For the past month or two I have noticed that when the engine is cold the level in the reservoir is below the "full when cold" line. However, when I drive the car and the engine warms up the level comes back up to the "full when cold" line. I thought that the reverse would usually happen.

I wanted to know if this sounds normal and should I top up the coolant or leave it be as it is not overheating nor am I getting any messages. The last time the coolant was topped up was about four years ago when I did the five year drain and fill.

 

Yes, bring it up to the full when cold line when it's cold.

 

That's normal....the coolant level should be at the cold mark when cold...similar to tires in that you adjust when cold and don't worry about what happens when hot. The level should stay the same or go up slightly when hot. Tires do the same, as does transmission fluid, power steering fluid etc. Don't overthink it, just adjust to that mark when it's cold and forget it.

 

Max-
You seem to be one of the few who has found that "Full Cold" mark on the front of the tank, most dealer techs don't know it's there!

As others mentioned, the level will rise (quite a bit) when the engine is warm, due to thermal expansion of the coolant.

Since the mark is at the front of the tank, parking on an upgrade will make the level look lower and parking on a downgrade will make it look higher. I used a big level and then put squares of plywood where my rear wheels sit, so my car really does sit level in the garage. That's perhaps splitting hairs a bit...

Coolant has to go somewhere, and the level in the tank shouldn't drop unless there's a leak to the outside or inside the engine. But I once had a situation where my level went down a bit, no coolant in the oil (Blackstone Labs), no visible leaks, no leaks with the dye/blacklight. Maybe the squirrels were sneaking in and drinking it at night.

If you don't find a leak with careful visual inspection, the GM coolant dye doesn't cost much and doesn't effect the coolant itself, except to make the color look a bit weird. Use a black light to check ~ every 500 miles until you find something. Or until you give up.

 

I will top up to the line when cold but I am wondering if it is possible that I don't have a leak? I probably won't have to put more than half a quart to bring to the line.

 

I'll bet it doesn't even take that much. I agree with Jim, they couldn't have hidden the fill mark any better than they did. A leak will continue to leak, so if the level has been the same for a while, then there's no leak. Fill to the cold mark, when cold, and then go enjoy the drive.

 

Jim, I will fill her up and keep an eye on the level (checking only when cold to compare an apple to an apple)

 

 

there is something written next to the "full cold" on the reservoir, does anybody know what it says?

 

PIEIN A FROID
Whatever the hell that means. Just looked at the original one in my cabinet.

 

PLEIN is French for Full
FROID is French for Cold

So I guess FULL COLD would be the saying.

 

merci beaucoup!

 

Just topped mine off a couple weeks ago....

From the manual:

When the engine is cold, the coolant level should be at the FULL COLD mark on the coolant surge tank. When the engine is hot, the level
could be higher than the FULL COLD line.

If coolant is needed, add the proper DEX-COOL coolant mixture directly to the surge tank, but be sure the cooling system is cool before this is done.

Fill the coolant surge tank with the proper DEX-COOL coolant mixture until the level inside stabilizes at the FULL COLD mark on the front of the surge tank.

With the coolant surge tank pressure cap off, start the engine and let it run until the upper radiator hose can be felt getting hot. Any time during this procedure, watch out for the engine cooling fan. By this time, the coolant level inside the coolant surge tank may be lower. If the level is lower, add more of the proper mixture to the coolant surge tank until the level stabilizes at the FULL COLD mark on the coolant surge tank.

Replace the pressure cap. Be sure the pressure cap is hand-tight and fully seated. Check the level in the surge tank when the system has cooled down. If the coolant is not at the proper level, repeat steps, then reinstall the pressure cap. If the coolant is not at the proper level when the system cools down again, see the dealer.

 

thanks for the info - I topped mine off yesterday when cold and it took a total of a half quart - I hope I don't have a leak as it has been about four years since I have added any coolant

 

If you haven't added coolant for four years, it's likely that you have no leak.

 

 

Just happened to see this post, about a week ago I noticed my coolant tank level was a bit low, and I check mine about once a week just to make sure there are no issues, My car is an 07 Z51 A6 DD with about 130,000+ miles on it. The car has been remarkably trouble free and has only required regular service and maintenance items. So a I added about a quart of coolant, A check of all hoses and possible leak sources revealed nothing, no coolant on the ground, no wet water pump, no contaminated engine oil, nothing, So I drove it back and forth to work for a couple of days and sure enough on the 3rd day I noticed the level was again down, this time up by the drivers side upper radiator shroud, I noticed a couple of drops of coolant that looked like it had splashed their, put since I know I wiped every thing up, these drops were new, so after removing the upper radiator cover, and starting the engine, after about 5 minutes of running, sure enough a few drops of coolant appeared from one of upper radiator tubes where it connects to the header tank, it's a very small leak and looks like a fatigue crack on the tube since there is no sign of any foreign object damage. Removing the radiator was not that bad considering, there is not a lot of room, The coolant that I drained was clean and clear, as is the inside of the old radiator, no build up or deposits and nothing out of the ordinary, I ordered a new radiator and new hoses since they are the originals and I have them off any way. The original hoses still appear to be in good condition so its more peace of mind than anything, I guess nothing lasts forever and I don't think it really owes me anything.

 

And on the C6, the full line mark is on the front of the tank towards the head lights. So coolant to the fill line when the motor is cold has the tank looking like it only 1/3 full, and plenty of room in the tank for the coolant as it heats up.

So truth is, most guys will have the tanks over filled when cold even, since the are gauging the coolant level from the side of the tank, and not from the full mark on the front of it instead.

 

They did a great job hiding the FULL COLD mark...though I guess they could have put it on the side facing the fender...then we would have to remove it to check the level.

 

It has been a week since I topped up the coolant and the car has been driven in all kinds of conditions - highway, stop and go, etc.

I checked the coolant level (while engine cold) and it has not moved so all is good thus far