How to reduce heat inside the cabin?

[bpossel]

Wouldnt it be easier to just replace the heater valve o-ring and "fix" the on, off issue?
It's really not that difficult.  I would be happy to answer any questions on this, as I am sure others would as well.
Bob 

[awolff280sl]

I agree that fixing a leaky heater valve would be a better solution than an "ugly" by-pass, but this didn't work for me. I had the heater core on the bench when I replaced the valve, and I made sure that it was closing properly. But after all was said and done, I was still getting heat in the cabin. I'm unwilling to tolerate this if I want to drive the car in Florida during the summer, even though my A/C works well. So, I went about trying to find the causes of heat in the cabin.
1. The heater core still warms up even with a well-functioning valve: I've come to the conclusion that this is because the heater core will conduct heat from hot coolant sitting at the closed copper heat valve, (as well as at the heater core output, but to a lesser extent). An effective by-pass will  eliminate this, at least at the intake pipe.
2. The firewall: I put Dynamat under a new firewall pad on the engine side. In the cabin, I put a layer of Dynamat covered by a layer of insulation material that I found locally. This material is like miniature bubble wrap sandwiched between foil.
3. Tranny tunnel: Used Dynamat plus the bubble wrap stuff
4. Exhaust pipes: Thermo-tec wrap (thanks Jim), heat shields (stock), and Dynamat plus the bubble wrap material in the cabin on the passenger side.
3. Differential heat: I could feel heat coming from my diff if I removed the parcel shelves after a good drive. Used Dynamat plus the bubble wrap.
4. Less than perfect sealing of closed cowl vent and side cabin vents: At high speeds I was able to improve but not completely eliminate air flow thrrough the cowl vent and side cabin vents using weather stripping. I still need need to close the chrome louvres and swivel flaps to eliminate all air flow at higher speeds.
5. Finding air leaks in firewall (used a light in the engine compartment in a dark garage, thanks Cees) and plugging them with 3M weatherstripping putty.
6. Window "tinting": I selected a material that reduces heat without significantly darkening the windows.
I can say that I have solved my heat in the cabin problem with all these measures. 

[thelews]

If the heater valve is like the 190SL, there is always a small amount of coolant passing through by design.  That's what the small slit is for off of the hole.  I haven't had the 113 valve out to know if it's different.

[jeffc280sl]

To each his own.

The original concept of the bypass hose was to try and reduce engine temperatures.  Many of us have turned the heater valve to full open when engine temperatures rise while sitting in traffic on a hot day.  I've also turned on the fan to move more air through the heater core to reduce engine temps. So I decided to try a bypass hose.   I began with just 2 tees and the bypass hose going over the head.  Engine temps are much lower and I now have no fear of a head gasket failure or other problems associated with over heating the engine.  It worked so well I decided to leave it in place.

A secondary problem was heat in the cabin with the heater valve in the off position.  The heater core valve is indeed like the picture in the prior post.  I thought the top groove was for an o-ring to seal the valve so that it would not leak out the top of the heater core tube.  I think mine also has a less pronounced groove in the bottom.  I thought maybe that also was for an o-ring but it doesn't appear deep enough and I was unable to get an o ring to stay in place.  This maybe the source for hot water entering the heater core when the valve is in the off position.  In any event I have tried to fix it.  For whatever reason my valve leaks and I have considerable hot air on my feet coming from the ducting when the valve is in the off position.   In the cooler months it doesn't seem too bad.  In the summer its very annoying.

The heater core bypass hose is already in place and Andy has a solution for my secondary problem.  The valve is a little ugly but it works great.  Someday when I have nothing else to do I may install a more modern valve from another automobile and install a hard pipe to carry water behind the head for the bypass.  That would be nice but right now I'm enjoying a cooler cabin and engine.

[thelews]

The top groove is for the O ring.  It's just not on in the picture.

[jeffc280sl]

Thanks John.

I had to blow up your picture to see the slot your speaking about.  I don't recall having a similar slot on my valve.

[bpossel]

Here is a pic of our heater valve.  This is a pic of mine.  The long screw and string is only used to help install the valve without it falling in the heater core.  There is also some plumbers lube to keep the valve movement very easy...
The W113 valves do not have the slit like the 190sl.
Bob

[J. Huber]

I may be one of the lucky ones but I have never experienced excessive heat in the cabin (especially in the winter   ). Oh sure, I have been out on very warm days, and with the top up, it can get stuffy and warm (no A/C), but this is more an external thing than an internal one. In fact, others have talked about the shifter and its box sizzling -- never felt that either... I guess my heater valve must work ok -- and I have some dynamat-like stuff down but that's about it. For best ventilation, of course, I keep the top down.

[jeffc280sl]

Its 92 today so a perfect day to check for cabin heat sources.  Now that I have the heater core shut off valve installed I can definitly say my cabin heating situation was caused by a leaky heater core valve.  The pic Bob posted looks like my valve.  If you look closely you can see a shallow groove at the bottom of the cylinder.  The tolerance of my valve and the heater core tube must be such that I have blow by and some amount of hot water always circulating through the core.  It has been suggested that MB designed the valve so there was always some hot water moving through the core.  If true this may have been an effort to reduce engine temps by relieving the head of some build up pressure of hot water.  Prior to installing the shut off valve I had heat at the gas pedal area coming from the heater ducting with the cowl vent open and the heater core valve in the closed position.  Now there is only cooler outside air coming from the cowl vent at my gas pedal foot.  It's ugly but I'm pleased with the mod and thank AWolff280SL for the idea.  No other cabin heating issues.  I have the original firewall pad and both exhaust heat shields are in place.  I also have dynamat and heavy padding under the carpet.