Please help coolant tee

So today was the day I changed the leaking coolant tee in the Passat. Got everything torn apart and cleaned up and put back together. I guess everything was going to smooth. Cause it went way faster then expected. Skip ahead a couple of hours and a check under the car to see if it was leaking and guess what. It was. Nice little drip drip drip. Opened up the hood shined the light through all the hoses and what not and you could see it dripping down the back of the block. Got my hand back there and could feel it dripping from the bottom of a brand new tee. So I got the car turned back around the the tandem pump back off. I’m waiting on a new tee before I take if back off the block

So here is my question. Is there anything that I can put on the new coolant tee and that O ring to help it seal all the way. Cause I really don’t want to do this again for a third time. Any help would be appreciated. The parts store at the stealership is open tomorrow. According to there website so I’m hoping they have a new tee and I can get the car back running tomorrow.

Thanks

If you have the tandem pump off, and all lines secured up out of the way, there isn't much there to cause you difficulty - the oring should be fine on its own, provided the mating surface is clean and dry, and nothing gets caught between the coolant manifold and the head upon installation.

My guess is that when you get it off again, you'll find that something got caught between the manifold and the block, or that the o-ring slipped out of place.

If you want to be extra careful, you can put a thin skin of permatex ultra grey silicone sealer on the oring, but it shouldn't really be necessary.

You'll need another tandem pump gasket as well...

Couple tips:

Aftermarket coolant flanges are often so bad they do not seal right away. I have run into this enough now that I only ever use OEM ones from Volkswagen, ESPECIALLY on the BHW due to the location and work involved in getting to them.

You do not need to remove the tandem pump to get this flange changed. In fact, I actually find it easier to do the flange first, and then the pump, if I am doing both.

If there was a leak caused by oil seepage, or worse, fuel seepage from the tandem pump, there is a good chance that either the small coolant vent hose is bad (goes around from the nipple on the head around past the fuel filter to the pipe near the glow plugs) or the hose from the lower part of the flange to the oil cooler on the engine. This is siamesed with another cooler hose, and sold as an assembly.

I always take the throttle flap off when doing this job, as it makes it easier to get in there and see what I am doing.

It was coolant leaking no doubt. got my hands back under the coolant flange and could feel it dripping. I could put my finger on the bottom and stop the drip. The flange was OEM from the dealer. The block was clean and dry. Got the old flange off Friday night and let it sit all night and until about 10 the next day and then wiped it off again. I double checked everything was clean and dry before I put it on. Not sure how you find it easier to change it with the pump in. It was a pain with it out. I read later on on Sunday that it is 7ft/lbs on those bolts so I actually tossed the torque wrench on the bolts and they were not at 7 so I got them there and so far so good I think. There was no puddle this morning. I may change the tandem pump gasket again since I took the pump back off to get to the flange on Sunday afternoon. The gasket was brand new Saturday afternoon and was only on the block for less then 12 hours. So I reused it due to it being Sunday and nobody was open that had that gasket. I may change it again since I have gotten good at taken it off and putting it back on.