23 hour later it was done; the engine transplant from my wrecked 1990 300E to my 1989 300SEL.
What a job, I hope I don’t have to do that again for a while. Several stuck bolts, one busted bolt, and lots to switch over. The alternator bracket, AC compressor/PS pump bracket, bearing (fan) bracket, water return lines, motor mount brackets, and a couple of sensors had to be changed. Additionally, the throttle linkage had to be changed along with opening and closing a few vacuum connections. I left the transmission in the car and had to line up the engine to get it connected; that was a job. In hind site I think it would have saved time and effort to take it out and put it back in together. It was worth it though the engine runs like “Jack the Bear”, just perfect.
There is one vacuum connection that I am unsure about and I could use a little help. The front most sensor, a thermo vac valve, on the top of the head has two vacuum lines running to it. One line, which is on a slightly angled fitting, runs to the top most nipple on the underside of the air flow sensor. The other line on the thermo vac valve, which is a straight fitting, seems to run to an “Acorn looking” valve. The acorn valve has three ports. The line from the thermo vac sensor runs to a straight fitting on the bottom, then a 90 degree fat fitting on the top of the acorn valve runs to the bottom nipple on the air flow sensor. There is a third fat port in the center of the acorn valve that I currently have plugged, as I am not sure where it goes. The engine runs perfectly, but this is clearly incorrect, and I am uncertain of what to do. I know this is a confusing description, but if anybody has an idea for me, I’d appreciate it. I’d post a picture but I can’t seem to get it to work.
Many thanks to this forum, especially the guys that have answered some of my previous questions. This was a big job, and I couldn’t have done it without the help. DG, thanks for helping me with the rear seal; it worked great.

Thanks!

Congratulations on getting it all done.
Is either the donor engine or the 300SE a California car?
My Texas 300SE has no vacuum lines as you described (I don't think).
It uses vacuum lines to control the vapor cannister, ignition, EGR, air pump, tranny, and brake booster. But nothing going to a thermal switch on the head or to the air intake.
One place you might look is in ************************. They have vacuum schematics for various cars with the parts identified.

DG

Thanks for the input DG.
Neither of the cars is California.
There must have been a change in the engine management system from 1989 to 1990, The donor engine, from the 1990 300E had an EGR valve, but no thermo vac valve on the top of the head, and my 1989 300SEL was just he opposite. When I swapped engines I had install the 1989 the thermo vac valve into the 1990 head. I also had to plug the EGR vacuum line at the intake manifold. There was also a significant difference as my 1989 had no smog/air pump and the 1990 did. I actually had to plug a small exhaust hole in the head that fed into the pump.
Good idea on the Performance site. I’ve bought some parts from those guys before, I’ll have a look.
Thanks Again.

Good idea on the performance site, but no help there.
Does anybody have a vacuum diagram or a 1989 300E, SE, or SEL they could check to see where these lines are supposed to go? I appreciate any help or ideas.
Thanks.

Ouch, Sounds like they made a lot of little "smog" changes just to keep us off balance.
I have an '86 engine manual; I'll check later today to see if they have some diagrams. Maybe we can learn something. But reading these factory manuals is like going to the dentist.

DG

OK, I may have found some help in my 1990 engine service manual.
There is a schematic of a fuel evaporation vacuum system.
It has some parts similar to what you described.
I'll try to describe it, my scanner is dead:

1. Throttle body or air intake has two vacuum ports on it as you described, upper and lower.
2. 50 degree C thermo valve (red) has two vacuum ports on top, and appears to screw into something (the head obviously). Port A is straight up, port B is canted about 30-45 degrees.
3. Purge valve has one port in center of side A, two ports in side B.
B-1 is in the center, B-2 is near the edge.
4. The diaphram appears bigger than the purge valve. It has one port on top, side A; and 2 ports on bottom, side B.
B1 is in the center , and B2 is near the edge.
5. the charcoal cannister has 3 ports: 1 in the center, 2 near the edge, and 3 near the other edge.

OK, let's hook those babies together with vacuum lines.

1. Upper throttle body goes to thermo valve port B (the canted one).
2. Lower throttle body goes to purge valve B1 (center).
3. Thermo valve port A goes to purge valve port A.
4. Purge valve B2 goes to diaphragm A.
5. Diaphragm B1 goes to canister port 1.
6. Diaphragm b2 goes to canister 2.
7. Canister 3 goes to the fuel tank.

If you draw this out, all the vacuum ports should be connected to something.
There will be 7 vacuum lines, including the line to the tank.

Maybe this will helo; that's the only vacuum routing I found in the manual.

DG

DG I appreciate your extra effort and tenacity trying to get me squared away.

I’ve got the upper line on the throttle body going to the canted port (B) on the thermo vac valve; your research verifies this is correct, so half the riddle is solved. You indicate that the lower throttle body line goes to a purge valve. I’m uncertain what a purge valve is. I currently have the lower line hooked up to some kind of valve, that was left in my engine bay, after the Malay of reconstruction. For various reasons, I believe it to be the correct location for this line. It is a black plastic valve, shaped like an acorn, about the size of a golf ball, with three vacuum line connections coming from it. One from the top (if it was an acorn, it would be the top) that is a larger ID line. This is where I have the lower throttle body line plugged in. One from the bottom (again, if it was an acorn) which is a smaller ID line. This is where I have the line from the thermo vac valve port A plugged in. There is also a connection on the acorn valve in the center, that I currently have plugged. I don’t think I have a charcoal canister, I don’t remember seeing one on the 1990 300E donor car either. If I would have it, where would it be?

I think I’m of at least average intelligence; but this is starting to make my head hurt. I’m starting to feel like a dullard; can you help me along some more?

OK DG, with your help, more research on the forum, and my AllData account, I’ve almost got this figured out. What I’ve been referring to as the “Acorn” valve is the “Purge” valve. I have the lines connected properly to the purge valve and the thermo vac valve , all I need to do is connect the purge valve to the charcoal canister diaphragm and I’m golden. I can’t find the charcoal canister or the diaphragm that’s supposed to be connected to it. Does anyone know where it would be? 1989 300SEL.

Yep, seems you deciphered my rantings pretty good so far. I rechecked the dwg, and the purge valve does indeed have a larger vacuum line coming from the lower throttle body port. And it looks like a big acorn as you said.
My dwg indicates only 2 ports on the top of the purge valve, so I can't help you there.
My '91 doesn't have this configuration, and the wife has it today. But I do remember a vacuum line goes to purge or diaphragm way over in the front left corner, kinda behind the left headlight. I'm not sure if the canister is there. I can check tonight. However, in looking through the manual, it shows rough dwgs of two cars, one a 190 and one maybe a 126. It indicates the purge valve is indeed where I said, but that the canister is located low in the fender well behind the left front wheel! Which would require inner fender panel removal probably. It looks like a long square coffee can.
I'll eyeball mine tonight when she gets home.

DG

Hey, it started sleeting here, and the wife brought the MB home at lunch.
I checked the hose routing.
Mine is definitely different, has no thermo valve, but instead has an electrical vacuum solenoid over on the left fender, right below the purge valve.
I'm sure it's opened and closed by a temp signal, same as your thermo valve.
1. The hose from the purge valve that should lead to the diaphragm and canister disappears into a hole in the left front inner fender. So apparantly the diaphragm and canister are indeed between the inner/outer fender.
2. The vacuum solenoid has a 3rd port, a pressure-balancing port to relieve vacuum when the switch clicks. I bet the 3rd port on your thermo valve is the same thing, just a vacuum relief. So you probably should leave it open?

Hey, that should fix you up, all items accounted for, correct?

DG

Hey DG, thanks for helping me along with this project. Sorry to hear it’s sleeting in Dallas. If it’s any consolation, it’s supposed to be below zero here in Hudson Wisconsin tonight. The best thing I ever did was put a little heater in my garage. It allows me to keep my cars running during the winter.

I see your point about the vacuum relief port, but I think mines different. From what I could gather from this site the thermo vac valve on my 1989 activates/deactivates a vacuum line that is powered by the upper and lower ports on the throttle body. This line, is connected via the purge valve to the charcoal canister (which I can’t seem to find) in order to vent fuel tank gases to the throttle body for combustion. With that said, it stands to reason that the purge valve would have to be physically connected to the canister to capture the gas. Based on your input, I’m going to look again at the left front corner of the car, and I’m going to crawl around under the driver’s side and see if I can spot this thing. The good news is that the car runs GREAT. For years I’ve been suffering with a bad idle and poor mileage and the engine swap has left me in great shape.

Again, I REALLY appreciate your help, and hope I can repay the favor some day.

No problem. I learn a lot about mine by chatting with others on here.
I once took off the right inner fender lining (the plastic one inside the wheel well) to check on the coolant overflow bottle. I bet the charcoal canister is in the same spot on the left fender. Pull the wheel and start unbolting all the little screws.

DG