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...
32 Reviews
Garage in Leytonstone, 5 years of experience
Here at BSRC LIMITED, we treat your car like it’s our very own. Our team of professionals uses only the highest quality products to fix, paint, repair, adjust or realign. We only fix what needs to be fixed, ...
PIERPAOLO • 21st December 2025
Land Rover Discovery Sport • Timing chain replacement
463 Reviews
Mobile mechanic in Tamworth, 15 years of experience
Ive been a mechanic for 15 years im hybrid trained and level 3 trained technician ive worked for a major leading company and decided to run my own business im also mot trained so have a good understanding of...
PAUL • 21st December 2025
Peugeot RCZ • Diagnostic Inspection
77 Reviews
Garage in Wembley, 15 years of experience
Experienced Automative Mechanic with over 15years of hands on expertise in diagnosing and repairing vehicles. Specialised in repairing vehicle engines, Servicing, Clutch repair, Brake system and Electrical c...
99 Reviews
Mobile mechanic in Gloucester, 6 years of experience
6 years of experience in various garages and one year as a mobile mechanic
MATTHEW • 21st December 2025
Ford Fiesta • Battery replacement (vehicles without stop/start system)
149 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...
CLAIRE • 21st December 2025
Nissan Juke • Brake discs and pads replacement - rear (both)
1 Reviews
Garage in Accrington, 5 years of experience
worked on vehicles since a young age. we repair vehicles we purchase vehicles we also sell vehicles
ANDREW • 21st December 2025
1288 Reviews
Garage in Horton, 20 years of experience
Jon owns and operates SMS Autocare and has been running the business for over 15 years in the Slough area. Prior to setting up SMS Autocare Jon completed his apprenticeship and was then a mobile mechanic for...
487 Reviews
Garage in Thornton Heath, 7 years of experience
Welcome to AUTO PRO, where automotive excellence meets customer satisfaction! With over 7 years of hands-on experience in the auto industry, we take pride in being your trusted partner for all things automot...
185 Reviews
Garage in Walsall, 15 years of experience
AA Approved Repairer RAC Accredited Repairer NHS Discount Up to 30 Years Experience throughout the whole company Air Conditioning Service/Re-Gas
CHELSEA • 21st December 2025
Vauxhall Corsa • Alternator replacement
11 Reviews
Mobile mechanic in Brentwood , 5 years of experience
Experienced and qualified Automotive Mechanic with over five years of hands-on experience working for local garage . Skilled in diagnosing, repairing, and maintaining a wide range of high-performance vehicle...
DAVID • 21st December 2025
Land Rover Freelander 2 • Car Won't Start Inspection
62 Reviews
Garage in Lutterworth, 15 years of experience
Hello there! My name is Nathan. I have worked in HGV breakdown / recovery and been a mechanic for many years, offering over 15 years experience. I am happy to assist wherever possible with any car,...
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
- A&D Autocenter, London
- AC,S Mobile Air Conditioning Services, Newtongrange
- Brakes And Tyres On Your Drive Ltd, Runcorn
- Humberside Motors Ltd, Scunthorpe
- Marra Motorsport Ltd, Workington
- Mobile Vehicle Services Limited, Broughton Astley
- NH Auto Centre, Birienhead
- R.J Hatch Mobile Motor Mechanic, Gloucestershire
- Roxam Works Garage, Coventry
- SR MECHANICS, Scunthorpe
- Sprint Motors Ltd, Leek
- St Albans Autocare, Ashton-under-lyne