1996 Cadillac Seville SLS - with Northstar System Over heat problem

Try bleeding air from system like this remove cap from overflow tank fill with antifreeze to full mark leave cap off and start vehicle and let idle you will notice level in tank start to rise this is normal once thermostat starts to open level in tank will drop add more antifreeze to full mark then put cap back on. No promises but I hope that it will work for you.

You may be the latest victim of the infamous Northstar head bolt fiasco.

Thank you firebird338! I have actually done that too but when I did it I used water to refill and it did NO GOOD at all. It seems to hold out longer when I add that orange antifreeze but that stuff is expensive. I can not figure where it is going to either....unless it is simply boiling out of the overflow while running down the road. There seem to be NO puddling under the car when parked hot and sometimes it does not disappear for days and other times it is gone is an hour or two. It is really a mind bender for me.

Boiling the water out of the system is indicative of a leaking head gasket. This may not show up when the engine is cool. Look up the Northstar head bolt issue if you don't believe me. There is a fix but it is expensive.

O, another thing my mechanic has now added those pellets to the cooling system twice and so far we can not see that they have had any effect at all. I have noticed that it seems to help if I keep the RPM's up to around 2500 so I manually shift from 1st to 2nd to 3rd and drive in D only after I get up to speed on the open highway. On city streets, I have been keeping it in 2nd and 3rd most of the time. That helps to avoid the overheating but man it is murder on the gas mileage.

Thanks again for the tip regarding the head bolt issue. I have read that a few different place and it may be the case but I keep hoping it is not.