I have to replace the heater hose that goes from drivers side of cylinder head at rear to heater core.

My 1983 300SD has that little stub that feeds what is described as a windshield heater.

I ordered the wrong hose and am wondering what will happen if I leave
the stub to windshield heater unconnected.

Where I live it goes into the 20's. Don't really know what they mean by "windshield heater".

So two questions what does this actually heat and can I use
the hose that has no stub. (cheaper too, that hose with stub is 3 to 4 times the cost).

__________________
80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250

on the w126, i don't think it has a front windsheild heater. only the rear is heated, and that by an element that runs the length of the windshield, which is heated by an element that goes up the back side of the c-pillar.

whatever it is that's attached to the heater core, it's not to heat the front windsheild

__________________

On 126 chassis vehicles there is a coolant heated heat exchanger inside of the lower windshield, this warms the lowest part of the windshield preventing an accumulation of snow or ice that is swept there by the wiper motion.

It can be disconnected without too much of a problem, the only issue would be to close or plug both the coolant feed and return lines to prevent the loss of coolant. There is a thermostatically controlled valve which controls the coolant flow into the heat exchanger. This valve and the associated hoses are located beneath the cowling which also covers the wiper transmission.

You can disconnect the small inlet hose from the heat exchanger and loop it back onto the return pipe bypassing the heat exchanger completely.

In your case it sounds like you will need to get in there and plug the return line so as to prevent coolant loss from it and the new incorrect line without a heat exchanger inlet opening doesn't need any sort of plugging.

The heater was added during R&D to keep the wiper blades from freezing down in cold weather.



Have a great day.

__________________
ASE Master Mechanic
asemastermechanic@juno.com

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

https://www.boldegoist.com/

the heater valve is not located under the cowl--it's located in front of the cowl behind the firewall. you can replace the w126 style heater valve with the w123 style, which doesn't have as many openings for hoses, and then just fold over the unused hoses, and use the hose clamps to clamp them shut

__________________

The "valve" in question is not the "heater valve" more commonly referred to as the mono valve. The heat exchanger valve; that controls the flow of coolant to the windshield heater you didn't even know existed, is located under the cowl as I've described. It is thermostatically controlled by a wax pellet which reacts to ambient temperatures keeping the valve closed when ambient temps are above freezing and opening the valve when ambient temps get low enough.

Obviously playing the fool is a part you relish; but being a fool is another matter, it's often better to keep quiet and let people think you are a fool than to speak up and remove all doubt!


INAPPROPRIATE
B.C.

Wrong three times..
Please stop.
A slow correct answer beats all wrong answers.

* The W126 does have a windshield heater.

* His issue can be quickly resolved by plugging the coolant feed hose from the mono-valve where it is attached to the thermo-valve MB# 126 830 04 84. First attached picture.

Fastlane: thermo-valve
http://catalog.peachparts.com/item.wws?sku=1268300484

Changing the mono-valve as you suggest, would reduce the heater core flow 50%, directly impact heater performance, and NOT fix his issue. Second attached picture.

The correct mono-valve unit is MB# 000 830 37 84 Third attached picture.

Fastlane: mono-valve unit
http://catalog.peachparts.com/item.wws?sku=W0133-1600853



The W123 unit is MB# 000 830 29 84 Fourth attached picture.
No longer available NEW...

Attached Thumbnails

       

i have no problem being wrong--i just don't like being called a fool when i make a mistake...

__________________

I'm pretty sure in addition to this, the OP would also need to plug the other hose to/from the heat exchanger otherwise coolant would flow back thru that hose, thru the heat exchanger, and out of its inlet, back thru the thermo valve when and if it is opened or leaks and finally drain out of the system thru the hose from the thermo valve which normally attaches to the small bib on the mono valve. I don't think plugging only one hose of the two connected to the heat exchanger will keep the system sealed up.

No.
His issue is that the wrong hose was ordered.
He got a straight hose = Two opening MB# 126 832 20 94.
The small steel windshield coolant return tube will be open.
The tube could be capped, however, it is easier to find/make a plug for the feed hose to the thermo-valve.

He needs MB# 126 832 30 94 ONLY FOR USE WITH WINDSHIELD HEATER = three way hose.

Fastlane:
http://catalog.peachparts.com/item.wws?sku=W0133-1613948


The attached picture should make it clear.

Attached Thumbnails

 

I never knew my 126 had this feature. I do recall that my AUdi's and VW's had many more problems with the wipers freezing up, but I thought the Mercedes was just fortunate. Actually I think I noticed steam rising from the lower area of the windshield but assumed it was just a really effective defroster.

Wipers that hide in a trough are a pain in the...here in snow country. My Lexus, Camry and my Chrysler all suffer from Icy trough syndrome. Toyota's solution is a "Winter" switch which keeps the wipers up on the windshield when they are turned off.

I miss my 126. I wish I'd never sold it.

__________________
1979 240D, 4spd manual, Power Sunroof, manual windows, 147k miles, Pastel gray/Black MB Tex.
1991 300D 2.5 - Smokes like it's on Crack!

Sounds like a typical Toyota approach to the problem. A band-aid fix instead of a real fix. I drive every day in snow and bad weather, and my wipers work perfectly every time. The W126 is awesome!

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Yes. I was going to say that, but I talk too much as it is already.

Toyota probably does this so they don't have to replace wiper linkages, gears, etc. under warranty. Few owners even know about the feature, but it gives Toyota an easy out if your wipers break, because the feature is mentioned in the owners manual.

__________________
1979 240D, 4spd manual, Power Sunroof, manual windows, 147k miles, Pastel gray/Black MB Tex.
1991 300D 2.5 - Smokes like it's on Crack!

Thanks for the explaination and illustration, that makes it clear! I didn't have a 126 car in front of me and it's been about six or seven years since I had a problem with a pinhole leak in the heat exchanger on one of my SDLs. So I didn't recall the exact arraingment of the plumbing.

When I first bought the SD back in 02, I replaced all the hoses under the
hood. one of them item # 71 in post #11, at that time was $85, while the
straight hose was $13.

we don`t get the cold and snow here on the west coast, so it isn`t that
big a deal to have.

I don`t know the price today, but still probably quite significant.

Charlie

__________________
there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works