Hello,
I have a 1999 monte carlo ls with the 3.1 liter engine in it. The car runs fine, but i am having a problem with coolant. After running low on coolant, i flushed the cooling system because black sludge forming on the bottom of the reservoir. After flushing the system, i filled it back up again and in about 3 weeks it was low again. There seems to be no leaks on the driveway. I understand that 3.1 liter GM motors have gasket problems because of the Dex-cool coolant they use where coolant will leak into the oil. However, my engine was switched over to the green coolant by the previous owner, so thats what i filled it up with again. I changed the oil 500 miles ago, and the old oil was black. Now, after 500 miles the oil isn't really blackened it seems more brownish that is why i am wondering if this is the coolant mixing with the oil. The oil level hasn't seem to have gone up, but like i said i would have thought it would have been black after 500 miles of driving. I would like to add that the car runs just fine now, and i need help fast see if i will need to change some gaskets or something simple before something happens to the motor. Any help would be greatly appreciated. If you have any idea of what is going on, please let me know.

Thanks,
Luke

You have the classic symptoms for an intake manifold gasket leak. It's a design flaw in the gasket that can be made worse by Dex-Cool. However, just switching to green coolant will not eliminate the gasket leak problem. Get it fixed ASAP. And, stop using the green stuff. If you don't want to use Dex-Cool, switch to an extended life yellow HOAT coolant.

I put blue devil head gasket stop leak a year ago.It is 60 dollar a bottle
but a year later no leak.I also put motorkote oil additive and the tap noise
from liffter is gone. I only had a small manjfold leak so this may help some people.I dont know about sticking cheap stop leak in because it is more for radiater leaks.

Sounds like a temporary fix to a potentially permanent problem.

I agree. That is a very poor way to fix a problem that is inexpensive to fix in the first place if you do it yourself.

I dont think 1000 dollars is cheap and alot of people cant or dont have a place or tools todo it yourself and i would say a year is not temporary.I will let you no how long it last