I try to go for top speed in my e39 540 i bmw but it gone only for 210 so why ?

the output speed sensor is located on the top of the drive extention housing. See:
https://www.realoem.com/bmw/enUS/showparts?id=DD63-USA-04-1998-E39-BMW-528i&diagId=24_1882
item 4

Studebaker Silver Hawk

Sounds like solenoid switch,which is in top of the starter is bad or possible starter gone bad.

bmw have twin turbo
when move from first to second could be possible
check engine and gear box oil

Speed sensor might be gone

DID the top just stop? Have you lowered it before? If you have lowered it before then I am sure you are doing it correctly (parking brake set) Go to a place that is familiar with repair convertible tops. Like the dealer or a bmw specialist. they should charge a couple hours or less to tell you what is wrong. You can try a couple of things yourself but even for an experienced mechanic it is difficult. If they have a bmw code reader and not a generic one, it may tell you what sensor or motor is at fault. Sometimes the switch itself goes bad. Try pushing farther down on the switch or apply pressure at an angle on the switch. That will only work if there is a bad contact on the switch, and if it works you have a bad switch, but I doubt it. Go into your manual or online and it will give you information on how to lower your top manually. When you lower your top manually you disengage the motor (which is in the trunk). Then you could try to engage the motor and see if it will lift up and close. Sometimes this will re-time the top and that is all that is needed. Otherwise get it to the dealer. If your mechanic wants 1000 he does not want to fix it or does not know how. The motor may cost a 1000, but usually it would make noises or poop before going out and most repairs are sensor related. Hope that helps

I would say no more than 210 F, Say you have a thermostat listed at 185, or 195, they open up at that temp, the engine under normal driving will run between 195 and 210, you really don't want to see 250. even though coolant boils at 265+, in a pressurized unit, and some cars are supposed to run that hot, I don't like the idea. Hope this helps.

mostly these happen when your suspesion is gone, get your car checked the suspension need attetion

Unfortunately there are several possibilities that are common to causing the light to come on. I would suggest taking the car in to a dealer and having them read out the fault memory. Such possibilities are a failed speed sensor, a binding DSC/ACS actuator cable, or faulty DCS/ASC control unit. If you know how, you can disconnect the speed sensors, and check for voltage output across the the terminals inside the connector going to the speed sensor while rotating the wheel. A dealer should charge you about an 1hour fee to check out your system. Due to the cost of parts involved, I would recommend having it checked before just guessing.

You have oil leaks getting on the exhaust system, they are getting into the car, have the car checked over to find source of leaks.