Coolant issues
 

So my 2001 SSEI does magic and is making anti freeze disappear. I filled the overflow tank up twice this week. It's not blowing white smoke. The oil is not frothy and there is nothing hitting the ground. Any ideas?

It's eating it, but at a rate that its not producing white smoke.

Do you know when the last time the lower intake gaskets have been changed?

Second changing the lower intake manifold gaskets if the old style has never been changed, and if there no visible exterior coolant leaks, if the coolant gets into your cylinder via failing LIM gaskets, you could ruin your motor, as coolant will not compress in the cylinders, you could easily throw a connecting rod through the block.
The old style nylon 6,6, framed LIM Gaskets are known to fail at around 60k miles and up, I recommend replacing them with the Fel-PRO Aluminum Framed LIM Gaskets.

If you tackle the job yourself, and need links, and or video to help you with the job, let me know.

What about the upper plenum leaking?

Has the vehicle been pressure tested for external leaks?

no upper plenum on a ssei

I stand corrected.......a SC'd engine....

So I am a big idiot. I changed my thermostat here a few weeks ago and insist have had a big bubble in it bi filled it up 2 days ago and now it is happy. Coolant level has stayed the same. Just took an entire gallon of coolant to fill it. Must of had more on the ground after the thermostat change than I realized.

Thanks for updating us on your findings.
I still recommend changing that lower intake manifold gasket if it has never been changed to the aluminum framed LIM Gasket, if you plan on keeping the car for a while anyway, it will fail eventually.

It's not a matter of "if" but a matter of "when" the lower gasket will fail.

Thanks everyone. I am going to see if I can track down the original owners and see if they did it. I am only the second owner of the car so I hope it won't be too hard.