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
81 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...
21 Reviews
Garage in London, 20 years of experience
Deniz Auto Repairs is a fully equipped DVSA approved MOT station with a total of 3 ramps and fully qualified mechanics with technical expertise. We ensure to deliver first-class customer care and good value ...
JOHN • 24th October 2025
Volvo V50 • Clutch replacement
69 Reviews
Garage in Ballyclare, 8 years of experience
Pat Smyth garage limavady-- 6years Kerrs Tyres-- 2 years Proficient in suspension work, car diagnostics, mot prep, electrical diagnosis of car systems, dpf and adblue systems, I specialise in Mercedes, ha...
PEDRO • 24th October 2025
Vauxhall Insignia Grand Sport • Diagnostic Inspection
11 Reviews
Garage in Nottinghamshire, 40 years of experience
T&G Automotive is a family run service and repair centre for all vehicles. Quotes upfront - no unexpected bills. Competitive prices within the local area. Our mechanics have over 40 years experience with all...
SCOTT • 24th October 2025
Vauxhall Mokka X • MOT with collection & delivery
335 Reviews
Mobile mechanic in Irmingham, 6 years of experience
Experienced mobile mechanic. Offering professional, reliable, and convenient car repair solutions brought directly to your location. Trusted for quality workmanship and customer satisfaction.
71 Reviews
Garage in Blackwood, 20 years of experience
Xtec Mobile Mechanic is a well established with mobile vehicle repairs, serving and Diagnostics that specialises in Fords but covers all other makes and models.
37 Reviews
Mobile mechanic in Aylesbury, 6 years of experience
I work on all types of mechanical work from service, break pads and clutch work. I am very time efficient and effective and doing what I do best. This is a new account. I have experience in doing clu...
130 Reviews
Garage in Towcester, 6 years of experience
We are a race team at heart and do hi-spec race car builds. We also like to see people get the same level of attention to detail on there road cars. From low end to high end you will receive the same level o...
138 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...
LAUREN • 24th October 2025
Toyota Yaris • Brake discs and pads replacement - front (both)
29 Reviews
Mobile mechanic in Pontypridd, 16 years of experience
Paratech Maintenance provides professional vehicle servicing and repairs for a wide range of makes and models. Our team is fully qualified, insured, and committed to delivering reliable, high-quality work.
C • 24th October 2025
Ford Kuga • Vehicle Health Check
100 Reviews
Garage in Blackburn, 5 years of experience
I have a level 3 qualification in the motor vehicle industry and Auto electrics. I was a technician at the BMW main dealer. I also do vehicle Remap’s, EGR, DPF and adblue solutions.
RYAN • 24th October 2025
Audi A6 Saloon • Clutch replacement
49 Reviews
Garage in Nr Leominster., 35 years of experience
Having worked on thousands of Vehicles, Here at Carbon Pro Limited & Pro Tuning & Tyres, our experienced Mobile Technicians are capable of repairing and refurbishing a Vast range of vehicles. Our primary Bus...
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
- 3rd Avenue Autos, Milton Keynes
- A B AUTO SERVICES, Dewsbury
- A R Autos, Bishops Waltham
- Autorel, Ross On Wye
- Beresfords Mobile Mechanics, Bakewell
- DMS Tyres, Stoke-On-Trent
- GREASY MONKEYS LTD, Birmingham
- HQA AUTOMOTIVE LTD T/A Gallowgate Mots, Glasgow
- Ivan Ganchev, St Helens
- LEE J, Irvine
- Lcm Autos, Hull
- Mam Auto Electricians Ltd, London
- Masmobilemaster, London
- Peterhead Terraclean & Auto Services, Peterhead
- Premier Vehicle Services, Essex
- RD9 Automotive Group, Tunbridge Wells
- Trusted Car Repairs And Sales, Coventry