so that is my question in a nutshell, will the tanks from the same year dt175/dt250 be interchangeable?

.

What year DT250?

.

.

1975

are they the same size , same tank just with differant graphics

.

I've not tried that particular interchange, but I'm very doubtful you can switch them.

The 250 tank appears much longer, and has a capacity of 2.4 Gal, . . . whereas the 175 tank only holds 1.8 Gal.

.

.

oh that would have been a good indicator
thanks

Generally the 125/175 are interchangeable, and the 250/360/400 are interchangeable. The former are slightly smaller framed bikes and the parts are too.

I'm glad you said "Generally", because I know of a 125/175 exchange that won't work .... even though they are both within the same model year.
I also found that a 78 DT175 model tank will not fit my 1981 DT175, even though the external shape and dimensions are identical . . . Yamaha went and slightly changed the mounting locations.

.

.

I think that generally needs to be added to almost every statement we make about these bikes

The side body panels from the 77-78 DT125/175 don't interchange with the 1980 125/175 either! They LOOK the same, but mount differently. I am surprised that there is one of the same model year that does not fit.

My guess is the USA 125 and 175 tanks might not interchange somewhere in the 1974-1976 era...

From 1969 to 1973 the frames and engine mounts were pretty much if not completely identical between the 125 and 175.

The 175's got the new engine design with different mounts in 1974 while the 125's stayed with the earlier AT/CT engine mounts (and the electric start engine). That means that between 1974 and 1976 the 125 and 175 frames are different... so my guess is it's in this era that the 125 and 175 tanks could have different mounting...

As said, the first year 1978 monoshock has some differences from the 1979-81 models... but I think the 125 and 175 were back to sharing the same basic frame/motor mounts like they did from 1969-73.