The offset varies, but most low offset wheels work well, from about 10-25mm Some of the AMG and other tuner wheels from back in the day were even lower offset (0mm!) PCD is 112mm

Temperature wise, it should stay at about 80-90 when warmed up. It sounds like your thermostat is duff. You might find that the car behaves fine after changing it, as when the engine is colder, it'll be running rich.

Fuel shouldn't be getting near the throttle body, you are probably seeing the residue of the blowby gases/oil collected in the throttle body/air meter.
If you want to clean it out, use some carb/brake cleaner and plenty of rags.

Make sure you aren't using the 'E' Setting on the gearbox, use 'S'. This doesn't mean sport, it means standard. E will never use first gear, whereas S will if you floor it. Other than that, the switch doesn't do anything else to the shift points etc.

Cheers,
Ben

Ah ok, ill give that change, and the coolant flush, hoping this will help it a bit! The only thing I am worried about is overheating in the south of france, if we get caught in traffic! Yep the E setting is not fun! Especially when your trying to pull out on a round about!

Thanks for the advise mate, ill get onto Gsf and get a new t/stat!

Do you have pictures of the car?

Once the problems are sorted, you may find, if the car has not succumbed to rust nor rot, you have a safe, comfortable car that could last you for hundreds of thousands of kms. 139,000 is NOTHING for a well kept 6 cylinder one of these cars.

I have always been bewildered why, in your country, these fine cars have never received their proper attention and adulation. "Crapheap" indeed? A Renault Clio is more worthy of that moniker. In your country my observation is that cars are discarded like used tissue paper every 2-3 years. Because of the MOT tests, or for whatever other reasons, vanity, the strange "company cars" phenomenon, or whatever....

A W126 Merc is the opposite of all that, it is engiineered to last decades.

YOu may find you want to keep it. Also, have a look at www.benzworld.com in the W126 section, which has been acclaimed to have the most intense worldwide focus on these models. I am a moderator there and would welcome you. But if you sign up, don't do so as Crapchallenge, your welcome could be chilly.

Good luck in your endeavors.

__________________
1991 560 SEC AMG, 199k <---- 300 hp 10:1 ECE euro HV ...

1995 E 420, 170k "The Red Plum" (sold)

2015 BMW 535i xdrive awd Stage 1 DINAN, 6k, <----364 hp

1967 Mercury Cougar, 49k

2013 Jaguar XF, 20k <----340 hp Supercharged, All Wheel Drive (sold)

I'm not that familiar with the 6 cyl engine, but before you place an order, check to see if you have the plastic thermostat housing. If so, order one of these at the same time as they are prone to cracking at this age.

Cheers,
Ben.