HOW-TO: Replacing M119 Coolant Thermostat (500E, E500, 400E, E420)

[Lowman]

thank you for all replies.Ill dig into it..when the time comes to do the swap..but i reckon i just go with the waterpump thats allready in there as the car has no cooling issues at all..and doing the waterpump /thermostat replacement is just a preventative maintenance .

But one thing i DO consier even more..is the electric fan conversion..now that would be a nice one i think

 

[gsxr]

Jelmer did the electric fan conversion - search the forum. You need a MAJOR electric fan, and it will need the 150A alternator upgrade. Depth is an issue, also noise is a problem too... aftermarket electric fans that flow enough CFM are noisy!

 

[mikeym]

Planning to put in new thermostat this weekend...what is the best way to bleed air from the system? On the E320, it was nose down, nose up and then MB added a screw to the thermostat which makes it super easy at least on facelifted models. Wondering about the procedure for 119... thx

 

[gsxr]

Planning to put in new thermostat this weekend...what is the best way to bleed air from the system? On the E320, it was nose down, nose up and then MB added a screw to the thermostat which makes it super easy at least on facelifted models. Wondering about the procedure for 119... thx

Fill the block from the upper radiator hose until you can't get any more in, THEN fill the plastic reservoir. After it reaches operating temp it will burp, level will drop... let it cool off and then you'll add about 1 quart to top it off correctly.

If you don't fill the M119 via the upper radiator hose into the block, you are almost guaranteed to have problems.

 

[a777fan]

Planning to put in new thermostat this weekend...what is the best way to bleed air from the system? On the E320, it was nose down, nose up and then MB added a screw to the thermostat which makes it super easy at least on facelifted models. Wondering about the procedure for 119... thx

Great to hear! I’ll be doing this in the near future. You’ll have to stop by and help out.


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[mikeym]

Great to hear! I’ll be doing this in the near future. You’ll have to stop by and help out.


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NP, glad to help from my learning.
Compared to M104, this is a lot more involved. And want to slap the mofo who designed the thermostat housing and decided to make the third bolt almost inaccessible especially with the 90 degree elbow hose in place.

Anyone has suggestions on how to free the thermostat housing before I use a hammer? I tried wiggling back and forth and got some bruised knuckles but it is not budging.

 

[gsxr]

Anyone has suggestions on how to free the thermostat housing before I use a hammer? I tried wiggling back and forth and got some bruised knuckles but it is not budging.

Remove the 90° hose first, then the t-stat comes out easily. Note that if you did not drain the block, you'll get a coolant bath. Re-installing the hose is fun, note the 2 ends are different diameters, and it only fits one way.

BTW, did you actually read the first post in this thread? It covers all of the above, with photos. Post #2 mentions the block drain, and #3 refilling through the radiator hose...

 

[mikeym]

Remove the 90° hose first, then the t-stat comes out easily. Note that if you did not drain the block, you'll get a coolant bath. Re-installing the hose is fun, note the 2 ends are different diameters, and it only fits one way.

BTW, did you actually read the first post in this thread? It covers all of the above, with photos. Post #2 mentions the block drain, and #3 refilling through the radiator hose...

Yes I did, couple of times The first question was to see if there was an equivalent way to bleed like late model E320 (e.g. using a screw on top of thermostat).

After removing spring clamps, I tried removing the hose but it wouldn't budge. Since it was not in great condition, I decided to cut it and removed it. Even then, the 3rd bolt was a pain but I have taken that off. Drained the block as well.
After doing all that, I was tried to remove the thermostat housing and it wasn't budging. Will try again.

 

[JC220]

I tried to remove the thermostat housing and it wasn't budging. Will try again.

They can be quite hard to break loose. On mine I had to get a very tight grip on it and hit it with a rubber mallet at the same time until it came loose. It took quite alot of force to break the seal

 

[mikeym]

They can be quite hard to break loose. On mine I had to get a very tight grip on it and hit it with a rubber mallet at the same time until it came loose. It took quite alot of force to break the seal

Thx. I used a flat screwdriver and a hammer and couple of quick taps freed it. Looking at the condition of the thermostat and the golden brown coating around that area, I don't think the thermostat has every been changed on this car in 22 years.

 

[mikeym]

Anyone else tackling this job in future and trying to open the block drains, get a 6mm swivel socket. Otherwise, it is a pain to get the bolt out. My crappy craftsman universal swivel heads are too loose and was too lazy to go to the store to get new ones.

 

[mikeym]

Finally, got the thermostat done and back on the road. What a pain it is to put back the short 90 degree hose. I would not want to do this job twice and probably just get it done next time. I tried putting the hose after the thermostat but it was almost impossible to get it into place.

Below is how I did:
1) I put the hose on the thermostat first and pushed it all the way so that it is as close to the neck as possible.
2) Place the other end on the water pump side.
3) Position the thermostat in place. (I had marked the bolt which places the hole in the thermostat to the top).
4) Use a plastic trim tool to pull the hose over the water pump outlet and set in place. Takes time but doable.
5) Remove the bolt for dipstick and turn it bit. Getting the third bolt started was the hardest part. I use a magnetic holder to hold next to the hole and used my hands to get it started.
6) Use a 1/4" drive socket with swivel joint adapter to put the third bolt of thermostat in place.

As I said earlier, I want to meet the mofo who designed the thermostat including the third bolt, slap him/her and take away their license and diploma.

 

[mikeym]

This is the pic with the new thermostat, car reaches the 80 degree mark faster and now sits just above the mark. Glad to get it back on the road.

 

[LWB250]

Definitely a pig of a job, despite looking super easy. First time I did one it probably took me 30 minutes and numerous swear words to get the hose over the thermostat.

Dan

 

[a777fan]

View attachment 73974

This is the pic with the new thermostat, car reaches the 80 degree mark faster and now sits just above the mark. Glad to get it back on the road.

Damn you, your rear sunshade and your Canadian spec cluster!





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[Duh_Vinci]

Only use the OE/OEM thermostat. Check if your engine uses the early or late style, they are not interchangeable. Early OEM is Behr, late OEM is Wahler.

More t-stat info is in this thread: https://www.500eboard.com/forums/showthread.php?t=6830

Thank you for the thread, just installed new thermostat, coolant, drain plug into SL500 project... Glad I found this thread, as to no surprise, when I searched few online catalogs, the older style, separate thermostat was coming up as "Fits your car", where it ended up being self contained with in the flat housing. My car is late 1994 build, and all I had to do is look at it, and compare with the pictures in the tread.

Two "wobble" 1/4 drive extensions (one short, one long) worked perfectly in removing that harder to reach bolt at the engine side.

Regards,
D

 

[Trae]

FWIW, I just did this job and it was a breeze with this write up.

Took your recommendation and replaced the 90 degree short hose. Taking the hose off made the job easy and the back bolt (normally inaccessible due to the hose) came out easily with a 10mm deep socket. Just make sure you are flush with the head of the bolt so you won't strip it.

Tighten bolts to 89 in. lbs. (10nm).

Tip for short hose installment. Use Wurth Rubber care and is slides on easily.

 

[Benzy Boy]

I have a lazy thermostat too. When the weather is around 0C outside it takes years to reach 80 if at all. At idle it gets closer to 80 but when cruising it drops down again. Oddly my heat works fine though at all temps.

 

[Benzy Boy]

Can't get the 90 degree L hose out for the life of me
I even managed to find the perfectly fitting thick hook to grab onto it and pull it off with all my strength and no budge but the entire car is shaking instead lol

 

[gsxr]

Yeah... the 90° hose is no picnic. Worst case you can cut it off and replace with new (OE only), but with enough prying it will usually break free...

 

[gerryvz]

With enough effort, you can work it off -- it can put up quite a struggle, though. Perhaps try taking the butt/handle of a large screwdriver, and push in on the center of it, backward toward the engine. That may free enough of the ends of the hose off the flanges to get it loose.

Otherwise, cut and replace, as the @gsxr said. It's easy enough to replace it with a new one, and this honestly should be done every 10-12 years anyway. They're cheap enough.

 

[Benzy Boy]

Edit: I got it. Made some frankenstein wobble plus adapter-adapter 10mm thing on a 1/4 ratchet.

I cut the hose out but I cannot reach the third bolt. I tried a tiny 1/4" wrench with a wobble and a deep 10mm and they're both just barely off from getting a good grip around the bolt. On my M119 there's an addition structure beside the dipstick that blocks the wrench as well. Any ideas?

 

[Benzy Boy]

Tip for reinstalling the 90 deg L hose: Remove the serpentine belt for space and dab a little bit of dielectric grease on the outside lip of the metal segments and it pops right in by simply pushing it. Reinstall took literally 30 seconds for me which was a big surprise. Job is finished, thanks for the write up!