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My recently purchased 86.5 928 has an interesting solution to a supposed design flaw of the 928. As far as I read, the vacuum operated valve, that shuts off the coolant from entering the heater core, is not that great, as it allows hot coolant to enter the core once the engine is shut off. This can lead to uncomfortable situations in the hot AZ heat where you get into a boiling hot car from the 110F heat outside, when you stop the car for a few minutes. The PO of the car solved this problem, by installing a manual valve on a heater hose, that replaces the short connection behind the engine with a long loop. I'll be honest, I hate how it looks and I have never tried to open the valve, so I don't even know if it works. I have seen the car running slightly hot also and I am questioning whether this hack may be responsible.
So, what are expert thoughts here: 1) Is this actually an issue that needs solving? If so, I'd rather have a normally closed electronic valve that can be opened with a powered switch. 2) If not, should I convert back to OEM? 3) Could this cause the car to run slightly hot? Any other thoughts or input are welcome. I haven't seen this anywhere else on other 928s, then again, most of you live in colder areas.
My recently purchased 86.5 928 has an interesting solution to a supposed design flaw of the 928. As far as I read, the vacuum operated valve, that shuts off the coolant from entering the heater core, is not that great, as it allows hot coolant to enter the core once the engine is shut off. This can lead to uncomfortable situations in the hot AZ heat where you get into a boiling hot car from the 110F heat outside, when you stop the car for a few minutes. The PO of the car solved this problem, by installing a manual valve on a heater hose, that replaces the short connection behind the engine with a long loop. I'll be honest, I hate how it looks and I have never tried to open the valve, so I don't even know if it works. I have seen the car running slightly hot also and I am questioning whether this hack may be responsible.
So, what are expert thoughts here: 1) Is this actually an issue that needs solving? If so, I'd rather have a normally closed electronic valve that can be opened with a powered switch. 2) If not, should I convert back to OEM? 3) Could this cause the car to run slightly hot? Any other thoughts or input are welcome. I haven't seen this anywhere else on other 928s, then again, most of you live in colder areas.
I may be wrong, but this does not seem to address the original issue of the design flaw. It is also vacuum operated and therefore floods the core with hot coolant after engine shut off.
All one has to do with the stock valve is disconnect the actuation arm and manually close the valve and if one wants a little more security wire the arm closed. Then if one wants the valve operational simply reconnect the arm.
On the other hand I never use the heater so I simply bypass the heater matrix and leave the valve closed. That way there is no chance of coolant stagnating in the heater core and causing corrosion related damage- not that is likely to happen.
All one has to do with the stock valve is disconnect the actuation arm and manually close the valve and if one wants a little more security wire the arm closed. Then if one wants the valve operational simply reconnect the arm.
On the other hand I never use the heater so I simply bypass the heater matrix and leave the valve closed. That way there is no chance of coolant stagnating in the heater core and causing corrosion related damage- not that is likely to happen.
That's interesting. Unlikely I will use the heater also. Since this solution loops above the engine I do have worries of bubbles being in it. With your method, one would need to remove the air box each time they wish to open the valve. That does not sound convenient. That's why I thought a normally closed and electronically operated valve would be good.
I may be wrong, but this does not seem to address the original issue of the design flaw. It is also vacuum operated and therefore floods the core with hot coolant after engine shut off.
Why, is there a vacuum in the core with the valve closed that hot water rushes into?
All one has to do with the stock valve is disconnect the actuation arm and manually close the valve and if one wants a little more security wire the arm closed. Then if one wants the valve operational simply reconnect the arm.
On the other hand I never use the heater so I simply bypass the heater matrix and leave the valve closed. That way there is no chance of coolant stagnating in the heater core and causing corrosion related damage- not that is likely to happen.
The valve fails internally, wiring it shut..isnt resolving that issue and water still flows.
Why, is there a vacuum in the core with the valve closed that hot water rushes into?
My understanding about the way the valve works, is that it is normally open and that the vacuum keeps it shut. Once the engine shuts, no more vacuum, allowing hot water to enter the core. Is this wrong?
My understanding about the way the valve works, is that it is normally open and that the vacuum keeps it shut. Once the engine shuts, no more vacuum, allowing hot water to enter the core. Is this wrong?
Ya...but engine off, no pump to put it there...right?
There's already water..in the core from the other side of the system.
I found this write-up. Slightly more elegant. I still think a normally closed valve would have been way easier. Especially one that is not vacuum operated.
I found this write-up. Slightly more elegant. I still think a normally closed valve would have been way easier. Especially one that is not vacuum operated.
I actually don't know how big of an issue it is. I could test it by opening my manual valve. But there seems to be quite a lot of talk and write-ups about it, so it is likely not an exact non-issue for people who live in places where the temps go up to 110-120. See here, for example:
I actually don't know how big of an issue it is. I could test it by opening my manual valve. But there seems to be quite a lot of talk and write-ups about it, so it is likely not an exact non-issue for people who live in places where the temps go up to 110-120. See here, for example:
09-05-2021, 03:07 PM
Input on heater core manual valve
