Is there a negative effect upon adding new transmission fluid to the old one with out a flush?

There is no negative effects. i am a mechanic of thirty years.

If the old fluid has gone bad for whatever reason, you won’t be “fixing” the problem by adding new… you’ll just be diluting the old crap.

But I don’t see why it would cause problems.

I can only tell you this. A Sgt. in my police department, bought a new Mercury car years ago. and never changed the oil in the engine. When it was low, he just added more.

It was ready for the junk yard in about three years. Gunky engine.

Tedd is correct. If there are metal shavings in your transmission oil now, they need to be removed and fresh transmission oil only….installed.

I’m super broke at the moment. I’m willing to do a tranny flush but I feel a little bit poured out when I installed my radiator. So I’m thinking a quart should be fine four about 2 weeks. What are your thoughts?

Should be ok as long as it’s the right type for the car. There are quite a few different types so check a manual to be certain. Pretty hard to get it back out if the wrong stuff goes in.

Are you changing transmission fluid or coolant? You have me confused.