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Need Help Understanding Vacuum Lines

Started by avantbenz, 29 September 2018, 05:33 PM

avantbenz

First off, I've done a lot of searching but maybe I'm too much of a noob to understand a lot of this stuff. Will you someone more experienced please lay it out for me?

I'm having a tough time understanding where a lot of the vacuum lines go and what they do.

For instance, I took my thermostat housing to a mechanic recently to get a broken bolt removed. When I got the part back the two small black nipples (for lack of a better word) protruding from the thermo-valve that sits on top of the thermostat housing were gone. The car seems to run fine without them being hooked to the vacuum system but I don't know what they were for and I'd like to fix it if possible. I have some spare vacuum line related parts but nothing seemed to fit over the small and shallow holes left behind where the original black nipples were. Can I easily fix this? If so, how?

I've looked for a good vacuum map and I found this which seems really helpful but I still don't know where any of these lines actually *go.* http://photobucket.com/gallery/user/Assault591/media/cGF0aDpDYXIgUmVzdG9pcmF0aW9uL1ZhY3V1bSBMaW5lcy9CZW56VmFjdXVtRGlhZ3JhbV96cHNkNGMyMzgyNy5qcGc=/?ref=1

For instance, the green line that seems to be going somewhere to the right of the engine block (as seen from a drivers perspective) - where does that go? Is that a constant source of vacuum? I'm looking for a constant source of vacuum line to tap into for my new electrical upgrade climate control kit from one of the forum members but I can't seem to find it.

Please help!
Daily Driving 'Patience' ~ 1980 300SD

Diesel 617

Looks like I should update that map, I made that years ago as a basic reference for myself.

The green line that seemingly goes into the firewall without any label, actually goes to the transmission shift modulator.

Could you take a clear picture or two of the part in question. The thermostat housing have nothing to do with the vacuum system. Maybe your talking about the egr? The only points where vacuum connects in the engine bay are the shut off/shift valve, cruise control (black/yellow line) and the servo unit, and of course the brake booster it self, which is connected by the thickest line.
X3 1980 300SD Blown Heads, trans -Retired
1980 450SEL Parted out/Scrap
1980 450SEL to Diesel Parted Out/Scrap
1979 280SE Euro Spec Cloth Seats Sold
1979 300CD Daily Driver - Sold


Inventory of w116 Parts
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Squiggle Dog

I believe the thermovalve on top of the thermostat housing would cause the engine idle to drop lower once the coolant started to warm up. I ended up just removing all the vacuum components on the valve cover of mine and then adjusting the linkage so the idle would be where I wanted it. But, that doesn't help you if you want to put it back to original. I think the intention was to somehow help reduce emissions by dropping the idle lower when the engine warmed up.

I can't remember if the vacuum lines going to the thermostat housing came off of the vacuum pump, the brake booster line, or the lines at the injection pump. I tend to rip off unnecessary things. If you want to make it like original, I suggest replacing the thermovalve instead of trying to repair the thermovalve. There is no need to plug the holes in the thermovalve if you want to leave the vacuum lines off of it.

You can probably just tee off of the vacuum booster line or one of the lines at the firewall for your climate control upgrade.
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1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Heated Seats, 350,000+

avantbenz

Quote from: Squiggle Dog on 30 September 2018, 01:33 PM
I believe the thermovalve on top of the thermostat housing would cause the engine idle to drop lower once the coolant started to warm up. I ended up just removing all the vacuum components on the valve cover of mine and then adjusting the linkage so the idle would be where I wanted it. But, that doesn't help you if you want to put it back to original. I think the intention was to somehow help reduce emissions by dropping the idle lower when the engine warmed up.

I can't remember if the vacuum lines going to the thermostat housing came off of the vacuum pump, the brake booster line, or the lines at the injection pump. I tend to rip off unnecessary things. If you want to make it like original, I suggest replacing the thermovalve instead of trying to repair the thermovalve. There is no need to plug the holes in the thermovalve if you want to leave the vacuum lines off of it.

You can probably just tee off of the vacuum booster line or one of the lines at the firewall for your climate control upgrade.

Thank you, Squiggle! This is immensely helpful and timely. Today, while replacing the thermostat cover on the housing unit, I somehow over-torqued the bottom bolt while either the o-ring or the short hose under it wasn't seated properly and I cracked the cover. So, looks like I'll be ordering a new thermostat housing cover tonight and hoping family can shuttle me to and from work until it arrives. I also cannot seem to get the short, fat hose (part #N900271042012) seated so it doesn't leak. It's brand new so it shouldn't be causing any problems but it's driving me nuts. Clamps are tight.

Anyway, now that I know the thermo-valve isn't necessary I'll look for a cover that doesn't have it. Unfortunately the cover description (part #617-203-13-74-MBZ)  at Pelican Parts doesn't an image (and I can't find an image anywhere else) so it's hard to tell. https://www.pelicanparts.com/cgi-bin/ksearch/pel_search_2016.cgi?command=DWsearch&make=MBZ&description=A6172031374 - The part I broke has a part number on it of 617-203-14-74 so I hope maybe the 13 instead of the 14 is the thermo-valveless option.

Diesel617, thank you for making the map at all - it was very helpful and with this clarification helps even more. Does the brake booster line need to be that thick? I'm trying to replace all the lines and connections for the vacuum and I don't have one that thick - just wondering if I can use a slightly smaller one and get the same effect.
Daily Driving 'Patience' ~ 1980 300SD

avantbenz

#4
Quote from: Diesel 617 on 30 September 2018, 01:20 PM
Looks like I should update that map, I made that years ago as a basic reference for myself.

The green line that seemingly goes into the firewall without any label, actually goes to the transmission shift modulator.

Could you take a clear picture or two of the part in question. The thermostat housing have nothing to do with the vacuum system. Maybe your talking about the egr? The only points where vacuum connects in the engine bay are the shut off/shift valve, cruise control (black/yellow line) and the servo unit, and of course the brake booster it self, which is connected by the thickest line.

Attached is a picture of the vacuum line leading from what I *think* is the 3/2 Vacuum Valve heading toward what would be the termo-valve on top of the thermostat housing (housing not pictured) and the EGR. The line looks like it might have originally been purple. If I'm no longer going to use the thermo-valve or the EGR should I just plug the line? I did some reading and found this on Uncle Ken's site:

QuoteTo diagnose problems related to these valves, it is important to understand their function. Many believe that they exist solely for the purpose of shifting the transmission.  While others believe their only function is to control the EGR. Not so.  They actually serve a dual purpose. Their primary function is to control the operation of the EGR valve. Their secondary function is to work in conjunction with the vacuum control valve on top the fuel injection pump (VCSV) to aid in transmission shifting.

Some argue that you should just remove the 3/2 valves, plug off the EGR, and plug the two vacuum lines going the the VCSV. I strongly argue against that. I will agree it is possible to get some transmissions shifting better by doing this - especially if there were vacuum leaks at multiple locations in the 3/2 valve assembly as well leaks in the EGR itself.

I don't have to worry about emissions and, frankly, I want less on the car that will break and require maintenance so I'm inclined to just stick w/ the EGR Delete kit and maybe get rid of this 3/2 way valve. Is there anything in what I'd like to do that I should worry about?
Daily Driving 'Patience' ~ 1980 300SD

avantbenz

Also, I tested vacuum to what looks like a mostly solid (if not solid) green line just above the brake booster and near the brown ignition vacuum line and it doesn't hold vacuum at all. It looks like this is the vacuum line that is responsible for the center air? If so, is the only way to fix it by removing the climate control push button panel? I just recently installed an electronic solution for the climate control and I'm trying to trouble-shoot my blower motor coming on when I push any button other than DEF but I'm wondering if I can even get the blower motor to work if I'll get any air out of the center vents if this green vacuum line doesn't hold vacuum?

I'm attaching a picture showing what I'm referring to - the red arrow on the diagram is the line that doesn't seem to be holding any vacuum at all.
Daily Driving 'Patience' ~ 1980 300SD

Diesel 617

That green/black line going into the car is responsible for the climate control. However, that is where everything starts to get very interesting. While it is the feed line there are numerous others pods and switches behind the dash, as well as a pod inside the heater core itself.
To test all of them you will have to pull the climate control panel off (there are two small screws on the underside of the wood panel, remove the ash tray. Also remove the glove box liner, (pry the pins up that line the perimeter of the liner with a razor blade or very small screw driver). As remove the passenger carpet vent box directly under the dash to create more access room. You'll want to test from the servo vacuum block in the engine bay with golf t's plugging the lines inside the car.

As for the main vac line, unless there is a major crack, it can be left alone. There is enough vacuum in the system to keep the system tight.
X3 1980 300SD Blown Heads, trans -Retired
1980 450SEL Parted out/Scrap
1980 450SEL to Diesel Parted Out/Scrap
1979 280SE Euro Spec Cloth Seats Sold
1979 300CD Daily Driver - Sold


Inventory of w116 Parts
[url="https://www.ebay.com/usr/vintagepartsandstuff"]https://www.ebay.com/usr/vintagepartsandstuff[/url]