: 99 STS running cold (yes cold!!)

01-25-11, 02:38 PM
My 99 STS is running cold, 13 months after HG (studs) job. Used to run straight up on the temp gauge all the time on the highway until 2 weeks ago, now only at about 10 o'clock. Does this sound like a thermostat problem, stuck open or partly open? Any and all thoughts would be great. Mileage has dropped big time from around 26 highway to about 20. Heat seems to be OK but I think less than before. car has loads of power, no codes showing!!

01-25-11, 03:01 PM
As in your other two identical posts in this Forum, the possibility is a stuck (partially ?) open thermostat.

The Northstar thermostat is in the heater return circuit and acts initially on heater return coolant temperature in order to control thermostat opening which then allows radiator partial or full flow. You'll notice, over time, that the engine takes quite a bit longer to warm up in winter than spring or fall. This is partly due to the operating heater air blend circuit which takes quite a bit of heat out of the coolant.

Talk to Chris (RippyPartsDept) up in Vendors ^^^ or look in www.rockauto.com. At this time of year (where are you ?) you might be better off having a dealer or local shop do the thermostat and coolant change unless you're a decent wrencher with a garage.

01-25-11, 05:30 PM
Thanks for the quick reply and sorry for the triple posting, wasn't sure I was posting correctly. Definately a dealer/local shop fix as I have no garage to work in and the temp outside today is -14, wind chill -30. Love the car in the winter, goes through snow really well with new winter tires on.

01-27-11, 10:11 PM
you run regular all season tires and a dedicated winter set? i have michelin a/s tires and they are very good. close to a set of 1/2 worn blizzaks that i sold with last car.