Hello,

I am experiencing an interesting issue with my car which is particularly apparent while highway driving. The outside temps were between 50 and 60 degrees. While cruising on the highway at ~80mph my coolant temp goes to the bottom

.

I know the gauge isnt broken because here is what my oil temp looks like at the same time



If I slow down to ~50mph the temp looks like so



FYI there are no coolant leaks, I have replaced the thermostat and radiator cap and the car is running on e85.

What could be causing the car to run so cool?

Did you try replacing the Temperature senors on the Thermostat Housing? OR check the senors out to see in they are working correctly? You also might have a water pump problem( Too much pressure or too lowe of pressure) .Also is it having any running issues when the temperature goes that low?

What you described is a classic symptom of stuck-open thermostat.

This.

My car did this exact same thing. It ran so cold I had to change the cold enrichments on my AEM until I figured out it was an open thermostat. Then one day it stuck closed and killed my HG, so don't wait too long.

id replace your t stat it may be stuck open. does the car warm up normally??

mine was the opposite, i couldnt go 2 miles before it overheated... thermostat is a easy and cheap fix

The car runs fine. I dont think the sensor if bad because it reads normal when the car is DD and usually sits right below the center. The water pump issue is interesting. My car now has 44,000 miles but its now on its 3rd water pump. Killed the 1st one at 14,000 miles when i blew the head gasket and another one crapped out on me last summer at around 30,000 miles so now in onto my third

I thought this exact same thing hence why I replaced the thermostat. I could replace it again but is there a way to check if its bad before i buy a new one?

The car does seem to warm up fine which is also interesting. If im just kicking around town the temp seems to be normal. The temp really only gets super low during highway driving.

I see your car is a 2005. What is the current mileage?

44,000 miles

this just happened to me a week ago in my IV and replaced my t-stat and fixed the issue

Was the temp fine dd around town then went cold on the highway?

I thought it was the thermostat hence why it was replaced before.

The car comes up to temp fine which is also why im questioning the thermostat.

do you have an aftermarket thermostat?

Nope, thermostat is OEM

well my car was warming but takes forever and when i drive it in the highway.. my temp goes down since the air that passes through the rad fins cools the coolant.

but it fixed the issue after replacing the t-stat