Ok so here it is.
1993 seville sts, 4.6 northstar 149,000 miles.
I am 3rd owner of this car. I have had it about 6 months. I have only put about 5k miles on it. Been in and out of the shop for ignition problems and a lot of vacuum leaks. I don't know when(if any) maintance was done on the coolant system.
I got the car, check coolant level, it was low added about a gallon. drove it a little bit (300 miles) everything was fine. Changed oil, checked trans fluid, etc... all good. Until a few weeks ago. it's been local driver (ignition problems) now it's a daily driver. 200 miles a day.
I had intake gasket put on it about 2 weeks ago, prior to that. I added about 1 1/2 gallon of coolant. now i have added about 2 gallons since the intake gasket.It's been about 2 weeks since the intake, about 2k miles. The low coolant light comes on and it takes about 3/4 gallon. So a total of 3 1/2 gallons in 6 months, 5k miles.
No visable leaks. I park in the same parking spot at work and at home, no leaks on the ground. I have been all around the motor with a light, nothing. No coolant in oil or trans fluid. The coolant is bright green when I top it off. There is no puddles, no white smoke, or sweet smell. It doesn't overheat or run hot. The passanger side floor is dry. 192 degrees the whole time it's running.
I have seen very small ( 1/8 " ) particles floating in antifreeze when I top it on, a few 2-3
I heard on the northstar motors, when the head gasket goes, the coolant and oil don't mix ???
Oh.. I had pressure test done on system 2 days ago. 15 psi held for 25 mins with no dropping off at all....
ANY IDEAS ???