Jerry Feather

I found the COLD WATER LEVEL indication on the side of the coolant tank in my 88 S4. It consists of an arrow from the sticker on top down to just about half inch above the tank's middle seam. Then, with the aluminum replacement tank I have been doing some measurements with I find that the new sensor will just barely float the cork when the coolant is at the low level mark. Just about anything below that will drop the cork and turn the low level warning on.

Compared to the original sensor, as stated numerous times in this thread by me and Roger, that is about an inch above where the original will give the cold level indication.

Nothing in the information about this sensor and its indications even suggests that the level of coolant when the low indication is given is also some kind of "minimum!" The only purpose of the sensor it to tell when there has been a coolant loss of something less than a quart. With the level at the COLD mark, just about any loss of coolant is going to give the Low Level indication. What needs to happen to justify use of the new shorter sensor is to determine if the coolant level can be maintained at about half inch to inch above the original cold level mark.

Imo000

Speculation? What part is speculation?

Imo000

You really believe that the trigger point of the OE sensor doesn't mean minimum? Is it logical to expect that this point is a minimum established by the factory during severe weather and severe condition testing (then they added a bit more for safety)?

Imo000

I agree, in most conditions a 1" higher level of coolant wouldn't matter but still the new sensor will not be accurate so it's purpose will not be as designed. It's like having an inaccurate oil dipstick. It will tell you the oil is dropping but that's it.

DKWalser

Imo -- Jerry is referring to your statement that Porsche precisely determined the minimum amount of coolant for the 928 and labeled the coolant reservoir accordingly. That is, your assertion that a sensor that sends a "too low" signal earlier or later than the original sensor would have is providing false information, and your hinting that using such a sensor might be worse than having no sensor at all (because it might give the driver a false sense of security or cause the driver to ignore warnings). This, lumped together, is speculation on your part. Unless you have personal knowledge of what the Porsche team did or did not do in this regard, you are speculating as to what they did and what they knew. Your speculations may be based on reasonable assumptions, but they are still speculations. The size and shape of the reservoir bottle may have more to do with the space available than it did with an extensive study. Similarly, where they set the fill mark may not have been determined with any precision. It's possible there was a range they were comfortable and simply picked somewhere within that range for the fill mark based on other considerations, such ease of manufacture.

The real question is why you're so determined to tell everyone it won't work? Jerry, after significant time and effort, is tying to test the sensor to verify that it works. If it doesn't, Jerry will either come up with a fix or he won't sell it. So, in the interim, what is the harm in waiting on the test results? It's not as if Jerry's trying to foist an unproven product on the public.

Jerry Feather

Mj reports that he installed the new sensor in his 928 and that it functions just as the original one, with no low warning either hot or cold. He doesn't, however, report what the coolant levels are in his tank, either cold or hot. I have asked him for those readings.

I found one other data point online in a lengthy report by someone who showed his way thru replacing his expansion tank in a 928. The most interesting thing about it is at the end he shows maintaining the coolant level at about an inch or little more below the top of the tank, rather than just above the middle seam.

I need more input about the ability to commonly keep the cold coolant about an inch or inch and a half above the mid seam. If I have to do all of this myself it will be some time before I am comfortable trying to market these new sensors.

Again, I know exactly where the new and the old sensors will trigger the low indication; and that is right at about the middle seam for the new one and about an inch and a quarter below for the original sensor. The cork on the new sensor does not float until it is fully submerged, at least in plain water; the original one at about 3/4 submerged. That means that if Mj's is working correctly and he is starting at the Cold Level Mark, just about any loss of coolant is going to send the low warning, rather than nearly a quart of loss for the original.

I'm not sure just what all circumstance are that might lower the coolant level below the Cold fill level, except loss, and it may be that the only one is coolant loss, but I am not comfortable thinking that any minute loss is what we want for the warning to come on about.

I am still hoping that some of you will go out and add either a pint or a quart of coolant to your tank and tell me what happens to it hot and cold.

Luis A.

Reviving this thread to find out what the outcome was. After reading the whole thing and sitting at the edge of my chair the discussion abruptly dies... What happened?! Is someone selling the cap and seals to make the BMW sensor work?

ReDesign by FEATHER

I completed the development of the alternate Coolant Level Sensor/Sender and left it pretty much just where the last post by me says. I did recently sell one of them to a new young member with his order for some of my other items, but have not started a thread about the availability of these generally because of the lack of any additional testing or feedback about keeping the level of coolant in the overflow bottle a bit higher than the level mark on it.

If anyone else is interested in trying one of these in their 928 they are available for $45 plus $5 for S&H.

Luis A.

Thanks for the reply Jerry. I am going to pull mine out and fully characterize whether it's functioning or not as the "coolant" indicator seems flaky right now. And rule out pressure sensor malfunction.

Do you have a website describing your offerings? Can't find it on The Google...

ReDesign by FEATHER

I don't have a web site, but my offerings are listed in my signature. You can probably do a search and find a thread about most of them here on Rennlist 928, which is just about the only place I do any marketing.

Jerry Feather

I didn't push the sale of these replacement sensors mainly because of all of the missinformation about the different level that the sensor will need to function at. I think the onlly one I sent for use is the original one I modified for Mj. He reported that it works whether hot or cold. No one else gave me any feedback about trying to keep the coolant level in the overflow tank at about an inch higher than the level mark on it. I think Mj's sensor is simply floating in thin air above the coolant. At least he has a nice white cap and the tank is sealed.

I lately fiound that I mistakenly relied too much on information about the BMW sensor from others on this forum and from the bad information that the BMW sensor was a direct repalcement for the 928 sensor, even though we all knew that it was not, at least in terms of fit. What I have found out is that that is not the only difference. I happen to have an original sensor laying around near my computer so it recently occurred to me that I ought to check to see if they function in the same manner notwithstanding the difference in length. What I found was that all of my efforts in this project were wasted. The 928 sensor makes an electronic connection when the float drops to the bottom, which is of course intuitive, but the BMW sensor, that I have nearly a hundred of, makes the electonic connection when the float is at the top. DUH! I wonder if the opposite configuration of the contacts on the top of the sensor might be a hint to the opposite manner of functioning.

Anyway, that pretty much kills this project except for the outside chance that there is actually a similar alternative sensor that functions like the 928 and might adapt easily to the 200 caps that I had made, or that the caps I had made might be useful to some minor extent to repace an original. There is a post in this thread way above where someone says that they purchased some kind of the repalcement sensor that had a white cap and that it works perfectly. I still wonder what that really was. I actually seriously doubt that, but I may form time to time search for such an animal.

P.S. That was GUY in post 27 above.

Zirconocene

I've been learning a bit about relays in connection to a headlight harness that I want to make for my 944. It's a well-known project and problem for those cars. Anyway, as I was reading this thread and what the outcome was due to the function of the new sender vs. the old, I wonder if a small relay wouldn't be the answer to making this work. I know, it's an extra layer of complexity, and I'm not actually suggesting that something like that be incorporated, but it struck me as a way to try to reverse the signals that the BMW sender is providing. I'm not an EE, so there are probably other ways to do that but this one is in line with other things that are currently living in my head.

Bummer about what happened with this project, but I love the pictures of the design and machining work.

Cheers

Jerry Feather

Thanks Zirco. That is not a bad idea and probably would work. In fact that is probably how the BMW sensor itelf works in real life. The problem with it is what you suggest, that it would make the use of it too coplicated. It really needs to be simply a plug and play situation.

One of my thoughts is that maybe there is some other sensor somewhere in the world that could be adapted that functions the way ours does in the 928. I have searched eBay which lists over 8 thousand collant sensors and have found one that looks like it has possiblities, but I cannot tell from its pictures and listings how it actually works. I have ordered one to see just how it works and if like ours, just how it too might be adapted to the modified BMW sensor top which will still be needed for the tank seal and cap and for the connection. That will mean that it takes two different sensors to adapt into one with my new cap, so the cost will be much more than I had planned, but still much less than a Porsche Factory one.

I don't have great hopes for this new idea because I have a hunch that the 928 coolant sensor is much like the 928 gas cap; that is, there is no other like it in the world.

Wisconsin Joe

Porsche, there is no substitute.

Sorry, couldn't resist.

Jerry Feather

Interesting point, Joe. However, when you think about it that slogan leaves a lot to be desired. Since in most, if not all contexts, a substitute suggests something that works but of lesser quality, whether in sports, automobile racing, clothing and just about everything else. For Porsche that slogan results in suggesting that there is noting worse than Porsche to substitute. In fact with the fabrications I have created for the 928 that holds true since all of my creations are better than Porsche and most have been highly successful as replacements for the stuff Porsche came out with.

I think my slogan is going to be "Jerry - Has a better replacement!"