Cabin too hot: Heater Bypass?

[AdelaidePagoda]

Hey folks, well summer is almost here in Australia and the hot weather has arrived. My question is about how best to reduce the hot air coming in from under the dash through the heater core. On a warm day the hot air around driver and passenger feet is noticeable and I would like your thoughts on installing a heater bypass hose to reduce it over summer and turn the tap back so it provides heat in winter.
More detail: engine temp is always stable around 80 degrees. Brand new firewall pad installed last year. Car always has the top off, summer and winter and only drives on days without rain. I know how how the heater levers work to direct airflow and they work perfectly. Radiator heavy duty and recored and flushed recently. 

I have searched and read the forums and the heater bypass hose seems to help keeping cabins cooler, so any personal advice and experience is warmly welcomed. Although yes, it is not original (easily reversed) and some bypasses look very ‘ugly’, over the head and primitive three way taps. Has anyone found an elegant way to do this if I do proceed?  Examples attached.

Thanks in advance for your advice.

[thelews]

Why not just fix (replace) the valve.  I have no heat issues in summer.

[BobH]

There are some examples on here, those who suffer hot cabins seem to agree it helps, just need to find a suitable inobtrusive valve

https://www.sl113.org/forums/index.php?topic=6087.0

[Paul & Dolly]

I disconnected the heater Valve link to the left hand heater control slide, and fitted a 12 volt solenoid valve to the heater outlet pipe, do I can independently control L and R heat.
Also when the solenoid valve is off, no water flows through the heater matrix.

Paul

[yves]

And you added an emergency opening cable for the Hood   

[Paul & Dolly]

Very observant, Yves

Paul

[dirkbalter]

Why not just fix (replace) the valve.  I have no heat issues in summer.

I second above. I am actually a little shocked by the patch jobs done or suggested to avoid dealing with the actual problem.   

[Duncan200]

Just move to Melbourne Dave, problem solved😂

Doug.

[rwmastel]

My question is about how best to reduce the hot air coming in from under the dash through the heater core.....I know how the heater levers work to direct airflow and they work perfectly.

I don't understand the problem.  If the levers work, then they stop the flow of water through the heater core.  No??  The core should not get hot.  Why bypass, if the flow is already stopped?  Help me understand how heated air could be flowing out?

Maybe you need some Dynamat or similar material to insulate the sheet metal from exhaust heat.

[Pawel66]

I would start with checking if all the heating levers work. Then if the valve shuts off and if it does not, repair is relatively simple and parts available.

Then I would make sure that all the plugs and grommets are there in the firewall.

[DavidAPease]

Dave has an early '64 model.  I wonder if it's before Mercedes added the hole to access the heater core valve?   I believe that would make repairing the valve considerably more challenging.

          -David

[Pawel66]

Thank you for pointing that - I was not even aware there were cars without this opening.

[Cees Klumper]

@Rodd, I think the answer is in Dave referring to the levers directing the airflow - not the flow of coolant.

[AdelaidePagoda]

Thanks everyone for all the advice.

Doug, yes Melbournes cool weather would fix it, Adelaide is already heating up and 40/ 100 degrees days are not far away! 😀

David/ Pawel, yes, my 64 does not have the firewall plug so access is more complex and time consuming, in fact I cannot find anything in the forum to suggest anyone has ever attempted a heater valve repair without access through the firewall plug. I am sure it is possible just requires expertise to extract the core from under the dash. When was the firewall access hole introduced to W113’s?

I will test the heater levers again and see if there is a combination that shuts off the hot air, but so far this has been elusive on hot days. Why did they make the controls so un-intuitive 😂

rwmastel, yes I think Dynamat would also help insulate the cabin from engine heat, although not the hot air that seems to be the heat source as it wafts in, most noticeably during acceleration. I do have standard exhaust shields in place.

thelews/ dirkbalter, I think yours is the best solution, if that is the root cause of the issue, however finding someone willing to repair it may be a challenge in my city. Plus without a firewall plug, access to the heat core valve is more challenging/ time consuming/ expensive.

[Bshaunessy]

Dave / Adelaide Australia:
  BTW:Lucky guy to have to wrestle with hot weather!  Snowing here today in Canadian Rocky Mountains and my 1970 280 is put to bed for the winter.

   I had a similar excess cabin heat issue.   I serviced the heater valve ( cleaned and new , proper o-ring) but there is a small weep hole in the valve that still allows a small amount of flow, even if valve is fully closed.
    There is a post on this forum ( I searched but could not find) with a good tip,that worked for me : pull and service heater valve BUT install 180 degrees from where it should be.   This provides a 100% shut off. ( flipping the valve 180 degrees isolates the small weep hole in the brass valve body).  This is a simple operation you can do at the beginning of the top down driving season and , if desired, can easily reverse when weather gets cooler.
   I understand you do not have the heater valve access hole on your early edition 230 SL. Q? Perhaps cut an access hole ( shudder!)  where MB later provided one?

  Also….this post should be moved from "GENERAL DISCUSSION" TO "INTERIOR , ETC"

EDIT
   I indicated above that there was a small weep hole in the valve body that allowed fluid bypass when valve fully closed.   MY MISTAKE : this is the case with the almost identical heater control valve for the MB 190 SL ( I have a 1957 MB 190 SL) but was modified by MB to remove this weep hole for the 230/250/280 SL series.   So….reversing the heater shut off valve May or May not completely shut off coolant flow in the 230/250/280 SL series…..it seemed to work for me.

[rwmastel]

@Rodd, I think the answer is in Dave referring to the levers directing the airflow - not the flow of coolant.

The lever with the red marker (wedge? arrow?) should shut off the heater core valve, thereby no longer allowing coolant to flow through the core and heat it up.  Problem solved?  Maybe I'm mistaken?  Yes, the lever may move, but that doesn't mean it's operating the valve.  I'm just going by what AdelaidePagoda said - the levers "work perfectly".

Nice tip by Bshaunessy about flipping the valve 180 degrees to achieve full flow shutoff.  I've not heard that one.  Without a valve access hole in the firewall, AdelaidePagoda has a big job ahead to confirm and/or correct the actuation of the valve.  I'd be tempted to cut a hole!

[Pawel66]

I'd be tempted to cut a hole!

My thoughts exactly.... Horror job!

[dirkbalter]

Thanks everyone for all the advice.

thelews/ dirkbalter, I think yours is the best solution, if that is the root cause of the issue, however finding someone willing to repair it may be a challenge in my city. Plus without a firewall plug, access to the heat core valve is more challenging/ time consuming/ expensive.

Dave,
I wasn't aware that you don't have the access port. Without it, I can see that that this is quiet a challenge. 

[WRe]

Hi,
why don't you create the same access (hole with rubber) to the valve as the later models. It was certainly intended as an improvement.
...WRe

[rwmastel]

I will test the heater levers again and see if there is a combination that shuts off the hot air, but so far this has been elusive on hot days. Why did they make the controls so un-intuitive 😂

I looked in the Tech Manual at how these controls work for heat.  Nice pics at the bottom of this page: https://www.sl113.org/wiki/Electrical/HeaterControlValve
I had forgotten that the red control on the left has a cable that pushes open the main plastic flap to direct air over the heater core (instead of bypass the air past it), and that flap has a rod that pushes the heater core valve open.  So, in one action you're controlling air flow and water flow on/off.  I suggest that something in that series of connections isn't working.

[mdsalemi]

It's all merely anecdotal evidence, but to me, our beloved Pagodas are HOT cars. Driving in them for any length of time when the sun is bright and high in the sky on a summer day when the temperatures are at 90+F degree s (32+C) can be an uncomfortable experience. Many cars of the era are similar, in that they had higher revving engines and poor insulation compared to today's daily drivers. Remember little details like our aluminum bonnet/hood without any insulation pad were designed as part of the cooling system. All I have to do is touch the chrome shift bezel on my automatic Pagoda when driving under these summer conditions to realize I could get burned, it's so hot. There's heat coming from the engine into the passenger compartment as well as from the exhaust and the transmission--even with the heat shields in place.

I don't think there's a lot one can do to direct this heat elsewhere. Now, a full flow of coolant into the heater core is a problem for certain. But once that is fixed, there's still just too much heat and not enough ways to dissipate that heat to make our cars unpleasant to drive under summer conditions.

Unsolicited and in a surprise move a few years back, when I lived in Michigan, an independent mechanic here in the south called me out of the blue, asked if he could send me the official MB "heater bypass kit". I said sure, why not? So, it sits in the box. I have yet to open it and see what it's all about. I think he must have removed it from a car in for service and simply didn't want to bother to sell it, so I was the lucky recipient!

[AdelaidePagoda]

To close this chapter out, I found the root cause under the dash and now the levers shut and isolate the heater core valve off and voila, problem solved. It took some detective work but now resolved and no need for a, less than original, heater bypass.

Thanks all again for your insights and encouragement 🙏🏻

[rwmastel]

I know how how the heater levers work to direct airflow and they work perfectly. 

Did your car surprise you and levers were not working perfectly?  Was it a broken or disconnected part?  A foreign object blockage?  Something else?

[AdelaidePagoda]

One of the lower levers was disconnected. Now almost perfect temperature, even on the hottest day (with the top off of course).

[rwmastel]

Ah, the old "disconnected control rod" trick!  Glad it all worked out.