W163 ML270 Thermostat replacement and broken fuel line

[MOZ]

Hi guy's,
Thought I would pass on some info to help someone else in the future.

As seems to be common place on ML270's my thermostat was not working correctly and was either fully or more likely slightly stuck open as my engine was constantly running cool around 60 degC.

Having done a lot of research ans being reasonably mechanically minded, I bought a replacement and had a crack at it last weekend. My research had highlighted a common potential risk of damaging one of the plastic fuel pipes that run very close to the thermostat (which go brittle over time).

Being extremely cautious and methodical I managed to remove the old Thermostat without too much trouble. it is tricky and tight in there (I did remove the Oil filter first) and you do need to maneuver around the fuel pipes.

Unfortunately while fitting the new thermostat during one particularly fiddly bit (aligning a strange double ended bone/mushroom shaped pipe which totally relies on a press fit at both ends- this worried the hell out of me) yes you guessed it, the bottom of the thermostat nudged the fuel pipe and the crappy plastic T piece snapped (as seems to be common during this procedure). Be warned any one trying to change the thermostat - this is a very likely risk.

As I was doing this on Saturday afternoon- clearly MB parts dept had closed, and I needed the car on Sunday.
With this fuel line broken, the car was completely disabled. I didn't have any bits to be able to bodge it so begrudgingly declared defeat and resorted to calling out the AA to see if they had any T pieces and pipe that could repair it.

They didn't have anything to make a permanent repair but did use a short length of rubber hose and a couple of jubilee clips) to cover over the snapped off part (Ignoring the broken T branch that goes off to some bleed type pipe mechanism on top of the engine) and just made a straight Join across the cracked part sealing the line between the low pressure and high pressure pump. This worked a treat and after a fair bit of cranking, the car fired up and runs fine (without the branched off T piece - clearly not needed for the car to run) in fact I'm not entirely sure what this does - maybe someone on here can enlighten me - is it for purging and drawing the fuel through?.

Clearly this is a temporary fix and I have now purchased the correct part - which is a fully moulded 3 piece pipe molded into 1 part ( part number A6120703232 - cost £38 incVat from stealer) which I will hopefully get round to fitting this weekend.

But thought I would share the danger of changing the thermostat with any budding DIYers and also that if the 3rd way does snap off, you don't need to worry about that branch off part for a temporary fix to get you back on the road again, just ignore it and bypass it with a straight through joint temporarily.

Hope this experience helps some others. The thermostat change is a bit fiddly but straight forward apart from the fuel line risk. Engine now runs at its correct 85 to 90 degC, and hopefully a bit more fuel economic
All the best.
Moz

 

[Dee James]

Hi Moz, thermostat replacement is a job on my to do list on my ML so i read your post with interest - especially the bit about the brittle pipes, i think i will probably just change that part at the same time to be on the safe side!

Did you drain any coolant out from the bottom before you started and if so how much?

Any particular tools needed?

 

[MOZ]

Hi Dee,
I took the engine cover off first to assess the job before dropping the coolant. You need an 8mm socket (for the male torqx bolts or propper toqx femakles if you have them but the 8mm socket worked fine). ideally you want a small ratchet with extension bar for this too as the access to the 3 bolts on the thermostat is restricted access. it would be good to have a magnetic pick up too as you may drop a screw or 2? I Cracked the bolts first before dropping teh water to make sure they weren't seized.

I removed the engine under tray (you may want to get a couple of plastic clips and screws from MB for the undertray as you are likely to snap one or 2 (to be fair I just tywrapped mine back on in the 4 locations.

I drained all the coolant by removing the bottom radiator hose (I had read a lot of posts as to whether this was a good way to do it or not (there is supposed to be a proper drain down there somewhere, but I just dropped the bottom hose as seemed to be the general concensus) - you need a bucket capable of holding 12+ litres and it needs to be low enough in height to get under the bumper ( so a wider squatter bucket is best) I believe the system holds 12 litres, I reckon I got about 11 out of mine so possible a little left in the heater matrix etc, but I was happy with that.

Removing thermostat is pretty straight forward after that, just watch those fuel pipes.

depending on where you get your thermostat from (its the whole housing) you may find that you have to knock out and re-use the temperature sender out of the old one (some may come with a new one?).

There is an awful double ended push fit hose (no jubilees or circlip or anything) about 4 inches long which joins between the bottom of the thermostat to the top of the engine block, which is a bit of a git to realign (this was the bit I slipped with and damaged my fuel line, you have to put it in at an angle and slip both sides in as you slide the thermostat into place. I reused this pipe, but you may want to play it safe and buy a new one of these (not sure how much it is)

Put all the pipes back on and refill the system. From recommendations I bought the official MB antifreeze 6l and also bought 6l of distilled battery top up water from Halfords to make my 50/50 mix.

Fill the header tank and let it fill where it can and top it upto the level. You will probably only get about 4 litres in to start with as the thermostat will be closed, give the top hose a queeze to try to agitate it and encourage some air out. set your internal heater to hot and Fire up the engine and let it warm up that area. after a while of idling, the temperature gauge should start to rise and when it hits around 85 to 90 the thermostat will open and the water will rush into your radiator (you will probably see your water level light appear on your dash too, but you shouldn't be in the car at that point you need to be ready to top up the header again and just keep doing that (give the top hose from the thermostat to the radiator a few squeeze to try to encourage air out of the system, and just keep going until you are happy you have got most of the water back in. Once your happy enough is in, replace your header tank cap and take the car for a decent spin.
By this point (probably 20 mins + of idling) I was a little worried that I wasn't getting any heat in the car and was worried there was nothing flowing in the heater matrix, but withing 2 or 3 minutes of setting off for the spin, the heat started to pour out of the heater and hey presto.

Check the fluid level when you get back it may have gone down? top it up when everything has cooled down, and just keep an eye on it for a few days as the rest of the air if any will work its way out, and you may need to top it up a little again.

I dropped 11 litres out and had 10 back in before I took it for a spin, and have put another 1L in the following day.

Hope this helps. Its not too bad if your reasonably DIY handy, a bit fiddly, just be patient and watch those fuel lines.

all the best.

MOZ

 

[Dee James]

thanks for the excellent write up Moz i appreciate you taking the time to be so concise, i`m sure that it will come in handy not just to me but to anyone else planning on doing the same

 

[Jane270ML]

Nice and comprehensive write-up Moz, many ML owners will benefit from the above, just what forums are all about.

 

[W210Virgin]

Chaps

No need to drain the rad, although in some ways this is more convenient. All that needs to be drained is the level until it is below the thermostat level and you can get this more or less by draining at the expansion tank, and there's also a connection on the rad about midway near the expansion tank. Save the fluid in a clean container and just re-add when you're done. I agree re the pipes. Mine cracked slightly at the tee, although I did not realise it at the time. I suggest that the plastic pipes are removed before you start and indeed they are a PITA. Removing them carefully is probably a bit less risky than breaking them during the 'stat install IMO. The route under the HP pump is particularly tricky with the rad in the way and the pipes in here are perilously close to the fan blades!

 

[MOZ]

Good point W210Virgin, you don't need to release all of the coolant.
I did due to the fact the car is 12 years old and felt it was near enough to the 15 year coolant life to bite the bullet and do that at the same time too.

My guess is that if the thermostat needs changing then the car is probably getting on a bit (unless this part is so unreliable that it occurs quite early?)so in my opinion worth doing, but certainly not essential.

Thanks for adding that.
Moz