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Got the 1.2 bar expansion tank cap from German Auto Solutions

60K views 113 replies 36 participants last post by  KWN-E39 
#1 ·
From Gary (German Auto Solutions). It's a thing of beauty. The top is engraved steel and the relief valve is "Reutter" - the OEM supplier for the OEM expansion cap. The beauty is that "if" the temp is getting too high, it will release the pressure much sooner than the OEM cap, thus having a chance for the plastic parts to last longer. I would venture to affirm that if the cooling parts will rupture due to pressure, at a lower pressure the damage could be smaller, i.e. the crack could be just that: a smaller crack, which could allow you save the engine. At higher pressure, a crack will develop very fast in a big rupture, where one could loose cooolant very quickly.

Thanks Gary. Beautiful product. :thumbup:



 
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#49 ·
I'm sure most people have gathered this from the ongoing discussion, but it still probably bares mentioning for those how are interested in the finer details; the coolant cap is a differential pressure relief valve. It will vent at 1.2 or 2.0 bar above whatever the ambient absolute atmospheric pressure is at the time. So technically it will vent at a little different absolute pressure even based on weather conditions.
 
#50 ·
So there's a bit of discussion on what "normal" operating temp range is for our cars once warmed up. Most of the figures I've seen for my m52 have been ballparks ~88-95. We know when and at what temp they overheat at, but what I would like to know is the factory stated standard operating temperature. With out knowing this value it leaves a grey area between "running hot" and over heating. I don't like grey areas.
 
#51 · (Edited)
what I would like to know is the factory stated standard operating temperature..
I'm not sure how much applies to the M52, but for the record, we covered the M54 & M62 (thermostat) temperatures in this thread:
- What is the temperature of the coolant & when the thermostat opens under normal conditions (1)


Here is the cooling system flow through the M52 engine:
 

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#52 ·
This interesting description was on the other thread:

The nipple on the expansion tank is not an overflow tube.

The other end is connected to the radiator via the nipple on the top of the LH/hot radiator tank. The hose goes under the top of the radiator shroud to the nipple on the hot tank. As far as I can work out its a continuous bleed from the hot tank to the expansion tank to remove any air trapped in the top of the radiator.

If you take off the cap you will see coolant flow from the hole in the side of the filler neck. What happens when the cap is in place is one of those questions I haven't been able to work out. The hole exits into the neck between the 2 O rings on the cap. I haven't got around to cutting open an old radiator cap to find out.

You will notice the top radiator hose has an S shaped section between the bleed nipple and the radiator. This is to stop air trapped in the radiator tank from getting back into the head etc.

I have also cut up my old expansion tank to see what is inside. I don't have the level sensor switch (low level instrument panel and you need the high level panel and the "I" data bus etc) but its a Hall Effect switch which is triggered by the magnet on the level float.

I think the cover in the other half of the tank is just a stilling arrangement to stop the coolant level sensor from being activated by water flow from the auxiliary water pump.

Its operating all the time to ensure enough water is pumped through the heater because of the unusual cooling system flow through the head and block. The M52TU and M54 engines cooling systems are completely different to the earlier single vanos M52 engine which has a conventional cooling system arrangement.

They use a minimal water flow through the block with maximum precisely controlled water flow through the head. At high engine speed and load the aux water pump is needed to ensure adequate flow through the heater as most of the water flow is back to the radiator. There is a PDF on one of the E46 boards which explains how it works but I can't find it right now.

Also don't remove the radiator cap if the engine is hot. Apart from the risk of scalding you can end up with air trapped in the system and then its back to square one and the cold bleed process all over again. How do I know? Been there and done that!

Also don't open any of the bleed screws with the engine hot or cold after you have successfully bled the system. All you will do is let air back into the system. You can test this with the engine cold. Take off the radiator cap and check the coolant level then undo the top radiator hose bleed nipple and observe the water level rise in the expansion tank as air enters the top hose and the water finds its own level in the system.

You now have air in the system and have to do the cold rev bleed procedure to bleed the system again. The normal level in the expansion tank is below the water level in the top hose. The water level in the top hose and the engine block, head etc is held there by a sort of siphon effect and opening the bleed screw destroys this and allow air to enter the system.
 
#55 ·
I just realized, from Aussie528i's post below ... that the fluid flow through the expansion tank is DIFFERENT for each of these four E39 engines;
1. M54 expansion tank fluid flow
2. M52TU expansion tank fluid flow
3. M52 expansion tank fluid flow
4. M62 expansion tank fluid flow

Bluebee,
There are a number of different threads on the board so maybe they need to be combined. I have read many of them and there are some quite divergent views about the cooling system components and how they work. Many don't understand that the M52 and M52TU engines are completely different animals. It probably would have been better if BMW had called the M52TU the M54 and the M54 the M54TU. The M52TU has much more in common with the M54 than with the M52. The fact that the M52TU has a throttle cable but is still "fly by wire" seems to cause confusion as well.

Regards
RonR
 
#59 ·
One question arose in a different thread today about the REVERSE of the venting:
Radiator caps usually have a one way check valve to allow air into the system if pressure falls below atmospheric. I assume the BMW cap does too.

Keep in mind that there is always air plus water & EG vapor in the top of the expansion tank. When the system cools overnight from the temperature during the bleeding process the vapour contracts which reduces pressure, perhaps below atmospheric at which point the cap's check valve opens to allow air to enter and equalize pressure. If the check valve doesn't operate properly, the rad hose collapses. The effect would be magnified if the bleed isn't complete and there is another air pocket in the head or cabin heater circuit.

I think this effect is the reason that many people report having to add a bit of coolant the next morning after bleeding the system. Once that 2nd small fill is done the system is stabilized to ambient temperature and no further addition is needed (at least we sincerely hope
So, I ask: Does the GAS 1.2 bar cap (or the original 2-bar cap) have such a check valve?
 
#61 ·
It has been known by most that the temperature gauge on the E39 is "dampened" such that the needle on this gauge will remain approx. dead center over a range of coolant temperatures, but to now know that this range is 75 degrees-113 degrees C is ridiculous in my mind. I can see BMW wanting owners to feel safe and not get overly excited about needle swings up or down, but I think if the gauge was not dampened to this degree, we might be able to observe trends in our cars before they become "critical". Most that have reported sudden over-heating state that one minute the gauge was dead center and then all of a sudden it shot up to "pegged" at the over-heated end and they were trying quickly to find a place to immediately pull-over. I believe if BMW trusted owners to be able to see what is really going on temperature-wise on our cars, we could decide for ourselves whether we need to take proactive action based upon driving our cars everyday and getting used to "what is normal". I just love that BMW feels a need to protect us from reality! "WE CAN'T HANDLE THE TRUTH"-says Jack. :thumbdwn:
 
#62 ·
I think if the gauge was not dampened to this degree, we might be able to observe trends in our cars before they become "critical".
So true. A few months ago my gas mileage started deteriorating but I attributed it to the colder temps. After a while I noticed that my temp gauge had moved slightly (about 1/8 ") to the left of centre so I unlocked my display to check the actual coolant temp, it ranged between 68-70 deg C. Once I changed my thermostat the coolant temp bounced back to 95-97 deg C and my mileage improved by 20%.

I can only guess how much gas I wasted before my temp gauge finally let me know that something was wrong. Now that I know just how much damping is on the gauge (almost 30 deg C) it seems more like an ornament than a source of info. I'll be unlocking my display on a regular basis from now on.
 
#64 ·
Interesting proposition, Gary. I think I would like to place a gauge like that in the opening for the Foglight switch and then relocate the FL near the seat heater switches somehow.
 
#65 ·
The "real" temp gauge would be nice to have. Fitting might be an issue to make it "standard". I use fog light switch, so I would not buy it if it's made for that spot. Maybe something that clips to the center vent, or the driver's "A" pillar?

Where are you with the new CCV?
 
#69 · (Edited)
Gary, you are absolutely right and would make the whole deal easier to make and could be hidden under the dash somewhere. Perfect, as we can always get digital temp. from the DIC if we hear the adjustable alarm start to go off. You could adjust up a little at a time until you know it is set for say 110 degrees centigrade. I'll buy the first one. all you need is three wires- GND, +12VDC, and temp input. You researching how to access the temp. input wire in the best manner would be great and with a full 12VDC available to the buzzer, it could be damn loud! :thumbup:

Make it adjustable with small CB pot.

Bill
 
#72 ·
And I'll buy the first CCV.
Realistically: how long do you think until it's ready? Or: realistically, there isn't a good solution in sight as of yet?
I still am 100% convinced and committed to the current design concept. The main problem has been the success of the other G.A.S. products and the lack of human resources to ease some of my load so that I can devote serious time to the CCV.

I just received our second FDM rapid prototype for fitment testing. The mounting location is very constrained and it's been a challenge to juggle the dimensions to allow easy access to removing the cap for servicing the unit. Once the physical dimensions are worked out I can make a real functional prototype for testing.

As far as the human resources issues goes; our engineering intern has postponed finishing his degree and is now working here full time to help move things along (although I share him with my partners engineering firm). I'm also currently interviewing accounting applicants to take over my accounting responsibilities, which will free up even more of my time. Long term prospects for having a lot more design and engineering time look good, but short term is still a problem due to tax season and getting the new personnel up to speed.

We are also looking at the prospects of purchasing a new live tooling 4-axis cnc lathe in the fall. It would be a big asset in machining a lot of the CCV parts as well as some of our other current products. Rest assured that the CCV will go into production with or without the new lathe. The new lathe will just lower the production times and cost.

We have a bunch of REALLY good product ideas in the pipeline, just not enough people right now to help see them to fruition. Once a few more products are on line, the cash flow will help allow us to bring additional people on board. We have 3.5 really good design people right now, so further personnel additions will probably be machinists.

I'm sorry this has been dragging on for so long, please do not get discouraged or think that there is a lack of commitment on our end to see the product through.

Gary
 
#76 ·
Well, you sold me. Just ordered one, in black. I was just noticing how ugly the factory cap was last night. :thumbup: My first "mod" on this car! Other than the ultimate cupholder, of course. Guess Im no longer a purist. :(
 
#80 · (Edited)
I was doing some research for someone needing a coolant bleeding DIY, when I ran into this cryptic sentence:
The expansion tank does not have an overflow tube. Coolant is vented through the cap (cap is hollow inside) and any over flowing coolant will leave white stains around the top of the expansion tank. This is normal but leads some people to think their expansion tank is faulty and leaking
So, if the expansion cap is the one-way coolant overflow valve (with a two-way air check valve built in), then what is the purpose of the so-called expansion tank overflow tube that goes from the expansion tank neck to the top of the radiator?
 
#81 ·
So, if the expansion cap is the one-way coolant overflow valve (with a two-way air check valve built in), then what is the purpose of the so-called expansion tank overflow tube that goes from the expansion tank neck to the top of the radiator?
I thought that as the coolant was heated, it "expanded" and moved from cooling system (radiator) to the expansion tank. After the car is stopped (cools), coolant is drawn back into the radiator.
E28 & E30 expansion tanks have hoses that vent excess coolant to the ground.
 
#82 ·
I just saw this discussion today and thought of an earlier post JimLev made about a 1.2 bar cap possibly presenting "a problem with the tu motors running at 108°C on very hot days". Here is the link.

http://forums.bimmerforums.com/forum/showthread.php?2018384-*****zo-Pshovest-Spirti-Force-etc-Temp-vs-Pressure-update&highlight=pressure

This stuff is a bit beyond me and I did not read through this whole thread, but I thought this info may be useful to some of you who understand better. If this is just cluttering up the thread with unrelated info, let me know and I will delete it.
 
#84 ·
I can't 100% certain, but from my analysis of the system I've learned the following:
  1. The cap has a blow off valve (OEM calibration of 2.0 bar, GAS calibration of 1.2 bar) that vents excess pressure through passages in the perimeter of the cap.
  2. The cap has a 1-way check valve that allows air to pass in the opposite direction if the expansion tank pressure drops below atmospheric pressure during cool down.
  3. The little hose connecting the top of the radiator to the top of the expansion tank helps to bleed off trapped air in the top of the radiator. I also believe, based on the flow path of that hose through the pressure relief section of the coolant cap, that it also makes sure that an overfilled system will vent excess coolant, and after successive heat cycles, return the coolant levels to normal. In a normal system there is coolant flow through that hose and if the system exceeds the blow off pressure of the cap, the cap will vent both trapped air from the top of the expansion tank and coolant flowing through the little hose. That is why you see coolant residue on the top of the expansion tank if the cap vents. If the cap only vented trapped air from the top of an overfilled expansion tank, the system would over pressurize every time the car was run and the system would remain overfilled.
 
#87 ·
#85 ·
I just saw this discussion today and thought of an earlier post JimLev made about a 1.2 bar cap possibly presenting "a problem with the tu motors running at 108°C on very hot days".
We removed the manual clutch fan and disconnected the aux fans and tested both an M52 and M54 engine in real time while monitoring system pressures and temperatures up to full overheat temperatures (Gage pegged on full hot and dash warning displaying) and the system never exceeded 1.2 bar of pressure until temperatures exceeding 125 deg C.

Gary
 
#86 ·
I thought that as the coolant was heated, it "expanded" and moved from cooling system (radiator) to the expansion tank. After the car is stopped (cools), coolant is drawn back into the radiator.
This is how almost all US manufactured cars work, and I think it is the simplest and therefor best way to do things. In this method the expansion tank is not pressuerized and has an extremely low failure rate. In most European cars the expansion tank runs at full system pressure and actually has constant coolant flow through it. That is why there is such a high failure rate in this type of system. The problem is compounded by BMW's choice of a 2.0 bar venting pressure for these cars.

Gary
 
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