I am looking into buying a second hand car from a reputable Mercedes-Benz dealer (not just some dodgy salesman by the side of a road lol....).

Anyway, there are a few maintenance/mechanical things which I want to check, but I don't quite understand how and I was wondering if you could help explain HOW I can go about physically checking these things when I go and visit Mercedes and have a look at their second hand cars. The things I want to check are as follows:


Yes I have read online that here in the UK the tyre must have at least 1.6 mm of tread depth across the central 3/4 of the tyre and across entire outer circumference. Great... but how do i physically check that? I read on some sites that there is a tool you can buy which can help you figure this out. But I haven't been able to find out what this tool is. Do you know what it is..... OR .... do you know of any techniques I can use to roughly figure out if the tyre is in good condition??

I was also looking into wheel alignment. So far the only thing I have found on this is that you can ONLY test this by taking the car for a test drive and testing to see if the car drives to one side when you let go of the wheel. Is this correct?? Is there anything else I can do to check if the alignment has gone?


I will be checking the oil, looking at the exhaust fumes and generally listening to the engine and seeing how smooth it is to drive. Some people online have stated that you should check the engine gasket and the cambelt for dry rotting.... but how an earth can I check those things at the dealership.. I would have to physically open the engine... which obviously won't be allowed. Are there any other types of physical checks I can realistically do when inspecting the car? Please be descriptive... I could really do with as much detail as is possible.


I know this is getting a bit off topic but I will try and keep it as mechanical orientated as I can.

In general how can I haggle over the price? The car I am looking at is a 2012/2013 Mercedes C180 Coupe and most of the prices I have seen online are around 17k (GBP) to about 20k (GBP). So lets say I find one for around 17/18k, could I offer the salesman 16k? Would that be considered rude? How much can I realistically lower the price?

Lets say the car needs 4 new tires or a new exhaust. Could I get the repair included in the deal?

Side Note

I have searched a lot online BEFORE writing this question, so please consider keeping this question open. It is a genuine question with lots of mechanical/maintenance related detail.

Once again, I have read other posts online (even on this site) about what to check when buying a second hand car... but none of them go into detail about how to physically perform these checks.

Thanks for your time, Dan.

  • @T.J.Crowder All updated! Sorry about that.
    – Dan
    Commented Jul 17, 2015 at 7:15

6 Answers 6


The below are very easy checks you can do while buying a used car.(from anywhere for that matter of fact)

  • Engine

This is the most complicated/expensive part to maintain/replace.

  • Head Gasket check: Open the oil filler cap or the dip stick for any milky white substance, like mayonnaise, if it is present then stay away, it means the head gasket is broken and coolant is mixing with the oil.
  • Check for any possible oil leaks on the engine itself, if present this means that one of the oil seals have given way, usually cheap to repair.
  • Check the underside of the engine, if there are any possible leaks, any sign of liquid leaking from the engine bay one of the hoses might have leak (there are a host of things which carry fluids on a car so I cannot list out all of the fluid leak symptoms just check anything that is not water)

Since you have mentioned it's a dealership there is a good chance of them cleaning it up so the other way to check is taking it for a drive and then checking the underside

  • check the battery

  • The multimeter/voltmeter will have two prongs sticking out red(+ve) and black(-VE) turn the middle knob to 12 or 20 volt scale, connect the prongs to the corresponding terminals on the battery the reading should be around 12.24 to 12.66.

            12.66v . . .  100%
            12.45v . . .  75%
            12.24v . . .  50%
            12.06v . . .  25%
            11.89v . . .  0%
  • Check the alternator: Again using the multimeter, follow this link for a detailed guide on how to check it, I am pointing it out here since a new alternator is cheap but the labour cost is massive. How to check alternator

  • Check for any burnt smell (usually unlikely but give it a shot)

  • Cold Start: DO this step in the beginning, have someone start the car and look at the exhaust; if you see lot of black smoke then you have problems.

  • CEL check: Check for the check engine light; if it's ON then you have issues with the sensors or the ECM.

  • Belts: have a look at the serpentine belt, the one which connects the compressor to the engine and alternator, check for dry rot there.

  • check service records: Insist on having look at service records, look if any parts have been changed. check if the timing belt or chain has been replaced.

  • Idle check: do a cold start and wait for some time, check if the car is idle properly and not cutting off, if it is then might be issue with fuel delivery or intake.

  • Cranking: Check if the car is cranking properly and does not require you to crank it like a mad man to start.

  • Transmission:This is the next important component of a car.

  • Start the car, put it into first and move, note if you are having any issues in getting off the line.

  • Check if you don't grind the gears while shifting.

  • To check the clutch, put the car in second or third while standing still and release the clutch, the vehicle should nudge and shut off, if you have issues with the clutch plate or the assembly then your car will keep on moving instead of stopping.

  • Put the car in reverse, it should not grind. (not a major issue)

  • I am not a automatic driver so here is a link to how to check auto transmission (just make sure your car does not jerk while shifting into modes abruptly) How to check automatic transmission

  • Suspension

  • Stand near the top of each wheel arch and press down with your hands, the car should retain its position albeit with a small bounce, if it's more or less then either your damper or coil is gone. (Do this for all 4 wheels)

  • manually inspect the coil/damper for any oil leaks to know their condition.

  • On a car with McPherson type suspension check if the shocks are not completely wedged into the body(sort of depends on the vehicle type)

  • While the car is still start it and turn the steering full left and right, you should not hear any clanks or creeks from the con rods.

  • Take it out on a drive, find small and big potholes on the road, insist on going bad roads, check if your car does not hit with a thud while going over bumps. ( unless you are buying a sports variant which will)

  • Look at the service history for any previous accidents, this is important since lower control arms do not break easily but when they do they cost a lot to fix.

  • Body

  • First and foremost, pop the bonnet, look underside of the bonnet for any repair work, check if the rubber seal around the bonnet is intact, if you spot any abnormalities even in the paint it means the car has had a frontal collision.

  • Check for rust on the underside of the car, check if the subframe (outline of the car) is intact and not dents or deforming is there.

  • Check if all the panels fit properly else the car might have been involved in a crash.

  • Though subjective, check for the paintjob and overall dents on the body (I personally don't mind scratches)

  • Steering alignment, check if the steering is aligned properly by doing a test drive( also notice the free play of the steering

  • Electricals

  • Again this is sort of subjective and can help in bargaining the price , you can compromise on some parts here.

  • Check if the power windows/seats/mirrors/lights/stereo are working if not then I would start to negotiate prices(lol)

  • Check if the power steering is working, it should not be hard.

  • Check if the airco is working and the AC works on all the settings (if not auto climate control) pop the hood check if the compressor is engaging.

  • Have a look at the interiors especially under the carpet for any rust, if so then the underside has a leak through which rain water can seep in.

  • Brakes:

  • check if the brakes are functioning properly and you can actually stop the vehicle depending on the pressure you apply.

  • Check for any rough sensation on the foot while breaking (might be issue with master cylinder)

  • watch out for any squeaking sound or burning smell from the brakes.(can be fixed easily)

  • Have a look at the disc ROTOR, if it's rusted then the car has been standing still for a long time, look at any rough edges or damages to the rotor if so you need to change the pad together on both side will be sort of expensive.

  • Tyres

  • Since it's the law in the UK I advise you to have the measuring device but there will be small studs on the tyres which indicate the wear points (sorry for no image will update when I get time)

  • Tyres should have even wear throughout if not then might have issue with the camber adjustment.

  • There should be no abnormal deformities in the tyre like a bubble.

  • Check the alloys for any cracks.

  • Finally the documents:

  • Check for proper documentation

I will update this once I get time, as of now this should be hopefully helpful

  • 4
    You have good advice here ... for someone with mechanical ability. Dummy this down some with specifics. For instance: How do you check the battery? You and I know. The OP probably does not. How do you measure the tread of the tires? What do you check them with? The OP is not a car guy ... flesh out your answer a little with more specifics. Don't be afraid to use a picture to show your point (ie: pics are worth a 1000 words?) Commented Jul 16, 2015 at 10:42
  • 3
    @Paulster2 Wow what a superb answer! But I agree with Paul. Could you go into more detail as to HOW you physically check these things like the battery or the tires? I am a car enthusiast, I love V8 cars. But I am young and still have a lot to learn.
    – Dan
    Commented Jul 16, 2015 at 10:45
  • @Dan - No offense meant about "The OP is not a car guy" ... I just meant to make the answer as if the OP was not a car guy. You are asking the right questions. Still, if you don't know, you don't know. Some things can be completely confusing to the uninitiated. I'm sure Anarach will flesh out the answer for you. Commented Jul 16, 2015 at 10:49
  • 2
    This is a superb answer! I will also take on board what has been said here when buying my next car, thanks! Commented Jul 20, 2015 at 19:33
  • 1
    @Dan This is not the place to place this request , we would be glad if you come over to our petrolhead chat room .. Hoping to see you there..chat.stackexchange.com/rooms/340/the-pitstop
    – Shobin P
    Commented Jul 28, 2015 at 7:49

Tyre depth gauges look something like this (amazon link) - you can buy them in any automotive store. You press the green bit against the tyre and push the middle bit into the tread groove. The slidy bit at the top will then tell you the depth. Buy one and have a play, it's easier to see than to explain!

You should be able to see the 'wear bars' - raised bits in the middle of the bigger tread grooves. They are 1.6mm deep, so if they are flush with the surface of the tyre, it's worn out. Bear in mind that 1.6mm is the minimum - it's better to have more, and many people recommend replacing at 3mm. You should also replace any tyre with cracking or damage, or that is over 6-8 years old (hopefully not a problem on a 3 year old car!) Look for signs of uneven wear on the tyres (e.g. one side of a tyre wearing more than the other) - that'll show up if the alignment is out. If there is damage to the wheels (e.g. scuffing from a kerb), ask if the alignment has been checked.

You can't realistically check the cambelt or head-gasket when buying a car, but look for any visible signs of problems. If there are leaks, check what they are and where they are coming from. If things look suspiciously clean, be suspicious... A three year old car won't have needed a cambelt replacement yet, unless it's done astronomical mileage, so you won't need to worry about that.

Look for a car that has done about average mileage (roughly 8-12k miles per year), and that has full service history (I'd expect all secondhand Mercs of that age to do so)

If you have a more experienced friend you can take along, do so - not only can they give you advice, but a second opinion is always useful. On the test drive, trust your instinct, if something feels wrong, it probably is. Check the stuff on Anarach's list. Check that the numbers match (the VIN number on the dashboard and the ID plate should match those on the registration document, and the engine number should match). Check for any outstanding finance - many companies online do vehicle ID checks, the AA, RAC, and HPI are the most well-known in the UK. If the dealer asserts that the car is 'HPI-free', ask for a certificate.

Haggling is very subjective, and off-topic here. Most dealers won't think you rude, but may well say no! Asking for something to be 'thrown in' like new tyres or repairs is quite common - check they have been done before you accept the car!

  • 1
    To bolster what you said about trust your instinct ... one of the things which a salesman does when selling a car is to get an emotional attachment from the buyer to the car. If you can get that emotional attachment, selling the car becomes much easier. Be objective when buying a car. The second person can help with that, as long as you will take their opinions into consideration during the purchase. Good advice here, btw. Commented Jul 16, 2015 at 11:13
  • 1
    "Experienced friend" - yes, indeed. But preferably somebody who understands what you need in a car (as opposed to what he/she needs). I would add: don't buy on the first day, or the first vehicle you test-drive. Test a couple more, on different days, from the same or other establishments. That will give you some perspective.
    Commented Jul 16, 2015 at 13:02
  • @ALANWARD Exactly , should never settle for the first car.
    – Shobin P
    Commented Jul 16, 2015 at 13:31
  • @Anarach, I made that mistake myself a quarter-century back. ;-) Good times, buying one's first car.
    Commented Jul 16, 2015 at 13:36
  • 1
    @ALANWARD That is a good point! I won't rush anything. Buying a car is a big commitment and costs a lot of money. So I definitely don't want to rush things. Still though, being a car enthusiast, I am so excited too!! haha.
    – Dan
    Commented Jul 16, 2015 at 14:00

It's strange that practically none of the answers have any advice about price. The general rule about sales of both new and used cars is that there is room for lowering the price, and you should only in exceptional cases pay the asking price. Let's see if the answer gets deleted as off-topic as I agree that the main purpose of this site isn't to give price shopping advice... But what I include in this answer does not get obsolete quickly so let's see.

When I purchased my current car (bit over 50 000 EUR, new car) I asked for 3% reduction in price. I didn't ask for more, as I knew I wasn't the best possible customer because I didn't pay the car fully with cash and I had an old car for the dealership to sell to somebody else. I got practically that amount of price reduction I requested. I wish I had asked for a slightly larger amount of price reduction; I might have had even slightly larger actual reduction in price.

If you pay fully with cash and don't have an old vehicle for the seller to sell, you are considered a very good customer and then you can easily ask for more.

About used cars, the way to go is to prepare a detailed list of what you find to be wrong with the car and use that as an argument for reducing the price. I wouldn't consider offering 16k for a 17/18k car rude, if you have some reason why you offered just 16k. Just don't expect a 1-2k reduction (6-11%) in final price, you will probably meet somewhere in the middle. The 16k for a 17/18k car is a very good starting point for your initial offer which you should be prepared to increase.

However, if purchasing a used car, I would much rather go for a good car that isn't cheap than for a car in poor condition that is cheap. So for the types of cars I would buy, I would offer initially perhaps 8% less than what the car is sold for (perhaps with a minor list of reasons, typically non-issues like needing new tires soon or having timing belt replacement soon) and would be extremely happy if I got a 5% discount as the final offer and would be somewhat satisfied with a 3% discount. This applies when paying fully with cash and not having an old vehicle in exchange.

Including repair in the deal is a good choice if the true cost of the repair is unknown. But if you know what exactly needs to be repaired, it may be best to do the repair after the sale by paying from your pocket. Especially if the car needs new tires, you have far more options if you decide yourself where to purchase the tires and what model to select.

And about offering your old car for the seller: the transaction cost of selling a used car professionally in developed countries is about 3000 USD / EUR (USD and EUR are close enough to each other to be able to say this). There are personnel costs, property costs, liability costs, inventory capital opportunity costs, etc. in selling a used car. So if you expect the final selling price of your old car is less than 3000 USD / EUR, you should sell it directly to some other private person. For such a car, a professional seller could offer you even 1000 USD / EUR if you're buying an expensive new car in the same deal, but this is taken from the price reduction you could otherwise get. So it's best in this case to separate the deal of selling the old car and buying the new car into two.


Checking the battery requires a battery tester and disconnecting the battery; the next best manner is to hook the car up to the correct service equipment and confirm it is the right battery for the car and use any test protocols available on the equipment and car, meanwhile also checking the charging system.

After that, use 'close visual inspection': look at it very carefully, make sure it is the right model, amperage and type of battery. Before looking at a particular model of car look it up online and find out what battery it should come with from the factory. You should find out if it is an AGM battery or conventional lead-acid type. If it is not the same as original, then is it suitable based on specifications -- should have more CCA and more CA (Cold Cranking Amps / Cranking Amps), and should have the same or higher Amperage rating (some batteries are rated with Amps in addition to CCA and CA.) Group type refers to the battery's dimensions LxWxH, such as 'Group 42', but there are several systems in use, so cross reference and be prepared based on model, or else just look at the thing and see if it fits the battery pan and the cables look original, good condition and are not corroded with lead-sulfate crystals. The outside of the battery should be clean and without damage to the plastic or the labels and not appear to have leaked.

Geez, you could take a course in battery inspection, there is always more to learn. But those basics ought to help. Where I live, in the SE USA, I can go get a battery for my BMW 335i at a cost of ~US$135.00. I will have a choice of which to get. My car has a computer which is programmed when the battery is installed so that can be checked by the dealer or a shop with the right equipment and software (there are literally dozens of computers in the car, which has its own network to allow them to speak to each other and to the service port....) So a battery is not such a big factor as some other things. I like to have a 'straight' car that has not ever had a wreck that incurred frame damage. Not only should you drive the car and test it, but ride in another car behind and beside and see that it rides straight down the road, and that the wheels and tires do not wobble or hop and track straight down the road.

That is my two pence.


I've speed read this so excuse duplication.

Service history is important. Make sure all stamps are present and consider calling the garage(s) who stamped them to confirm each service took place.

You're spending a lot of money on the car.

When you've lined up the final choice, I'd consider spending a few hundred more and get the RAC or AA to inspect it.

They'll check for accident damage too which you might not be able to unless you're under the car. They'll also tell you the items that are likely to need attention soon. Useful when discussing final price.

I usually try to find out who owned the car previously.

Good luck with it.


As Nick said there are wear indicators. Most will have little arrows on the side wall to show you where the indicator bars or raised areas are. On the side of wall of tires there is the date of manufacture stamped as 4 digits. The first two represent the week in the year it was manufactured and the last two the year. May be difficult to spot at first but gives you an idea how old the tires are.

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