Bypassing heater cores on a W111 coupe

[wwheeler]

It seems one my original heater cores is leaking a slight bit. I wasn't planning on restoring the dash for a couple of years and would prefer to put this off if I can. Looking at it, it would appear that most of the dash must come off to get this done. Is it really that bad? I know the W113s are that bad but the W111s have a little more room.

Another thought is to bypass the heater cores and let them lie dormant. Has anybody done this and how do you do it?

Thank you for your help!

Wallace

[66andBlue]

Wallace,
with the original MB supplied by-pass (p/n 130 586 0202, for manual transmission cars) you could switch the flow to the core on or off. The kit is now NLA but my mechanic still has an original one and I can provide you with photos of all the parts and instructions if you want.   Otherwise this discussion here (and especially "jeffc280sl") might tell you how to make your own:
http://www.sl113.org/forums/index.php?topic=7297.0

[wwheeler]

Alfred,

I am always amazed with your depth of knowledge! Yes, please send pictures if it is not too much trouble. Would also be helpful to this site to see what the "factory" fix is. Just out of curiosity, why was this available for just manual trans cars?

Seems like most have used this type of repair to resolve overheating issues. Is that true about the lack of coolant flow in the head when the heater valves are shut?

Thanks again!

[66andBlue]

Wallace,
standard disclaimer: I know nothing ..... take my advice at your own peril! 
I happened to talk to the shop owner about overheating issues and he mentioned that he had installed these by-passes in lots of late 280SL cars. As he explained to me MB supplied two different kits - for manual and automatic cars, respectively,  the connections into the cooling circuit are different.  I plan to go by next week and shoot photos of his NOS kit and post it here.

[Desertpagoda]

No kit is needed to bypass the leaking cores. What is needed is a 4 ft length of 5/8 or 3/4 heater hose. Remove the hot water supply hose from the driver side of the head. Put one end of the bypass hose here. Then go to the pass side of the waterpump housing and remove the heater water return hose. Put the other end of the bypass hose there. Refill the system and burp it. This is an ugly but honest way around a leaking core. It is possible, maybe even likely that your leak is a valve rather than an actual core. These can be seen above and to the pass side of the tunnel. Keith

[GGR]

It is possible, maybe even likely that your leak is a valve rather than an actual core. These can be seen above and to the pass side of the tunnel. Keith

Yes, these are accessible and you can sort them out without dismantling everything. You should determine if the leak is from there before bypassing the system as replacing the seals may not be much more work than installing a by-pass..

[wwheeler]

Thanks for the replies. No, it is definetly the cores. I replaced the seals a few years ago and no drips there now. There is weepage around the seperation lines in the plastic case and occasionally some will trickle down the heater duct for the back seat.

If I can just bypass, I probably won't worry about replacing the core for a few years until I get to the interior restore. Another more elegant bypass trick I thought of, is to make a copper pipe assembly and replace the stock steel pipe that runs along the firewall and right engine bay. You can use 1/2" copper pipe and a series of 45s and 90s. You can then run plugged pipes into the rubber firewall grommets to give the assembly support. On the left side, just run a hose from the end of the copper tube to the elbow coming off the head. Paint it black and no one will ever know.

What do you think?

[66andBlue]

Wallace,
as promised here are the photos of the NOS kit for manual cars and an installed by-pass in a W108 sedan (parts car) with automatic transmission.  
However note, these kits were NOT intended for your earlier engine.  MB intended these kits only for the late M130 engines with the 212 degree sensor at the back of the head.  On manual transmission cars the metal tubing connects into this port and then goes down and across below the engine, comes up again, and then runs along the right inner fender until it is connected with a rubber hose to a Y in the radiator return hose.  On cars with automatic trans mission a rubber hose crosses above the engine, runs along the right fender and then connects into a Y in the tubing to the water pump.  The hose clamps in the kit were all Norma clamps.
I was told that the overheating problems were mostly in the back of the engine and for this reason the coolant was removed from the block as far back as possible.

[wwheeler]

Alfred,

As always, you are the master of attachment graphics. Those dots make it very clear what you are talking about. Because it is hot coolant, shouldn't the dots be red?  I was wondering what that fitting was for. A sensor makes sense and didn't know it was back there. Yes you are correct and that would not fit on my engine but supports the above idea of making a by-pass pipe. Thank you so much for your efforts in posting this. Hopefully it will help others who have to make this same decision. If I can remember, I will post a picture of my creation once it is done. Hopefully have it done in a couple of months.

Wallace

[wwheeler]

Well the heater by-pass tube is complete and in a record time of one month. This piece is of course unique to a W111 as other models have different plumbing. Not as bad to make as you might think. I'll paint it black and no one else will know.

044 pic is the by-pass tube
048 is the tube in position
063 is an old engine pic with the factory coolant supply tube

A bit overkill but will look nice for the few years it is on until the interior is restored. I pressure tested all of the joints (about 28 total) with soapy water and NO LEAKS! No more wet feet.

[wwheeler]

By-pass update. I have ran the engine a few times since installing the by-pass and no leaks! Works great but no heat in the cabin.

Don't touch the tube when the engine has been run because it is firecracker hot! I used a satin black radiator paint.

[Marrs]

If my car only gets hot after sitting still in traffic on a hot day, this won't do much for me correct? I thought I read a comment here or on the linked thread that it only works when moving.
Also, with this bypass in place, does it matter what the heater settings are or are they altogether bypassed and it's irrelevant?
Putting a valve inline in the bypass would allow me to switch it so coolant again flows through the heater core if I do want cabin heat?

[wwheeler]

I think it would help an overheating car but not why I did it. My heater cores were leaking and wanted a way to by-pass them. With this system, there is no possibility of heat in the cabin. Doesn't matter what the temperature lever settings are because there is zero coolant in the cores.

You could use a hose temporarily to test and see if it helps. It circulates coolant from the thermostat housing to the driver's side of the head. Doesn't matter if the car is moving. The heater cores would dissipate more heat, but the by-pass pipe by itself gets pretty darn hot. Plus that and you are circulating more coolant should definitely help your hot engine. It would probably take a bit longer to warm up in the winter though.

If it does help, that would indicate that the cooling system is less than 100%. Could be one component or a combination of many.

[ja17]

It looks like we have two different issues going in this thread.  One issue is the factory added coolant by-pass kit solution for improving engine cooling. The other issue is Wallace's leaky heater core, which he has by-passed out of the cooling system for temporary fix so he can continue to drive and enjoy the car until he is ready to fix it.

As you recall Alfred, we also by-passed the heater core on  your pagoda so you could overhaul the heater box and still be able to drive and move the car. With your very temporary solution we just took a length of heater hose and two hose clamps to by-pass the heater core out of the cooling circuit.

Wallace, looks like you were an excellent plumber in another life! Your temporary by-pass should be factory approved and certified!

[66andBlue]

Hi Joe,
indeed, that is what we did to ship the car to you and back.
At the beginning of this topic Wallace asked  "Has anybody done this and how do you do it?"  and my reply was just an information that MB had done it on some cars with a kit to cool the engine
 And yes, as a result there are two issues under discussion here.
Personally I think Wallace's kit looks better than the one from MB.  

[wwheeler]

It is still working well. Just don't touch it while it is running HOT, Hot and Hotter. I guess it is really hot because you getting a FULL flow of coolant. With the heater cores, it would probably restrict the flow quite a bit even if they were wide open.

I probably shouldn't even asked the first question about removal of the cores. I guess I knew that one.

I counted a total of 28 soldered joints on the home made bypass pipe! I could have used soft copper tubing but wouldn't have looked as good. This is a hobby for fun afterall. I enjoy soldering except when it is under the house with 80 year old copper pipe. That never works out well and I usually call a real plumber. Nothing better than brand new copper.   

[PeterPortugal]

Hi Wallace,

After searching the forum for info this post came up so I'd like to take the opportunity to pick your brains again !!

When i bought my car it came with a bypass system like yours (much cruder though)....but I just didn't realise it at the time !! In fact I knew nothing about these cars whatsoever.

Some way down the road and I know more now. My cores had obviously been bypassed because they leaked and I sorted this out. Getting that heater box in and out is a nightmare. All the work to get it ready to come out is time consuming but manageable. Physically removing it, and even worse, replacing it is only for the very patient ! I'm sure once you've done a few you get a knack for it but first time is challenging. It's getting the nosecone of the fan to clear it's housing that gave me the trouble.

Anyway I digress.....I fitted the pipe which connects the heater cores to the water pump (this wasn't there in the previous "lash up". It might not be the right one exactly (it did have 190 written on it) but it seems to fit OK. My dillemma is that the pipe is a smaller diameter than the connection on the water pump so I had to "stretch" the connecting hose over this part. It didn't seem right to me. Can you remember how yours was done?

Regards

Peter

[wwheeler]

Hi Peter,

You're right, that isn't right. What you need is the infamous dual diameter heater hose. It is molded with two sizes. When I bought my car, it had some rig where two hoses where clamped together with a coupling. Somewhere down the line, I found it needed this special hose. Needless to say, I now have the correct hose now. For my car 111024, the # is 111 831 00 94. Hopefully yours is the same.

BTW, the bypass is working very well and one day, I will dive in and replace the cores. I have two brand new ones collecting dust waiting for that day.

Have fun!

[PeterPortugal]

Hi Wallace,

Part sourced and purchased. Thanks very much for your help.

I also note from reading the whole post that it is speculated that with the heater valves closed and a hot ambient temperature that overheating can occur - hence Joe's mention of the factory bypass kit.

Is this is a common problem which is likely to occur or just maybe the "straw that breaks the camel's back" if the cooling system is not 100% e.g. radiator clogged, water pump impeller worn, etc, etc. I'm wondering if i should consider fitting a bypass as Portugal does enjoy long, hot Summers. I have no aircon so the cars radiator is completely exposed to the airstream.

Would appreciate the thoughts of the forum !!

Regards

Peter

[wwheeler]

Peter,

It is more of a straw that broke the Camel's back. If you HAVE to do that bypass to keep the engine cool, then something else (or many things) are wrong. It is a weak point with the 280 engine. My W111 always ran right near 180*F in Texas in the summer with the heater set up, and you are not going to get much hotter than that. Only time the engine would get hotter is at high speed on the highway or stuck in traffic. Still never got to the point of being a concern.
The bypass allows free flow of coolant into the rear of the head which does indeed aid in cooling. Still shouldn't be a must do.

[PeterPortugal]

Ahhh yes I get you now. If the heater valves are closed then coolant will not circulate out of the cylinder head via this route and will effectively "stagnate".

Obvious when you think about it.

Appreciate your reply as always. The heater bypass is "on hold".

[wwheeler]

I believe the heater valve cores have a tiny slot in them that always allow a little bit of coolant to get past. So not totally stagnant but very little flow.