E46 COOLING SYSTEM GUIDE - overheating/coolant/etc
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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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Zell, you obviously didnt read any of my posts on the cap.
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No sir I did not.
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Post #23 , #32
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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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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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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.
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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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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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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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.
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.
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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