Engine temp cools while driving in cold weather
Thread Starter
10th Gear
Joined: Jan 2022
Posts: 13
Likes: 1
From: Texas
Engine temp cools while driving in cold weather
I’m not sure if this has already been posted, but if so, I couldn’t find it. I have had virtually no problems with my 99 RX300. The last couple of years this has been an issue in the winter.
I will let my car idle until it gets to normal driving temp, but when I start driving my engine temperature, it goes all the way back down to C. It’s the cold air, but it shouldn’t do this, right? I assume it has something to do with the coolant going through when it doesn’t need to or something but I honestly have no idea.
currently I have 282,000 miles. I made sure that I change the oil regularly.
No, check engine, lights or warnings.
I have asked the local Toyota dealership(Lexus is an hour drive) and they look at me like I’m crazy…
any ideas would be greatly appreciated.
I will let my car idle until it gets to normal driving temp, but when I start driving my engine temperature, it goes all the way back down to C. It’s the cold air, but it shouldn’t do this, right? I assume it has something to do with the coolant going through when it doesn’t need to or something but I honestly have no idea.
currently I have 282,000 miles. I made sure that I change the oil regularly.
No, check engine, lights or warnings.
I have asked the local Toyota dealership(Lexus is an hour drive) and they look at me like I’m crazy…
any ideas would be greatly appreciated.
Last edited by Nate99RX; Dec 15, 2022 at 04:00 PM. Reason: Adding more info
Thread Starter
10th Gear
Joined: Jan 2022
Posts: 13
Likes: 1
From: Texas
Racer
Joined: Oct 2009
Posts: 1,298
Likes: 323
From: nj
CL Community Team
Joined: Apr 2001
Posts: 16,557
Likes: 1,385
From: Austin, TX
edit snip ...
I will let my car idle until it gets to normal driving temp, but when I start driving my engine temperature, it goes all the way back down to C. It’s the cold air, but it shouldn’t do this, right? I assume it has something to do with the coolant going through when it doesn’t need to or something but I honestly have no idea.
... edit snip
any ideas would be greatly appreciated.
I will let my car idle until it gets to normal driving temp, but when I start driving my engine temperature, it goes all the way back down to C. It’s the cold air, but it shouldn’t do this, right? I assume it has something to do with the coolant going through when it doesn’t need to or something but I honestly have no idea.
... edit snip
any ideas would be greatly appreciated.
As others have pointed out, you need to replace the thermostat. There is a DIY posted [check the DIY sticky thread].
Your mpg would be suffering with stuck open thermostat and also with idling to warm up.
Salim
Thread Starter
10th Gear
Joined: Jan 2022
Posts: 13
Likes: 1
From: Texas
Another thing I forgot to mention.. when it does this I am unable to get the car to shift beyond second gear.
For example, if I do get the car warmed up and drive it, and as soon as it cools back down to C, on its own… if I have to slow down on the highway for traffic and go to speed back up, I then have to speed up very very slowly otherwise it won’t shift.
Even if I do go slowly sometimes it won’t shift in that situation. Does that make sense? If not I’ll try explaining it another way.
Trending Topics
Driver
Joined: Jan 2022
Posts: 63
Likes: 14
From: Colorado
How cold of outside temps? Run a piece of cardboard in front of the radiator and see if that’s it. I do this with my truck when it’s cold. Just have to keep a close eye on temps and take it out if it gets hotter than normal.
ClubLexus Stories
Celebrating Lexus & Toyota from Around the Globe
8 Tips for Improving Your Hybrid or Plug-in Hybrid's Efficiency!
Michael S. Palmer
10 Best Lexus Models No One Remembers
Joe Kucinski
TRD Off-Road Premium: Best 2026 4Runner, Except This One Thing
Michael S. Palmer
Top 10 Lexus & Toyotas to Drive Before You Die!
Joe Kucinski
Top 10 Lexus/Toyotas With The LEAST 5-Year Depreciation
Joe Kucinski
Lexus LC500 Convertible Auction: A Preview of Rising Values?
Brett Foote
GX 550 vs TX 550: Best 3-Row Luxury Lexus Family Hauler
Michael S. Palmer
9 Best Lexus Models You Can Buy for Half Price (And 1 You Shouldn't!)
Joe Kucinski
2026 Lexus NX Buyer's Guide: Models, Features, Prices & More!
Brett Foote
Thread Starter
10th Gear
Joined: Jan 2022
Posts: 13
Likes: 1
From: Texas
like anytime it gets below 50(f). In the summer time the engine gets to normal running temp and stays there the entire time.
Racer
Joined: Oct 2009
Posts: 1,298
Likes: 323
From: nj
Thread Starter
10th Gear
Joined: Jan 2022
Posts: 13
Likes: 1
From: Texas
that I can understand, but the engine shouldn’t cool back down. Which it does which leaves me consistently in 2nd gear. Hard to maintain Highway speeds of 75mph (Texas speed limit) in second gear.
CL Community Team
Joined: Apr 2001
Posts: 16,557
Likes: 1,385
From: Austin, TX
Signal from the temperature gauge tells the CPU to engage choke and the cpu tells the transmission to lockout higher gear thus forcing higher rpms of the engine and the driver gives more gas to reach the driving speed.
Based on the problem description and miles, the logical suspect it the thermostat [although any of the items listed above can be malfunctioning]. Problem can be confirmed when you take out the thermostat [you will see it crusted open].
If you have another theory, please post. Read the DIY and if you think it is beyond your abilities/tools/facility take it to mechanic. There is hardly any Lexus/Toyota skill required to change the thermostat.
Salim
Thread Starter
10th Gear
Joined: Jan 2022
Posts: 13
Likes: 1
From: Texas
There are sequence of things that are happening due to stuck open thermostat. Engine block is getting coolant from the radiator [Tstat is stuck open]. As you drive the radiator gets cooled by the air racing through it [with or without electric fan]. This drops the temperature of the coolant.
Signal from the temperature gauge tells the CPU to engage choke and the cpu tells the transmission to lockout higher gear thus forcing higher rpms of the engine and the driver gives more gas to reach the driving speed.
Based on the problem description and miles, the logical suspect it the thermostat [although any of the items listed above can be malfunctioning]. Problem can be confirmed when you take out the thermostat [you will see it crusted open].
If you have another theory, please post. Read the DIY and if you think it is beyond your abilities/tools/facility take it to mechanic. There is hardly any Lexus/Toyota skill required to change the thermostat.
Salim
Signal from the temperature gauge tells the CPU to engage choke and the cpu tells the transmission to lockout higher gear thus forcing higher rpms of the engine and the driver gives more gas to reach the driving speed.
Based on the problem description and miles, the logical suspect it the thermostat [although any of the items listed above can be malfunctioning]. Problem can be confirmed when you take out the thermostat [you will see it crusted open].
If you have another theory, please post. Read the DIY and if you think it is beyond your abilities/tools/facility take it to mechanic. There is hardly any Lexus/Toyota skill required to change the thermostat.
Salim
thanks again everyone and huge thanks to you Salim!
Thread
Thread Starter
Forum
Replies
Last Post
mnm27mnm
IS - 3rd Gen (2014-present)
18
Jan 19, 2014 04:47 PM