merope

I probably did not explain the issue well enough, let me try again. Even with completely well working components (everything brand new and working as should), once the engine shuts off and the system loses vacuum (which it does), the valve opens and allows heat from the engine to transfer to the heater core via convection, due to the lack of a heat trap. If you get into your car in the 120F Arizona weather, the core roasting the inside to an even higher temperature, will not be really a nice environment to sit it. And your A/C will have to work overtime to first cool off that core before it can even start to cool the cabin. That's not comfortable. There is a reason it has been discussed and why the PO changed it to this, I am sure. And it wasn't because the components weren't changed (they were). But, it could be that I am misunderstanding how the system works.

merope

The issue here is that you are telling me that:

1) This is a non-issue if the system works as it should. I have presented evidence to the contrary, with people obviously working on this as a problem to fix. They would not do that if a simple part switch/maintenence would fix it.
2) Then you are telling me, that even if it does do what I am saying it does, it is a feature and I should live with it, because it is safer. Where I live we get morning frost maybe 5 days in a year, and I will not drive the car then. In the winter,
it can get chilly enough that I may want heating though. It would be nice to be switch over, if I wanted to. But I don't want to fry in the summer, which is unbearable. My best guess is that you have not experienced these weathers. If you have,
well then, you are better at it than I am.

Speedtoys

Im saying, if it fails, its not a safety issue in cold climates that need defrosters.

The OE valve sucks..use a better one since they exit.

If you want to plug it up..fine...

But hot water doesnt gush in, it doesnt rise in, and the system designed...fails the way it does for a reason.

Im explaining the system as it's designed. With a working valve and vacuum system, there is no issue to work around for most people.


You wanted to say there us a design issue, I dont believe there is..that's all. I dont know better, I just know that if it fails in cold weather, you're not towing the car.

merope

Sure, but I don't live in one. But, occasionally, it will be nice to have some heating.

I'll look into that, for sure. But if they open up the same way with the loss of vacuum, then they aren't any better for this particular issue.
I understand that they won't leak, which is great. I think my car already has an aftermarket one, based on the brass ring connection there.

Well, sorry to say, but there has to be a reason for the workaround. I'd like to hear the opinions of others on this. The system
was designed in Germany and not in Abu Dhabi or Arizona.

That's great and all, but I am looking for more than an opinion here. The vaccum line solution I posted seems intriguing, but it also relies, I think, on a good vacuum
system. I don't live in a cold climate and won't ever need to tow the car because of frosting. Excessive heat burning up the inside of the car is the issue I am faced with.
I see you are in Boulder Creek in CA, where the average temp in August is 89. We get that in October and regularly have peaks above 110 in the summer. You must appreciate
the different circumstances we live in.

fiatrn

@merope - you understand the system correctly, with one caveat - there is a vacuum reservoire that holds vacuum onto the system after engine shut down. In a perfect world (Germany?), the engine will have cooled to ambient temperature before that reservoir "empties" and the system reverts to opening the heater valve and letting hot water into the heater core. The world is imperfect, and any small vacuum leak causes the system to revert to an open heater valve much faster than engine cool down occurs. The larger the leak, the quicker the hot water gets into the heater core. Add in the possibility of a leaky heater valve (I've read reports of them leaking at any age, from nearly new to really old), and you could get a hot car just a few minutes after shutdown.

The solution that was used in your 86.5 is safe enough, though not pretty - it won't change the cooling circuit, and should not make the car run hot. If you are running hot, look elsewhere.

When I bought my 86.5, the p.o. had used a similar valve, but put it where the stock heater valve goes. It worked very well for keeping the cabin cool. But I, too, wanted to be able to utilize heat, and accessing the valve by jamming my hand under the airbox even once was a miserable experience.

There are a lot of options for modifications to fully functioning stock systems. Here on RL I've seen people wire valves shut, get different brand valves that (it seems) don't suffer the leaks, use manual 944 valves, modify the electric/vacuum interface, and talk of other solutions like entirely different HVAC control mechanisms.

The first order of business should probably be to get the stock system workning as designed and see if it functions acceptably for you. If not, then start exploring the various options to modify the system to keep the hot water out.

merope

Thanks, this was a really useful response. What do you think of the solution I linked to previously: https://members.rennlist.com/captear...rvalvemod.html

I'd need to think about whether this would hold the vacuum better.

I have smoked the old lady and didn't see any leak, but obviously that does not mean that there isn't one small enough to allow this to happen. My hood is generally hot to the touch for almost all day in the AZ summer, even in a garage.

Draining the system and experimenting is a long time, that I don't wish to spend on this, if someone else has already figured it out. I think all my valves are relatively new. And yeah, the current setup looks quite ugly. What did you end up doing?

Geo1965

Ι am combining the stock system with an aftermarket manual valve installed after the OEM heater valve. The default setting is 'everything open` so the original heater valve operates as it should. In the summer I still let the original valve operate normally BUT I shut the water supply on the manual valve. For convenience I operate the manual valve by a cable discreetly hidden under the dashboard. Best of both worlds?

FredR

Yours may fail but mine have never failed- not once in 21 years of ownership and that considering my hot climate. The actuators can fail but then in my case I do not use them. The valve is a simple disc valve and it is spring loaded - when the actuator arm is disconnected and the disc is in the closed position the pressure pushes the disc into its seat and seals it.

Because they look icky I preemptively replace them- I change my coolant every 4 years [the pH is still 8.5] and every third change I change out the valve. These things are now one of the few custom 928 items you can purchase for less than $100 and at $30 a pop arguably they are the best 928 buy out there.

Oh- I forgot to add, during my recent major maintenance project in February last I found the actuator on my flappy had gone south. That damned thing is now getting close to the $100 a pop mark just for the pissy silly actuator. As I do not use the actuator on my heater valve I cut the actuator support bracket off the heater valve and fitted the heater actuator to operate my flappy- it was a tight fit and required some imagination and it may well fail prematurely but it was a shot!

Lateral thinking in action but do not tell the manufacturer this or the price of heater valves will zoom.

Maybe I should get Roger to send me a couple of new ones before this leaks out and they hit the $100 mark!

FredR

There is a passive vacuum system and the heater valve is connected to it but it does not hold vacuum onto the system after engine shutdown- quite the opposite- it releases the vacuum and the valve defaults to its natural position with the valve open and therein lies the problem - works well for cold European climates in winter time but compounds the heat soak issue in warmer climes
As I am aware that is a constant feature across all model years but maybe yours is different? Common sense should of course prevail and this kind of mod is intended
to used very occasionally such as once in spring and once in autumn type of thing. If more flexibility is required it does take much imagination to locate even a 2nd valve of the stock type somewhere practical albeit space is a bit cramped.

Jfrahm

With a manual override valve the heater core is still connected as a backwater, this is an issue as convection and heat soak will warm it up. There is no flow in either case, with or without manual override, as the water pump is not turning.
It'd be simple enough to test the effectiveness, just measure center vent temps after hot starts, with and without the manual valve engaged. My guess is that it won't matter enough to be worth futzing with.

I have a manual valve on one of my cars but the AC is not presently working. I installed it when I had heat 100% of the time before I determined that the heater valve had failed internally and was passing hot coolant in the closed position. My valve is on the return line where it's easy to get to, right by the jump post. I can run this test sometime in 2022 if things go to plan and I get the work done on my diamondblau 87 S4 auto over the winter.

I suppose I could test how long to get the vent temp down to normal with just ambient air.

merope

How on Earth were you able to install a valve AFTER the OEM one and how do you operate the cable? Photos would be appreciated. Mine still has the OEM and that will work, if the manual valve is opened. So, very similar, just the location of the valve and how its operated is different. I bet yours looks nicer.

I was thinking of using something like this:

https://www.ebay.com/itm/202461554366

It is a 12-24V normally closed valve. One could easily route an on/off switch either in the engine bay or into the cabin. It would be in addition to the OEM valve, just like in your case. If you want heat, on those rare occasions, supply power to the valve for those few hours of driving and enjoy. I am just uncertain of the quality of this product (hey, ebay!) and whether I could make everything fit. I'll just assume I'd be able to find power for it somewhere.

Landseer

Flaw with stock system is not the fail safe concept, but instead the cheap construction of valve itself. ( Whoever was in charge of that probably cut their teeth on the windshield washer system. I mean it's pretty much stupid to use carbon steel sleeves to line filler neck and reservoir. No excuses.
Same thing for flimsy gate and seal inside valve. Bad choices.)

Electric valve could be made to work. When building a pesticide sprayer, I had sourced a spare stainless Spraying Systems 3/4 inch valve with viton seals for exactly that service 6 years ago but haven't installed it. LoL.Best laid plans.

Speedtoys

Ya..you still heat soak thru the firewall, but there's no convective activity....where are the "hot" and "cold" hoses? They're both at the top of the heater core..water cant rise, water cant sink. It needs a pump to displace itself,

merope

I guess then all these people working to find a solution to this issue were idiots and were experiencing some placebo effect.

FredR

Well you know what they say these days: "Designed by computer, built by robots and driven by idiots"