W203 C Class Thermostat Replacement Instructions

[CyberNinja]

This "How To" instruction should be useful for anyone considering doing the task themselves, since many people have been enquiring about engine running temps lately. Someone on another MB Forum generously provided me with this fantastic guide, and I simply wanted to say thank you.

It could be worth it to change the oil filter at the same time since the operation is considerably easier with it off. Handle with care because the filter housing is made of plastic and is reused. (I did the oil change as well).


Replacement of the C270 CDI W203 thermostat.
The C220 CDi W203 appears identical.

Equipment needed: a ratchet and an extension bar, preferably with a ½" drive, and a length of 4′′ or 6′′.
These are the socket sizes: 6mm, 7mm, and 8mm.
Housing socket for oil filters.
The ideal Star/Torq bits are E12 and T27, which are ½" drive sizes.
Joey is just right.
Proper axle supports.
Scraper for soft materials.

Food items:
Ice Melt
Degreaser Cloth that is lint free
Dental floss

Thermostat Gasket and Housing.
The oil filter housing's "O" ring!
(If you think it's worth it to change the rusty pipe between the house and the block all at once)

This is what the novices try...

To keep the coolant from leaking out of the under-tray tray...
The first step is to use axle stands to raise the vehicle. Make sure you have enough space to lift the engine out of the undercarriage using an 8-millimeter socket.

Starting at the top, use the T27 socket to remove the engine covers.

Determine what you can remove to simplify the task at hand.
Going from the gasoline filter to the pump, I chose to disconnect the fuel delivery pipe. To prevent dirt from getting inside, I removed it from the fuel filter can and sealed the exposed hole.


Additionally, I used a T12 to secure what appears to be a test point that I removed.
The fuel rail sensor cables were also disconnected by me.

Open the header tank to release system pressure after the engine has cooled.
I turned off the water mains after that.

WARNING: The system may still be under pressure.
First, I used a 6mm socket to remove the little bore from the header tank.

After that, the 7mm socket leads to the radiator via the large bore hose. The fuel cooler is reached by means of an additional tiny bore pipe.

I decided it would be a good idea to remove any debris and grime from the region before removing the housing bolts. Keeping impurities out of my coolant pipes.
After using a tooth brush and a water-washable degreaser to scrub the area, I rinsed it off with clean water.

A further "hose" can be found beneath the thermostat casing; bring it to your attention.
Flared ends adorn this rigid 2 or 2 1/2" hose. The clamping force between the thermostat housing and engine block is all that's needed to keep it in place. I reused the hose, but if you want to replace it, now is a good time to do it.
The only way to modify it is to remove the housing.
Keep in mind that this hose will detach after the housing is unscrewed.

You should also inspect the state of your hoses at this time.

Take the sensor cable out of the enclosure. Use a little screwdriver to push the little clip release.

One E12 bolt is on top, and two are below; locate them.

In an effort to avoid accidental drops, leaks, and other problems, I refrained from removing the oil filter housing.
Removing this made my life lot easier, as I soon realised.
After I took it off, I used a lint-free cloth to tightly wrap the exposed part and climbed over to prevent any bits from falling in.

Remove by cautiously cracking off the bolts one at a time using a size E12 torq bit.

I had to use considerable force to pry my housing off the block.
The aforementioned "short stiff hose" immediately set out on its own as it became free. Declining the engine's side.
When taking the housing apart, remember this.

Be cautious not to scratch the metal surface as you use a cloth and scraper to clean up the area. It should go without saying that you shouldn't hurt the face!

The replacement component will have a rubber gasket; install it.

As you insert the "short stiff hose" into the corresponding hole in the block, carefully position the housing so that the "short stiff hose" lies in the housing's bottom opening; do this while avoiding obstacles like a fuel rail.
When everything is in place, insert the bolts into the housing and tighten them.

Verify that the housing is perpendicular to the block and that the "short stiff hose" is securely attached. When you're satisfied, tighten the bolts; but, be careful not to strip the threads by going too far, since you're forcing a strong bolt into a soft block.
A torque of 9 Nm is recommended.

Get a new housing for the oil filter right away. Reduced torque to 25 Nm. I should have gotten a fresh 'O' ring, according to the rules.
While shopping for a thermostat, you can consider adding this to your wish list.

Reattach all of the hoses once they are snug.
Simultaneously, I replaced the clips on my hoses. The big radiator hose was the last thing I attached. Prior to replacement, I will attempt to fill this hose with coolant.

Make a mixture of coolant once all the hoses are reattached.
I was able to pour three litres into the top hose before it began to leak out of the housing.
Secure the hose and clip.

Fill up the tank on top.


Mounted behind the headlamp on the driver's side of the C270 is an electric water pump. (I looked at my C220 CDI W203 and couldn't find a pump like that.) Turning the key starts it up.

In the off chance that it would aid in releasing air locks, I let it run for ten minutes.
Once the gargling became excessive, the sounds ceased.
I proceeded to start the vehicle and let it to warm up.

It seems like the car is heating up and cooling down normally, and I don't have any air locks, either.

If you're paranoid (like me), check the header tank levels and keep an eye out for leaks throughout the following few days of running.
So that I could look for leaks, I left the engine covers off.
Nothing has gone wrong after 600 miles.
In comparison, my automobile reaches 80 degrees in 15 minutes at 60 miles per hour, with an ambient temperature of 5 to 6 degrees Celsius, and it starts to warm up in about 10 minutes.
The temperature ranges from 85 to 95 degrees Celsius.

For anyone who has never changed a thermostat before, I hope this serves as a warning.
It will save you £185 in labour costs.

[TDudette]

Thanks for making it available "over here"; I've sent this tutorial to several folks on the other side since, as far as I can tell, W203 (and similar) diesels have a thermostat problem; I had to replace mine in the first year after purchasing the vehicle. It was well worth the little investment because it not only got the engine up to temperature but also raised mpg from 40+ to 45+, making the heater operate.

[DreamWeaver]

repair work on the thermostat unit

An immediate inquiry. Putting sealant on the thermostat housing is optional. Given the presence of a rubber ring, I am uncertain as to whether sealing is still necessary. The thing is, I've always been told to use sealant on joints that are exposed to both water and oil.

[CyberNinja]

I simply used the rubber "gasket" that came with the thermostat instead of sealant. The mating surface should only be clean and flat.

For less than a main dealer and with MB Club Discount, I purchased my stat from www.eurocarparts.com. Use the code mbclub25 when you check out.

[CyberNinja]

https://www.eurocarparts.com/?utm_source=awin&utm_medium=affiliate&utm_term=ecp+homepage&utm_content=Skimlinks&awin+traffic&utm_campaign=Sub+Networks+78888&sv_campaign_id=78888&sv_tax1=affiliate&sv_tax2=815061&sv_tax3=Skimlinks&sv_tax4=forums.mbclub.co.uk&sv_affiliate_id=78888&awc=3997_1772805337_4b44d7a114434ef16adf4284e38ce336

[WordSmith]

Greetings, I have recently completed this task; your description is really clear and concise. Just so you know, the 2003 model year W203 270CDI on my car has the E10 and T30 sockets. In order to completely remove the top bolt, the E10 driver must be very tiny so it can fit into the narrow space. I managed to fracture the bolt off and free it halfway with my 3/8" socket drive, but it got "caught" on a hexagonal fitting. To fully remove the bolt, I switched to a 1/4" drive 9mm socket. In the event that anyone is in need of purchasing the Torx and E-Torx drivers, I hope this information proves useful.