Recently I replaced the LIM and UIM gaskets on a 3.8L. The 3.8L was in a recently purchased Bonneville I purchased at night in the poring rain at a Virginia new car dealer.
When I brought the Bonneville home, I noticed coolant pooling on the ground. Later took out the pressure tester and found a leak on the passenger side of the engine. Could not clearly tell if it was a coolant elbow or LIM gasket- I replaced them all.
I also replaced the coolant overflow container. I cleaned the coolant overflow container on my Son'* S10 last year- it took me all day. I asked myself why are the insides of this newly purchased Bonneville and the S10 so nasty- yet on my 2001 SSEi with 230k miles it is spotless inside?
I am speculating that when coolant leaks and/or air gets into a cooling system running DEX, over time a lot of souring of the coolant takes places which in turns leaves nasty residues and deposits. On both the new Bonneville and S10- they were purchased with leaking LIM gaskets and likely were leaking for a long. On the SSEi, although the highest mileage of the three, the LIM was changed very early and there was never a coolant leak or air introduced into the cooling system.
Here are pictures of the before and after coolant overflow tank. I sense a dirty coolant tank on a DEX coolant vehicle might be a indicator of a vehicle being run with a coolant leak over many months/ years.
Also I am inserting a link to a Bonneville for sale on CL, I sense it to has had a long term coolant leak looking at its coolant overflow tank- all possible signs of neglected service and maintenance. The seller of this Bonneville cleaned up the engine cover and air box- but the coolant overflow tank tells a very different story of how this car was (not) taken care of:
2001 Bonneville SSEi, 219,000 miles.
Whats in my driveway:
1998 Chevy S10 4x4 ZR2, 1999 Olds Bravada, 2001 Pontiac Bonneville SSEi, 2007 Ford F-350 regular cab 2WD, 2008 BMW 335i coupe (Wife'* replacement for her Bonneville). The Bonneville is my favorite of all the cars in the driveway.