How does a car engine work?
A car engine is your vehicle’s powerplant - consisting of cylinders, pistons, crankshaft, camshaft, and ancillaries - housed under the bonnet. It burns fuel to produce the torque that makes your wheels turn.
A modern car engine is essentially a controlled sequence of small explosions (combustion events) that convert chemical energy (fuel) into mechanical energy (motion). Most cars use a four-stroke internal-combustion engine.
A car engine orchestrates millions of tiny combustion events every minute. Most car engines have 4, 6, or 8 cylinders. They fire in a staggered order so that there’s always at least one piston in its power stroke - this smooths out torque delivery and reduces vibration.
By precisely coordinating intake, compression, ignition, and exhaust across multiple cylinders, it converts fuel into the rotational force that ultimately turns your wheels.
What happens during an engine diagnostic or inspection?
An engine diagnostic is a structured check to find the root cause of warning lights, rough running, overheating or loss of power, so you only pay for the inspection and then for any fixes needed (if you want).
A mechanic will generally listen to the symptoms you’ve noticed, checks fluid levels and visible leaks, and may take a short road test to confirm the fault and capture data (if the car is driveable).
They connect a diagnostic tool to read fault codes and live sensor values (airflow, temperatures, fuel trims, misfire counters, etc.). This quickly narrows the hunt to ignition, fueling, air, or mechanical issues.
Under-bonnet inspection of hoses, intake pipes, belts, wiring and connectors; simple voltage/earth checks to rule out obvious causes before any deeper tests.
You’ll get a clear explanation of the fault, any supporting test results, and a fixed-price quote for the repair where possible.
In reality, many “engine” worries turn out to be repairable components (e.g., sensors, coils/plugs, leaks, water pump/thermostat, timing belt/chain work). If a more serious issue is found, your mechanic will explain options and costs before any repair is started.
How do I know if I need an engine replacement?
Here's some ways to judge whether your engine is truly beyond repair and likely needs a rebuild or full replacement.
Red flags that often mean “engine out”
- No oil pressure or loud bottom-end knock (deep, metallic thud that rises with revs) likely means bearing failure; running it will destroy the crank.
- Seized or won’t turn even with a good battery/starter could be internal seizure or hydrolock.
- Severe overheat followed by constant white smoke, mayonnaise in oil/coolant, or external cracks
- Heavy, persistent blue smoke and very low compression on multiple cylinders
- Glitter/metal in the oil or sump
- Repeat head-gasket failures after a previous repair indicates underlying block/head damage.
When repair (and not replacement) might still be sensible
Problems confined to the top end: single-cylinder low compression from a valve issue, a first-time head-gasket failure on a non-overheated engine, or noisy tappets/cam followers.
Clear external causes you can fix at the same time (e.g., water pump/thermostat on an overheating car, oil leak that starved the engine).
What does an engine replacement quote cover?
ClickMechanic does not provide a full engine replacement or engine rebuilds but we are able to help with most engine-related repairs.
Top Mechanics For Car Engine Replacement & Rebuilds
25 Reviews
Garage in Birmingham, 15 years of experience
I began my career in Zimbabwe in 2002 before moving to the UK in 2004. My first role within the UK was in Wolverhampton with Audi for over 4 years from 2006-2010; I moved to work with Oxford BMW for 3 years ...
JASON • 1st March 2018
Ford Mondeo • Full exchange engine replacement
83 Reviews
Garage in Leicestershire, 19 years of experience
I began my car repair experience in a Peugeot main dealer. I spent three and a half year there and then two years Renault main dealership. I then worked on a variety of cars in backstreet garages and built m...
SAMANTHA • 21st October 2017
485 Reviews
Garage in Southampton, 20 years of experience
I began my career as a mechanic when I was 17 years old in Portugal. When I was 22 years old I set-up my own garage in for around 7 years before moving to the UK in 2007. I worked in various garages in order...
235 Reviews
Garage in Lowestoft , 30 years of experience
I began my career in Chadwell Heath at a garage called High road Station which is where I completed my apprenticeship. I was with the business for around 6 years, I moved to Wallinghurst Garage in Billericay...
111 Reviews
Garage in Arundel , 20 years of experience
Been working on cars from a very early age to get to where I am today. From diagnostic work, wiring, engine replacements to general service and brakes. No job is to big or to small.
CARLOS • 8th January 2026
157 Reviews
Garage in Trowbridge , 7 years of experience
Hi, I started my journey in car and mechanics business 7 years ago and have been committed to learn all I can about cars and how they work to better my self and experience to customers. I have been working...
DAVID • 8th January 2026
Ford Focus • Brake discs and pads replacement - front (both)
9 Reviews
Mobile mechanic in Birmingham, 13 years of experience
Worked in an independent garage and a dealership. I can complete the following to a high standard: . MOT test . Services and repairs . Brakes . Exhaust . Steering . Suspension . Light diagnostic wor...
DAVID • 8th January 2026
Ford EcoSport • MOT with collection & delivery
1 Reviews
Garage in Gloucester, 8 years of experience
As a qualified Master technician, I pride myself on providing honest and quality repairs and ensuring good value for money by accurate diagnostics and live data readings. After training and running my own co...
43 Reviews
Mobile mechanic in Cattistock, 16 years of experience
16 years experience as a mechanic, now mobile based. Love what I do and always happy to help.
PAUL • 8th January 2026
Ford Mondeo • Battery replacement (vehicles without stop/start system)
203 Reviews
Garage in Portsmouth, 21 years of experience
Over the years I have worked in various garages, carrying out mechanical repairs, including, servicing, general repairs, mot repair, cambelts/timing chains, clutches, head gaskets, engine replacements etc I ...
JOE • 8th January 2026
Fiat Grande Punto • Clutch replacement
79 Reviews
Mobile mechanic in Hull, 19 years of experience
19 Years Experience Ford Master Technician Ford High Voltage Training Love what I do.
126 Reviews
Garage in Sittingbourne , 15 years of experience
TC MOBILE MOTORS Carrying out diagnostics inspection Servicing Cambelts Timing chains Engine rebuilding Brake pads and discs Suspention repairs DPF repairs and more anything needed i can repair...
10 Reviews
Garage in Alloa, 10 years of experience
Working around cars for 15 years . Time served 10 years . With Arnold Clark . And GTG training facility. Servicing. Brakes , clutches , gearboxes. Drivetrain. Suspension work. Air conditioning F gas trained ...
CHRISTOPHER • 8th January 2026
Mercedes-Benz A-Class • Starter motor replacement
154 Reviews
Garage in Northampton, 7 years of experience
As a dedicated mechanic, I take immense pride in my work, knowing that every repair and every adjustment I perform keeps vehicles running smoothly and safely. My hands are skilled, my mind is sharp, and my p...
IGOR • 8th January 2026
Infiniti Q30 • Glow plugs replacement (all)
148 Reviews
Garage in Manchester , 22 years of experience
We are a small family-run company. We offer recovery and repairs. We will provide as much advice as we can before carrying out any repairs. We are approachable and always happy to help. Some of the repairs w...
PIARA • 8th January 2026
Renault Grand Modus • Crankshaft (CKP) position sensor replacement
Frequently asked questions about car engine replacement & rebuilds
Read our answers to questions about car engine replacement & rebuild costs, symptoms and more.
How much does a Car Engine replacement cost?
The cost of a full engine replacement can vary wildly. Depending on your vehicle and using a used or reconditioned engine the replacement can cost from £1000 to over £5000 for the biggest engines. It is advisable to get an opinion from a mechanic on whether the engine perhaps can still be repaired, provided no catastrophic engine damage has occured.
Book a trusted mechanic today
Get an instant quote, then book a vetted mechanic to fix your car at your home or office.
- Vetted mechanics
- Save up to 50%
- Fast online booking
Mechanics that undertake car engine work
- Army Mechanic, Lyneham
- B And G Autotechs Ltd, Oldham
- BHP Automotive Ltd, High Wycombe
- MASUMIN MOTOR SPARES LTD, Milton Keynes
- Mobimech, Dartford
- Prompt Smart Repairs Ltd, Marston