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Questions tagged [engine]

Internal Combustion Engine. Most engines in road going vehicles are 4-cycle internal combustion gasoline engines.

58
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9answers
696k views

What actually happens when there is not enough oil in a car engine?

When a car is topped up with oil, it clear to most people that you are supposed to fill it to the recommended amount as specified by the manufacturer (normally on a dip stick). What exactly are all ...
37
votes
10answers
65k views

Is it necessary to 'burn in' or 'break in' a new car?

I've just bought a new 2011 plate car. I've heard stories of people 'burning in' engines for the first few hundred or couple thousand miles using methods such as: Not driving above 50 mph. Varying ...
36
votes
3answers
319k views

What does a water like drop coming out of the exhaust of the car signify?

Sometimes while driving in the traffic, I come across a car or two which would be dripping water-like drop from it's exhaust steadily in a break of 4-5 seconds. I tried to ask a couple of people at ...
35
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2answers
7k views

Why are the blades of car radiator fans unevenly spaced?

Fans that look like this: Is it to somehow help the balance of the engine?
35
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3answers
6k views

Changing Firing Order in a 4 Cylinder Car

Backstory In motorcycling you can get cams that change the firing order and time from a traditional 1,3,4,2. It's was very common in American road racing in the 1990's to hear 4 Cylinder engines ...
33
votes
8answers
11k views

Why do manufacturers detune engines?

I was wondering why a manufacturer would detune an engine. An example -- there are many others -- is the Mercedes-Benz OM612 engine. Same engine, lower (peak) power output in the Sprinter than in the ...
30
votes
11answers
33k views

Spark plug broke off in engine - can I drive the car?

I own a 2004 Volvo XC90 T6 2.9L AWD with 6 cyl. (Twin turbo, with catalytic converter.) While changing the spark plugs, one broke-off (all the ceramic below the threads and possibly the metal finger ...
30
votes
8answers
7k views

Why is engine displacement frequently a few CCs below an exact number?

I've noticed that engines are rarely exactly 1.5 liters or exactly 4.0 liters, and I'm okay with that. It makes sense that engines would have some arbitrarily ideal size for specific applications, so ...
29
votes
4answers
345k views

what is difference between DOHC and SOHC?

I want to know the SOHC and DOHC configurations. On what factors an engine manufacturer decides to go with SOHC or with DOHC, what should I choose? DOHC or SOHC?
29
votes
3answers
12k views

Static vs. Effective compression: Why does higher effective compression not require higher octane gas?

Background I've been trying to do a lot of research on boost lately because I'm planning on running a moderate turbo setup on my daily/light-duty-autox car in the future. I'm trying to get into the ...
28
votes
7answers
8k views

We have fuel injection, why not air injection?

I'm finishing studying EFI systems, which set me thinking about induction more generally. We inject fuel from a high-pressure common rail for many good reasons. We're capable of making stratified ...
28
votes
2answers
18k views

Why do two-stroke engine exhaust pipes look so strange?

Two stroke gasoline engine exhaust pipes are shaped strange. They expand into a wide diameter and then shrink down to a very small diameter where the exhaust gasses emerge into the environment. - ...
28
votes
1answer
2k views

5-Stroke Engines - What are these things?

What is a 5 stroke engine? Why aren't they using them in vehicles right now? Is this a new thing or has it been around for a while?
26
votes
4answers
73k views

What are the Advantages & Disadvantages of a Boxer engine?

I know that boxer engines are those which have pistons moving in the opposite direction. Also the fact that since they sit low, the center of gravity is lower which causes better handling. Why don't ...
26
votes
4answers
448k views

What actually happens when there is way too much oil in a car engine?

I saw the answers to a question I posted recently highlighting the disadvantages of having too little oil in an engine, but that got me wondering what if the complete opposite were to occur! I know ...
25
votes
5answers
27k views

Is it really impossible to fix a seized engine?

I had an engine seizure that happened while I was driving the car: it ran low on oil and suddenly the engine stopped working (with a bit of smoke). Now after being towed, I have left the car (and ...
25
votes
6answers
198k views

What are the risks of overfilling a small engine with oil?

I recently overfilled a 4 stroke lawnmower engine with oil. It has been run for about 1.5 hours while overfilled. It smokes a lot right after being started but after 30 seconds or so the smoke clears. ...
25
votes
6answers
41k views

Is Start & Stop technology good or bad for my car? (Alfa MiTO)

I was recently in the lucky position to obtain an (almost brand new) Alfa Romeo MiTo, Progression. Like many new cars coming out these days, it has "Start & Stop" technology that turns the engine ...
23
votes
3answers
92k views

Is starting your car with the A/C on bad?

I was always yelled at by my father when I was first starting to drive when I left the A/C on when I turned off the car, and then later turned it back on, with the reasoning that I was ruining / ...
22
votes
11answers
293k views

What happens if a single spark plug unexpectedly goes down in a multi-cylinder engine?

AFAIK vehicle manuals say owner must replace spark plugs every N miles. Suppose he fails to do so and a single spark plug unexpectedly dies in an engine with multiple cylinders right in a freeway. ...
22
votes
2answers
19k views

Why doesn't the engine stall out when you come to a stop with an automatic transmission?

When you come to a stop with a manual transmission you have to push the clutch in or take it out of gear to keep the engine from stalling out. What keeps the engine from stalling in an automatic ...
22
votes
7answers
62k views

Aluminium engine vs Cast Iron engine

What is the advantage that the aluminium engines provide over the cast iron engine apart from the fact of rusting and weight reduction. Manufacturers like to boast about their all new aluminium ...
22
votes
9answers
37k views

What happens if I change the oil when the engine is cold?

I have always changed the oil in my vehicles with the engine hot, because the manuals always say to let the engine reach normal operating temperature first. Oil change instructions all over the ...
22
votes
2answers
13k views

Why do we need to cool air after it leaves a turbocharger?

When we are using a turbocharger to compress the incoming air, the air gets hotter. Usually this hot air is cooled by using an intercooler before it's passed to the engine. What is the reason behind ...
21
votes
5answers
16k views

How do you un-seize an engine?

I have an older engine that is seized. It is a 1953 Desoto Hemi. How can I un-seize it? I have sprayed Sea Foam Deep Creep down the plugs and let sit for weeks. As well as transmission fluid. To no ...
21
votes
4answers
3k views

What are the benefits of a dry sump?

I've heard references to dry sumps, usually in reference to racing engines. But more recently I came across an article about a 'supercar' which stated that it had a dry sump. What are the benefits of ...
21
votes
4answers
2k views

proper oil for 1940's era aluminum ford engine

I would like to know the proper oil to use in a Ford GAA engine from around 1945. Could be as late as 1958. From a series of photos of a GAA being restored on Flickr. Currently this engine has all ...
21
votes
7answers
290k views

Is idling bad for your engine?

If I sit in my car for 30-40 minutes with the AC and the car idling, does that "hurt" the engine, or does it simply waste gas and pollute the air? Would it be better if I turned off the car? A ...
20
votes
6answers
5k views

What is regenerative braking and why don't we use it?

I know that many electric cars use regenerative braking to enable the car to become more efficient by converting what would otherwise be lost heat energy in to a more useful, reusable form of energy. ...
20
votes
4answers
86k views

Why does a Turbocharger only produce boost when the engine is under load?

Why does a turbocharged car only produce significant boost whilst the engine is under load? Is is something to do with how much exhaust is being produced or is there some kind of valve mechanism that ...
19
votes
10answers
59k views

What is the purpose of plastic engine covers?

I have a 2010 Toyota Corolla. What is the purpose of the large plastic cover that stretches over my valve cover? Does it have a particular function? Are they just for looks? Or are they designed by ...
19
votes
4answers
169k views

What is a rod knock?

What is a rod knock? What causes a rod knock, how bad is a knocking rod, and how can I tell if a rod is knocking?
19
votes
6answers
127k views

When is an engine flush a good idea?

I have heard really mixed opinions about the necessity of engine flushes. My quick research suggested that manufactures do not recommend doing them. In addition, I have heard of extreme cases of blown ...
19
votes
3answers
13k views

What does under-square and over-square mean?

When building an engine, the terms over-square and under-square come up. What do these terms mean? How do they apply to engine building? Which is better for what purpose? Can you give examples ...
19
votes
3answers
44k views

Lugging the Engine (Manual Transmission)

So...lugging the engine obviously isn't something that is good. But why? For example when you feather a clutch to get the car moving, it lugs for a quick moment when you hit the catch point (When ...
19
votes
3answers
72k views

What does a flywheel do and what is it connected to?

I understand roughly how an engine works and that there is a crankshaft which is able to turn the flywheel using internal combustion. I have just realised that I have got absolutely no idea how the ...
19
votes
1answer
7k views

What is happening when a two-stroke engine is said to be “four-stroking”?

Many years ago, I was involved in a hobby of building and flying model aircraft. The aircraft used alcohol-fueled 2-stroke engines with glow plug ignitions. When these engines ran rich (and always at ...
19
votes
1answer
19k views

Is this what is making my car sound like a racecar?

Recently, my car (2000 Mercury Grand Marquis) started sounding like a racecar: the engine became very loud. There's clearly something going wrong with the exhaust system. I'm trying to understand ...
19
votes
6answers
40k views

Is it OK to mix oil of different viscosity in a Wankel engine?

I have a Mazda RX-8 (with a Wankel rotary engine). Mazda advises North American owners to use 5W-20 oil. The engine was just replaced 200 miles ago by the dealer so it currently has 5W-20 in it. ...
18
votes
6answers
3k views

How can you tell if the engine is not brand new?

My MazdaSpeed 3 engine blew up, so I bought a new one. When I saw my new engine, it was painted in gray color. My previous mechanic said it was brand new and he bought it from a company from eBay. ...
18
votes
7answers
9k views

Why or why not increase engine efficiency by running the car “fuel-lean” (using a turbo or supercharger)?

Everyone wants their cars to use less fuel, right? I read the following passage about running the car fuel lean from this website: Run the engine fuel-lean, that is, use excess air. It is well ...
18
votes
6answers
7k views

Where does the power in an idling engine go?

When the engine is running, but the vehicle is not moving fuel is still being consumed, where does the energy go?. I am guessing that it goes in rotating the flywheel and crankshaft and stuff, but I ...
18
votes
4answers
19k views

Why do Harley Davidson engines suffer from such poor performance?

The modern Harley Davidson engine has very poor power output. Even when highly modified a 130HP engine can cost tens of thousands of US Dollars. Here are specs on one of the modern engines. Harley-...
18
votes
10answers
65k views

Engine oil change and getting rid of old oil completely

After running the vehicle for a certain distance usually we will change the engine oil. This will not only give engine new life with the brand new oil but will also get sludge and other sediments out ...
18
votes
7answers
10k views

2000 Jetta runs rough, shudders on cold start only on wet days.

This is an issue I've had off and on for, embarrassingly, at least a year: On misty or wet mornings, everything starts out fine but, a few minutes into the drive (like clockwork. I even know the ...
18
votes
4answers
70k views

Driving in second gear at 65+ mph

I accidentally drove my 2000 Grand Marquis on second gear on the highway. I was going 65 for like 5 minutes and tried to get it to 70mph but the car was shaking, when I realized I put it into regular ...
18
votes
3answers
166k views

What exactly is a “burnt valve” and what causes it?

I've come across this term a couple of times in the context of diagnosing engine-related issues, but don't know what it refers to. Here is an example from an automotive forum I frequent: I gotta ...
18
votes
2answers
3k views

What is a leak down tester and what can I do with it?

Background There are quite a few head gasket related questions on the site. Coolant or water in the oil, oil in the coolant or water in a radiator, etc. I'm thinking that some instruction on howto ...
18
votes
3answers
8k views

Is it true that most of the engine wear during its life time occurs during a cold start up?

I have heard this idea several times, but is it true? Theories I read about why that might be true: The engine is running rich at startup because it is running in open loop, which can cause damage ...
18
votes
2answers
9k views

Why did Ducati decide to use the desmodromic valve train rather than a more tradition valve train?

Ducati's use a unique method to open and close their valves. It's called the desmodromic valve train. The desmodromic valve system does not use springs to close the valve, it uses the cam and has a ...