Baffled By A Toilet Ghost!!!

I'm truly baffled here. I'll try to lay it all out and be as clear and brief as possible. I'm hoping someone can help.

I've got a Mansfield 160.

Noticed tank water levels dropping for no reason (approximately 2 inches overnight).

Removed tank and changed the assembly with a mansfield part. New bolts and seal. Problem persisted.

Replaced that part with an old fashioned flapper valve assembly and new flapper, bolts and seal. Problem persisted.

Bought a seal repair kit just in case the new assembly's seat had an imperfection I didn't notice. This repair kit came with a ring, some silicone and a new flapper. Still 2 inch drop overnight.

Read that there might be a suction from the fill tube if it's below the water level. Checked that and the hose is nowhere near the water.

Read that sometimes if you have the water level set too high, the water will find its own level (don't know if I believe that one, but...). I lowered the level 3 times to where now it's almost down to half a tank. Still I lose water.

Thought maybe I'll go back to the mansfield parts thinking maybe I had gotten a bad one. Nope... same problem.

No water on the floor...
No moisture around the back and under bowl...

When I put some blue toilet cleaner in the tank I saw no blue ending up in the bowl... none leaking onto the floor... yet the level still dropped.

Like I said... baffled. Someone please have an answer to this! I've spent the last 4 days at Home Depot and I'm almost at the point of just saying screw it and buying a hundred dollar toilet and installing it. Oh, and btw... house (and toilet) is only 4 years old.

There's a good chance that there's a fact lurking there we don't see.

Did you propagate the blue dye all the way through the water in the tank, or did it just collect at the bottom? I had one of these a few weeks ago where the poster said he used dye and none of it ended up in the bowl. When we found a crack about an inch from the top of the overflow riser, he allowed as how he hadn't mixed the dye uniformly through the water, because he was focusing on the bottom of the tank. So...was all the water in the tank blue, or just some? Did you leave it all overnight and the water still went down but none ended up in the bowl and none on the floor?

As you have adjusted the water downwards, has it fallen 2" each time, regardless of where it starts from? If you left it longer, would it fall more than 2"?

Does it fall to the same place each time? Or is it a firm 2" regardless of where starts from?

This may help us find a solution. I would use food coloring well-mixed in the water to test.

I know that Mansfield has an adapter for its flush valve to help prevent siphoning, but it wouldn't be necessary with a flapper-style valve. When you had the flapper-style valve in, did you have the refill tube daylighted over the top of the overflow riser?

I wouldn't get the $100 toilet. I would stay the heck away from Home Depot, and find someone who would sell you a Toto Drake (original model, CST744E) for around $200, and end up with a great reliable toilet that you'll be happy with and which is easy to fix. You have probably spent the difference in parts already.

Let's diagnose before we buy anything more; I think you have all the parts you're going to need for a while. We just need to figure out what's wrong. Try the food coloring. Turn off water. Leave overnight, see how low it goes. And whether it will go lower if left off longer.

What fill valve does it have?

Okay... before reading these replies I went back to HD and bought a new fill valve and installed it. It had the original standard one that comes with the toilet. It seemed to be fine, but... I bought an HC630 which now that I look at it seems to be brandless. It says "Fast Fill." It's blue and has the lock you can engage to shut off the water. Also comes with a 6 year guarantee. (I now see a small label "Blue Source.")

Anyway... seems to still be dropping. I just adjusted it to fill it to a drawn line I made in the tank. It's around 2 inches below the overflow. I tried it once and after an hour or so it went down about 1 inch, maybe less. I'm going to leave it alone and see what happens tomorrow morning. So... I'm marking my watch: Started at 2:15pm today... I'll let you know where it's at in the morning.

(For the record, I don't think there is anything left to replace.)

BTW... about the dye. Last time I used a blue bowl cleaner. I didn't actually go out and get dye. That's on the agenda for tomorrow. Where can I find a deep colored dye?

It wasn't likely to be the fill valve, based on your description, except if there was a refill tube siphon.

Just use food coloring from the supermarket.

Could your spouse or kids be pranking you?

It's possible that the gasket underneath the flapper valve assembly is bad or the nut holding it to the bottom of the tank is loose. You may try removing the tank and tightening the big nut.

Also, the valve seat where the flapper seals may have some debris on it.

But, if it only drops 2", and never drops further, it's not likely the flapper valve, since if it was, the tank would empty to that point.

If you let the toilet sit say overnight, how low does it go? Where it stops is the level where you want to look for a problem.