How to do a fuel filter change on w123 – Petrol engine

How to change the Fuel filter

So how do you change the fuel filter? It is in theory simple, but in practice it can be quite messy and also tricky to fully access in the rear end fuel delivery system on the w123 chassis. You also need to make sure you have as low fuel as possible or drain the fuel tank dry.

There is a high explosion and fire risk when dealing with petrol fumes, so don’t light up your cigarette and avoid sparks!


Make sure you inspect the fuel delivery system, since a lot of parts there might need to be changed along with the fuel filter, and since you are already draining fuel you don’t want to do this again in 2 months. See the older article on How to re-haul the rear fuel delivery system on w123 (gasoline)

Part requirements:

  • New Fuel filter
  • Optional parts:
    • Fuel delivery assembly rubber bushings – I highly recommend to change these
    • Fuel pump
    • Fuel accumulator
    • Fuel hoses
      • Main tank hose
      • High pressure hose
      • Low pressure hoses
    • Fuel hard line and fittings


  • Spanners
  • Sockets
  • Hose clamp


You need to access the rear end fuel delivery system on the rear right end of the car. It consists of the fuel pump, fuel filter and the fuel accumulator. They are suspended from 4 rubber bushings secured in a weird metal clamp. It is partly hidden behind a plastic cover near the right rear wheel.


Start by removing the battery, trust me, you dont’ want sparks while working under the car with petrol fumes! And don’t smoke!

Then jack up the rear end of the car up on jack stands and block the front wheels from rolling. As extra safety measure I always leave the jack in raised position on the same side as I will be working.

Remove the rear right wheel and you have better access to the fuel delivery system. Locate the plastic cover which is held by a few screws, use a long thin socket extension to remove these.

Fuel delivery assembly w123

Now you have to drain the fuel from the tank to avoid petrol spills and excessive fumes. This can either be done with using a vacuum pump with a  hose down into the filler neck, or by disconnecting the main hose to the fuel pump. It will also leak fuel from the delivery line to the engine, and this can be blocked from continuously dripping with a hose clamp on the high pressure hose. Make sure the clamp is of high quality with no sharp edges, since a new high pressure hose is quite expensive.

Fuel filter removed
Fuel filter removed. Notice the high pressure hose is clamped.

When the fuel is drained. You can start by loosening the 2 lines that connects to the fuel filter. The left side (from rear) is the high pressure line and the right is the hard line. Notice the position of the two copper washers on the hard line fitting.  A lot more fuel will now drain out from the filter so take care. It is possible to remove the filter from the cage without removing the whole assembly.

Rubber bishings fuel pump w123
Installing new rubber bushings for fuel pump assembly.

If you need to also change the rubber bushings, then change them one by one and you don’t have to take the whole assembly down. Alternatively to get better access you can secure the assembly with zip ties while changing them.

Fuel delivery assembly w123
New bushings installed


Installation is pretty much reverse of removal, but you have to remember to use the new copper washers that followed with the new filter. Also I found that you need to torque down the screw between the hard line and the filter for it to not leak.

After everything is put together and you have put some fuel in the tank, try to start the car, it should not take long for the engine to fire up after you crank it. The fuel pump is pretty quick pushing fuel through. When the car is running, go back and inspect carefully if fuel is leaking and check for any wetness.

New fuel filter installed on w123
New fuel filter installed.

If it’s dripping or you can see wetness, shut off the car. Tighten the bolts, wipe off the fuel so it’s completely dry and try again. I had to redo this step twice before it was properly sealed, and the leak was indeed between the new copper washers and the hard line. The copper washers will actually start to seal better when exposed to moisture and some small corrosion will start forming in the gaps.

Be sure to check for any wetness under the rear end of your car after you parked it the first times, since leaking fuel is bad for your wallet and is a potential fire hazard.

Cheers, Robs out!

How to change the Thermostat

Changing the Thermostat

Too hot or too cold engine will result in power loss and inefficiency in the combustion process. In the worst case total engine failure. The thermostat is actually a wear item that should be changed every 5-8 years. In some cases even between every season if you are living very far north where the winter temperatures varies extremely much between the summer season. I think this applies even for Norway especially in a Diesel where it’s difficult to get the engine warm in the winter.

Is your engine experiencing climate change?

So how do you change it? Is it difficult? I will tell you all if you hang on with the article.


Parts you will need

  • New thermostat. Thermostats have different temperature  ranges where it is fully open, check with the manufacturer/ owners manual what is recommended for different ambient temperatures. For cold weather thermostats that open later are common, i.e. it will open at a higher engine temperature.
  • New upper radiator hose and clamps? Evaluate the condition of the upper radiator hose, change if it’s worn. Since a broken radiator hose might cause catastrophic engine failure. Also the hose clamps might break if they are old and rusted.
  • Engine coolant.


  • Screwdriver
  • coolant catcher/pan
  • Funnel
  • socket tools
  • Wire brush


Start with emptying the radiator coolant. There is a plug on the underside which can simply be open by a screwdriver. When it is fully drained don’t forget to put the drain plug back in. Then go to the next step.

Upper Radiator hose w123 M110 engine
Loosen the Upper radiator hose.

Now you have to remove the upper radiator hose. Each end is attached with hose clamps. Hopefully the hose clamps tightener are easily reachable. They usually can be loosened with a small socket or a screwdriver. Choose the socket if you can since you might just destroy the screw notches if it’s stuck. Be aware that more coolant might come out when you loosen it so be ready to catch it.

After removing the upper radiator hose you have access to the thermostat housing. It is attached with 3 bolts. These on the M110 engine is usually ok to get out, but on some other engines like the OM617 they are terribly constructed. Now you have to take extreme care not to ruin the bolts otherwise your quick fix will turn into a long and unpleasant affair. The aluminium housing of the water pump housing will stick to the steel bolts after some time.

Thermostat housing w123 M110
Unbolt the thermostat housing. Notice the heavy deposits of aluminium oxide on the neck.

After the housing is removed, you have access to the thermostat. Just pull it out with your hands. Also note the placement of the rubber gasket. This have to be replaced by the new gasket which comes with the new thermostat.

Thermostat w123 M110

If you really want you can test the old thermostat by boiling it in a kettle with an accurate thermometer. When the spring opens is when the thermostat is heat rated. Probably your old one has deviated slightly from it’s original heat rating. If you are totally paranoid you can the test the new one as well!

Thermostat housing without thermostat w123 M110
Clean the housing of dirt and oil residue before putting the new one in.

Clean up the housing before putting the new thermostat in the water pump housing. Put the gasket on top of the thermostat as seen below.

New thermostat w123

Before putting it all together you have to clean off the oxidized aluminium from the thermostat housing. It is important to avoid coolant leaks in the future. This is easily done with a simple wire brush.

Oxidized thermostat housing w123
The aluminium oxidizes when in contact with water when air cannot reach the surface, such as here between the neck and the rubber hose.
Thermostat housing w123 M110
The oxide comes off easily with a wire brush. Now it will make a much better seal with the rubber hose.

The bolt on the thermostat housing should be tightened down until both the surface of the metal meets. Do not over tighten the bolts since you will end up stripping the soft threads in the water pump. Then you will be in big trouble. Use only a small ratchet to avoid the large torque. Get your new upper radiator and clamps ready.

New upper radiator hose w123 M110
New upper radiator hose and clamps.

After fitting the new upper radiator hose. You have to refill engine coolant. This is not as simple as just pouring in new coolant and closing the lid. You have to let coolant circulate and get out the air out from inside the engine.

Start by turning the heater on MAX inside the car. This will allow for coolant to circulate the entire system. Ideally you should have a large funnel which can be screwed down into the radiator, but this is a specialized tool which most of us don’t have. So start pouring coolant until you see it forming though the opening, but don’t make it full. Now you have to turn on the engine with the radiator cap open so air can escape from the engine. CHECK for coolant leaks!!! Did you remember to tighten the radiator drain plug? While the engine is running you will probably see the level decrease slightly while the engine burps, but bear in mind that coolant also expands as it heats so a level change might not be visible. When the engine starts to get warm and has burped some, try filling until the minimum mark and close the radiator cap.

Then go for a short spin. Observe the temperature gauge closely. Mine increased suddenly until over 100°C then did a sudden jump back down to 80°C when the radiator popped open. I might have had some air still in the engine and the thermostat might have been slow on the first opening since it was new. It never run above 80°C after that one time. To be on the safe side, stop the car if you see such sudden peaks in the temperature gauge.

When you are back. Let the engine cool down at least one hour, before tempting to open the radiator cap, since most likely coolant will pour out and scolding your hands. After one hour open the radiator cap and refill coolant until it reaches the maximum mark.

Cheers, Robs out!

AC Part2: How to change the AC compressor (York R4 type on M110 engine)

How to change the compressor
A DIY tale

Is your compressor crappy? Dried out for the 15 last years and making squeaky sounds and for sure not giving any refrigerations at all? Well in this second part of the AC system we will embark on the journey to change the broken compressor. A critical part and the one to often fail due to the mechanical nature of operation and lack of maintenance.

This guide will only cover the York type compressor in an M110 engine.


The AC compressor pressurizes the refrigerant from a vapor state into a liquid state and at the same time increasing the temperature of the liquid by drawing mechanical energy from the engine via a drive belt from the crank shaft.

Some compressors are lubricated by the refrigerant itself, but the York R4 compressor has it’s own lubrication by oil inside the crank. Lack of lubricating in the compressor crank in combination of little or old refrigerant is the most common reason for these to fail.


To change the compressor you need to make a lot of preparation even though changing the compressor is not such a big job in itself. This will include emptying the AC system of refrigerant at a professional workshop. You cannot do this at home because the refrigerant can actually deplete the ozone layer (if it’s an old type of refrigerant, this is common in old cars) and they are all extremely potent green house gases that should be disposed of properly. Also a big preparation is getting hold of new spare parts, not only the compressor, but also a new receiver/drier, new gaskets for hoses/connections and compressor oil. You probably need a new pulley for the drive belt as well. You will also need some special tools to finish the job.

Parts and Preparation:

  • Empty refrigerant at a workshop!
  • Get a refurbished or new compressor, can be quite expensive
  • Get new gaskets, they are like 2$ only…
  • Compressor mineral oil compatible
  • New Reciver/drier (must always be changed when changing the compressor)
  • New pulley bearing for drive belt
  • New AC compressor serpentine drive belt


  • Big selection of long and short spanners, also ones with ratcheting mechanism to reduce time
  • Socket tool set
  • 3/8 inches spanner
  • Clutch/bearing remover (to remove the clutch from the compressor shaft)
  • Small funnel
  • Brain: Some ingenuity to loosen the clutch (not easy since the compressor shaft and the clutch will rotate together)


Getting access to the various bolts and nuts around the compressor is not easy. They are awkwardly placed and there is not much space to get leverage for the spanners. Be prepared test your patience! This job is not super difficult, but will save you tons of money compared taking it to a workshops, since they will use a few hours just to remove and assemble the compressor, unless they know the car really well. And lets face it, no one knows the car like you do yourself.


WARNING: Do not proceed unless the AC is emptied of refrigerant!

Now that is out of the way, let’s proceed to the fun stuff. Disconnect your battery to avoid shorts! Locate your compressor, it’s the big thing hanging off the passenger side of your engine. The compressor probably has a serpentine drive belt if the AC has been in use before. This must be loosened first by using the adjusting screw on the AC pulley, which located on the upper part at the front of the engine. If you are not using it after, then just cut it off with a knife to save time, the compressor should have a good belt otherwise it might just slip. There is very little room between the pulley and the fan housing, but you do not need to disassemble anything when replacing the pulley.

Start by checking the pressure in the AC system, it should be empty, but just to be sure use a pin and press on the Schrader valves sticking out on top of the  AC hoses. There might be a slight fizz due to a small pressure building up in the empty system.

R¤ Compressor mounted on engine
Compressor fitted on engine, notice the location of first bolt and wires on the right side of the compressor. (This is a new compressor f.y.i. and the AC hoses should always be disconnected, not shown here!)

Then you can start unbolting  the compressor mounts, there should be 5 bolts holding the compressor in place. On the right side there is a supporting rod holding it on the corner, start by unbolting this. You must also disconnect the wires to the clutch actuator.

AC Compressor R4 Compressor M110 engine
Location of bolt on the front side. There is one like it under the clutch as well (not pictured here)

Two are located on the front left side, one above and one below the compressor. Until now these were the easy bolts, now the hard part starts. There are two more bolts located on the back left side of the compressor, and these are pretty hard to gain access to. Also you will have little room for the spanners, so if you have spanners with a ratcheting mechanism you will save tons of time here.

AC compressor bolt location R4 York on M110 engine
Location of 2 last compressor bolt location. Tricky location.

The bolt that is lowest actually is a long long with a cylinder, that comes off going all the way through the exhaust manifold. Don’t loose this cylinder part, and be prepared to save all shims and remember the bolts’ locations, since they are not all the same, use pictures and notes if necessary.

AC compressor bolt R4 York M110 engine

Notice the long compressor bolt and its’ cylinder.Just before the last bolt gets loosened completely you can detach the compressor and stop if from falling, it’s quite heavy so don’t crush your hand when it might fall unexpectedly.

AC compressor and manifold bold M110 engine
Don’t loose the bolt or any of the shims! They are there for a reason….

Now that the compressor is off the engine, you can begin to remove the bracket that is attached on the right side of the compressor. This is pretty straight forward and requires little explanation, it is just attached by a few bolts. There is also a bracket still on the engine block, it is not necessary to remove this, but you can if you want to clean the area around it etc.

PROTIP: Since the compressor is removed, now you have the perfect opportunity to replace the lower radiator cooling hose, which is nearly impossible to replace when the compressor is mounted.

AC Compressor Bracket R4 York M110 engine
AC Compressor bracket attached to engine block. Not necessary to remove this.
R4 York AC Compressor Bracket
Bracket hold in place by 4 bolts (the bolts are removed in this picture).

Since your new or rebuilt AC compressor does not come with a clutch and the clutch magnetic actuator,  we have to transfer the old components over to the new compressor. Removing the clutch is the most difficult part of this job, since the compressor crank shaft will rotate when you try to loosen the clutch center bolt. You need a way to keep the compressor shaft from rotating while loosening the clutch bold. Easier said than done.

AC compressor Clutch R4 York
This will not work… Trying to loosen the clutch bolt…everything rotates…duh!

I ended up placing the compressor housing in a large wise, then using some large welding pliers (adjustable) to grab onto the inner clutch plate and while holding it still then also unbolting the clutch bolt. It was not the most elegant solution and I recommend you to find a better one, since in my case the outer plate got slightly scuffed by the pliers.

When the center bolt is loosened, the clutch is still pressed on the crank shaft. You need to find your clutch/bearing removal tool, it looks like some spider joint out of a horror movie. Unfortunately it’s a tool that seldom gets used, so don’t put too much money into a tool like this, borrow from a friend if you can. I think I only used it once earlier when I removed the center drive shaft bearing. Place the outer spiders around the clutch wheel and start tightening the center screw. This time you can use a long rod between the spider legs to act as a lever while you tighten the spline, you will hear a loud pop when it comes off. It has probably rusted in place after so many years.

Removing AC Compressor clutch from R4 York
Pulling off the clutch from the compressor drive shaft. Prepare for the big pop when it comes off.

The last part to disassembly is the magnetic clutch actuator. It is held by 4 bolts on a bracket, but be warned, they are Imperial sized! This is the first time I have come along imperial sized bolts on my Mercedes, but the York compressor is not made by Mercedes and this is just how it came from the original manufacturer in the United States. You actually need a 3/8 inches spanner, if you don’t have imperial sized tools, go out to get only this one spanner. I almost rounded out one bolt at first since I was dumb enough to try a metric spanner which didn’t perfectly fit.

R4 York Compressor clutch actuator fittings
3/8 spanners required, notice the almost rounded out bolt since I used metric spanners.

After the clutch assembly is off, you can start by assembling the new compressor.

R4 York Compressor
Everything disassembled from old compressor. The old compressor you can deliver in for a rebuild and get a few dollars actually. Don’t throw it!

WARNING: Do not forget to refill the York Compressor with mineral compressor oil before assembly, otherwise it will break!

Forgetting the above step is pretty serious. So before anything else, let’s go through how we refill and measure the right quantity of oil. Also keep the protective dust caps on the compressor fitted at all time until the very end.

Make your own dipstick from a piece of steel wire, make a marking at 57mm and 41mm from the end.

york compressor dipstick

On each sides of the compressor is one small bolt in the middle, these bolts are the filler holes for the oil. They are quite small so a small funnel needs to be used. You need at least 355ml of fluid (12 oz) which s corresponds to around 57mm on the dipstick and it should never be below 177ml (6 oz), 41mm on the dipstick. Use normal mineral compressor oil,  some even use engine oil, but do not use ATF.

The compressor comes with a small quantity of oil in it already, pour this out before pouring in the new oil, it is not important to get all out. Put the dipstick in over the crank case at 45deg as shown in the image to proper measure the fluid level, the crank key should be facing up, there is a small nob on the shaft. It should not be hard to crank it by hand.


When filled up to the right level, start assembling the compressor. Now in opposite order of the disassembly. Remember to keep the protective intake and outtake protective caps on until you are ready to connect the AC hoses back on.

There is no need to over tighten the clutch center bolt since it will also tighten itself over time when the clutch is actuated.

When the compressor is mounted on the car, remove the protective dust caps and make sure there are fresh plastic gaskets on the inlet and outlet holes on the top of the compressor. Tighten the hoses firmly, but do not over-tighten them, the workshop will make sure the gaskets are not leaking when filling your AC system with refrigerant. Over-tightened gaskets will need to be replaced.

Next step

You cannot change the compressor without also changing to a new receiver/drier, otherwise your new compressor might fail too early and all the job you just have done might be in vain. This is the next part of the AC series, so stay tuned for part 3.

Back ground story

To be honest my AC system has not been operational in the last 8 years or so due to a broken compressor. I just didn’t get to the job of fixing the AC system until now, because you know… (Norway is cold most of the time and you really only need AC like 3 months of the year, but then it’s really nice to have on those few really hot days)

Cheers! Robs out

How to replace tie rods, center drag link and steering damper on W123

When your car steering starts to feel floaty and maybe the car is starting to drift to one side so you constantly have to correct when going down a straight road, consider changing the steering linkage components and do a wheel alignment.

I will describe how you replace the tie rods, the center drag link and the steering damper only. I will not describe how to do a wheel alignment, because professional wheel alignment equipment is needed.

Changing the idler arm bushing is also possible if you experience a knocking sound going over bumps, but this procedure will be described later in a separate article.


Get the parts needed for this job, they are quite cheap since they are normal wear items on a car.
Parts you should get:

  • Right and left side tie rods
  • Center drag link
  • Steering damper
  • Idler arm bushing (job not described in this article)

You will need a special tool for removing the tie rod ends, this can be picked up quite cheap. Either a tie rod fork or a tie rod press tool will do, the latter will not render the tie rod bushing seal useless, but if you are only changing the parts then this does not matter. Additionally you will need a hammer, a torque wrench, some hex tools and some spanners.


Start by raising the front of the car on to jack stands, make sure you block the rear wheels. You will have to be able to remove the front wheels to gain access to the tie rods and also be able to turn the wheels.

Because you are working around the brake rotor, it is important that you wear a dust mask and get a bucket of soapy water and start cleaning the brake rotor and the area around to get rid of all the harmful brake dust before you do any other further work. Think of your health!

When you have cleaned the brake dust, turn the steering wheel all the way left if you are working on the right side, and vica versa.

tie rod tool
Use of tie rod press tool to pop the ends off

Get a small pick and clean road grime from the top of the tie rod so you can get a hex tool inserted in to the top. You will loose the bolt with a spanner, but because the whole tie rod end will rotate you have to counter it with the hex tool. When he bolt is off you will notice the tie rod is still extremely stuck. Hit the side hard a couple of times with a hammer to knock the rusted component loose, this might help to loosen it. Insert the tie rod press remove tool and start tightening until the tie rod pops off, this can sometimes be violent. Be careful and don’t lie under it when this happens, because it can happen quite suddenly and the tool and parts might fall on top of you, ouch!

You have to repeat the process twice on each tie rod for both of the car’s sides.

When you have gotten both off, measure the length by counting the turns the tie rod end can rotate before it comes off, it is important that this is exactly the same for the new tie rod. The new and old tie rod should have exactly the same end so your car will have the same handling properties, so it will not be too much “toe in” or “toe out”. The workshop will do the last alignment with reference to the manufacturer specifications after you take the car there. Tighten the tie rod adjustment screw so it will not rotate when the lengths are right.

w123 steering damper
New vs old steering damper. Old one was leaking and in bad condition

Time to take the steering damper off. This is the easiest procedure, it is held in place with two bolts only.

w123 steering damper bolt
Steering damper bolt on the frame side.

One end is attached to the frame of the car while the other one is attached to the center drag link.

Now it is time to get the center drag link off, the procedure is the same here as with the tie rods. Except you don’t have to adjust anything.

W123 center drag link nut
Unbolting the center drag link nut

The fitting is pretty much straight forward, but remember to use the right torque settings for the tie rod mounting nuts. You should tighten them down only to 41Nm, the tie rods will be stuck in the steering arm and the nuts have plastic inserts in them. Remember throw out the old tie rod ends nuts since thee plastic self tightening mechanism is word. The new tie rods and drag link comes with new nuts and be sure to use these. Loosing control of the car because of some old nuts would be as stupid as driving off a cliff.

Safety warning:
You absolutely have to take the car to a workshop where they will do a new wheel alignment. This must always be done right after changing the lower suspension parts!

Cheers, Robs out!