Coolant Reservoir Level In Winter

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Quick question for you guys on an observation I made this morning. It's 22* here (finally warm!) and decided to do a quick once-over on the CX-5 while it was in the driveway. Everything was good to go, as expected, except for the coolant. On the reservoir tank it read about 2" below the low line, I popped the Rad cap and it was full to the top. Mind you this is on a cold engine.

The system is clearly full, I'm not having any external leaks and my UOAs don't indicate an internal leak. It seems as though the very cold temps are causing the fluid to be pulled into the block, I'm just surprised by the amount.

Any others notice this much variance with their reservoir tanks?
 
To me the coolant level is supposed to be at the full line cold. It doesn't matter if it is summer time cold after sitting over night or winter cold. It should be at the full line cold. That is my understanding. When the engine has been off for it to cool down to existing outside temp.
 
As the coolant heats up it expands and goes into the reservoir. When it cools it gets drawn back into the radiator. Just like cooking something on the stove with a pan half full. It gets hot enough it boils over.
 
Originally Posted By: Snagglefoot
There definitely is a coefficient of expansion for the fluid. How cold did it get and have you driven the vehicle yet.

SF


We've had lows in the negatives for the past 7-10 days. Just yesterday morning was -10*F on the drive to the office. This morning it was driven 2 miles then parked in the driveway for about an hour and a half before I did the once-over.
 
I've noticed this as well; if it's very cold, it will be w little low; once it warms back up into the 50s/60s, it's back to where it should be. Seems logical and normal to me.
 
I observed the same thing with a VW golf, the system filled to the correct level at 70f in the garage (overnight) then put outside where it sat for 2 days.
It went down below 0f and took 200ml to bring it back up to the same level. I removed the excess once I knew exactly how much the difference was.

VW sometimes will flash a red coolant light meaning the coolant is low in very cold temps, the contacts were to high in the bottle, a revised bottle with the contacts lower is now regular production and for service and addresses this issue.
 
The coolant does contract a little when it's really cold. I would make sure at freezing or 32F it's at cold full. If it's below cold full at 0F no big deal.
 
Depends on the temp you added the coolant last. Full at 70 degrees wont be full at 10 degrees. Just like tire pressure.
 
Originally Posted By: Donald
The coolant does contract a little when it's really cold. I would make sure at freezing or 32F it's at cold full. If it's below cold full at 0F no big deal.


This is my thought as well.
 
When its really cold, nearly every vehicle I service has low coolant in the reservoir. Ive come to expect it and top it off to the fill line on the reservoir. Seems to me as normal thermal contraction and expansion. As long as the radiator is filled all is well.
 
After sitting overnight, I make sure the level is up to the cold mark. That's it and I do not worry where it ends up when the engine is warm.
 
Last edited:
Originally Posted By: Thax
When its really cold, nearly every vehicle I service has low coolant in the reservoir. Ive come to expect it and top it off to the fill line on the reservoir. Seems to me as normal thermal contraction and expansion. As long as the radiator is filled all is well.


My thoughts exactly. Went down to the Mazda dealership and bought some FL22 ($25/gal!), this way I know with 100% certainty I've got the correct fluid for a top off.
 
Originally Posted By: RamFan
Originally Posted By: Thax
When its really cold, nearly every vehicle I service has low coolant in the reservoir. Ive come to expect it and top it off to the fill line on the reservoir. Seems to me as normal thermal contraction and expansion. As long as the radiator is filled all is well.


My thoughts exactly. Went down to the Mazda dealership and bought some FL22 ($25/gal!), this way I know with 100% certainty I've got the correct fluid for a top off.

if your coolant doesnt have a leak then your fluid loss is evaporative and mostly water as it expands it pushes a volume of hot vapor out the overflow and as it cools it sucks back in dry air. ethylene glycols boiling point is much higher than h20 so the vapor is mostly h20. Your remaining coolant is therefore concentrated.

Therefore, if you are splitting hairs and concerned about the correct topoff, you should topoff with distilled water, not coolant.
 
Last edited:
Originally Posted By: raytseng
Originally Posted By: RamFan
Originally Posted By: Thax
When its really cold, nearly every vehicle I service has low coolant in the reservoir. Ive come to expect it and top it off to the fill line on the reservoir. Seems to me as normal thermal contraction and expansion. As long as the radiator is filled all is well.


My thoughts exactly. Went down to the Mazda dealership and bought some FL22 ($25/gal!), this way I know with 100% certainty I've got the correct fluid for a top off.

if your coolant doesnt have a leak then your fluid loss is evaporative and mostly water as it expands it pushes a volume of hot vapor out the overflow and as it cools it sucks back in dry air. ethylene glycols boiling point is much higher than h20 so the vapor is mostly h20. Your remaining coolant is therefore concentrated.

Therefore, if you are splitting hairs and concerned about the correct topoff, you should topoff with distilled water, not coolant.


This sounds like great advice right here
 
Originally Posted By: raytseng
Originally Posted By: RamFan
Originally Posted By: Thax
When its really cold, nearly every vehicle I service has low coolant in the reservoir. Ive come to expect it and top it off to the fill line on the reservoir. Seems to me as normal thermal contraction and expansion. As long as the radiator is filled all is well.


My thoughts exactly. Went down to the Mazda dealership and bought some FL22 ($25/gal!), this way I know with 100% certainty I've got the correct fluid for a top off.

if your coolant doesnt have a leak then your fluid loss is evaporative and mostly water as it expands it pushes a volume of hot vapor out the overflow and as it cools it sucks back in dry air. ethylene glycols boiling point is much higher than h20 so the vapor is mostly h20. Your remaining coolant is therefore concentrated.

Therefore, if you are splitting hairs and concerned about the correct topoff, you should topoff with distilled water, not coolant.


But, you need a balanced mix and therefore just suggesting water only could lead to future problems with a weak solution. Personally, unless it is tested for strength, I'd still add a 50/50 mix, but that's me.
 
Originally Posted By: irv
Originally Posted By: raytseng
Originally Posted By: RamFan
Originally Posted By: Thax
When its really cold, nearly every vehicle I service has low coolant in the reservoir. Ive come to expect it and top it off to the fill line on the reservoir. Seems to me as normal thermal contraction and expansion. As long as the radiator is filled all is well.


My thoughts exactly. Went down to the Mazda dealership and bought some FL22 ($25/gal!), this way I know with 100% certainty I've got the correct fluid for a top off.

if your coolant doesnt have a leak then your fluid loss is evaporative and mostly water as it expands it pushes a volume of hot vapor out the overflow and as it cools it sucks back in dry air. ethylene glycols boiling point is much higher than h20 so the vapor is mostly h20. Your remaining coolant is therefore concentrated.

Therefore, if you are splitting hairs and concerned about the correct topoff, you should topoff with distilled water, not coolant.


But, you need a balanced mix and therefore just suggesting water only could lead to future problems with a weak solution. Personally, unless it is tested for strength, I'd still add a 50/50 mix, but that's me.


I agree, I'd rather add a few ounces of premix in the winter until a full fluid change is due. At the rate we drive, I'm looking at every 7.5 years. If the evaporation rate stays linear, we're talking roughly 3-4 cups of top off coolant during that time.
 
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