Temp gauge drops when 35f or colder outside

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I noticed when i warmed up my car today for like 15min the temp gauge went up to the middle mark like normal and anytime i warm it up goes up to normal always but once i started driving for a few minutes it started dropping and the more i drove it went down to about 160f-165f but it wouldn't go more down then that and i noticed this only happens when the weather outside is under 35f like today it was -20f windchill. Now when temps are 40f and up the temp gauge stays in the right spot what could it be?

coolant is full

1999 oldsmobile lss
 
Did it ever reach operating temp again while driving, or did it stay in the decreased position?
 
well if its like 40f outside or more it will reach it while driving and be fine but when the temps are like 35f or colder when i drive it will go down.
 
Originally Posted By: boostedtsiawd
well if its like 40f outside or more it will reach it while driving and be fine but when the temps are like 35f or colder when i drive it will go down.


If you're saying it doesn't rebound after the dip, then I also think you should look at the thermostat.
 
That's a 3800 V6 in that car. The thermostat is two 10mm bolts and a little bit of coolant. Drill a small hole in the replacement near where the gasket sits and locate it at the 12 o'clock position. That will help drain out any air in the cooling system.
 
I was told this=

It's the cold weather, and its normal. Both my NA and Supercharged engines have dips down to 180 and 170, respecively, when the outside temp goes down to 40. The cold air in the intake cools down the intake manifold (where the temp sensor is) and the cylinder walls. Also air passing thru the engine bay while driving cools the engine even though the coolant thermostat is closed. Heating up the cabin interior also reduces the engine temp. You can place one or more sections of cardboard in front of part of the drivers side of the radiator to help raise the engine temp. Cover 50% to 90%, depending on outside temp and how the engine temp responds. You can also turn the Cabin air on recirculation mode to cut the amount of outside air that has to be heated up.
 
and this=when idling in park there is no air flow thru the engine bay, no air is being forced into the cabin due to the speed of the car, and the air flow into the throttle body is only 1/5th the air during hwy cruise.
 
I have owned 4 3800s and they all did what you describe. The advice here is good, but at those temps, even with a new t-stat you won't see a difference. My current 3800 with a couple of year old 10,000 mile OEM T-stat will run cooler in cooler temps. It is the nature of the 3800, if you have not owned one, you will not know.

Even when I hook up the scanner I can see it doing that exact thing. 165 does not hurt a 3800. The performance T-sat is 160.
 
When your thermostat opens it allows super cooled water into the engine, and thus, the temp drops. Its a lot more pronounced on really cold days.
 
Originally Posted By: boostedtsiawd
I was told this=

It's the cold weather, and its normal. Both my NA and Supercharged engines have dips down to 180 and 170, respecively, when the outside temp goes down to 40. The cold air in the intake cools down the intake manifold (where the temp sensor is) and the cylinder walls. Also air passing thru the engine bay while driving cools the engine even though the coolant thermostat is closed. Heating up the cabin interior also reduces the engine temp. You can place one or more sections of cardboard in front of part of the drivers side of the radiator to help raise the engine temp. Cover 50% to 90%, depending on outside temp and how the engine temp responds. You can also turn the Cabin air on recirculation mode to cut the amount of outside air that has to be heated up.

Pretty much, It is just how the 3800 acts. You have a good one drive it with no worries.
 
It scared the sht outta me i was like what the [censored] is going on. I was told if i wanna keep the gauge in the middle in these super cold days put a piece of cardboard in front of the radiator but is it really necessary to do that? I just feel like the gauge going down to 165-160f is bad..
 
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Those 90's GM cooling systems with the gauges that don't dummy up within certain ranges to appear normal. My cavalier has the same issue, infact I drove it to Maine in the dead of Winter and at 70 mph it was dropping down to like 130 degrees. After that I started putting a grill block on in the winter and enjoy quicker warm ups with an MPG boost on the highway.

BumperBlock.jpg
 
I like to use the infrared gun to check coolant temps You really don't want to run an engine below about 160 as then more cylinder wear.
 
Like others already mentioned it's time for a thermostat. Get an OEM replacement, not some cheap aftermarket part.

Drive the car for about half an hour and take a reading from the highest point of the thermostat housing and compare that to the temperature your thermostat is supposed to open at. That should give you a pretty good idea if your thermostat is working or not w/o taking anything apart.
 
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