Can New T-stats Get Too Old?

[GM Guy]

Hey all,

I installed a pair of new AC Delco t-stats in my 99 C3500, and haven't been too happy with the temp. It seems to fluctuate from 180 to 200, I feel it should be at 190-195 and stay solid. This is on a late 99 C3500 with the factory HO balanced flow WP with the thread on fan clutch. Is it restrictor fitting time, or are the old stock t-stats the cause?

These had been sitting on the shelf (inside the house, which usually doesnt get above 85 in the summer) for 5 years roughly, so I am curious as to if that would affect it at all.

Any input appreciated, thanks!

 

[schiker]

If in a air tight sealed plastic bag I think they would be good for several years. If open in box might could dry out wax pellet if seal dried out too but don't feel strongly about it.

Might be bad new but doubt 2 bad. Probably some entrapped air or other issue 20 degree swing is excessive unloaded. Gauge flaky? What is ECM reading?

Might need to cycle fully open 3-4 times to homogenize wax pellet again. But should hold steady after that. Try burping air again at bleeder and or hose.

 

[THEFERMANATOR]

For the 1st opening or 2 of the day it is normal to get a big swing in temp from the massive inrush of col coolant from the radiator, but after you drive a few miles it should steady out.

 

[WarWagon]

Still have the heater core restriction in the system? Usually at the crossover to heater connector that we hate on 1995 and older stuff. Did this act up before the t-stat change?

 

[schiker]

What temperature are the stats are they the same temperature? Is it under a load or just regular driving? How many warm up cycles on the new stats? Does it continuously fluctuate or just initial few minute after reaching normal temp? How long does take to swing temperature and what is ambient.

Just a light load 60-90F ambient I would expect rock steady temp after warmed up fully and no appreciable change in load. ~10-15 minutes after start up I rarely see my gauge move unless above 90F ambient and ac load in slow traffic, hill, or pulling weight. Then it's still pretty slow and predictable.

 

[GM Guy]

warwagon, new quick connect fitting from GM, diesel specific with a slight restriction (plastic x in the flow path)

Schiker, same part number Genuine AC Delco.

Update: it did fluctuate less as the trip went on, but I am still not overly pleased. Will try cleaning grounds and changing the dash sensor to see if its in the guage. any under dash grounds for the cluster?

Do you guys think I need the restricted bypass?

 

[JayTheCPA]

As schiker hinted toward . . . Is the dash gauge in synch with the ECM's sending unit?