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Old 05-14-2012, 10:59 AM   #201
Stinger9
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Your coolant loss is too high and if you have any indication that the radiator is leaking, we just replace them in the US because they are only $150 here.
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Old 05-14-2012, 07:46 PM   #202
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Anyone ever try using a expansion tank cap off a 2001 Land Rover? The Rover has a lower psi rating and fit's perfect.
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Old 05-14-2012, 08:10 PM   #203
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They look to be made by the exact same manufacturer. Would a lower psi rating benefit anything? It'd keep the system under less pressure, meaning that it will have a lower boiling point. Would it preserve the expansion tank longer? The only worry I'd have would be overheating.

BMW: 30 PSI
1999-2004 Land Rover: 15 PSI

You may be onto something here if it prolongs the cooling system life; however, BMW chose 30 PSI for a reason. We all know how hot our engines run, it may be that the Range Rover engines run cooler.



By using a 15 PSI cap, you are effectively reducing the boiling point by about 37 degrees F. Note that this does not take into account the increased boiling point properties that the anti-freeze adds, too, which is not much (~15 degrees F).

What is the normal operating temperature of our engines?
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Old 05-14-2012, 08:20 PM   #204
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Zell, you obviously didnt read any of my posts on the cap.
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Old 05-14-2012, 08:22 PM   #205
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Zell, you obviously didnt read any of my posts on the cap.
No sir I did not.
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Old 05-14-2012, 08:29 PM   #206
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Post #23 , #32
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Old 05-14-2012, 08:30 PM   #207
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The Range Rover doesn't run at a cooler temp, i've ran the lower Rover cap for a year now on both my bimmers
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Old 05-14-2012, 08:32 PM   #208
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It would have to be 15psi relative to the atmosphere wouldn't it? Meaning that the absolute pressure would be about 30?
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Old 05-14-2012, 08:45 PM   #209
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Meh, worth a shot. I might just pick one up. Only 11 bucks. But with the improved expansion tank...is it an issue anymore?
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Old 05-14-2012, 08:49 PM   #210
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Went back and read your post Blocked Out,, AMEN!!!
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Old 05-14-2012, 09:08 PM   #211
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It would have to be 15psi relative to the atmosphere wouldn't it? Meaning that the absolute pressure would be about 30?
I gotta be honest , Im not very good with these terms. All I know is that whenever our system reaches an internal pressure higher then 2.0 bar / 29psi (200kpa), the caps inner vale would open and the pressure would be released and maintained at 29psi (200kpa)

The other (E30) cap has a rating of 1.4 bar / 20psi (140kpa) and therefore it would maintain the inner pressure of the system at that level.
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Old 05-14-2012, 09:18 PM   #212
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Gonna buy the E30 caps tomorrow, THANKS Blocked Out
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Old 05-14-2012, 09:21 PM   #213
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You're welcome, just make sure its the same part number as NOT all E30s had that cap. Check the part number. And when you get the cap make sure it says 140 on the bottom of it.
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Old 05-14-2012, 09:52 PM   #214
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So BMW has engineers with years of schooling just for this topic along with all kinds of test equipment. Also factor in real life testing as I've personally seen a fleet of BMW's wired for instrumentation riding around Death Valley when it was 115 degrees there. They've designed there ET pressure relief cap taking into account all the features of our electrically heated thermostat controlled by the ECM. I'm betting most on here could not begin to explain how and why the heated thermostat works.
But with a little bit of high school physics we're all going to run out and buy an ET cap with a pressure threshold of 1/2 of what came with our cars. Does the term unintended consequences mean anything to anyone?
Really, yes we have ET's that split open once in a while, but for the most part if we keep our systems renewed, we do not need to worry about reengineering our car systems in this instance. It would only take one occasion under unusual circumstances to boil out enough water to perhaps overheat our engines before we have a chance to notice all is not right. I'm keeping my prescribed ET cap.
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Old 05-14-2012, 09:53 PM   #215
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I gotta be honest , Im not very good with these terms. All I know is that whenever our system reaches an internal pressure higher then 2.0 bar / 29psi (200kpa), the caps inner vale would open and the pressure would be released and maintained at 29psi (200kpa)

The other (E30) cap has a rating of 1.4 bar / 20psi (140kpa) and therefore it would maintain the inner pressure of the system at that level.
I'm not entirely sure if the stated pressures are relative to the atmosphere or if they're absolute. Relative would make more sense to me. A cap that regulated to 1-bar absolutely would effectively be the same as not having a cap at all
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Old 05-14-2012, 09:54 PM   #216
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I'm not entirely sure if the stated pressures are relative to the atmosphere or if they're absolute. Relative would make more sense to me. A cap that regulated to 1-bar absolutely would effectively be the same as not having a cap at all
You are correct. Gauge pressure, not absolute.
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Old 05-14-2012, 11:50 PM   #217
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You are correct. Gauge pressure, not absolute.
In that case Zell's table is wrong - the right column should be shifted down by 1 bar. In which case even the RR cap would allow enough pressure to build to not have to worry about the coolant boiling at normal temperatures
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Old 05-15-2012, 12:15 AM   #218
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Heaven forbid us dumb high school grads try something the highly paid engineers have all figured out. I haven't found much that can not be improved Stinger, are you an automotive engineer? I could care less for most of them, there's never enough R&D.
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Old 05-15-2012, 12:27 AM   #219
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I don't understand the obsession or desire to tinker with systems put into place by actual engineers. BMW engineers at that. Like Stinger said, a well-maintained cooling system means you'll never have a problem.

Blocked out, have you actually measured your coolant temps while driving? I'd suspect a lower pressure cap would lower the boiling point of your water/coolant and thus cause cavitation which would decrease efficiency and run a higher risk of an overheat. Since our gauges are buffered, you could be well near overheating and not even know it.

Personally, I see no need to tinker with the caps. The resources BMW has on all design specification and internal data is well beyond any information we'd ever have.
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Old 05-15-2012, 12:42 AM   #220
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Heaven forbid us dumb high school grads try something the highly paid engineers have all figured out. I haven't found much that can not be improved Stinger, are you an automotive engineer? I could care less for most of them, there's never enough R&D.
Playing the "I'm really more stupid than you even think card" will not cut it for much. I know you know stuff. And "anyone who pursues learning lots about complex science is an idiot" indicates your respect for education. Your advice therefore is stay ignorant?
Sure I know some stuff can be played around with and even improved. I put in a Stewart pump and poly CAB's and KONI FSD's. But I just urge caution when making snap change decisions around a complex system that none of us completely understand.


Footnote: Engineers are not that highly paid.

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bleeding, coolant, cooling system, diy cooling, expansion tank, lower hose sensor, overheat, radiator, radiator hose, temp sensor, temperature sensor, thermostat, water pump

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