I am nervous. I am only doing this till my heart is content that everything is working fine. Few people on here, whose opinion carries weight, have suggested not doing this. YOU, made me nervous. lol.

Wow , I'm sorry I have revived this old thread now. lol

I ended up grabbing the original 2bar cap... New hoses , new expansion tank.
New hoses because when changing the expansion tank , the quick connects did not seal anymore , I was forced to order all new hoses. So basically with that logic , every time the expansion tank fails , the hoses need to be changed????? 200-300$ extra.
How possible is it that it's the cap (vent) that fails and makes it impossible to vent out the pressure? Maybe it's as simple as changing the cap every 2 years as a prevention work. 20$ :dunno: :dunno:

I use the 1.2 bar cap for almost a year now. "0" issues so far, even in hot temps during summer. I checked the coolant level oddly enough last weekend, and it was at the same level it was at the end of summer.

To JCL: if BMW would have placed a 4 bar cap, would you run that one too? Just curious.

If BMW had installed a 4 bar cap from the factory there would logically have to be some other reason for it, since the system wouldn't normally get to those pressures. But if it was factory supplied then I would expect that the cooling system was designed for those pressures and that all components subject to higher pressures were validated during the development phase. So yes, although it is an artificial example, I would leave it there.

I used to lead an engineering product development team for a tier 1 automotive supplier. Automotive components are usually spec'd for a reason. The important thing is to know the reason for a performance spec before attempting to redesign a portion of an integrated system. Always watch out for unintended consequences.

Radiator caps used to be ne of the regular things changed when a cooling system was being repaired, back in the day. They were considered a maintenance item. I used a radiator cap pressure tester as part of every cooling system check, to check the seal and the release pressure.

These days, a cap failure is more likely to be caused by improper coolant, deposits, hard water, and so on, IMO.

BINGO!!!!!!
So they (BMW) have the SAME 2 bar cap for all model range cars built between 1997-2003, but not so for different other years. One more thing to make this confusing is the fact that the 2 bar cap was used on 4 cylinder, 6 cylinder and 8 cylinder engines. Each with different temperature AND pressure related specs for their cooling system. Enter the bean counters, and the result is: use the 2 bar cap for every model lineup, no matter the engine displacement, cooling spec etc. It's much cheaper......
And I think even for the v8 the 2bar cap is overkill. Also loosing coolant slowly might allow you to salvage the engine vs. a sudden rupture of any of the cooling components with a total loss of coolant. The temp needle and the "gong" will be there in both cases.
just sayin'

I don't understand your point.

If a 2 bar cap was used then components like the expansion tank would have needed to be validated against that expected maximum pressure. The operating pressure will be different for each model, as you say, but what does that have to do with designing, building, and testing the expansion tanks to handle 2 bar plus a safety factor? It would be far cheaper to have one expansion tank spec than a different one for each model. The bean counter argument works in both directions.

The system was designed to have a 2 bar cap. It worked that way for 6 years of production, according to your data, and has worked for 10+ years since then. If a failure occurs now, it is not likely a design issue, or a manufacturing issue, but a (lack of) maintenance issue. Latent design issues don't hide for up to 17 years and then jump out to bite you. And putting a lower pressure cap on it is just a band aid designed to cover up poor maintenance practices and low quality aftermarket parts, IMO.

My parts are all new, and OE purchased from Open Road BMW. Even the e30 cap.

Then you should quit worrying.

Again and I'm glad Slick chimed in, as well as Dorin. I understand and agree with JCL that it was spec'ed for a reason, but I still will most likely switch to an E30 1.4 bar cap down the line. My M54 doesn't get run in the Arizona desert, and even after running in the summer and shutting down when hot, my pressures won't rise high enough to 2 bar, or even come close to 1.4 bar.

My hoses, expansion tank, t-stat, are all new and my coolant is filled to proper level with 50/50 mix. The first thing like I said earlier in the thread, be sure your cooling system is up to snuff first, coolant cap pressure should be last thing to worry about.

I'm not gonna argue in here with the others, but there are members running the 1.2 or 1.4 bar (in Slick's case) cap with not a single issue whatsoever, no losses of coolant anymore than before they switched the cap, so this tells us that the system pressures don't go anywhere near the 1.4 bar E30 cap, let alone ever get to 2 bar.

Point is, if the system is getting enough pressure to vent at 2 bar, you better be pulled over with the car off bc you have bigger problems.

Since I would never let my system get up to those kind of pressures, I have no issues using an OEM 1.4 bar coolant cap in the future, or a GAS 1.2 bar cap as well.

It's not about "using the correct cap", its about making sure your system is up to snuff, parts wise, mixture of coolant wise, etc. Like I said prob on the first 1 or 2 pages, REPLACING THE COOLING CAP IS NOT A SOLUTION TO ANY PROBLEM WHATSOEVER. But as Slick has shown, and many many E39/E46 members have shown on forums outside of Xoutpost, there are no negative effects to lowering the "safety valve" on our cooling systems to 1.4 bar with an OEM BMW part.