grdtii

I just purchased a 2002 C4S with 30K miles...just noticing that the coolant level in the reservoir is dropping about a pint or so every day or so...probably around 50-70 miles worth of driving...no evidence of a leak under the car...no smoke...no smell of anti freeze...I assume the leaking is only occuring under pressure and that it is leaking onto something hot and evaporating. The weather has been particularly hot as well...and I wonder if having the a/c on in the car has any affect. Notwithstanding the drop in level, the car temp is running absolutely perfect. Any thoughts?

logray

You should never drive it below min mark. If it is low enough you risk introducing air pockets which can cause engine cracks (and much larger problems).

It is possible there is air in your system and since you've added more coolant now it is able to purge this air out, thus requiring more coolant. However eventually it should "fill up" and you will be done filling it.

Or it is possible you have a leak somewhere, in the tank or a hose.

When the car gets hot enough the bleeder valve opens by itself thus allowing the system to bleed itself to a certain degree.

Or on a cold car you can manually pull up the bleeder valve to ensure it gets bled (although there are more exact procedures on doing this properly - you should search/read up on the subject).

If you have a vacuum system (such as uview airlift) you can test for leaks (it should hold 25psi, if not there is a leak and hairline cracks should become visible) and also use it to refill the system properly without any air.

Or take it to a shop that has a vacuum system.

Divot

Bad reservoir caps are well documented sources of coolant loss. Check your cap number, and if it ends in less than 03, replace it. I think they're up to 04 now. Cheap and easy.

ivangene

check your oil dipstick

if it doesnt look like a chocolate milkshake-

highly possible you have an air pocket that keeps getting less...in which case you should not drive the car...you should have the air removed!!

pl

Check the bottom of your reservoir, use your finger to wipe it
Therea may be a hair line crack, which only leaks out during high pressure, and it dried right away because of the high temp of your engine.

Barn996

I agree. Our coolant tanks are notorious weak links in the cooling system as are the coolant caps. If your tank is yellow it's probably an original.

grdtii

Thanks for the advice....will check and update.

white99c2

My car lost coolant for months before the crack in the tank was big enough to leak all the way down to the ground. Prior to that I think it was leaking right on top of the exhaust and boiling away before it ever made it's way down. I had an Indy shop do a pressure test and they came up with zip. Get on the ground and look up under the drivers side tail pipe for stains and evidence of leaking coolant.

jyoteen

Methodically, check:

1. Coolant Expansion tank cap. I replaced this after my coolant started dissapearing. But no luck

2. Coolant Expansion tank itself. I replaced this following 1. It was cracked, but coolant still was dissapearing somwhere, but at a much slower rate

3. Had to replace both radiators. Coolant never hit the ground, but the plastic endcaps/connections were leaking ever so slowly.

Now it's ok.

Pac996

Easy quick thing to do is make sure the caps seal doesn't have imperfections, dry rott, cracked or caked on stuff between rubber and plastic. Dirty rubber will let gases escape even under low pressures.

grdtii

Just topped up the level a little this morning...to the middle of the arrow by MIN on the reservoir...I drove around town for around 10-15 minutes to the point where the car was fully warmed and the fan came on. When I got home, I just checked the level and was a little surprised that it was all the way up at the lip of the top half of the reservoir...just below MAX...I wonder if this is just how this car operates. I was told that some 996s do purge at a level where you would think it was low. Anyone else have this situation. I am wondering if it is not a leak at all...

Macster

My experience with a properly operating cooling system is with the A/C on the engine coolant runs cooler than it would otherwise. The reason is the A/C turns on the fans and these run continuously. The fans running continuously while the A/C is on keeps the coolant temp lower and at a more consistent temp level than relying upon the fans to come on when the coolant temp climbs to 212F.

Sincerely,

Macster.

grdtii

What's strange is that the temp gauge stays right in the 160 range...even when I sat in over an hour of heavy stop & go traffic recently....the only movement is the level of the coolant in the reservoir....as I listed above, I noticed that after running for a short time...a/c off, the level in the reservoir expanded from in the lower portion of the arrow by the MIN designation to the top of the lower portion of the tank right below the lip of the cover of the tank, by the MAX designation. I am wondering if the operating level of fluid on my car is lower than the MIN level and that when it is operating at temperature, the fluid is evaporating out of the bleeder valve?

C4CRNA

It's an expansion tank. When the car is hot the coolant level should be near max.
When cold near min. Thats the normal range.

100plus

Change, water pump, thermostat, expansion tank and cap and hoses around the engine. VUALA!

Thats what i did ... haha