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#4520815 - 09/19/17 11:58 PM Engine Running Too Cool ?
Merkava_4 Offline

Registered: 01/30/07
Posts: 17501
Loc: Clovis, CA
2000 Buick LeSabre

When I got back to the car from the grocery store, I decided to take the car for a little test trip and watch the water temperature. A/C was off for the whole trip. At the start of the trip, water temperature was 167F and ambient temperature was 70F. Took the car on the freeway for 21.5 miles. As soon as I got on the freeway, the engine starts cooling off. Stayed between 155F and 156F for the whole trip. Exited the freeway and drove about two blocks to the house.

During the time the car was sitting in the driveway at idle waiting for me to open the garage door, the temperature spiked to 182F. The same exact trip the day before with the A/C on, the engine reached a maximum temperature of 176F. Thermostat is not supposed to open until 192F.

What you guys say ?

#4520816 - 09/20/17 12:00 AM Re: Engine Running Too Cool ? [Re: Merkava_4]
Chris142 Offline

Registered: 06/05/03
Posts: 16339
Loc: Deplorable in apple valley, ca
Thermostat stuck open
02 Wrangler super-s 10w30
87 F250 proline 15w40
04 Tahoe super-s 10w30
Z400 Lucas 10w30
KLR250 Maxima 10w40
Can am maveric edge 5w40
57 case tractor 15w40

#4520819 - 09/20/17 12:02 AM Re: Engine Running Too Cool ? [Re: Merkava_4]
3800Series Offline

Registered: 08/02/14
Posts: 1450
Loc: Gulf Coast, MS
Same exact thing with my Regal. Car hit a equilibrium on the highway and once you got off the balance shifted.

#4520821 - 09/20/17 12:06 AM Re: Engine Running Too Cool ? [Re: Chris142]
zeng Online   content

Registered: 09/01/15
Posts: 2039
Loc: Malaysia
Originally Posted By: Chris142
Thermostat stuck open


#4520824 - 09/20/17 12:18 AM Re: Engine Running Too Cool ? [Re: Merkava_4]
Nick1994 Offline

Registered: 02/19/13
Posts: 9626
Loc: Phoenix, AZ
OEM thermostat replacement only Merk. My grandparent's Trailblazer had the thermostat replaced and it ran warmer, turns out the Stant opening was a lot smaller than the OEM one.
2015 Hyundai Sonata 2.4L 74k PU 5w30 & OEM
2000 Toyota Camry 2.2L 227k M1 AFE 0w30 & Wix
1996 Jeep Cherokee 4.0L 145k M1 HM 10w40 & Fram Ultra

#4520830 - 09/20/17 12:24 AM Re: Engine Running Too Cool ? [Re: zeng]
Colt45ws Offline

Registered: 08/15/06
Posts: 9589
Loc: Central Washington
Originally Posted By: zeng
Originally Posted By: Chris142
Thermostat stuck open


Ive replaced probably half a dozen thermos in just mine and a couple of friends cars for this same behavior.

Replace the stat.
2002 Ford Crown Vic PI 207k, Ex-Kootenai County, ID Unit #42
Down for engine swap
2003 Ford Crown Vic PI 75k
Castrol EDGE HM 5W30, Fram XG2

#4520882 - 09/20/17 02:39 AM Re: Engine Running Too Cool ? [Re: Merkava_4]
Dave9 Offline

Registered: 08/28/17
Posts: 138
Loc: Cincinnati, USA
Maybe T-stat but maybe not. The way those are geared, along with the 3800 torque (if/when in good shape) they're barely loafing along at a steady (speed limit) on the highway.

Owners of others cars will not understand that my same generation with a 3800, could run at 40MPH IDLING. Bad side, shifting was anything but performance oriented, and the gearing and high torque wears down brakes faster, like a train pulling when you brake to slow down.

Up to you, you can pull the t-stat and test it in a pot of boiling water if you like, but at that point I'd throw a new one in just because it makes sense to do so while it's so accessible.

However if it were me, I'd warm it up first then drive it like I stole it to get the temperature up, blow a little carbon off the valves, and see if you get that typical temperature plummet that happens when coolant gets around the t-stat rating then suddenly cools down the engine a few degrees because it opened.

#4520931 - 09/20/17 05:59 AM Re: Engine Running Too Cool ? [Re: Merkava_4]
Tman220 Offline

Registered: 09/20/16
Posts: 135
Loc: MN
No need to over-analyze, no need for a pot of boiling water. It runs too cool and its the thermostat's fault. With the correct thermostat that engine will run pretty steady 194-197F on the highway.

Edited by Tman220 (09/20/17 06:10 AM)
2012 Regal GS Turbo PP 5w30
1994 Camaro Z28 LT1 355 CI, 430 RWHP PP 5W30

#4520941 - 09/20/17 06:38 AM Re: Engine Running Too Cool ? [Re: Merkava_4]
edwardh1 Offline

Registered: 01/17/03
Posts: 2828
Loc: Coastal South Carolina
if the oem has a hole in the stat (to allow bipass water circulation), get a stat that has that too.
Prius? In line water heater? Solar?
All save energy, but may not save money (complicated, no DIY, parts hard to get, , parts expensive, etc).

#4521004 - 09/20/17 08:21 AM Re: Engine Running Too Cool ? [Re: Merkava_4]
KrisZ Online   happy

Registered: 12/23/06
Posts: 7124
Loc: Toronto, Canada
A stuck open thermostat is much harder to spot in warm climates. In Canada it's quite easy but you have to wait for the late fall/early winter to see the temp. gauge not reaching the normal position.

I also vote for a new, OEM thermostat.
2015 Dodge Grand Caravan-21k miles.
2006 Mazda 3-155k miles

#4521097 - 09/20/17 10:15 AM Re: Engine Running Too Cool ? [Re: Merkava_4]
RoGuE Online   confused

Registered: 02/05/08
Posts: 670
Loc: Atlanta, GA
I just had this issue on my Malibu where the temp gauge didn't move at all from cold. Replaced the thermostat and all is well. I was getting a P0128 code. Do you have access to a scan tool?
2007 Chevrolet Malibu
2.2L Ecotec

#4521391 - 09/20/17 02:44 PM Re: Engine Running Too Cool ? [Re: Merkava_4]
SHOZ Online   shocked

Registered: 06/28/03
Posts: 5519
Loc: Illinois
I changed t-stats on both my Hyundais this summer. Both OE and both were 'lazy'. they would run about 180-183F n the highway. But in the winter when coasting and slowing down the temp would dip below the 180F marks. Since changing them the run 185F-190F.
2008 Hyundai Accent 1.6L 5 sp manual hatchback
2010 Hyundai Genesis Coupe Track 2L Turbo 6sp manual

#4521473 - 09/20/17 04:59 PM Re: Engine Running Too Cool ? [Re: Merkava_4]
JMJNet Offline

Registered: 09/06/07
Posts: 881
Loc: TX, USA
Since it is a Buick, get ACDelco T-stat only not aftermarket.
  • 2017 Toyota Sienna
  • 1995 GMC Suburban 6.5L Turbo Diesel

#4521833 - 09/21/17 02:35 AM Re: Engine Running Too Cool ? [Re: JMJNet]
Merkava_4 Offline

Registered: 01/30/07
Posts: 17501
Loc: Clovis, CA
I've already had the new ACDelco thermostat sitting in the box for about 12 years. I even have a couple of extra seals that go around the "saturn" perimeter. What I don't have is the thermostat housing gasket. I got two on special order. Nobody stocks them anymore. Thanks for the replies guys. smile

#4521880 - 09/21/17 06:15 AM Re: Engine Running Too Cool ? [Re: Merkava_4]
mk378 Online   content

Registered: 09/27/15
Posts: 1267
Loc: USA
Thermostats with a rubber seal that wraps around the edge of the flange don't need any other gasket.

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