Good morning, JONNNO73,
Is it always below the minimum only when it's cold? From the information you provided it sounds like you checked it cold, and the level was under minimum. Then you drove it for an hour and a half and stopped checked the coolant and it was below the minimum level. So, the engine was hot when you checked it the last time? But it was below the minimum? Just want to make sure I am understanding correctly.
It sounds like your coolant is low which could be causing an air bubble around the temperature sensor.
So as the coolant moves sometimes the sensor for the temp gauge will be covered in coolant and other times there would be just hot air which could cause the erratic reading.
I would perform a coolant pressure test on it. You can find these testers online or you can rent them from your local auto parts store. I will add a picture for you.
This article will help guide you through the test:
A few things to note:
I would make sure the vehicle has cooled down over night and fill the coolant to the proper level when cold. I usually stop a little below the max fill line.
Look at your radiator cap. There should be a PSI rating on it for your system. Should be around 16 PSI. This is what you will pump the system up to with the tester.
After it has been pressurized your coolant hoses should be hard. Now get a bright light and look for any leaks, something as small as a drip over a period of time can cause air in the system. So, you want to look really good.
After that with the tester connected look at the gauge, has it moved?
If so, you have a leak somewhere.
At this point I would check where the tester is connected and make sure it isn't leaking there and any hose connections on the system.
After checking I would pump the system back up to 16 PSI or if it hasn't moved just leave it. I would leave it on there for a good half an hour and come back and check the gauge and see if it has moved.
If so, you have a leak somewhere if there is nothing visible externally you may have a leak internally like a bad head gasket.
Let me know what you find, and we can go from there.
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Wednesday, April 19th, 2023 AT 5:41 AM