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

80 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 Great Yarmouth , 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...

50 Reviews

Garage in Leeds, 6 years of experience
Worked 6 plus years in a garage doing diagnostics repairs brakes servicing suspension steering and mot testing.

28 Reviews

Garage in Crawley, 11 years of experience
MOT Testing: For cars, vans, and motorhomes up to 12 seats. we do Car Servicing and Repairs, Air Conditioning Regas and Repairs, Brakes, Exhausts, and Suspension Repairs and all sort of diagnostics.
KEN • 23rd August 2025
Ford Fiesta • MOT with collection & delivery

2 Reviews

Mobile mechanic in St Helens, 30 years of experience
I am a mobile mechanic with 30 years experience in the motor vehicle industry. Throughout the years i have worked for Main dealerships as well as independent garages. 15 of the years in the trade i worked...
LUKE • 23rd August 2025
Kia Picanto • Brake discs and pads replacement - front (both)

120 Reviews

Garage in Trowbridge , 7 years of experience
Hi, I started my journey in car and mechanics business 6 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 w...

15 Reviews

Mobile mechanic in Newcastle Upon Tyne, 10 years of experience
10 + years experience doing vehicle repairs ranging from cars to commercial vehicles, most of which I do mobile for the customers convenience. I offer a wide variety of services including: Brake repl...
LUCY • 23rd August 2025
Nissan Juke • Diagnostic Inspection

185 Reviews

Mobile mechanic in Milton Keynes , 12 years of experience
We can carry out all types of repairs no jobs too big or too small
RAYMOND • 23rd August 2025
Vauxhall Mokka • Car Won't Start Inspection

152 Reviews

Mobile mechanic in Leicester, 7 years of experience
If you require car services such as advanced professional car diagnostics, electrical repairs, dash cam installation, cambelt replacement, clutch replacement, tire puncture repairs, jump-start assistance, or...
ALEX • 23rd August 2025

24 Reviews

Garage in Midhurst, 39 years of experience
We have over 50 years combined experience in the car repair industry. We are skilled in all car makes and fully qualified to level 4 . We solve diagnostic issues .

166 Reviews

Garage in Aldershot, 15 years of experience
Mobile mechanic, pick up and drop off car if extended repair needed, full diagnostic, full service, clutch, suspension, engine repair, cam belt, DPF cleaning, brakes, exhaust and more.

37 Reviews

Mobile mechanic in London , 20 years of experience
Hi this is Jose I started very young in the automotor mechanics industry 3 years in a vehicle technical institute 2 in the university I worked in different garages all over South America 6 years as a s...
BARRY • 23rd August 2025

31 Reviews

Garage in Dartford, 10 years of experience
Mobile vehicle repairs for Dartford and surrounding area's.
MICHELLE • 23rd August 2025
Suzuki Swift • Gear linkage 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
- A. L Autos, Gwent
- AT & GD Commercial Services Ltd, London
- CK Mobile Mechanics, Fontwell
- Denmark Street Motors, Berkshire
- Drm Mechanical And Car Sales, Kilsyth
- J Walker Automotive, Hailsham
- MB AUTO SOLUTIONS, Ramsgate
- MBT AUTOGROUP LTD, Glossop
- Motorteck, Dartford
- Mymachineid, Cleethorpes
- NGS Autos Ltd, Peterborough
- RAPID RESPONSE TYRES LIMITED, London
- Uzi London Ltd /Clifton Garage, Nortampton
- Working On Wheels, Marlborough