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.
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.
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.
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.
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.
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!
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.
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.
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.
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.
Ever felt that the engine is not making as much power as it used to? And that the fuel economy has been slowly decreasing? The first thing you should check is the condition of your injectors. Unless you have a pressure tester for the injectors, you would have to guess out from the age of the injectors. If they are more than 10 years old I would suggest to change them, that said if the injectors are relatively cheap since they vary a lot in price between the models. They are still relatively cheap for the M110 engine. E.g. If you have the rarer M100 engine, it will cost you nearly a new house to buy new injectors!
I will describe how you change the injectors with new ones. Refurbishing the old ones is a bit more cumbersome and it needs a pressure tester which you can clean them with and test for release pressure and spray pattern.
Changing the fuel injectors is not difficult and you don’t need much preparation except acquiring new injectors, gaskets and o-rings. There are two gaskets per injector you will have to change or you will end up leaking fuel which is expensive. You can change the injectors easily in an afternoon. I also recommend to change the fuel filter at the same time to not clog up your new injectors.
Start with opening your hood and disconnecting the battery. Sparks can make explosions from gasoline vapor when you are working with the fuel system, and we don’t want that to happen.
Remove the air filter housing to get access to the fuel delivery system.
The four front injectors you can now access without removing more stuff, but to gain access for the last two, you have to remove throttle linkages, fuel hard lines and a fuel regulator. We’ll come to that later.
Two and two injectors are held in place by a single metal plate, to remove the metal plate loosen the injector hard lines first. The injector hard lines should not sit on very hard unless they corroded over time or they have been over tightened. Use two spanners, one 14mm to loose the line nut and one 12mm on the injector itself to to keep it from rotating.
When two hard lines are loosened you can bend them a little to the side to get more access and then remove the injector hold-down plate.
After the plate is removed you can pull out the injectors with you fingers, they sit loose in there. The injector housing will be left, This plastic housing you can just pull out straight too, but be warned, do not use excessive force and pull only the housing straight out with you fingers, don’t use tools or you might damage it. It most likely have become quite brittle by heat over the years. If they are in such a bad condition they are cracked, you have to replace them.
Most likely some of the injector housing gaskets do not come out with the housing, but is still sitting in the injector hole, use a small flat screwdriver and pry it carefully out.
After removing the first four injectors, the two back injectors are left, now the big job starts. See in the picture below that these things blocks access to the fuel injectors.
Start with removing the throttle linkage. Remove the pin and the c-clip along the ball joint. I use a wide flat screwdriver to pry the ball joints off. Remove some more linkages and then you are ready to remove the regulator.
Warning: Get a small collecting can of some sorts and tilt it towards the injector line shown in the picture below. Loosen it and fuel with shoot out with high pressure. Wait until the fuel stops flowing, then loosen the second fuel line connected to the regulator.
Also loosen the vacuum lines before removing the fuel regulator, it is fastened to a bracket with two small bolts.
Now you should have clear access to the last two injectors.
Now is the time to inspect the old injectors and look at those old brittle gaskets. It is a reason why your car was using excessive fuel…
My old gaskets were super hard, especially the round outer ones. No wonder why there was a lot of dirt around the injector area by the engine, they have probably been leaking a while. This job should have been done years ago. I didn’t notice it when the engine performance still was very good, but obviously not optimal when looking at this leaking issue. The old injectors I don’t even bother testing, I will just throw the old ones and put in new ones.
This is how you should assemble the injector with the gaskets:
Pop on the big rubber gasket on the injector itself.
Pop on the little rubber ring on the injector plastic holder.
Pop the injector holder into the engine block until you hear and feel a nice pop.
Slide all the injectors into the holders. Put the hold-down plates over them and tighten.
The injectors will now have a good seal and no fuel will leak. It is also a good idea to clean up the area around the injector holes in the engine before assembly. Also try to be super clean with the new injectors, keeping the plastic cups on as long as possible before fitting them.
No you also have the perfect opportunity to lubricate all the throttle linkages, such as the pivot points and ball joints, I know they have been neglected for years and we are all guilty as charged. However now is the perfect opportunity for redemption. Remove all the linkages and pivot plates, clean them and apply new synthetic grease that will last a while and hold up to water and heat from the engine.
When everything is bolted back together, there is no such thing as dreadful bleeding like in a diesel. Just crank the engine over a few times and the engine should start, it will run rough for a little while until the pressure have settled, and you might experience hard start the first couple of times before the first drive. This is the time when you realize if the electric fuel pump needs replacement or not, mine is some years old and still going strong, although it have been replaced a couple of times the last 15 years.
If you did enough work with cars you end up some day with the need of removing the engine, the very heart of any car. Think of it as heart surgery, but not entirely so complicated. Actually quite easy compared to many other car related tasks, but it’s a long job if you venture down this road.
So how do you take out the M110 engine from a Benz? I’ll teach you the dark arts of car surgery so stay with me in this dreadfully long post.
Always leave the transmission on the engine when pulling it out..
If you have either w123 or w126 the procedure is almost the exact same. The complication will be if you have an AC or not and small difference in wiring and placement around in the engine bay. Usually the bigger the engine the more difficult it is to get out since the space gets really tight and hard to get to places when removing stuff.
If you are doing major engine overhaul or need to do something with the transmission, it is best to just take out the engine with the transmission. Always leave the transmission on the engine when pulling it out even if just doing engine work.
Preparation is key like most things in life. Don’t plan to use your car in the next few days, or a week if you are new to car fixing. Taking out the engine can be done in under a day and putting it just takes a bit more time. This is definitely a job where more people can be helpful, so go get your buddies and offer them some beers.
You need to acquire an engine lifter also called an elephant jack, and some good quality lifting chain and shackles that are rated for some hundred kgs (I think the M110 is not heavier than 300kg, but you have to cross check that since I don’t have the exact numbers). A very nice tool to have is an engine tilter which you can hang from the lifter. It will make your life easier since the engine needs to get out of the engine bay beam at a very tilted angle, but it is doable without. I made it without, but it required some wrestling and tryouts with different chain lengths.
Other than that you basically need some jack stands and a basic socket tool set, and of course patience which is found at the bottom of the beer glass.
NEVER crawl under or have any body parts like your arm, or place your friends under the hanging engine and crane while lifting the engine. Then you won’t come at harm if the lifting mechanism should fail and the entire engine come smashing down. The engine will be needed to be lifted quite high to get over the front support beam in the engine bay and you must take lifting heavy objects very seriously. Also try to minimize the time of the actual lift, not leaving the engine hanging, but setting it down as fast as you have it outside the engine bay. This will minimize the time of potential hazards hanging from the crane.
The first thing you will do is to remove the battery and start to drain engine fluids. You will be removing oil and coolant hoses connected to the engine. Start with the engine coolant, open the heater switches to full heating then drain fluid via the radiator drain and the engine block drain. Check out How to do a coolant change on the M110 engine. Remember to put the caps back in in order to not loose them and to prevent dirt from entering the system.
Then drain the oil sump. When it has drained disconnect the hoses to the oil cooler next to the radiator, lots of oil will come dripping out of here as well so watch out.
It is not necessary to drain out all the automatic transmission fluid if you do not plan to do any transmission related job.
The third liquid to drain is the power steering fluid. Open the power steering reservoir cap and suck out the oil with a oil sucking pump. When empty disconnect the hoses to the power steering reservoir and be ready for more of this oil to come leaking out of both the reservoir and the steering box. Sometimes the hoses can be tricky to get off while the engine is still in the car. I could only get one off and had to connect the second hose when the engine was lifted slightly up.
If your car has an automatic transmission, the fluid is also cooled via the lower radiator and connected with two flexible hoses. It is not necessary to drain out all the automatic transmission fluid if you do not plan to do any transmission related job. Instead, when the car is standing level, disconnect the two flexible hoses from the hard lines which transports the fluid to the radiator. Some fluid will come dripping out, mostly from the radiator. Carefully clean the tips of both hard lines, then cover them securely with duct tape sealing the holes to prevent more fluid to leak out and preventing dirt to enter. This way you are not needed to drain the automatic transmission fluid which takes forever.
After the fluids are drained, start by removing the engine two coolant hoses connected to the radiator and all heater hoses connected to the chassis.
After the hoses are disconnected, the exhaust is needed to be removed. I really dislike this part since it involves heavy and big parts. Now you need to raise the car up on jack stands for access. I personally use ramps for the front wheel so I can just drive the front up, and then raise the back end up on stands. For me this is much quicker. If you have a car lift, then bless you sir.
With car up on jack stands, the exhaust needs to be loosened at the manifolds. You only need to loosen four bolts when you have the twin pipes, but they can be a pain in the butt since they always are rusty due to the heat.
When the manifold bolts are loosed, support the front end of the exhaust from under the car before you loosen the exhaust support that is on the transmission. Now the exhaust is only hanging by the rubber donuts at the back and sitting on the support at the front. One last thing to loosen before you remove the exhaust, is to completely is to remove the starter motor ground cable, which the exhaust pipe can get stuck at when you try to drag it out from the back of the car.
When the starter motor ground cable is loosened, lower the exhaust to the ground with removing your front support and removing/ cutting the rubber hangers. Be careful so it doesn’t fall on you since the exhaust system is very heavy. You should have some help when removing the exhaust system. Finish by dragging the exhaust out from the rear of the car while rotating it sideways so the front pipes don’t get stuck.
Also make sure the automatic transmission is set to neutral to prevent stresses internally if the transmission is set to park (the flex-disc bushing bolts are usually set to very high torque..
Now with the exhaust removed the fun part starts. The drive shaft has to be disconnected from the rear of the transmission output. First remove all the aluminum heat covers under the car. Block the back wheels from turning, by handbrake or the pedal brake or whatever, this to prevent the shaft from turning when you loosen the bolts. Also make sure the automatic transmission is set to neutral to prevent stresses internally if the transmission is set to park (the flex-disc bushing bolts are usually set to very high torque + corrosion). Loosen the drive shaft collapsing bolt first, which is located just in front of the center rubber bearing. This way you are able to collapse the drive shaft and remove the front part from the transmission later. Before removing the flex disk nuts, it’s a good idea to remove the transmission back support plate to get greater access with spanners, just remember to support support the weight of the transmission with a jack, slightly raising it so it won’t fall down when you remove the plate along with the rubber mounting to the transmission. Then finish by loosen the 3 flex-disc nuts that are connected to the drive shaft. The other three nuts you can leave in and the flex-disc will stay on the transmission while pulling out the engine. Check out How to Remove the Propeller Drive shaft.
Hopefully you managed to loosen the front drive shaft without too much effort and being strong like some 80s hero. While you’re already under the car, it is a good time to disconnect the three control wires that are connected to the transmissions along with the shifter rod. Place them out of the way of the transmission so they will not get caught or stuck later.
When you’re done with the transmission cables, it’s the time to remove the radiator and the oil cooler. They are held only with clamps and are easy to remove. However the fan needs to be loosened before the radiator can be pulled out. Take care of the sharp fins on the radiator to not cut yourself or to ruin it if you want to reuse the radiator.
When you think you have removed all the hoses and wires that are connected to the engine, then check again, and then recheck the recheck.
There are many wires around the top of the engine, like grounding wires and other various wires and hard vacuum lines. Before you start removing all the cables and vacuum lines, and there is a lot of them, use a camera or write down which one goes where in order for you to remember, then the reassembly will be much less frustrating! You can for instance write on a piece of tape what the wire is connected to and tape it around the wire. Make sure all the wires and vacuum lines that are connected to the chassis are disconnected before removing the engine, otherwise they will be ripped out and broken easily. I will not show all the images of every wire here, but will show some example pictures.
When you think you have removed all the hoses and wires that are connected to the engine, then check again, and then recheck the recheck. It might be a good idea to have an extra pair of eyes. Do not rush it.
Ok, so are you ready to remove the engine? No!! You have to unbolt the engine mounts to free the engine from the chassis first! Do not worry, the engine will not move or fall off while you do this. I do not have the picture here, but you need to unbolt from the underside of the car. There are one hex bolt on each side up inside some holes, use a torch to see them, and an extender for your hexagon bits. The are sitting there quite hard, so make sure you have the hex tool fully inside the bolt before applying force. If you round off these bolts you will have a huge problem! Once they both are removed, the engine is free from it’s base. Lower the car unto the floor again down from the jack stands.
Now and the engine can be pulled out. Move the front bonnet in the vertical upright position, in that way there is no need to remove the hood of the car. The bonnet mechanism is an ingenious design by Benz.
Move your elephant jack in position and use shackles to fasten the engine to the chain, the chain thick enough to withstand at least 300 kg. There are two “ears” which you can fasten to the engine at the rear, and one “ear” at the front of the engine. Take care to not damage any of the injector hard lines that are very close at the right side of the engine, if needed bend them a little to make more room for the shackles. The best would be to use an engine tilter to secure the chains in, but I didn’t have this tool, but it went fine without it, then you just more rely on a helping hand. Since I did not have the engine tilter, I adjusted the chain to be shorter at the front than at the rear ones, so the engine will tilt upwards at the front, in order to get the front part of the engine above the front chassis, and also lower the transmission under the firewall.
Slowly start lifting the engine with the jack, also making sure the transmission do not hit the ground or it gets stuck at the underside of the car. Make sure all wires are out of the way and they don’t get caught on something. Basically continue until the engine is high enough so it clears the front chassis frame, you might also need to shift the car a little back and forth by pushing it, obviously having the park brake off since you need to move the car often.
Never ever move the engine lifter while the engine is hanging high up. Just push the car backwards when the engine is high enough and immediately lower the engine so it sits just inches above the ground. Then you can start moving the engine it a bit around, but put it down somewhere safe as fast as possible.
I hope you liked the procedure, now go out and actually do it, cheers!
Back ground story of this engine pull out
Over the summer back in 2015 I had one goal with dealing with cars and that was to pull a M110 engine and transmission out of the rusty 280SE that had been standing still and taking up space for some years already. The car was destined to be scrapped due to rust, but the condition of the engine and transmission is surprisingly good after over 300.000 kilometers. So I got to it and pulled the engine with the transmission out and then the rest of the car got scrapped. Good riddance, it’s a huge car taking up space for nothing.
The fuel delivery system on w123 consists the fuel tank and a collection of components until it reaches the combustion chamber. This article will focus on the rear components until it reaches the CIS fuel injector assembly. The CIS system is pretty much a black box for me still. I will however go through how you change the fuel injectors and gaskets in another article.
I had to do a re-haul of the entire rear fuel delivery system when an entire tank worth of gasoline (~80 liters) had leaked out after my 280CE was parked for a while, totally delayed my plans for cruising in the summer by almost a week. This made me furious and is the reason for why I wrote this article.
It is up to you how many part you want to change. I would recommend to change all the rubber fuel hoses and fuel filters as a minimum!
New fuel tank filter (the first one)
New main fuel tank delivery hose
New fuel delivery filter (the second one)
New high pressure flexible fuel hose
Two other fuel hoses and clamps (see pics)
4 fuel assembly rubber mounts
[New fuel accumulator?]
[New electric fuel pump?]
So why bother changing the fuel accumulator? Well it can lead to problems such as warm start problems (yeah the M110 usually have warm start problems more than cold starts), this is due to the inability to hold fuel pressure after shutting down the engine and starting it before it gets cold. There are separate start up procedures either if engine is cold or warm. I thought a broken fuel accumulator was the problem with my car’s warm start problems, but it was in fact the old injectors and brittle gaskets that was the cause since they could not maintain fuel pressure.
Why bother changing the electric fuel pump? This has to be the number one reason why people are stranded in their cars with M110 engine. After some time (around 7 years if in daily use) it will with certainty stop working. The part is however quite expensive and I would suggest to not change it if is still working and not obviously very old. A maintenance tip instead of investing in a new part is to remove the corrosion on the electrical connections.
Pretty straight forward, just change all the fuel hoses and refit… OK I will guide you through it like Gandalf in the mines of Moria. Smelling fuel is usually an indication of leaking hoses.
Before you even start you have to disconnect the battery to avoid explosions. Then completely drain the tank, either by sucking up the fuel from the gas filler tube or by unloosening the main tank outlet hose from under the tank. I would suggest you drive the car nearly empty before undertaking this task. Make sure the area you are working in is very well ventilated since gasoline fume is highly explosive!
After the tank is drained you can remove the plastic cover start by removing the thick fuel hose connected to the tank. Just have a look at this one in the picture under which caused all the fuel in my car to drain out.
A massive 45mm socket is needed to remove and fit the fuel tank filter. Remember to replace the gasket as well.
Now you can remove the flexible hoses connecting the high pressure and the return hard lines. If you see rust on the connection then you have to be extremely careful not to round off the relatively soft metal on the hard line unless you want to go through with replacing the entire line. Believe me this is a shit job (my old hard lines were rusted and leaked fuel).
Disconnect the two electrical wires to the fuel pump and when all the fuel lines are disconnected from the body, you can go on and loosen the 4 bolts holding the bracket for the pump, fuel filter and accumulator. Beware this bracket can be pretty rusted and you need either to get hold of a new one or remove the rust and repaint the one you have. The rubber mount bushings are probably dried up or broken so you should replace all 4 of them.
On a work bench you can now go on with the job of replacing the components and the old fuel hoses. Look at the picture below on comparing new and old hoses.
Assembly is just opposite of removing. The main thing you have to consider is to make sure there are not any leaks before you start driving. Look at the picture below to see how the components should fit together in the assembly.
The best thing is that there is no need of special fuel bleeding or start up procedure when starting up the car after fitting all the lines together. Just refill the tank and crank the engine and it will start right up. Nothing difficult as with the diesel.
Then mount the assembly and fasten the hose to the fuel filter. Don’t forget to fit the electrical wires to the fuel pump and mount check for leaks when starting the car. When no leaks are detected, mount back the plastic mud cover to protect the components. Hopefully you will have no leaky days or being stranded by a malfunctioning fuel pump.