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Old 08-11-2019, 05:47 PM   #1 (permalink)
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BrennanK's Avatar
Join Date: Nov 2011
Location: Minneapolis, MN
Posts: 1,349

Bad New Thermostats?

I replaced both thermostats in my truck this winter when I replaced my water pump (Merchant). I put in two new OEM (Merchant) thermostats. My truck would always run 181*f (based on OBDII readings) unless it was above 80* or so outside then it would get to 191*f. It almost never wavered from those 2 temperatures when cruising. I have never seen my truck above 210* even pulling a heavier load and it would only be there during acceleration - never cursing.

I replaced them in the middle of winter and right away my trucks normal temperature was 185*. I thought that was probably normal given that the old t-stats were probably not closing fully or something. I just ignored it. Once the summer weather happened my truck will run around 195* around town with no load. Higher than I'm used to - but nothing crazy.

Now 2 weekends ago I pulled my first trailer since replacing the thermostats in the winter. I was pulling a 12ft u-haul enclosed probably around 4,500 lbs for 1000 miles. I was doing 70-75 MPH and it was 80-90* outside. Nothing too extreme in my mind. My truck would climb to 215* almost instantly and the fan would engage and bring it down to 197* or so and then within 15-20 min I was right back at 215* with the fan again. I got awful economy because the fan was on for what felt like 40% of the drive.

I am just perplexed. I replaced my thermostat and my truck acts like it's on the brink of overheating (fan always engauged) all the time with a trailer now. Is it possible to have thermostats that don't open fully? I never had a hot running truck before and the only things that changed are the water pump and the thermostats. I get these temps are a far cry from truly overheating, but it's much different than I'm used to.

I just want to get others thoughts. Am I over-analyzing this or should I look into testing my thermostats? I really hate having my truck act like it's running so hot with such a small load compared to what I've done in the past. I get wind, trailers, and whatnot all play a role, but I have towed 5-10 times now and it's acting this way consistently now.

2005 Black GMC Sierra 2500HD SLT - CCSB
AUX Radio Input (iSimple ISGM535) - High Idle Mod - Head Gaskets (June [email protected]) - OEM Cab Lights - LBZ Mouth Piece - All On Headlight Mod - Puddle and Footwell LED's - OEM Towing Mirrors - Uniden BCT15x Scanner - Gauges in Trippin' Overhead mount - Rigid Industries Dually Backup Lights - UC6 radio with LUX amp
-Stock tuning and staying that way

LBZ door badges, Kennedy lift pump, aux CAT filter

Last edited by BrennanK; 08-11-2019 at 05:52 PM.
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