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2008 Chevy trailblazer. Getting p0128. Cluster temp gauge sometimes doesn't move at all until 10 minutes later goes to normal temp. Just replaced thermostat housing last year. Warranty 12 months up. I have infrared gun and graphing scan tool. How do I test to see if thermostat stuck open? Monitor cts graph scan tool. Thermostat housing buried under generator. Thanks in advance. Joe
Before taking off for a test drive, let the vehicle sit overnight and compare the ECT and IAT, KOEO. They should be within 10 degrees of each other. That verifies that the ECT reading isn't skewed.
What's the OE thermostat opening temperature? 190 degrees? How high does the coolant temperature go if you let the engine idle for 20 minutes, or go for an extended test drive?
If the ECT never approaches 190 degrees, then suspect another failed thermostat. Make sure there's nothing to cause the engine to overcool, like a locked electroviscous fan clutch, or a thermostat temperature that's below OE spec. It's also possible to have hydrocarbons or other contaminants in the coolant that cause the rubber seals on the thermostat to swell and fail prematurely.
autojoe wrote: Cluster temp gauge sometimes doesn't move at all until 10 minutes later goes to normal temp.
Can't trust gauges because they're sometimes programmed to show people what they expect to see. Need to see what ECT is doing on warm up, after doing the cold ECT/IAT comparison Tyler recommended.
FWIW P0128 is a slow warm up code rather than a failed to reach operating temp code. My Astro sets it on cold mornings with the heat on full.......
Thanks both of you for reply. Cts is working fine. I have had stuck open thermostats before. Gauge moves slowly takes long time to get heat. Gauge will work sometimes. When it doesn't it will stay at 100 degrees and sometimes 5 minutes later jump to half way 200. Other times it will stay at 100. Plenty of heat 5 minutes later. The other day staying on 100 I grabbed snap on looked at ect showed 195.then looked at ipc coolant gauge and said 100.then I bidirectional controlled all gauges of ipc all went to max position. Then exited the test and gauge stayed at 100. I don't know why pcm only couple of times flagged p0128. I always have plenty of heat and obd2 generic always shows same coolant temp as enhanced data. I am leaning towards bad cluster. Never ran into something like this before and I seen a lot. Been doing this stuff since 1982.its just strange how it is acting. I never like just throwing parts at it like cts or thermostat. Lucky I didn't. Rest cluster working good. Sometimes it will work for couple days. Hit and miss. Thanks for your input. Appreciate it. Joe
Sounds like a cluster issue, thetemperature at which the thermostat opens can usually be detected at the top hose. Thermostats don't open much until the thermpstat is a good few degrees above thecold start nominnal temperature where it starts to open so once the engine reaches 192f (89C) it will only slowly start to warm the top coolant hose/ radiator inlet.
So the way to test is let the engine warm from a compeletly start and only after the temperature exceeds the thermostat opening themperture should you feel any warming at the radiator inlet pipe.
A good indication of the actual running temperature is to measure the temperature on heater/by-pass hose going from the top end of the engine into the heater.
Slow warm up and poor heater output can be caused by too high a concentration of antifreeze.
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