Car loosing coolant but


My car has an engine code of low coolant temperature reading so assuming thermostat got stuck open even though engine operates on normal temperatures after 10-15 mins driving.

The thing is my car started loosing coolant with literally 0 external leaks. Like 1-2 quarts a month and I feel like it is starting to loose more rapidly with time or maybe it is just me. My car holds almost 10 quarts of coolant. 2005 Malibu LS 3.5 liters

Is it possible failing or failed thermostat is the reason I am loosing coolant ? cause start of lose started around as thermostat failed. I didn’t change it for months I am lazy since operating temperatures are perfectly normal I didn’t see it as an emergency. I have obd2 scanner the app does few testes it was all good too so I don’t know. Any help would be greatly appreciated thank you for future replies :slight_smile:

Do you see evidence of an external leak?

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Have you checked your oil to make sure the coolant’s not getting into the oil?

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Coolant being lost has three places it can go. Out onto the ground. Into the oil sump. Out the tailpipe. These latter two usually mean a head gasket leak.

If your temp gauge is showing fine, there is nothing wrong with your thermostat. The only way a thermostat can cause coolant loss is if it makes the car overheat.

You can have a water pump that leaks only in certain positions or when running. Look at th weep holeon the bottom of your water pump and see if the inside of it is the same color as the coolant. If it is not, go have the system pressure tested.

My chevy had a low temp code, the guage showed things were operating well, but the engine was running a few degrees cool. A new thermostat solved the problem. It was not stuck open.

This happened on my Lesabre as well. I got the low temp code, and I changed the thermostat. Thermostat was actually ok, but the rubber gasket around it seemed to be letting a little coolant bypass the thermostat.

However, as someone else said, the thermostat will not be the cause of the coolant loss. Hopefully it’s an external leak that hasn’t been found yet. Otherwise, it’s got to be a bad head gasket, crack in the head, or maybe an intake manifold gasket problem. I’m not sure if this engine has coolant passages in the intake manifold for the last possibility to be viable.

Check the oil then pull the plugs. If you’ve been burning that much coolant for any period of time, the ceramic on combustion side of those plugs will be white as new.

Your low coolant temp code means the coolant is not coming up to temp in the time allotted. Based on outdoor temperature, the computer gives the coolant a specific time to come up to temperature. It isn’t closing all the way or opening too quickly.

The coolant loss could be from the water pump. That is a difficult leak to detect. If you can see the bottom of the water pump, there is a small weep hole. If there is a colored residue, the color being that of the coolant, most likely orange, then you need a new water pump.

If that isn’t it, the follow @TwinTurbo’s advice, except that only one or two plugs may be extremely clean, not necessarily all of them.

A stuck-open thermostat can cause overly rich operation, poor mpgs, and possibly damage the very to expensive to replace cat, so good idea to take care of that known problem first. Thermostat replacement is a pretty easy job on most engines. Coolant can leak out and still not drip onto the ground if the leak is slow enough, like a weep. It will contact warm engine parts and evaporate before leaking onto the ground. 1-2 quarts a month seems like you’d notice a leak under the car when parked overnight, but maybe not. The test to check for a head gasket leak anyone can do is have a friend follow you on a freeway approach. If they see white smoke coming out the tailpipe as you accelerate quickly from 0 to 60 mph, good chance you’ve got a head gasket problem. Hopefully that’s not the case, as it is pretty expensive to repair. Check the oil level too. If thje oil level is too high, coolant may be getting into the oil. This will quickly damage the engine bearings, so that has to be fixed asap.