German Auto Solutions 1.2 bar coolant cap

Their claim is that the standard BMW pressure cap set at 2 bar leads to high pressure in the coolant system, that in turn leads to system failures. I am aware when I was looking at Z4s I came across one with cracked expansion tank and I have heard of others with this problem. Their cap is set to 1.2 bar to reduce the pressure and their claim is this will reduce system components breaking down. But I do not know enough about engines to know what impact that will have on: performance, economy, reliability of the engine. I assume the engine may run at a different temperature, but my knowledge of cooling systems is not high.
 
And of course lowering the pressure reduces the boiling point, so your cooling system will be less efficient and more likely to boil over, warp parts with localised hot spots, etc
You could test it by putting tape over your rad and no cap and watch how long it last - ps don’t do it..... :headbang:
 
I wouldn't lower the cap "relief" pressure.


The system has been designed to operate at a specific pressure, it runs under pressure in order to raise the boiling point of the coolant. The 2 bar figure is that at which it vents at, not the pressure the system normally runs at. If the "normal" pressure in the system is therefore lower than 2.0 bar, a cap designed to vent at 1.2 bar could be close to venting under "normal" operating conditions.

Lowering the pressure also lowers the boiling point, so I would think that maybe in traffic, on a hot day with the AC on, a lower boiling point may cause issues. PLUS, it obviously lowers the pressure by venting the coolant, into the atmosphere lowering the level.

As an aside, in this cold weather, running with zero pressure in the system would not be an issue. Indeed, when [ref]kevbz4[/ref] rang me last week from his tour of Scotland to ask my advice as the car was loosing coolant, and the low level light was coming on 10 mins after topping up, my advice to him was to actually unscrew the cap so it was not holding pressure, and drive it home.. He got home fine with no further coolant loss or problems.

Mike
 
Not sure I really get any of this. Nominal operating temp for the coolant is approx 90'C. Because this is below boiling point there is no pressure. On a hot summers day, stood in stationery traffic, the fan is designed to kick in at 95'C, thus bringing the coolant temp back down to 85-90'C. In a healthy cooling system it should never get above 100'C (where pressure starts to build). What am I missing here?
 
ph001 said:
Not sure I really get any of this. Nominal operating temp for the coolant is approx 90'C. Because this is below boiling point there is no pressure. On a hot summers day, stood in stationery traffic, the fan is designed to kick in at 95'C, thus bringing the coolant temp back down to 85-90'C. In a healthy cooling system it should never get above 100'C (where pressure starts to build). What am I missing here?
Click to expand...

The system builds a head of pressure as the water heats, due to it being sealed. That's why all the warnings tell you not to open the cap whilst hot.

Mike
 
The low pressure caps are apparently ideal to use with waterless coolant and if installed properly should drastically improve one of the few weak aspects of the M54 i.e cracked coolant headers leading to overheating and HG issues. I think it may be a good preventative combo as these cars age TBH.
 
A lower pressure cap does absolutely nothing and can only do harm.
It doesnt lower the working pressure and if it would do that, it would let coolant out! (that is, out of the system!!!)
That is only acceptable in an emergency scenario.
If you want to lower the coolant pressure, it should be done with an alternate thermostat.
Also the cracking is a fatigue issue, not an issue of not being able to hold the pressure otherwise the reservoirs would crack the first time it gets summer and not after a certain number of miles (which seems to be the case)

The only use I can think of for this cap is for people who dont know how to fill the coolant system to the correct level and repeatedly top up the system to a too high level (as this cap only releases excess coolant more easily)
Sounds about right for american motorists... :poke:

^for waterless coolant systems it wouldnt make any difference as they dont build up pressure unless your headgasket is failing


BTW they pressurize/seal the system to bump up the boiling temp of the coolant, like a pressure cooker. From a performance perspective lowering that pressure could do harm. If the pressure would be relieved prematurely by an alternate radiator cap, the coolant could start to boil in places where temperature is highest (probably the head), resulting in reduced cooling (as a gas is far less efficient in transporting heat than a liquid), which in turn could lead to damage like excessive head warpeage etc. So overall not a really good idea.
 
GuidoK said:
A lower pressure cap does absolutely nothing and can only do harm.
It doesnt lower the working pressure and if it would do that, it would let coolant out! (that is, out of the system!!!)
That is only acceptable in an emergency scenario.
If you want to lower the coolant pressure, it should be done with an alternate thermostat.
Also the cracking is a fatigue issue, not an issue of not being able to hold the pressure otherwise the reservoirs would crack the first time it gets summer and not after a certain number of miles (which seems to be the case)

The only use I can think of for this cap is for people who dont know how to fill the coolant system to the correct level and repeatedly top up the system to a too high level (as this cap only releases excess coolant more easily)
Sounds about right for american motorists... :poke:

^for waterless coolant systems it wouldnt make any difference as they dont build up pressure unless your headgasket is failing


BTW they pressurize/seal the system to bump up the boiling temp of the coolant, like a pressure cooker. From a performance perspective lowering that pressure could do harm. If the pressure would be relieved prematurely by an alternate radiator cap, the coolant could start to boil in places where temperature is highest (probably the head), resulting in reduced cooling (as a gas is far less efficient in transporting heat than a liquid), which in turn could lead to damage like excessive head warpeage etc. So overall not a really good idea.
Click to expand...

I think you are shooting from the hip on this one and your knowledge of thermodynamics is 'iffy' TBH.

Firstly thermostats regulate water flow by monitoring temperature. Flow is not the same as pressure, it's a tricky concept but suffice to say changing a thermostat will alter cooling but not the working pressure in the system.
The only reason that the system is pressurised is to raise the boiling point of the water based coolant because boiling produces gas and gas is a poor conductor of heat leading to localised overheating. Using waterless coolant (like Evans) allows the liquid to rise to 180c without turning to a gas (boil) at atmospheric pressure, waterless coolant with a low pressure cap = the same or improved cooling at a lower pressure.
The additional benefits of waterless include drastically reduced corrosion and the obvious reduction of stress on pressurised componets, like hoses and headers. The downside is that the flushing and filling process is a pain and it's expensive. Waterless is used in many specialist motors including modern and classic racing applications.
 
Ewazix said:
I think you are shooting from the hip on this one and your knowledge of thermodynamics is 'iffy' TBH.
Click to expand...
Care to elaborate?
Firstly thermostats regulate water flow by monitoring temperature. Flow is not the same as pressure, it's a tricky concept but suffice to say changing a thermostat will alter cooling but not the working pressure in the system.
Click to expand...
I dont say anywhere that thermostats regulate either pressure or flow. I say that if you want to lower the coolant pressure, it should be done by an alternate thermostat. And that is something completely different. but maybe my knowledge of thermodynamics is indeed iffy.
The thermostat regulates flow at a certain temperature. Lower the temperature by means of a thermostat that opens earlier/at a lower temperature (as in: add more cooling/flow from the radiator) and the pressure drops.

The only reason that the system is pressurised is to raise the boiling point of the water based coolant because boiling produces gas and gas is a poor conductor of heat leading to localised overheating.
Click to expand...
That is indeed what I wrote in my post when I said:"they pressurize/seal the system to bump up the boiling temp of the coolant, like a pressure cooker"

Using waterless coolant (like Evans) allows the liquid to rise to 180c without turning to a gas (boil) at atmospheric pressure, waterless coolant with a low pressure cap = the same or improved cooling at a lower pressure.
The additional benefits of waterless include drastically reduced corrosion and the obvious reduction of stress on pressurised componets, like hoses and headers. The downside is that the flushing and filling process is a pain and it's expensive. Waterless is used in many specialist motors including modern and classic racing applications.
Click to expand...
Another downside is that waterless coolant has a lower heat capacity (waterless coolant is basically pure glycol), reducing the effectiveness of the cooling. And this is quite a considerable amount; water (pure water that is) has a heat capacity that is over 58% higher than the evans stuff. Thats why manufacturers add water to their coolant medium (50% or 70% or whatever freeze standard you use). Its not that they dont know the concept of waterless coolant, as waterless coolant is basically the additive you add to normal coolant (its all ethylene glycol based)

Corrosion is hardly an issue in the bmw engines that fit this cap. Everything is aluminium. If you have an iron block, copper radiator and some other bits of different metals, like found in old cars it can be an issue. but my car (3.0i) is now 14 years old, has done about 100k miles and if you open up the coolant system to look at the inside of the block or radiator its completely new. No corrosion anywhere.
Another reason waterless coolant is popular in classic cars is that they sit more than that they are driven, not pumping the fluid around. Mix that in with the cocktail of different metals and corrosion is accelerated if normal coolant is used. Its a product that is virtually only popular in the classic car scene, but the lower heat capacity makes it not the ideal choice for high performance/modern applications.

In any way this cap has no added benefit in cooling systems with waterless coolants and poses a hazard to premature mechanical failure in pressurized cooling systems. It's very debatable if this cap would extend life of components in pressurized systems.
 
Sorry, but the thermostat has absolutely nothing whatsoever to do with the pressure within the cooling system. It's job is to "contain" the coolant within the block until it reaches the thermostat opening temperature, this is to speed warm up, reduce wear and also for emissions reasons. Once it opens, should the temperature drop below a predetermined point, it will start to close again in order to maintain optimal operating temperature. This is vitally important on modern diesels, as less fuel being burned means they can start to run cold if say, sitting at idle in cold weather (aka my van lol!) None of this affects the pressure within the system. FWIW, a lot of cars now come with electrically operated thermostats, so that the ECU can more accurately control the warm up process and ongoing running temp, and react faster to changes.

Mike
 
If you have a broken thermostat stuck in the open position and you're going for a drive, the coolant will get so cold that you can easily open up the coolant reservoir without it boiling over. How is that not affecting the pressure?
The hotter the engine runs, the higher the pressure in the cooling system. Its called the Clausius–Clapeyron relation if I'm not mistaken.
 
GuidoK said:
If you have a broken thermostat stuck in the open position and you're going for a drive, the coolant will get so cold that you can easily open up the coolant reservoir without it boiling over. How is that not affecting the pressure?
The hotter the engine runs, the higher the pressure in the cooling system.
Click to expand...

Yes, TEMPERATURE affects pressure, the thermostat doesn't. What you are implying is akin to "having no petrol in the car affects the engine temperature"

Mike
 
The thermostat is a vital component in regulating the engine temperature.
Saying that that has no relation to pressure is saying that Clausius and Clapeyron were wrong.
 
GuidoK said:
The thermostat is a vital component in regulating the engine temperature.
Saying that that has no relation to pressure is saying that Clausius and Clapeyron were wrong.
Click to expand...


And so is fuel and oil. The thermostat is designed to control flow, not pressure, but yet again you must be correct. Not worth the time or effort replying to a thread once you have waded in, knowing it all.

Mike
 
Ducklakeview said:
The thermostat is designed to control flow, not pressure, but yet again you must be correct.
Click to expand...
Where am I saying that the thermostat controls pressure?

Let me quote myself what I said so that you can read it again:
GuidoK said:
The thermostat regulates flow at a certain temperature.
Click to expand...

And if you dont think that there is a relation between temperature (regulated by the thermostat) and pressure, do some reading:
https://en.wikipedia.org/wiki/Clausius%E2%80%93Clapeyron_relation
https://en.wikipedia.org/wiki/Antoine_equation
As these guys figured it out a few hunderd years ago.
But I gues they were know it alls too... :rofl:
 
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