does adding extra liquid to a slow cooker recipe change the cooking time?

Every time I make pot roast in the slow cooker, it is done cooking much earlier than the recommended 8-10 hours on low. Usually the meat ends up well done and tough in around 6 hrs. I thought it was a problem with our slow cooker, so I tried a new, larger one today, and made a larger sized roast, thinking that it would now take longer to cook. But when I checked it after only 4 hours on low it was already fully cooked and well done! The only thing I can think might be the reason is that I put more liquid in with the meat and vegetables than was recommended in the recipe. Does anyone know if the extra liquid could be what's making the meat cook so quickly? Or do I just have bad luck picking out slow cookers?

Re: does adding extra liquid to a slow cooker recipe change the cooking time?

I think if you add too much liquid it would def cook the meat much faster. Maybe try making it with the recommended amount of liquid?

Re: does adding extra liquid to a slow cooker recipe change the cooking time?

Next time I will, thanks.
I had thought that the extra broth would make the meat juicier, but I guess it did the opposite.