Questions tagged [engine]

Questions about vehicle engines. Most engines in road-going vehicles are 4-stroke internal-combustion gasoline or diesel engines.

Filter by
Sorted by
Tagged with
65 votes
9 answers
792k 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 ...
user avatar
39 votes
10 answers
67k 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 ...
user avatar
38 votes
3 answers
371k views

What does a water-like drip 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 drops from its exhaust steadily in 4-5 second intervals. I tried to ask a couple of people at the ...
user avatar
  • 685
37 votes
3 answers
8k 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 that ...
user avatar
  • 32.8k
34 votes
8 answers
17k 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 ...
user avatar
  • 1,125
34 votes
3 answers
11k 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?
user avatar
  • 1,658
32 votes
11 answers
54k 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 ...
user avatar
31 votes
2 answers
27k 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. - ...
user avatar
  • 32.8k
30 votes
9 answers
9k 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 ...
user avatar
  • 1,193
30 votes
3 answers
392k 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?
user avatar
29 votes
7 answers
10k 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 ...
user avatar
  • 529
29 votes
3 answers
14k 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 ...
user avatar
  • 643
29 votes
1 answer
3k 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?
user avatar
  • 32.8k
26 votes
5 answers
68k 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 ...
user avatar
  • 393
26 votes
6 answers
9k views

Does a Car Keep Moving If Neither Accelerator, Nor Brake Is Pressed?

I am not sure if if this is the right forum to ask this, but even my driving instructor cannot give me a clear answer, hence the question. Learning driving on a toyota vios, automatic transmission. ...
user avatar
  • 363
26 votes
4 answers
97k 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 ...
user avatar
  • 8,926
26 votes
6 answers
244k 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. ...
user avatar
  • 363
26 votes
4 answers
501k 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 ...
user avatar
26 votes
6 answers
42k 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 ...
user avatar
  • 523
25 votes
7 answers
26k views

Accidentally left car idling for 14 hours. What are possible consequences from this?

I have an 08 ford focus that I haven't been driving. I just turn it on and let it run for about 30 minutes every few weeks so that it's not just sitting. One time I left it running in the parking lot ...
user avatar
  • 359
24 votes
7 answers
9k views

How do cars drive through deep water as shown on many videos online?

I have read many warnings about driving a car through deep water. Some problems that this can cause is destroy the catalytic converter and in petrol engines water can cause damage to spark plugs. And ...
user avatar
24 votes
7 answers
8k views

How slow ( not zero) can a car engine run without hurting engine and saving on fuel

New cars have stop-start system (even though this has been available for a long time). My question is: why are car companies emphasizing shutting the engine down at a traffic light, rather than making ...
user avatar
  • 359
24 votes
7 answers
410k 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 ...
user avatar
  • 395
24 votes
16 answers
98k 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 ...
user avatar
24 votes
2 answers
17k 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 ...
user avatar
24 votes
3 answers
108k 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 / ...
user avatar
  • 592
23 votes
11 answers
331k 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. ...
user avatar
  • 1,366
23 votes
3 answers
22k views

If I am just replacing the car engine, do I need to replace the odometer as well?

I am considering getting a new engine for one of my cars and I was wondering if I'll have to change the odometer too. Since the car already has 220,000 miles on it, it would become a huge number if I ...
user avatar
23 votes
17 answers
73k 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 ...
user avatar
  • 4,910
22 votes
2 answers
24k 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 ...
user avatar
  • 592
22 votes
4 answers
3k 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 ...
user avatar
  • 2,859
22 votes
7 answers
77k 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 ...
user avatar
  • 8,926
22 votes
6 answers
191k 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 ...
user avatar
21 votes
5 answers
27k 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 ...
user avatar
21 votes
4 answers
4k 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 ...
user avatar
  • 1,186
20 votes
6 answers
8k 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. ...
user avatar
20 votes
4 answers
207k 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?
user avatar
  • 846
20 votes
5 answers
27k 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-...
user avatar
  • 32.8k
20 votes
7 answers
106k views

Does putting an automatic car into neutral at stop lights significantly harm the transmission?

I drive a 2013 Mazda 3, in case that makes any difference to the answer. There seems to be a few discussions on the web which indicate that putting an automatic car into neutral does not ...
user avatar
20 votes
3 answers
118k 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 ...
user avatar
20 votes
4 answers
102k 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 ...
user avatar
19 votes
11 answers
88k 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 ...
user avatar
19 votes
3 answers
16k 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 ...
user avatar
19 votes
3 answers
56k 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 ...
user avatar
19 votes
3 answers
217k 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 ...
user avatar
  • 39k
19 votes
2 answers
9k 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 ...
user avatar
  • 837
19 votes
3 answers
46k views

WHY does an engine stall? (manual transmission)

Before you write off my question as one that's been answered a million times already, I want to clarify. I understand that the engine needs to go a certain rpm and when you try to engage the clutch ...
user avatar
  • 291
19 votes
2 answers
13k 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 ...
user avatar
  • 32.8k
19 votes
1 answer
25k 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 ...
user avatar
  • 293
19 votes
1 answer
13k views

Why does diesel engine need a warm-up before the start-up?

When starting up, diesel engine needs approximately 5s before turning the key for ignition. Why is this neccessary and what can be damaged if you don't do that?
user avatar
  • 325

1
2 3 4 5
51