beran earms

In the process of fuel lines, injectors etc. I had wanted to check the heater valve because of constant heat in the cabin, so I removed it and checked it with vacuum. The valve seemed to operate properly and held vacuum for awhile but the question is should you be able to blow air thru' the tube with the gate shut? It doesnt require a great deal of force and you could actually get air to move both ways. I dont want to add this work to what I am already into right now but would like to stop the heat for the summer. My concern is if I wire it shut like I have read to do several threads, that this is possibly going to still allow coolant by. Also if I purchase a new one and I button up it still may not work on account of vacuum problem somewhere. So, do I wire it because this amount of blow by is normal. OR purchase a new one, install and wire it also, OR install a shut off temporarily and figure it all out later as its own job? I am self employed and my job is top priority and mentally and physically demanding and there are only so many hours in a day and sometimes I may need to leave this unattended for many days so really dont want piles of parts strewn about that I may not remember where they go otherwise I would like to do this while I am at it. I am open to some advise on this one.
Thanks for the help, JD

dr bob

Replace the valve. One of the common failure modes is as you describe, where coolant will pass through a closed valve.

Because it's a sliding-gate valve, it seals better one way than the other. We'd like the coolant flow from the head to push the valve tighter rather than try to bend the actuator arm pivot, so black end towards the head when you install the new one. New stub hose too, and inspect the nipple fitting on the head while it'a all apart.

beran earms

Makes sense, but what if its a vacuum problem elsewhere, will I need to then tie the new one shut for the time being? Also can you clarify "the nipple fitting on the head" I cant picture this.

mkhargrove

I am in Texas....I decided to just cap off the vacuum line and installed a $10 manual (**** turned to closed) valve for summer last year. It's a 4 minute job with a splash of coolant on the floor.

FredR

The valve default condition is open [i.e. no vacuum applied] so if you have a problem with vacuum the heater element will be exposed to hot coolant. It is quite simple to disconnect the actuator arm.

The nature of the valve design is such that pressure in the cooling circuit will help the valve to seal as it will push the gate into the seat. Needless to say air will leak past the gate to some extent far easier so trying to determine whether the valve is knackered is not quite so straight forward. A very small amount of coolant passing through is not going to be of any significance- the trick bit is knowing "how much is too much" and thus when to replace.

In my climate I do not need the heater so rather than let coolant sit stagnating in the heater matrix I took it out of the loop altogether. I have the valve physically present but it sits with the actuator removed altogether and the actuator arm wired closed. When I fill the system I manually open the valve to help correct venting/filling and close it off when the operation is complete.

dr bob

For hot season use it’s a simple matter to use a cable tie to hold the valve closed. You can add a permanent manual valve in series with existing valve, and just close that during your not-heating season.

The nipplefitting I mentioned is the fitting on the head where the heater valve connects with a short hose. Early versions had a steel sleeve in an aluminum base. Some corrode and come apart. If you have that version, update to the later all-aluminum version when it’s convenient. If you are replacing the valves and hose now, it will never be more convenient.

beran earms

Thanks for the responses. The nipple fitting has been removed and is an aluminum tube and everything looks good and very clean. According to Fred it is difficult to determine if "the valve is knackered" ( I live in a not so creative area, we just say "junk" or "all f.. up") I do get air by but I wonder if the force from hot coolant somewhat softening and pushing the plastic would push against and close it off enough? So the verdict... reinstall the original tie it shut and move on? I kind off would like to continue tonight and not wait for shipment of a new valve unless this seems a foolish plan. FWIW this car has under 60k on it and the parts look good, understanding its over 30 yr old plastic.

19psi

This has been mentioned as a replacement in other Rennlist discussions:
https://www.napaonline.com/en/p/BK_6601410

If you already have the old one out, it seems foolish not to put a new one in...especially since it's a wear and tear item and available locally for $15 bucks.

dr bob

The idea of coolant flow force pushing on the plastic and closing it is unrealistic especially if the sealing surface has already been compromised. If you can blow through it from front to rear with the lever squeezed to valve full-closed, it won't seal any better with coolant. The actual pressure difference across the heater loop isn't a lot in service. The whole system operates at pretty much the same pressure, with the water pump providing enough local differential to cause coolant flow through the whole system. The heater circuit sort of slipstreams the radiator and thermostat from the rear of the head back to the pump suction side at the water bridge. There's at least six feet of plumbing plus the valve and the heater core restricting flow through that loop. Meanwhile, the main coolant flow path back through the block or through the radiator is in parallel with the heater core loop.

The heater control valves are a very well-known weak spot, mostly for liquid leak-by. If you don't want to wait for a new valve to install, you'll want to find some other means of blocking coolant flow through the heater core. At least if you want to keep the cabin cool. Might be as easy as stuffing a plastic wine-bottle "cork" or some similar plug that fits snug in the connector hose.

I just installed my third valve a year or so ago in my thirty year old car. The first couple valves could have legitimately been replaced with block-off plugs since the car was living in SoCal. But I'm a stickler for having everything working perfectly as designed. The last failure was a vacuum diaphragm leak that was messing indirectly with AC performance. Our vendors are supplying a Mercedes valve that's identical in form to what Porsche supplied. I recommend that one before a cheap knockoff. The pieces for this surgery are small enough to go by two day Priority Mail, making it tough to justify a half-fast solution. Of course this stuff isn't hard to access for the work even if you decide to do it twice.

beran earms

Good info thank you dr bob. Does anyone have the number of the Mercedes part which is a replacement? I have a very well stocked dealership not far from me and could possibly obtain one today to use tonight.

dr bob

Take yours along with you and they will give you the right one without much effort looking it up.

StratfordShark

I bought and fitted the Mercedes version a couple of weeks ago.

Part number Merc part 000 830 57 84, or ask for heater valve for W201 Merc 190.

Rich9928p

On the subject of heater valve, when replacing the heater valve it is always a good idea to replace the little bit of hose between the engine side water pipe and the heater valve. For the 1985 to 1995 928s, it is part number 928.574.567.03 ... As I recall, it is a different size on each end so no "off the shelf" bulk hose can be cut to size.

The earlier 928s, 1978 to MY 1984 use p/n 928.574.567.02

Rich
928 OC Membership Chairman
1993 928 GTS Cover Girl
1987 928 S4
1979 928 5-speed rescue cover girl too
1979 928 Euro 5-liter track beast

beran earms

This is why I love this forum and love my 928 even more. The members here make care taking a great experience and you can tell it is more than just a car to most!

Thanks for all the help! JD

merchauser

did not know this hose is different size on either end. last time I just used bulk hose.