I hate to do this again. I'm getting really tired of asking questions. I'm simply not finding the info I need anywhere.
When I bought this 2003 STR, the previous owner had a new expansion tank, electric water pump and hose fitted.
Even though the temp has been rock solid, I suspected I was losing coolant somewhere.
This afternoon, I found that the lower hose connection to the expansion tank was dripping and could make it drip more by rocking the connection.
I pulled the tank out and found an O-ring in the hose. It looks to be ~17mm ID/ ~23mm OD.
I reinstalled hoping maybe the problem was it wasn't seated right, but no change. I tried a slightly bigger O-ring and it leaked badly.
What's going on here? Should I be able to rock this connection? Perhaps wrong hose/O-ring?
Sorry for spamming the forum.

 

Check the original O-ring very closely using a magnifying glass to see if it has any flat spots on it or any slight nicks or casting defects that would cause it not to seal. If you do not see any defects put a little dielectric grease on the O-ring and re-try. If this is the hose that has the Metal spring wire retention clip huh make sure that fitting is completely inserted such that the spring clip snaps in and holds it in place. I know that hose is hard to reach with the tank in place so maybe it’s not being all the way inserted. If none of that worksGo and buy a bunch of different O-ring kit’s to try to find the correct O-ring for that tube

 

I had the same issue with a new oem o ring. Used a little perfect seal on the o ring and problem solved. Rocking the tank will not even make it leak

 

Thank you for the reply. The O-ring looks new and I've refit a few times, making sure everything is on and the C-clamp is clicked in.
The fit doesn't feel positive...too much wiggle room. I'm suspecting the mechanic used an LS/Dorman hose or something?

 

What's perfect seal?

 

a liquid gasket maker seal stuff in a plastic jar. Now it may go by aviation form a gasket. If Karl sees this he will be able to explain better. Make sure the hose is not in a bind and lines up square with the tank nipple. It should pop on easily if lined up correctly

 

I've had minor issues there but mostly by not clipping the hose in correctly. It can fool you by appearing to be in place. Not much room to move in there and does require very careful checking that its clipped on.
I also recently noticed I hadn't tightened the LH side thermostat housing torx screw enough and had a tiny leak where the housing meets the engine. It was causing a fine coolant spray all around that area. I could only move the torx screw a fraction tighter but it does seem to have stopped the leak.

 

I found it. Good up to 400F and is resistant to glycol. How did you apply it?

 

Any chance the fitting or tank tube is damaged?

 

The fitting could be damaged even though it's new. I'm not sure what to look for other than seeing if it's a positive connection and checking the O-ring.
I knew some people here must have been through the same thing, seeing as how the expansion tank is a common problem with these cars.

 

brush it on evenly around the tank connector nipple. Let it dry no more than a minute and assemble. If it gets too tacky to slide the hose on, clean it off with acetone and start over. No need to apply to the o ring because the o ring will grab what is on the nipple and create the seal

 

I installed the tank using a slightly larger O-ring and a thin layer of Permatex aviation gasket maker.
No leaking so far. Thank you so much for all of your replies! Thanks, Scott for the Permatex tip!

 

Glad to help and always welcome. You will find the permatex sealant useful for a lot of applications. Especially for rubber and tiny imperfections