Because I am new to working on cars I expect a few mess ups and problems.
A week ago I decided to take everyone'* advice and change the thermostat to a 180 degree.
I got the thermostat, o-ring that fits around the thermostat, and I got the gasket for the hose to block.
After the change I found that the car is losing coolant due to the overflow tank getting lower and lower.
It take about 3 days to lose all fluid in the overflow tank and I don't see a drip or anything left in my garage on the floor. What did I mess up when I installed it? Do I need some liquid gasket or something.

Please help me I don't want to take it to a radiator shop.

How much coolant leaked or drained out when you did the thermostat change?

The same amount that the car borrowed from the overflow tank perhaps?

Well I have refilled the overflow a couple of times after the install so as to not let it get too low. so i'm not sure that matters. So now what?

That might depend on what engine you have. Can you put your year and trim level (SE, SLE, SSE, SSEi) in your signature?

Alright I have a 95 Bonneville SE non/SC Series II
Here is a little more stuff to go with this mess up
To get to the bolts on the hose fitting above the thermostat I had to pull of two small hoses
I believe they may be vacuum lines of some kind and when I pulled back part of the line came undone. a little silicone looking fitting was cracked and broke when I pulled back.
I just used old fashioned duct tape to fix it, could that be the problem?

Thanks for any help that I recieve

Well that'* interesting you say that, before I decided to go and mess things up worse I noticed I was having to refll the overflow once a month because it was pretty low. The intake failed at 160k miles and I am now at 201k miles. But the only thing now is that is loses that much in days instead of 4 weeks

What do you think now?

check your oil cap and dipstick when cold, do you see any milky looking crap???, is your
oil over full????

Check your oil dipstick for any coolant. How is the car running, any white smokelike exhaust?

Look around the thermostat area, ensure there is no coolant leaking. Ensure you closed the radiator petcock/drain ****.

Read the material JR's3800 put in the link above. It could be the difference between thousand or so dollars of repairs or a little over a hundred

Did you install a typical intake manifold or an updated version?