I've noticed a slight change on my factory temp guage over the past 2 weeks...at times the reading is actually cooler than usual. The outside temperature has no effect, it's happened on both warm and cold days. Previously, the needle has always been right on the line before the 210 mark, even after I installed the 180* stat. It usually takes 5 to 10 minutes then it levels out there. The other day it went up as usual, then dropped down to about half way between the 160 and 210 mark, and stayed there for a while, then rose back up. Some days it will rise up and level out, and others it will do this. Did it tonight as I went down the highway and stayed there for a good 10 minutes before rising back up and leveling out.

I haven't had a chance to check it with my AutoXray to see what the PCM is reading, I was just wondering if anyone else has experienced this. I was thinking air pocket at first, but I don't have any signs of losing coolant, and the heater is working perfectly. Maybe an issue with the thermostat or possibly the sender or guage? The T-stat is only a couple of months old, but it's a Hypertech stat, and I'm not so sure if it's a quality part. Any input would be greatly appreciated.

 

I have a 160. Truck runs around 175-185.
One time after changing pcms, mine acted strange and quite reading, after a 2 days it started working and I have not had any problems. Its also not very acurate compared to what I see on the scanner.

 

the guage is worthless. nothing more than a glorified idiot light. there is a fine line in there (at least with mine) that it will fluctuate. i am running a 160 and depending on the temperature, it can either be on the high or low side of around 180. or, you may have an air pocket. air pocket not good. burp me please!!

 

I think the system is pretty good and burped...might just be a case of the coolant temp being right on that fine line. Just wondering why this just started happening all of a sudden...(or maybe I just started noticing it). Thanks for the replies

 

I worked on a '99 truck that had a flaky ECT connection,
this drove the timing nuts (ECT reading from the PCM was
jumping all over the place, -50 to +300F) but the gauge did
not move much. Made the idle very unstable.

 

are there not two coolant temp sensors? one for the ECM and one for the guage? used to be that way.