How to do a fuel filter change on w123 petrol

Fuel filters get dirty

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.

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

Preparation

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
Tools:
  • Spanners
  • Sockets
  • Hose clamp

Procedure

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.

Removal

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

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! 

AC Part 3: Changing the Receiver/Drier in W123

The AC receiver/drier needs always replacing when servicing the system.

Luckily the receiver/drier is the most easily accessible and easiest component to change when servicing the AC system. It is located behind the front headlight in the engine compartment of the w123. If you were following my Part 2 of the AC system series, you might already have read that you always need to replace the receiver/drier when changing the compressor. The failure of the drier might have been the cause of failure of the compressor in the first place.

You can read about the drier/receiver function in AC Part1: Air Condition Systems 101

Preparation

For preparation you need not to do much else than emptying the AC refrigerant at a professional workshop, get a new receiver/drier and have some basic tools ready.

Parts
  • New Receiver/Drier (it comes with the necessary gaskets)
  • New high pressure AC hoses if they are cracked/worn/old.
Tools
  • Socket tools
  • Spanners

Procedure

If you haven’t emptied the AC refrigerant, take the car to a workshop and get them to empty and properly dispose your old refrigerant. AC refrigerants contains highly volatile greenhouse gases and needs to be disposed properly!

When back at your own garage. Start with opening the hood and disconnect the battery since you will be disconnecting some wires. Locate the receiver/drier behind the right headlight. It is the small canister with two hoses connected to it. Start by disconnecting the two high pressure AC hoses. Again this will mark the importance of emptying the refrigerant before, since we are dealing with high pressure systems and volatile gases. You might not be able to access both of them while the drier is connected to the chassis, then loosen the drier until you can access both hoses.

AC drier w123
Old AC Drier

As a tip the holes to the bolts going through the thin metal in the chassis might have started to rust. To avoid holes in the future you might want to get rid of the rust and paint over the area.

Disconnect the electrical wires connected to the receiver/drier, but remember how they were connected by marking the wires or taking pictures before. One is a pressure sensor for the compressor and another is a temperature sensor which controls the auxiliary fan.

AC drier
The Pressure sensor inlet has a protective cap which has to be removed.

The sensors do not come with the new receiver/drier, so these sensors have to be taken off the old one and put back on the new one before proceeding further. Be careful not to break off the brittle electrical connector pins, since they can be quite fragile. If you break it you need to find new replacements components since the AC system will not work without them. Also the pressure sensor will need a tight seal with the receiver/drier otherwise refrigerant will leak out. The pressure sensor has a small O-ring, replace the old one with a new O-ring that comes with the new receiver/drier as seen in the picture under.

AC drier pressure sensor gasket
The pressure sensor gasket

The temperature sensor sits at the top of the canister and can be removed with a 19mm spanner. It does not require any gasket. The pressure sensor can be removed with a 27mm spanner. Remember to replace the gasket before assembling it with the new receiver/drier.

AC drier Temperature sensor
Temperature sensor placement

After the the sensors are transferred you can install the new canister. Start by replacing the gaskets for the two hoses and tighten them onto the canister.

Replace the high pressure hose gaskets

Then finally secure the canister to the chassis with the two bolts to the chassis. If you have other AC components to change this is a good time to do it. For example you can replace the expansion valve which also is a common wear item on the AC system. Although the receiver/drier are more common to change.

At a workshop they will pressure test and fill up the the AC system and find any leaks if they are present.

AC drier w123
New AC drier installed

Cheers! Robs out.

Happy New Year and may 2018 be filled with classic cars

2018 and things to come..

2017 has been a fantastic year for this website, almost 100.000 visitors have found it’s way to this site. That is absolutely amazing and I thank you all for the support by reading. Lets hope 2018 will be even better and with more high quality articles.

I will continue to publish DIY posts and other classic car related posts in this year to come, so stay tuned.

What new can you expect from 2018?
DIY for the W140 S600 as something new and exiting. I hardly find any information for these cars on the internet.
Some long awaited videos will come up around Q2-Q3 where we will take a spin in some Mercedes classics.

Mercedes w123 driving in winter

How to change the Thermostat

Is your engine experiencing climate change?

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.

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

Preparation

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.

Tools

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

Procedure

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!