Thonburi is an active train depot so you will walk along mechanics and technicians accomplishing their real job and not some fancy shiny museum. It feels very real – I could almost hear the steam whistles!

"There are more steam trains left in Bangkok than one would imagine, you just have to know where to look. If you too are passionate about these magnificent pieces of Thai history you would take the time to check behind every wall, inside every old building and under every bridge of Bangkok, just as I did. So far I have spotted five different locations in Bangkok and two outside where these massive machines are still standing in perfect condition,..."

"Makkasan Depot is my favourite spot to find hidden trains in Bangkok, but also the most frustrating since access to the train depot is not allowed unless you go through a lot of official paperwork. Makkasan Train Station itself is an old, small but still active station dating from the beginning of 20th century and almost frozen in time. What is more interesting is the gigantic land located behind. For many years, several large steam engines were left here to rust in the open and, despite being fairly easy to spot from the expressway when driving from Suvarnabhumi Airport, very few people paid them any attention."

"The only steam engine left at Hua Lamphong Station is not really hidden but can be easily missed unless you know where to look, at the end of the leftmost platform number 25. The old architecture of the station itself is worth a visit. The engine in display is a Hitachi built in 1935."

Full http://www.bangkok.com/magazine/steam-trains.htm

I don't know why but Asian built trains don't appeal to me as much as a British or American built train.

But everyone would have to agree that some of the
American trains were the best and most powerful in the world.

This one at Phnom Penh train station is worth a look

In the 1980s and 1990s SRT used to run steam train excursions up to Ayudhya. Sadly I no longer have the photos but the turnout of the steam engine was magnificent - polished brass everywhere and not a single leak in any steam pipe. I wonder if there are still any engines in working order that run excursions now?

I think they may do do special steam train trips to the Bridge on the River Kwai in Kanchanaburi. I don't recommend Kanchanaburi as a day trip or overnight trip from Bangkok though, I found it overtouristed and not worth the effort.