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.
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.
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)
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.
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.
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.
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.
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.
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.
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.
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.
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.
After the clutch assembly is off, you can start by assembling the new compressor.
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.
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.
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)
Here comes the 4 part series you all have been waiting for. The ultimate on how to fix the air condition system in your already too hot car. Bored of driving sweating and always going around with the windows open? Now it’s the time, you have been letting this job off for far too long. Brace yourselves, global warming is coming!
I will cover a standard fix of AC system in four parts. Before even beginning you need to know the basics and the theory behind the technology, this will be covered here in part 1. If you are an expert on AC systems then just head over to part 2.
Part 2 will cover how to change the AC compressor. Part 3 covers the changing of the receiver/drier and the last and fourth part covers how you change the expansion valve. These three components are usually the ones you need to care about if your AC system is not working
Automotive AC Theory
Air conditions are based on the thermodynamic heat pump cycle and if you are really into thermodynamics you can dig into this topic really geeky and deep, but this is not the purpose here. The automotive AC works just pretty much like any refrigerator, this technology is old and proven, no rocket science really. A heat pump moves heat from one source at a lower temperature to another location with a higher temperature with using mechanical work.
Either used for heating or refrigerating the operational principle is the same, but here we are interested in the refrigerating part.
Mechanical work is needed to shift the heat to flow from a colder location to a warmer one since this is opposite to the natural heat cycle in the universe. The mechanical work in a car is made by the car engine.
The vapor-compression cycle is most common for automotive uses. Here it uses a recirculating liquid called a refrigerant that undergoes phase changes to absorb and remove the heat. Many of you have heard about Freon, but this is just a brand name for some types of refrigerant that was common in the olden days, now it is prohibited due to the ozone depletion of such CFC gases. Newer refrigerants do not deplete the ozone layer, but have high global warming potential, so it’s important that you don’t leak these refrigerants out into the atmosphere.
Vapor-compression cycles all have 4 key components: a compressor, a condenser, a thermal expansion valve and an evaporator. For most uses you will also find a fifth component which is the receiver/drier, this is always found in automotive AC.
Since the system is closed and recirculating it doesn’t really have a start, but lets start with the refrigerant entering the compressor. The compressor is the part that circulates the refrigerant and is driven by the engine through a tension belt. The refrigerant enters in vapor form at low pressure, but gets compressed by the compressor and it will form a high pressure vapor with higher temperature, known as superheated vapor. It then enters the condenser.
The condenser is a radiator where the superheated vapor runs through tubes where a fan or water cools down the vapor so it condenses into a liquid. Here the refrigerant removes away the heat to the flowing air or water. This is the part where the heat pump can be used as an oven, but in the car refrigeration is wanted and the condenser is just radiating heat into the atmosphere. The colder high pressure liquid is then routed to the receiver/drier as a saturated liquid.
It is located usually before the expansion valve in the high pressure part of the system. They serve three important functions:
Temporary storage container for refrigerant when system is not in use.
Filtering debris inside system.
Removes moisture that can have gotten into the system which can create corrosion and destroy the compressor.
The liquid then goes to the expansion valve where the liquid can drop a lot in temperature.
The Expansion valve (metering device)
The saturated liquid goes through the expansion valve where the pressure suddenly drops, the sudden drop in pressure lowers the temperature of the now liquid and vapor mixture to a much colder temperature than the temperature of the space which need to be refrigerated, like the inside of a car. The cold mixture of refrigerant then is routed to the evaporator.
Inside the evaporator, which is also like a radiator where tubes crisscross over metal fins to expand the possible area of which heat can be absorbed. A fan blower pushes warm air inside the car through the evaporator where the heat gets absorbed by the cold refrigerant and cold air comes out on the other side. This you will feel as the cold air conditioned air coming out of the vents. The liquid inside the evaporator tubes gets, you guessed it; evaporated into a vapor form due to the heating and carrying this heat back to the compressor completing the cycle.
I hope this was informative and covered the basics, so now you have the understanding of your car’s not so complicated AC system.
Why is the R129 SLs so cheap these days and the R107 SL so expensive in comparison? The R107 has already become a true classic since it started production back in 1971. The oldest R129s are already passing 25 years and becoming old. But they are ridiculously cheap compared to what you get. This is a common trait among luxury sedans aged between 20-30 years old before the prices start to go up again, but the SL is supposed to be a sports car and it is a convertible. These types of cars normally have quite higher prices than the aging luxury sedans.
The funny thing is that you can get a V12 SL600 fully equipped for just around 15k Stirling pounds. That’s crazy for a car that nearly cost 100K£ new back in the olden days, especially considering the inflated currency and the value of money back. Why would you even consider buying new car when you can get this luxury three pointed star of rolling ludicrousness for absolutely less than a single cruise holiday to the Caribbean? Also if you want one R129 in red, they are the most expensive ones, not many came in red and for some reason they are highly valued.
The R129 SLs are also reliable cars where the bigger engines have super strong dual overhead cam axles. Buy it, drive it and don’t bother opening the hood in between services. The only major thing you need to take care of here is the soft top that will deteriorate quicker than the rest of the car. But you probably have a garage right? You can even get them with a hard top which can be used for other seasons than the summer, perfect for northern Europe. Although my personal opinion is that you should avoid driving around in a convertible with the hard top on, what if the sun comes out!?!?
The styling has become timeless yet still feels modern even though it’s a 30 year old design. I have never heard anyone said that the R129 SL looks bad, and in the end that’s what matters right? To drive around in a cool car is first priority. Power, speed, comfort and reliability usually comes second when having a 2-seated mostly unpractical convertible. If you get the R129 you will get all of these except the practicality. Although you will probably fit your unused golf clubs while impressing your business friends that most likely are not good at gold either. (I would rather hang my muddy mountain bike off the back, throw in my diving gear in the boot along with the boots and back pack for hiking, but that’s just me)
So what are you all waiting for? Get out there and buy a cool R129 and drive it!
To be inspired check out these videos about the R129 from Harry’s garage and The Smoking Tire respectively: