I've owned quite a few 850s and x70s over the years, so I thought it might help potential buyers if I listed the common faults that I've come across over the years.
Firstly, rest assured that most 850s leak oil. Honestly, they do. Not as bad as LandRovers, but they like a little wee from time to time. 850 turbo engines usually leak oil from the turbo drain pipe (the thin gasket between the drain pipe and the turbo leaks, or the drain pipe itself can come loose), and from where the air hose joins onto the top of the turbo (the clips securing the rubber hose come loose). These are minor issues and are easily rectified. If there is an oil leak between the engine and the gearbox, then it is likely to be the feared 'engine rear main seal' or 'RMS' - replacing this means removing the gearbox and this IS an expensive job. IIRC a gearbox removal and refit is around a 7 hour job at the main dealer. IMHO its worth having this seal replaced (genuine part only!) whenever you have the clutch changed. Be aware that oil can run down this end of the engine from the cylinderhead, and appear to be coming from the rear main seal - the source actually being one of the camshaft seals. These are easy to replace, and you do not need to remove the camshaft to do it.
Remove the oil filler cap and look inside. You'll be able to see some of the camshaft lobes - if they're worn or the inside looks black and sludged up you know the engine has not been cared for. In the following picture, the camshaft lobes are in good condition, and the inside of the engine is a dark golden colour - indicating a well maintained engine.
The engine may sound noisy and a bit tappety when cold. This may only be due to sticky tappets (add some Wynns Hydraulic Valve Lifter Treatment) or it may be noisy injectors. The injectors do tend to be noisy on T5s which is a shame. Listen to engine again when the engine is fully warmed up (after a 30-45min test drive) - it should sound really smooth then. Check the brand of oil filter fitted - it indicates the budget/attitude of the previous owner. Volvo or Mann (who make the Volvo filters) are good. Budget brands are bad. This isn't snobbery - the OEM grade filters have better filtration, and have the critical non-return valve built in. This valve ensures that oil pressure is almost instant upon engine start up.
Engine oil. Check the dipstick to see how much oil there is, and what colour it is. If the level is low it could indicate a less than attentive owner. If the oil is black, an oil change is possibly overdue. It is unlikely that the oil will be a fresh golden colour, as the oil quickly takes on a dirty tone in these engines. Note that it is quite common to see a small amount of 'mayonnaise' on the dipstick, and this does not usually indicate a head gasket issue. However, if there is a lot of mayo on the dipstick, and under the oil filler cap, and visible inside the oil filler aperture, then further investigation is necessary.
Engine noises. Do the usual checks. Try to identify them during the test drive. Switch off cabin heater fan (these can be noisy). Is the noise engine RPM related? (PAS pump, aircon pump, aux belt tensioner or pulleys, timing belt idler or pulleys) or does it last after the overrun and then slowly lessen or change tone (turbo?). Is the noise wheel speed related rather than engine speed?
Radiator fan. Note that while the aircon is switched on, the radiator fan will run all the time - it isn't a fault ;) If the engine is cold, switch off the aircon and the radiator fan should stop.
Vacuum hoses. The turbo and PCV system uses quite a few vacuum hoses, and these suffer from age/heat degradation. They also suffer from cracked elbow joints, crumbling hoses and sometimes outright breakages. Damaged vacuum hoses often trigger a Lambda warning lamp. Some are a bit awkward to replace, but all can be replaced with silicon hose. This is a good example of a perished turbo vacuum hose -
PCV system check. PCV stands for Positive Crankcase Ventilation - this system pressurises the crankcase and sump etc, and forces fumes back into the engine to be burnt off. Its a good system but if part of it becomes blocked by oily sludge, the pressurisation can force engine oil seals out - including the dreaded rear main seal. Remove the oil filler cap and put a rubber glove over the opening. Start the engine. If the glove inflates then the PCV system needs servicing.
Genuine Volvo parts typically come to around £100, but the job is awkward and involves stripping the intake manifold off, along with removing the battery and airbox. IMHO its straightforward but getting at the bolt that holds the intake manifold to its support bracket is awkward - to the extent that some people call it a nightmare job (it really isn't). Its around a 3-4 hour job if you've done it before.
Fuel hose. There is a short rubber fuel hose that connects a rigid fuel line to the fuel injector rail. This cracks with age and should be replaced (get E10 compatible hose now that E10 is to become the default grade in the UK!).
Coolant hoses. Do the usual checks, along with checking the bulkhead fitting where the heater hoses connect into the bulkhead fitting.
This bulkhead fitting can show coolant leakage traces/runs indicating that the o-rings/fitting need replacement. While mentioning coolant, the heater matrix is prone to failure, simply due to age. Suspect the matrix is failing if the air from the vents smells of coolant, or if the screen fogs up, or even worse if you can see coolant stains in the footwell carpet. The heater matrix is a straight forward replacement and takes around an hour to do. It costs around £50 for a quality aftermarket replacement (by Nissens). Note that the heater matrix is a 'full flow' type - ie the coolant will flow through the heater matrix regardless of where the cabin heat controls are set. If the heater matrix fails catestrophically, then it is entirely possible for it to dump ALL the engine coolant into the footwells, with disastrous consequences for the engine. If it starts to leak and you MUST continue driving the car, then link up the two heater hoses in the engine bay to bypass the heater matrix.
Expect the protective convoluted tubing to have degraded. This frequently turns to dust and crumbles when you touch it. I took the following pic of my 850R as I have never seen this tubing intact before!
Also under the bonnet, check the positive battery cable - it should be secured with a clip on the battery tray edge. This frequently breaks leaving the cable to hang free - it then can chafe on the edge of the battery tray and potentially cause a fire.
Control cables. Note that these (in RHD) are no longer available - accelerator cable, bonnet opening cables (x2). If they're obviously damaged or the accelerator is stiff then expect to need to repair these (maybe a bicycle repair shop?). If the bonnet release handle operates in two distinct steps (releasing one side of the bonnet and then after a longer pull, the other side) then the cross car bonnet release cable needs adjustment or replacement.
Park the car on level ground. Look at the car - how is the car sitting? Does it look level? I mention this first as a car with a drooping back end can potentially cost a small fortune to put right. 850Rs and many other of the higher spec 850s were fitted with self levelling suspension. This works fantastically well, and is accomplished with sophisticated shock absorbers called 'Nivomats'. These can be readily identified as they are quite chunky dampers with bellows fitted over the shaft -
There are two main problems with these, and they're related. Firstly, they are hellishly expensive - the last time I looked (Jan 2021) they were around £600 EACH. The second problem is that they are getting difficult to find at all - so the prices are only going to increase. The cheaper option is to fit non self levelling suspension using aftermarket parts - H&R lowered coil springs and Sachs or Bilstein shock absorbers are said to be a good combination and cost around £600 all in.
850s are not generally rust prone, but they do have a few weak areas such as on the front wings, where they meet the bumper. The bumper rubs the paint away and holds wet debris between the bumper and the wing causing nasty rust. The wheel arch liners cause rust in the same way, usually along the lip of the liner where it touches the wheel arch. One area that you won't be able to check is under the sill covers. Wet debris gets stuck between this plastic cover and the sill underneath, allowing rust to develop unnoticed. Rust can form on the tailgate below the glass - the rubber trim running along the bottom of the screen holds wet debris and rust forms under the rubber trim.
I have to admit that is the worst tailgate I have ever seen on an 850! (picture found on the internet). The same thing happens under the rubber trim that goes along the top of the front windscreen. The rear bumper mounting brackets can rust spectacularly - suspect them if the rear bumper looks a bit low. The brackets are available new from Volvo fortunately.
[pic - rusty front wing]
The 'R' type spoiler is genuinely aerodynamic as you'd expect of a 150mph car. Because of this, it is affected by aerodynamic stresses and the spoiler often cracks where the inner vertical spars connect between the upper spoiler and the lower rounded lip (ie between the grills). It is much more obvious on lighter coloured cars. This is very very common and can be repaired at home if you can use a fibreglass repair kit. It will need repainting afterwards of course. There are various webpages showing the damage and how people have repaired it - I'd always bond in some metal reinforcing mesh to prevent recurrence. (NB you do not need to remove the entire bumper - unplug all the foglamp etc electrics, remove the arch liner rivets/clips, and then the lower spoiler can be unclipped from around the grey moulded edging and pulled forward and off).
Do the usual checks - looks for signs of accident damage such as the panel alignment not being quite right, different shades of paint, maybe tiny ridges at the edges of panels where masking tape has been used, leaving a ridge between old and new paint. Check the datecodes on the glass - Volvos of the 850's generation always had the manufacture date of the glass printed in the corner - for example '96' for a 1996 year of manufacture. It makes it easy to see if any of the windows have been smashed.
The grey plastic trim that goes up along the sides of the windscreen to the roof rails is often damaged - the plastic coating comes away from the aluminium underneath leaving it looking tatty. The strip can be replaced but it is fiddly to do.
The grey plastic trim on the top of the bumpers, and the rubbing strips on the doors, tend to fade making the car look old and unloved. Sometimes the fading is uniform, sometimes it takes on varying pale shades. There are various temporary fixes for this, including using shoe polish, peanut butter spread, and a hot air gun - these are all well documented elsewhere, however the improvement doesn't tend to last long. In my experience, you need to use a good quality plastic dye like Wurth's. Prepare the surface well and use the Wurth's plastic dye (anthracite is the correct colour) and that will last a year or more. For a truly permanent solution, you'll need to have the trim painted.
[pic - wurth's dye]
The headlamp wipers rarely work - they are usually simply unplugged or removed entirely. Replacing/repairing them should be straightforward, however the one on the driver side is lodged behind some rigid plastic wiring trunking - I've not yet managed to get the wiper motor out of this side!
Wheels. The correct style wheels for the 850R are the 'Volans' design in 17x7". The correct wheels for the T-5R are 'Titan' in 17x7". It is not uncommon for other style wheels to be fitted.
Tyres. Check tyres for uneven wear across the tread - this can indicate steering alignment issues. If really bad, has it hit a kerb, big pothole or worse? Tyres are 205/45x17 as standard on the 850R and T-5R - cheapo ones from around £50 plus fitting, Michelins upto £130+ each? Common non standard size is 215/45x17. These are a great fit and do not rub, and are also cheaper than 205/45x17. Check the plastic wheel arch liners for wear/damage if anything else is fitted - they could be rubbing the liner on full lock and this is an MoT failure. Again, the brand of tyre can indicate the budget/attitude of the previous owner - budget brands aren't ideal, but premium brands can indicate an enthusiast owner. Ditto the wear of the tyres - if they're down to the carcass, then perhaps the last owner skimped on maintenance - or simply thrashed the car and liked doing donuts?!
Brakes. The T-5R (and 850R) were only fitted with 280mm diameter front discs - as these do most of the work when braking heavily, they tend to get hot and warp, particularly if cheap discs are fitted. This causes the brake pedal to pulse when braking. (This is different to the ABS being activated - ABS activation generates a machine gun noise to accompany the kicking brake pedal). A common and useful upgrade is to fit the 302mm front discs from early S70/V70s. You just need a pair of the brake caliper carriers (usually £50 secondhand) and ideally the longer brake lines, although many people do not fit the longer lines. The calipers are the same - just mount them on the later caliper carriers and fit 302mm discs and pads. Its not a massive improvement as these are still quite small compared to modern brake discs, but the 302 discs along with Police spec brake pads (from Volvo main dealer FRF Motors in Swansea) make for an acceptable road package.
Upholstery. 850Rs and T-5Rs are 25+ years old. You can't buy new genuine Volvo upholstery trim for these any more, (but you can get reproduction seat covers from the USA) so any upholstery damage needs to be taken seriously if you want to retain the originality of the car. The plastic parts are common to other 850s, but the seat covers, door card inserts, steering wheel and wood dash parts are unique. Because of the desirability of the cars, you'll find it difficult to find one at a breakers yard (in the UK anyway) and so will need to search literally wordwide for replacements. Bobbles on the alcantara sections can be carefully removed with 800 grit sandpaper - honest! The pics below show a V70R seat that I repaired this way -
Headlining. The headlining material was originally glued to a thin foam backing, which in turn was glued to the fibre headlining board. Unfortunately, the foam layer degrades over time, turning to an orangey dust, leaving the headlining material to hang free. With the vibration of the car, the foam is torn and a bigger area of material is left to hang free - its an inevitable cycle leaving the headlining looking a mess. To replace the headlining, the entire headlining board needs to be removed. In an estate that is fairly straightforward, but in a saloon is it much more difficult although I have read descriptions online whereby people have managed to gently bend the headlining board enough to get it out of a front door... The headlining material on the sunroof blind can be replaced by removing the sunroof glass, then unclipping the blind from above/outside the car and withdrawing it - I always thought that it had to be removed from within the car (ie a headlining out job) but that is not the case.
Electrics. Check everything! 850 electrical items are usually very reliable, however the seat switches, sunroof switch and door locks can be troublesome. Seat switches suffer from the contacts becoming gummed up through lack of use, so you end up with the seat movement in one direction (only) not working, but the seat does move in that direction when using the memory switches. The sunroof switch suffers from the same issue and can be stripped down and cleaned. Door locks are another issue - they cannot be fixed and have to be replaced. The issue with these is that they use plastic discs/pins in their mechanisms which are now old and brittle so they break. The mechanisms are extremely complex and so even if you do break into the sealed unit, they are nigh on impossible to reassemble after repair. New parts are not available, so you can only replace them with other used parts.
Heated seats. Both front seats are usually heated. Rear heated seats were an expensive option so are rare and desirable - just because :) The elements in the seat can break causing the seat to fail to heat, just heat in one area - or worse, to arc and cause a fire in the seat foam! Replacement of the heater elements requires the removal of the seat and then the seat cover. It is DIY-able, but getting the seat cover back on, with it looking taut and tidy is a skill in itself.
Does it come with remote alarm/locking fobs? It is not difficult to program new fobs to 850s but getting the right ones can be awkward (there are 3 types) and due to demand, pricey.
Check the tailgate washer works. If it doesn't, it could be a blocked jet, or it could be a blocked inline filter which is under the boot floor trim on the driver side - I've had the filter pop off the washer hose entirely causing the washer fluid to spurt into the boot. Obviously that will cause rust issues if left long term, so if the washer doesn't work its something to check for.
Warning lamps. Check that they all come on with the ignition. In particular make sure that the TRACS, ABS and LAMBDA lamps light up - The TRACS and ABS ones can indicate a faulty ABS controller ECU. This is usually caused by dry joints within the ECU which you can fix yourself if you're handy with a soldering iron. Alternatively you can send it away for repair. The LAMBDA one usually lights up due to a vacuum leak or faulty O2 sensor - but its usually a vacuum leak. Its not unknown of for unscrupulous people to remove these warning bulbs if there is a problem...(yes I've been stung like this). A bulb failure warning lamp can illuminate even if all the bulbs are working ok - a false positive for a change! This is usually caused by a new bulb on one side of the car (eg rear sidelamp) and a corresponding old bulb on the other - the warning circuit checks the resistance (I believe) between sides of the car - if it differs by more than x, then the warning lamp is triggered. I always change bulbs in pairs to avoid this.
Aircon. Check that the aircon blows cold after a few minutes. To be honest, if you've found an 850 with working aircon you've struck lucky - its rare :) The aircon switch lamp will flash for a while after engine start if there is a problem with it (eg low pressure). Also check that the airflow can be adjusted from footwell to face to windscreen. These are cable/rod controlled not vacuum and the flaps and rods etc can be repaired, but it is an awkward job.
Diagnostics. These cars are not OBDII compatible. They do generate flash codes that can be read however. The T-5R has diagnostics ports/flash code reader under the bonnet, while the 850R requires a homemade flash code reader to be utilised (as documented on the web). Some codes can be read on the 850R using a bluetooth dongle and a cheap mobile phone application called '850 OBD-II'
[pic - 850R bluetooth dongle]
Mileage check. Despite their age, the instrument cluster electronically records the total mileage travelled, so even if the car has been mechanically clocked, the true mileage is stored in the cluster. It can be accessed via the OBD port using the bluetooth dongle and - RobertDIY has a video [add link] on YouTube. Note that the true mileage is only recorded in the cluster, so if the cluster has been changed, you won't get the mileage recorded on the original cluster (nothing is stored in the car's ECUs).