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Registered
1990 300SEL, 2005 SL500
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84 Posts
Discussion Starter #1
I think it’s a classic mono valve issue but only time will tell.
Here is the video from Ralf;
I like the way he explains things.

I already got most of it disassembled and will post the findings soon.
 

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Registered
1990 300SEL, 2005 SL500
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84 Posts
Discussion Starter #2 (Edited)
I suspect to long of an interval (storage) causing coolant to break down. Possibly some impure water added to the 50/50mix.
Valve repair and system flush should do.
 

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Registered
1990 300SEL, 2005 SL500
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84 Posts
Discussion Starter #4
Remove 2 screws holding the connector and a hood switch bracket.

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Move the bracket out of the way.

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Disconnect the electrical connector.
Undo 4 screws holding the mono valve. (Go slow and take them out by hand)

Now, I didn't need any tools to take the valve out. Gently wiggle it back and forth while pulling up. Some of them may be really stuck and you may need the hose pliers or something similar to pull it up.

Valve is out. Coolant does not look that bad.

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Than just one look at the mono valve screen and yes, cooling system flush is added to the list.

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That’s how it looks when pulled apart. Deposit/contaminant can be seen all around the valve. There is one small rip in the rubber seal (not visible in the pic). I also notice that the plunger movement is rough and jagged.

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Valve on the scale (free of liquid)

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I purchased this new aftermarket valve earlier just to get the new set of rubber seals.

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New valve weight is 70g but the spring tension is definitely lower. Electromagnetic valve engagement/holding power is lower as well. It doesn’t really matter as I will be rebuilding my old valve.

Since I performed the initial cleaning in the kitchen, I used no chemicals. Nice ripe lemon did the trick.
I squeezed the juice inside the valve around the plunger and let it sit for a while. Than work the plunger back and forth gently while adding more lemon. When I got to the point where the plunger movement was silky smooth I cleaned the outside and rinse well with water.

Assembled valve with new rubber seals and mash screen.

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All that's left to do is is to put it in the car.
It may be easier to place the valve inside the body first and than place the magnetic coil on top of it. (Just a thought)
 

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Moderator
1991 500SEC 50K mi. 1987 560SEC Now 153K mi. 2020
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4,412 Posts
Looks good so far.. Nice description & pics.

For reassembly, in my 560 about 10 years ago now, I think I did what you allude to.

MBL
 

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Registered
1990 300SEL, 2005 SL500
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84 Posts
Discussion Starter #6
No over the counter stock of Zerex G05 in my area. It needs to be ordered in. Go figure.
I may have to put the aftermarket vale with the old seals in the car for now. I don’t want all that effort to go to waste.
 

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Registered
1990 300SEL, 2005 SL500
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84 Posts
Discussion Starter #7
No Zerex flush available in Canada. 😳
Hello, Valvoline. Why not?
Anyway, this needs to be done. Looking for suggestions.
What’s the latest, greatest flush formula for our cooling system?
 

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Registered
1990 300SEL, 2005 SL500
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84 Posts
Discussion Starter #8
I’m looking for the cooling system diagram.
Any PDFs kicking around?
 

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Registered
1990 300SEL, 2005 SL500
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84 Posts
Discussion Starter #12
I did flash the system today. Finally :rolleyes:
Drain.
Complete, component by component rinse.
Full heat cycle with distilled water.
Drain.
Empty the system with compressed air (low pressure).
Refill with Zerex G-05.
2 full jugs, 3.78l for a total of 7.56l.
That’s pretty close to the manual which states 8l for the cooling system capacity. (1990 300SEL)
Overall, coolant and all the components were in excellent condition. I would even venture to say that the system was flushed not to long ago but the heater core must off been missed.

I’ll take it for a spin tomorrow and see how it works.
 

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Moderator
1991 500SEC 50K mi. 1987 560SEC Now 153K mi. 2020
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4,412 Posts
You are correct Martin.

That switch is for the alarm.

For reference, it is S62 in the images.

M

Screen Shot 2020-03-27 at 7.05.49 AM.png
Screen Shot 2020-03-27 at 7.07.13 AM.png
 

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Registered
1990 300SEL, 2005 SL500
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84 Posts
Discussion Starter #15
I found this switch on my car too, but thought it was some aftermarket addition for an alarm, because the wires coming off it were thin and not insulated well. So, what's the purpose of this hood switch?
It is one of the switches that serves the alarm loop. Fully functional alarm. 🚨
You got to test it It’s awesome, makes your Benz look like the undercover police cruiser. 👮
Lock your car than open the hood or should I say bonnet? 😎
 

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W126 1990 500SE (ASR) & W126 1991 300SE
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129 Posts
Ahh, so it is for the alarm, but it is a factory fitting, which is a surprise. Actually the previous owner had an alarm/immobiliser fitted about 3-4 years ago. Look what the savages did:
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So, in my case the factory switch does nothing, and this one located on the slam panel works with the alarm that is fitted. Why they thought it would be a good idea to cut the sticker off and drill two holes in the slam panel, when there is already a switch they could have used, I don't know.

I have a new sticker coming, and my plan is to get rid of this switch. Should be able to just remove the switch and join the wires up hopefully.

So, if the factory switch serves no other purpose, I'll wire it in to the LEDs I'll be fitting! :)
 
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