aradmahogany

To start, I mean this post as a kind of "funny".... I know about the thermostat issues and such. ANYWAY. Long story short last night I got the flat lined coolant temp and "---" temp readout for the second time in two years. Last year it only happened once, and it seems that way this year again. I live in Florida, and last night temps got into the high 30's. Not remembering what happened last year I just got in Gregg and went, letting the "drive" warm Gregg up, or so I thought. I usually have the temp readout up on the DIC, and Gregg warmed up pretty quickly to 174 but then the problem came....A HILL! Coasting down this hill caused the temp to drop to 172, hold for about 10 seconds, and sure enough, in the back of my mind I though "hear we go" and BOOM flat lined gauge and "---" readout. This AM I used my scantool and found the pending P0128 code sitting there... waiting for me. I killed it with a tap. I left for my office in Tampa (an hour commute) but I let the car warm to 100 degrees F before pulling out of my driveway. The car reached 180 in no time and for most of my commute was at 187-196, the usual when its chilly out. No code, no unusual cooling. Do you guys think the the ECU tuning for this code is a little "aggressive"? I mean, it didn't give Gregg more than 10 seconds to start climbing in temp before setting the code off. Last time it happened was a similar situation with a coasting hill.

Oldblue

And what thermostat did y'all install last year? What coolant did you use?

aradmahogany

Didnt even touch the thermostat actually. It happened that one day and never again through the season up until yesterday. As I recall, it was about February in 2015. Over a year I suppose. Also, Coolant was serviced last year (May or June I think?) With good ol Dexcool. Never have had any cooling or heating issues. Just these two out liars!

Oldblue

Then change the thermostat, it's 10 years old!

donbrew

Do you think ambient temperature may have something to do with it?

aradmahogany

I dont know because this morning was actually colder than last night and I drove a whole hour for my commute with absolutely no hypercooling issues. Warmed up to 180 within about 5-10 minute of driving.

whopper

Don't overthink it - just change the thermostat.

donbrew

What I meant was that all summer in Fla. it was warming up fast enough and staying hot enough, now it's cooling down a bit.

When I had a bad t-stat, no code, traveling on the NY Thruway at 80 MPH , ambient temp 20F, the temp would go down to 172F.

aradmahogany

My commute speed varies between 50 and 70 miles per hour. Once the car reaches180 it never drops under that even for a second. I think the ecu has an issue with the IAT(intake air temp) parameter while coasting downhill and it is still trying to warm up. To get specific the lowest it drops to is 183. That is why I think it may be a temperment with the ecu parameters. I'm still gonna order the t stat for when I really need to replace it. Maybe my t stat has only half failed XD . I recall reading up on the issue when it happened last year and in some gm vehicles as late as 2005 they had a tsb on flashing less aggressive parameters for the code because cars were throwing the code so much. My 2006 isn't too far off from 2005 and I'm sure they didn't come up with brilliant new ecu tuning parameters for these things. Just me with my tin foil hat on is all.

aradmahogany

And Oldblue I am pushing the limits because I want my t stat to secure a place in the Guinness book of world records for longest lasting original gm delta platform thermostat! I may already Hold the record!