends a lot on the engine but
you almost certainly have to remove the head(s) which is a fairly major job
costing quite a lot, resulting in new gaskets for the heads, removing the
exhaust and inlet manifold(s) meaning new gaskets for them too, and various
other work which includes keeping the chains in place or having to reset the
timing if it is overhead cam (which it probably is).
There are two methods. The above, and then grind / replace the valves cutting
new seats as necessary (the expensive, full repair). This probably sees you no
change from a grand, depending on engine, work needed, rates and so on.
The second method assumes the problem is gunk or dirt in between the valve and
the seat, so you spritz injection cleaner down the manifold / intake in the
hope that it will dissolve / wash the debris away and sort the problem. You can
do with having the engine running for this to work best. This is cheap and DIY
but won't sort out things like damaged seats or valve heads so you try this and
then invest hundreds in having the heads off and reconditioned.
Some engines are old and you can get heads for them for next to nothing, if the
engine normally outlives the car body. You can then grind the valves before
having the heads swapped, usually a relatively quick job compared to having the
valves done on your existing heads. If the engine is fairly new, this won't be
Apparently on date Thu, 08 Jan 2004 21:35:44 +0800, Brian Su
Apparently on date Thu, 08 Jan 2004 15:29:41 +0800, Brian Su
White smoke is usually steam and usually means that coolant is getting into the
combustion chamber, more often than not this is a blown head gasket.
Black smoke is more likely to be carbon compounds which can derive from petrol
or oil, if it's continually coming out it's most likely burnt oil.
A note here, when we had unleaded petrol, the exhaust pipe used to be black and
sooty when the engine was running overly rich, and would be a nice grey colour
when the engine was running properly. The grey was actually lead oxide, and
with unleaded fuel you won't be getting much of that so expect black sooty
A corollary to that, any smoke coming out of the engine is likely to be black
for that reason if for no other, but it's more often mixed with steam (as you
get water as a byproduct of combustion) and is a thin, grey colour when all is
I reckon I'd need to know a bit more about the engine, e.g. type and has it
started doing this recently. It might be that the cat has broken up and is
blocking the exhaust pipe making things run sooty and rich.
But there's a lot of reasons, broken ring, worn guides, etc, etc.
Hi there thanks so much for your reply guys.
Yeah could it be the cat having problems? Because I once pumped leaded
fuel into the car and ran it for a while :( It wasn't that much but
I'm afraid it's more than enough to spoil the cat.
As for using injector cleaners, I thought these were for fuel
injection engines only and don't apply to carb engines. Are there such
things as valve cleaners fuel additives?
Also, I've heard the danger that these additives may be corrosive to
the engine, how likely is this to be and what are the problems?
Why does the gasket need to be changed when opening the head?
On Thu, 08 Jan 2004 14:03:54 +0000, email@example.com wrote:
No. Cats either work, or dont, or break up and clog the exhaust system. They
cant make various colours of smoke. A cat in good condition will actually
burn blue smoke caused by oil combustion so you wont see the blue smoke at
Injector cleaners are aimed more at injection engines, but both are
basically a strong flammable detergent, although the "joe public" brands are
about as effective as a chocolate fireguard. Dont waste your money using
them in an attempt to solve a problem. If you use decent petrol (high
detergent) and the engine is in good order they are not needed.
Are there such
Yes, but almost exactly same ingredients as above. The only thing to clean
heavily carbonned inlet valves is either redex in excess 'poured' into the
inlet til engine stalls then let soak over night, and repeat (be careful
doing this) or strip the head and clean the valves manually. Again decent
fuel will prevent these problems anyways.
If used according to the instructions no. Can you imagine a additive company
staying in business long if their product caused damage to the engine?! Some
additives may damage the a catalytic converter though. Most as cat safe
however when used at the recommended doseage.
The head gasket, is usually a compressible composite gasket that squashes up
when the head is tightened down onto it and 'absorbes' all the minor
irreguarlitys in the head and block as well as sealing the water and oil
ways. They are usuable only once.
However you can have sintered stainless and / or copper and various other
trick material h/gaskets, usually for forced aspiration engines which are
re-usable, but you wont find these on a standard road car.
Apparently on date Fri, 09 Jan 2004 02:14:30 +0800, Brian Su
That would only contaminate it, it's not relevant to the question of the black
smoke. But if you can hear it tinkling when you shake the pipe about, it could
be blocking the pipe and making the engine struggle to breath.
Cleaners are usually just light volatiles. The sort that you put in the tank
are designed to come through the injector needle itself, carried by the petrol.
I don't mean those, I mean the sort that comes in a tin which you squirt onto
the thing you are cleaning. Petrol will do, but it's not ideal, it is of course
Additives are generally a waste of time because fuel comes with a decent mix of
detergents and stuff, much like oil additives are best avoided - much better to
change the oil than add something to it.
You can squirt injector cleaner into the intake fairly freely - if the engine
is running - because it will be sucked into the engine and burned to nowt. It's
unwise to do it to an engine that isn't running because it can lead to bore
wash. If you're lucky, the cleaner will take any lumps of stuff off the valve
seat / head and put the engine back to sorts. It's certainly worth trying
because it's cheap and easy. If it doesn't work, you're in the same position as
before so worth a bash, no?
You can get away with not doing it, but only when the gasket is still
relatively new. The reason you need to replace the gasket is an old one will
normally develop a leak if you don't, they will anyway once they're old enough
(oil leaks are almost always a duff gasket). Since a gasket is maybe a tenner,
say five to 25 and maybe you pay 30 for a complete upper set for an engine,
it's much more sensible to change the gasket for a new one when you are paying
250 quid to have the head taken off and put back on. Saves paying 250 again to
put a new one in anyway when the old one starts leaking, no?
If you are doing it all yourself, that's quite different. You can always spend
the next weekend doing the job again if necessary.
What do you mean squirt injector cleaner into the intake? How do I get
access to the intake manifold? Do you mean squirt it into where the
air filter fits on to?
Also just wanted to know what are the causes when an engine's oil
level keeps dropping rapidly? Besides a leak, what could be the
If it's a leak is it likely that the oil filter wasn't tightened
Thanks once again guys :)
What do you call rapid and on what car?
If theres no obvious leak then its either an unobvious leak (back of engine
maybe) or its being burnt by the engine, perhpas due to aged valve stem
seals or piston ring(s).
I wouldnt say the oil filter was likely to leak, unless it was fitted by a
complete muppet. If it is leaking, then just screw it up tight with your
hand, thats all the needed (assuming its not shafted)
Oil can only go in two places.
1) You have a leak. that should be obvious. Oil filter, a gasket, a seal,
oil cooler hose, sump plug, filler cap leaking etc.
2) The engine is burning it. So thats bore wear, broken oil control rings,
worn valve guides, worn valve oil seals, cracked block or head, blocked PCV
system forcing oil into the intake, excess blow by doing same, too much oil
in sump etc. To be loosing alot via this method you'd be driving with a
smoke screen behind you.
Apparently on date Sat, 10 Jan 2004 04:08:44 +0800, Brian Su
Yeah. Remove the air filter element, squirt it into the air going into the
engine, there ought to be a significant suction to help there, be sure that you
won't be dropping rings / bits of dirt / plastic tubes from the cleaner aerosol
into the engine, they'll not do nice things to it.
The airflow will pass through the manifold and through the inlet valves,
carrying the cleaner with it and with any luck washing the dirt off the valve
head / seat. If not, you've only wasted five minutes and a few quid on the can
Remember to put the air filter element back on, it stops dust and sand damaging
Could be, but you can see this fairly easily. Oil on an old engine commonly
comes out of lots of minor gaps and leaks, and then drips off the bottom of the
sump. This is pretty normal. If it is leaking rapidly, you'll be slipping over
in the garage due to pints of oil splashed all over the floor.
Sometimes the leaks are higher up the engine, in which case they'll only tend
to leak when the engine is actually running. Putting the car over some light
road (newspaper can do) and running the engine will show this up pretty
If the oil isn't leaking out this way, the engine may well be burning it.
Broken pistons or rings let oil into the combustion chamber, although mostly
you'll find broken rings charge up the crankcase and cause the oil to be pumped
through the breather instead. Valve guides will wear, and allow more oil
through than is needed. If your engine is burning oil, the exhaust smoke will
tend to be black.
As a rough guide, when the oil smoke intensifies when you are going flat out on
the motorway or up a hill, it's going through the breather system. When the
smoke intensifies when you lift your foot from the throttle after going flat
out, that's more often coming through the valve guides. You will need someone
in a car behind you to spot this most easily, it's not obvious from the drivers
You can also have what one of my cars has got. A decently clean breather, but
duff rings so the crankcase is always pressurised, especially under
acceleration. The oil comes out of the right hand rocker box and gets all over
the drivers side of the windscreen, top of the bonnet / wing, and all over the
car behind if they're too close. I plan to put new rings and measure the wear
in the liners in spring, while rebuilding the engine. Hopefully that will sort
out the blowby.
Hi, so what type of injector cleaner do I get and squirt down the air
intake? Will the normal petrol additives or injector cleaners do? I
mean those which I can get off the shelf like Redex Petrol Injector
I believe these products aren't made to be squirt down the intake
manifold so can you give me some simple guidelines to follow? as in
how much to squirt down at a time? What are the dangers involved?
choking the engine? flooding the carb? etc.etc.
Apparently on date Sun, 11 Jan 2004 00:12:06 +0800, Brian Su
No, not petrol additives. These won't go through the inlet manifold and wash
the valves, they will come through the fuel in minute quantities and only clean
the injectors themselves as the fuel passes through the injectors. And I
wouldn't bother with them at all, there ought to be something to do that in the
Ok, you're looking for an aerosol can which says it cleans carbs and is to be
squirted into the intakes. Halfords will sell some of these, they're all
generally much the same thing, truth be told.
You take the air cleaner out.
You point it in while the engine is running and press the nozzle down so the
stuff sprays out.
Pick a can that says this is what it is for, and it is to be used in this way.
Carb / injection cleaner, makes no odds really as you're actually trying to
wash debris off a valve.
If the engine is running I can't imagine what might go wrong, but check what
the can says just in case.
If it is a worry, just go straight to the mechanic's solution instead, this is
only a cheap and easy way to try a simpler solution - it's quite likely to
achieve nothing at all.
P.S. I do this regularly on my car, mainly to clean the airflow sensor. It's a
hot wire that has gunk burn onto it and gradually reads higher and higher. So
far, nothing bad has happened. Since you are pumping corrosive petrol into the
same places, I doubt it's going to harm the combustion chamber even if you use
fly spray or Mountain Breeze air freshener, but probably best not to
You ask a lot of questions on here Brian but I will be more tactful than Mr.
A good car maintenance manual will answer 90 percent of your queries and
will also have the benefit of not having to wait for us to get from under
the car and reply to you!
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