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- Real World Poser: I got an '82 pickup with a carburated 6-cyl engine. Aside from leaking a bit of oil and coolant, it runs just fine when it’s warmed up. Before it’s warmed up it hesitates badly during accelleration and seems to miss a cylinder. It takes about 2-3 minutes of driving for it to warm up enough to start blowing warm air out the heater vents, and run smoothly. I have to press the accellerator down ve-e-e-e-r-r-r-ry slowly, or it will start to buck and stall. (That’s in winter temps [30-35 F], in summer it’s faster) I also may have to crank it as long as 5 seconds to get it to start when cold. -And let me tell ya, when you’re late, those first couple minutes last forever.
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- What I have noticed is that if the weather is foggy, the engine starts almost instantly and runs perfectly right away. It still takes as long to start blowing warm air out the heater vents, but the engine doesn’t stall or hesitate at all. I can jump in and floor it, just like in a regular car! I dunno what kind of milage it gets in this condition, the fog don’t ever last long enough for me to figure the “foggy mpg” out. I just know that it runs perfect from a cold start, and seems to run normally from then on. I don’t knw if any droplets of moisture are getting through the filter, but there’s gotta be more moisture in the air.
- I do know that some WW II piston airplane engines used water injection, but it had something to do with being supercharged, which my truck ain’t. Some modern turbine engines also use water injection, but as near as I can tell, that has to do with the conditions they are designed to run in (at altitude, reduced atmospheric pressure and rather cold air temperature).
- Could I put water injection on my truck, and just use it for the first couple minutes? Should I mix water into the gasoline? - MC
No and definitely no.
In principle you’re right though. Water injection would improve power output by increasing the reaction mass in the cylinders.
Why does it make your truck easier to start from cold? I have no idea.
The reason water or steam is used in gas turbines is to increase the mass flow across the turbine and this gives increases of up to maybe 40% in the power output. As a rule of thumb you put in about the same amount of water as fuel. Also you get reduced NOx emissions as a bonus (because the flame temperature is reduced).
don’t mix water and gas (they won’t mix anyway). but you can get a water injector which should help. Can’t say it will solve your problem though.
Check out this eng. for a vacuum leak. Choke pulloff and settings should be checked also. An engine is nothing but an air pump.Air and fuel must be metered into the combustion chamber in the correct ratio 14.7 parts air to 1 part fuel. Getting an older worn in carburated engine to run just right is part art, part skill.MTS
I know someone will be along presently to correct me if I’m wrong.
Humidity increases density altitude. That is, if the air is moist the air is less dense as if you were at a higher altitude. Warm moist air has a greater density altitude. Cool air is more dense than warm air. (I haven’t finished my first cuppa joe yet, so I hope I’m saying this correctly.) So if your truck runs better when the air is less dense (humid or warm), than in more dense (dry or cold) conditions, it sounds like you’re running too lean. (i.e., your ratio of air to fuel is too great.) As **Booker57]/b] said, check the engine for a vacuum leak. Also check to see if the carburator is properly adjusted.
If you are leaking oil and coolant, where is it leaking from? Do you have water coming out of the tailpipe? I had this once (and the engine ran hot) and it turned out to be a warped head.
I am not a mechanic.
I thought about this, but I reckon the humidity doesn’t make the mixture richer.
This doesn’t really help with the OP’s problem, but its something I learned about water injection just yesterday. Water injection is sometimes used on over-boosted turbocharged or supercharged engines. High boost pressures increase the cylinder temp to a point where you can melt pistons. Intercoolers cool the air/fuel charge to make it denser for more power, but this doesn’t do much to cool the cylinder. You can use a method called fuel dumping to cool the cylinder with extra unburnt fuel, but this is wasteful and can cause other problems. There are companies that sell kits to inject water or a water/methanol mix into the intake to cool the cylinders. It can be either a crude system that injects a fixed amount of water, or one that links into the engine management system and does it smarter.
It would be more accurate to say that on supercharged and turbocharged engines, the compressors increase the temperature of the AIR when they increase the pressure, and it is the increased AIR temperature that makes everything else hotter. Intercoolers (some truckers call them “aftercoolers”) reduce the air temp before it hits the engine, and thus reduce the temperature inside the cylinders. This helps prevent burned pistons, but also helps prevent predetonation (that irritating knock you get if you run low octane gas in a high compression motor).
I built centrifugal superchargers for a company in So CA years ago, and we included water injection kits as a standard part of our Corvette kits, and they were an option for other applications. They help leech heat out of the air charge, usually right before it hits the intake manifold, with a fine mist of water.
MC, another option for your truck would be a nice Nitrous plate. It won’t help with the cold starts, but it might help you grenade that motor sooner, giving you the incentive to put a new one in… 
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- Actually, where I am they sorta will. In most US states (mine anyway) gasoline has to use 10% percent methanol, that does allow a certain amount of water to be absorbed into the fuel itself. I worked at a gas station at the time this law went into effect and we saw an immediate drop in the amount of water in the fuel shipments we received once they started sending methanol mix. One of the truck drivers said this was the reason why. -Of course, that means any gasoline now may already be saturated with water. - MC
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I think the second part of your assertion is most correct - “mine anyway”. I know of very few States where 10% methanol is “required”, and in fact in KS and MO I cannot even remember seeing it for sale for a while.
Why do you say this? It seems that you may be mistaking the term “water injection” as applied to IC engines (based on your GT example). Water injection is used by people in passenger cars, and I have personally removed a water injection system.
It’s effectiveness is poor to nonexistent in standard IC engines as a retrofit - more a psychological advantage IMO. But don’t say “no”, as in “no, it can’t be done”.
I agree 100% don’t mix water with gas, for the obvious reasons.
It’s clearly not an obvious reason to everyone just yet…
The reason you don’t want water in the tank is that it will sit on the bottom… The same place as the pickup tube for the fuel pump… When the tank is not being agitated, you’re likely to suck up a large puddle of water right off the bat when you start the motor. Since the motor was designed as an air pump, not a water pump, if you get enough water in a cylinder and force the piston through the compression stroke, you’ll probably start by bending the connecting rod, and things will get worse from there.
Part of the pre-flight check for most small piston-driven aircraft involves taking fuel samples from the low spots in the system where water is likely to accumulate while the craft is at rest.
Uhh…think about how a carburettor and fuel injection work for a minute.
There is no way possible you would get enough water delivered through a carburettor jet or (properly functioning) fuel injector to come anywhere near filling the cylinder with water. The principal danger is getting a large slug of very watery gas which causes the engine to cut out completely.
I did not know that. I have in the past considered adding water injection to stationary IC engines, but I had no idea anyone had done this to their cars. Not for the first time on SDMB, I stand corrected. :humble:
Uhh, ok, now think about doing it with a cold motor, and a fuel pickup sitting in a big puddle of water because somebody thought “50/50 sounds about right.” That means you’re pumping straight water into the cold intake manifold where some condenses and some passes into the cylinders. Not much, but the thing is, without a fuel/air mixture igniting and keeping the water vaporized, it’s not going to send much out of the exhaust valve (at the top of the chamber). You don’t have to fill the cylinder with water equal to the displacement of the piston’s full range of motion, but rather only needs to exceed the capacity of the combustion chamber around the valves and the small cylinder volume remaining when the piston reaches TDC. The real question is how long would that take?
Ok, yeah, most likely you’d quit trying to start it before you got that much water in there, but it could happen. 
Straying off-the-subject here…
Methanol and a handfull of other chemical oxygenates are added to motor fuels in regional markets (often by mandate) to help improve air quality. It’s a Clean Air Act thing, IIRC. And it is one program a city can put in place if the EPA considers the local air quality to be lacking.
I don’t remember off hand which exhaust components (COx, NOx, HC) the oxygenates attempt to minimize, but fuel efficiency sure takes a dive.
In my city, oxygenated fuel it is seasonal thing happening every winter to coincide with the time of year when we experience the worst air quality. I would guess that Kansas and Missouri have reasonably good air.
And to address the OP: I too had a car that ran much better at 100% humidity, preferably when it was snowing and above freezing. It felt very much like the manual choke was engaged. As for why it worked, I have my theories which lean heavily on the WAG:
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The water vapor doesn’t significantly displace fuel vapor from the incoming charge. It hitches a free ride just adding its own mass to the charge. So cylinder gets the usual amount of fuel.
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Then, the water acts to retard the ignition of the fuel/air charge, much the same way that higher octane fuel does, by raising slightly the ignition temperature of the fuel/air mixture.
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Finally, when the fuel and air ignite, the rapidly heated moisture becomes high pressure steam, exerting its own push on the pistons.
Conclusion: Neato. Moisture comes in for free, acts like expensive fuel, and gives a little something back. And all it costs is a little heat from the surrounding surfaces, which the coolant in the nearby jackets was already trying to remove.
I haven’t considered Mr. Carnot and what he would say about the heat. I’ll leave that one for the techno nerds.
[sub]Clever, huh? I accuse others of being techno nerds to imply that I, myself am not one.[/sub]
Sleepy Weasel
Nope, I don’t agree.It just might be possible in theory but in practice if there was just slightly more water than space in the combustion chamber at startup the engine would not turn over.
Having seen this happen when a head gasket leaked and put a small amount of water into the bores I can assure you that the con rods will not bend, the main bearing shells can get slightly dinked but the engine just locks up.This happened to be on a very large diesel engine and the momentum of the flywheel drove the piston up shearing the head bolts on that cylinder.
Now if you have in mind what happens to an engine whose air intake goes under water, like say the Renault Espace can when crossing fords, then yes serious damage can occur, particularly in diesel engines with their high compression ratios.
Duh! Good point, casdave.
That is where I’ve seen it happen, and I hadn’t factored in the difference between an already running engine that is suddenly submerged vs. and engine turned by just the starter… My experience has been with homebuilt “bulletproof” motors, but nobody builds one expecting to suck up a lungful.