overheating

I am new to BMW, I can only say what I have come across with my Petrol 92, 318IS, which had issues when I bought it, It had been worked on by BMW and Diagnostics showed issues that are misleading.
a neighbour has one also he is a BMW Mechanic, he was surprised, how I found the problem I needed solved, he had warned me about Water Pumps and associated parts causing problems.
It is clear that the cars were built to run Motorway, not a lot of Local driving or getting stuck in traffic.
The Thermostat system is set up with a groove on housing and no hole in the thermostat until of course it opens. What actual happens, is the groove gradually gets closed off with the residue, ITS LIKE CONCRETE, caused by short local trips, why BMW install a 92-94 deg opening temp thermostat. that means when it goes on short trips the Thermostat for the Top of the Engine does not get Coolant, when repaired mine, there was less than half a cup of coolant came out, yet the reservoir showed it was OK the Rad was OK. I normally only have old cars as I restore old Cars and Bikes, thermostats even on the earliest alloy engines back in the 70's the Thermostat opening temp was from as low as 78 but generally around 82 - 88 max degrees, the other point was they had 3/32" hole in them at the top, which had a small waxy type float through it this asured that it did not block up and also allowed coolant in even on short trips. I changed my thermostat which was NEW and installed by BMW Dealership for a lower opening temp.
Regardless of what Diagnostic print out say, Lift the Hood, after a short trip and if the Top of the engine seams hot, too hot too touch, THEN IT IS NOT GETTING COOLANT, the other tell tail sign is the Fuel Lines getting SOFT, injection fuel lines and vacuum lines are fairly stiff. The thermostat can be removed completely mind you have to put the housing and hoses back on; until you get one.
A few things that happen when Thermostats don't function; 1) It puts pressure on the Gaskets, and Water Pump, it does not always show up on Dials or Diagnostic Checks. and 2) in the case of Fuel Injected engines, which most are now, it causes sufficient heat up and around that area that the Fuel is vaporising in the fuel lines that are being heated, SO THE PETROL PUMP IS GOING CRAZY trying to get fuel into the Engine to make it run.
It is only when there is a Failure of either the Coolant or Fuel system that the Actual issue shows up.
The previous owner to my car, was told the Problem was Timing Chain and Adjusters, BECAUSE THAT IS WHAT THE DIAGNOSTIC CHECK SAID IT WAS, THE BILL WAS TO BE IN EXCESS OF £700 TO GET THE TIMING REPLACED.
Quite often it is good to look at the old fashioned way about tracking down problems, a £10.00 THERMOSTAT CAN CAUSE AN ENGINE SIEZURE OR AT LEAST MAJOR COSTS, and when they do go, it is always when it is raining or on the motorway or in the middle of rush hour traffic, never outside you house. BMW it seams do have have a Historical Issue with failing water pumps and thermostats, If I get another after my present one, I am taking the thermostat out and put in one that I know works, or out all together, Living in Scotland we don't get a lot of heat or long summers, so having the car always warm inside is not an issue.
Jimmy