I just purchased this vehicle over a month ago… It drives very smoothly, but right after I got it the check engine light came on. I took it to the shop and one of the spark plugs was misfiring so they changed all the spark plugs. My temperature gauge sometimes reads about a 1/4 of the way above the midway line and I do notthink it is normal. No other lights have come on on my dashboard so I am trying to figure out why it does that and what I should get looked at. Also, I was checking the overflow for the coolant and I saw what looked like brown sludge like substance - about two small clumps in the overflow… I read about the problems GM has had with the gasket and oil getting into the coolant reservoir. what should I ask the mechanic to look for, or should I just get the gasket changed before something goes wrong.?
The coolant GM uses, Dexcool, has a history of sludging if air gets into the cooling system. What I would do is have the cooling system flushed of all the Dexcool/sludge and refilled with the regular green or one of the universal coolants.
Ditto. I would do a coolant flush and change the thermostat also. Running above temperature will also kill your gas mileage.
Keep an eye on the coolant level in the overflow tank. When the level started dropping slowly after I changed the coolant on my 2000 Blazer in 2003, it turned out to be a leaky intake gasket. My mechanic found traces of coolant in the oil during the next oil change. Check the radiator cap for any corrosion, if the cap is not sealing properly air gets into the system and causes the sludging.
Since it’s due, I would replace the radiator cap and the Dexcool with regular green coolant as suggested by Tester at the least. A dealer or mechanic should be able to check for a leaking intake manifold gasket or just keep an eye on the coolant level.