Spring Forward this weekend! Another reminder that we've survived another winter, although in Southern California we have it easy. We did have our share of cold snaps, and rain (which we need) but now we get to deal with beautiful warm days which will become hot, edge of desert broiling.
Heat is tough on our cars as well--the internal combustion engines which are the mainstay of our daily transportation operate on the edge of disaster. They need to be up to 190-200 degrees Fahrenheit to operate with reasonable power, but beyond that the materials of which the engines are made start to do bad things. In other words, it's a compromise between efficiency and slag.
Most modern engines work at 1 bar pressure, roughly 15 pounds, which allows the coolant to resist boiling at the top of the temp range. BMW, however, has been raising their coolant pressures to 1.2 bar, 1.4 bar, and most are now up to 2 bar. The higher pressures at these temperatures put stress onto the cooling systems--we see this in the number of replacement expansion tanks we sell, as well as hoses and other cooling components. In fact, we sell more BMW reservoirs than all the other cars we deal with combined. When I get a call on a coolant reservoir, my first thought is "what kind of BMW do you have?" There are several different designs and part numbers used on various BMW's. and we sell them all. In most cases, we can get both the original factory brand, and alternate manufacturers' replacements, usually at a lower cost. (We do stay with manufacturers that we are familiar with and have a good service record with.) We also have or can readily get most thermostats, coolant caps, hoses, and other related components for most of the German and other European cars. We also carry an assortment of the VW black plastic coolant connectors and housings at significant savings; we do appreciate samples as do find things on cars that are not clearly cataloged.
We also recommend the use of specific factory coolants. There are several families of chemicals which are used or not used on different cars and engines; it is not only a case of heat transfer capacity, but compatibility with the variety of increasingly complex alloys used in the engines, radiators and other components. When we first started seeing aluminum heads on Mercedes engines some years ago, when there were not a lot different coolants supplied, I recall seeing cylinder heads we had removed for service with beads of coolant weeping through the aluminum combustion chambers like they were sponges.
We normally keep in stock the factory coolants, in original trademarked containers, for Mercedes, BMW.and Mini, in gallon jugs of concentrate. VW/Audi has just come out with a G013 coolant that they are listing for all watercooled engines, which we also have in the factory gallon jug. We also carry Pentosin coolants that cover most European cars. We also have or can get the specific factory formula coolants for Asian vehicles as well. 
