Class 175s to Great Western Railway (GWR)

[whole diary]

[johnneyw]

Saw my first 175 in GWR^▸ (Great Western Railway) territory today at Totnes station just as I arrived at about 13.30.  It was Exeter bound and running about 8 minutes late.  20 mins later boarded my first refurbed XC^▸ (Cross Country Trains (franchise)) Voyager... reasonable enough but they still seem not to have sorted out that unpleasant air in the carriages containing the WCs^▸ (Wiltshire Council (Unitary Authority), was Wiltshire County Council until March 2009).

[Chris from Nailsea]

You can't polish a turd: Voyagers are crap.

That's only my personal opinion, based on experience, by the way: not an official view from the Coffee Shop forum.  CfN^▸ (Chris from Nailsea, an administrator on this forum). 

[REVUpminster]

175116  to Laira today. Delayed for 70 mins near Acton Wells but arrived 8 minutes early at Laira

Ely :3: 175005/008, 175104 (175008 is in two halves)

Wolverton :9 : 175004, 175102/103/105/106/107/108/109/110

Laira : 14: 175002/007/009, 175114 ex Ely; 175001/003/006/011, 175101/111/112/113/115/116 ex Wolverton

Long Rock : 1 : 175010 ex Ely

as of 28 May 2026

[trainbuff]

20 mins later boarded my first refurbed XC^▸ (Cross Country Trains (franchise)) Voyager... reasonable enough but they still seem not to have sorted out that unpleasant air in the carriages containing the WCs^▸ (Wiltshire Council (Unitary Authority), was Wiltshire County Council until March 2009).

They are what they are

[trainbuff]

You can't polish a turd: Voyagers are crap.

That's only my personal opinion, based on experience, by the way: not an official view from the Coffee Shop forum.  CfN^▸ (Chris from Nailsea, an administrator on this forum).  :

- But you can roll it in glitter!



Edit note: Quote mark correction, for clarity.  CfN.

[plymothian]

175s use a similar effluent system to Voyagers; the waste is stored in an upright tank behind the toilet rather than slung below and some stink as bad.

[TaplowGreen]

175s use a similar effluent system to Voyagers; the waste is stored in an upright tank behind the toilet rather than slung below and some stink as bad.

So whilst you can't polish a turd, you can store them on board the train.

[JohnM]

175s use a similar effluent system to Voyagers; the waste is stored in an upright tank behind the toilet rather than slung below and some stink as bad.

AI's view...

The Voyager "Boiled Sewage" Flaw

The severe odor issues on the Voyagers came down to an incredibly unfortunate layout of the underfloor components, combined with a bad choice of location for the climate control system:

• The Heating Problem: On the Voyagers, some of the engine exhaust piping was routed directly alongside or underneath the Controlled Emission Toilet (CET^▸ (Controlled Emission Toilet)) retention tanks. In the summer—or when the engines were working hard—the extreme heat from the exhausts effectively "cooked" the raw sewage inside the tanks, causing intense gas build-up and a foul stench.
• The Intake Problem: To make matters worse, the fresh-air intake vents for the passenger saloon’s air conditioning system were located under the chassis, right in the vicinity of those heated effluent tanks.
• The Result: The air conditioning system regularly sucked in the escaping sewage fumes and actively pumped a concentrated aroma of warm, stale urine and sulfur directly into the passenger cabins, particularly around the vestibules.

Why the Class 175 Avoided This

While the Class 175s were designed and built at roughly the same time (late 1990s to early 2000s), they were manufactured by Alstom, whereas the Voyagers were built by Bombardier.

Alstom's packaging layout underneath the Class 175 frames was entirely different. The effluent tanks were isolated cleanly from the engine exhausts, and the air conditioning pods were mounted on the roof rather than drawing air from beneath the chassis. Because of this, the 175s generally smell like a normal train inside—their underfloor issues were strictly mechanical and flammable, rather than olfactory.

[plymothian]

Yeah the 175s avoid the cooked sewage problem, but there is a stale urine smell on some units, probably linked to their storage.

[JohnM]

Yeah the 175s avoid the cooked sewage problem, but there is a stale urine smell on some units, probably linked to their storage.

Don't know if this ties in with your observations (and it might just be making stuff up, wouldn't be the first time...):

My previous breakdown missed a specific flaw that is very real for the Class 175s.

They absolutely do have their own distinct effluent tank smell issue, and it comes down to a different design vulnerability than the Voyagers.

On the Class 175s, the problem is caused by the underfloor air conditioning condenser units. Unlike the Voyagers (which sucked air in from under the chassis), the 175s have their fresh air intakes on the roof. However, their air conditioning condensers—which handle the heat exchange process—are located on the underframe.

Because of how Alstom tightly packed the underframe components, these condenser units sit directly adjacent to the toilet retention tank breather vents. When the train is in motion, the aerodynamic pull around the underframe creates a pressure differential. The air con condensers end up pulling the vented air directly from the effluent tanks and circulating it through the cooling systems. The result is a highly localized, distinct sewage odor that regularly sweeps through the passenger saloons, especially when the toilets are heavily used or the tanks are near capacity.

It turns out both fleets suffer from toilet odor issues, just via entirely different engineering headaches—Bombardier cooked the sewage from the exhaust, while Alstom's layout caused the cooling system to accidentally draft from the tank vents.