Coolant dropped a gallon?

[Dominic123]

I have a 2004 996 C4S with approx. 155K; I noticed a couple months ago that the coolant was below the minimum level; level stayed at same level until I had an oil change about a month ago; coolant was topped off and have been driving for a month with no issue; just checked last week and all good; then today while leaving work the coolant level low warning light came on and down a gallon.

 

There are no leaks anywhere and I haven't seen any fluid on ground in garage.

 

They did have to drop engine about 3 months ago and had to replace coolant along with new reservoir tank; anyway that there could have been an air void?

 

Car runs fine; any ideas?

Edited July 15, 2014 by Dominic123

[Ahsai]

Have you checked the dipstick for coolant? It's unlikely you have air void for 3 months. The other possibility is a cracked tank where coolant drops and burns on the muffler but a gal in a week is a lot.

[Dominic123]

I did check dipstick; really not sure what im looking for yet no bubbles or discoloration; oil was just changed a month ago and looks fine.

 

I do know when it was down it stayed at that level for 2 months and now a gallon in a week; if it was a bad head gasket wouldn't car run rough?

[Ahsai]

If there's no coolant in the oil, I think the best course of action is to pressure test the cooling system and get a new coolant cap.

Edited July 15, 2014 by Ahsai

[RFM]

If your car is a Tiptronic, check out the possibility of coolant infiltration, through the ATF cooler, in to the gearbox. This does not happen very often but still possible.

[Dominic123]

Mine is a manual; I did have the air oil separator replaced 3 months ago and it does have a coolant line that runs to it yet no leaks anywhere.

 

I have already replaced cap with new reservoir tank.

 

If it was a bad head gasket, could the gasket hold sometimes, then leak?

 

Maybe I need shop to pull plugs and see if any coolant.

[JFP in PA]

Mine is a manual; I did have the air oil separator replaced 3 months ago and it does have a coolant line that runs to it yet no leaks anywhere.

 

I have already replaced cap with new reservoir tank.

 

If it was a bad head gasket, could the gasket hold sometimes, then leak?

 

Maybe I need shop to pull plugs and see if any coolant.

 

 

You have two potential pathways here.  The cooling system has been opened, so it could be just an air pocket.  Or it could be more serious, such as a cracked head.  These engine's never blow head gaskets.

 

If the car was in my shop, we would top up the coolant tank to the correct level and then pull a vacuum on the cooling system with the Uview tool.  If there is air in the system, it will "burp" out under vacuum and the tank level would drop.  If there does not seem to be any air coming out, I would hold a 25-26" level of vacuum for about half and hour to see if it starts to drop, indicating that air is entering the system somewhere inside the system.  If there are signs of dropping vacuum, I would next pull the plugs, looking for obvious signs of one or more cylinders with "steam cleaned" plugs.  If any are found, I would then do a leak down on those cylinders as confirmation before pulling the engine to disassemble it.

[Dominic123]

Thanks for the input; topped off coolant and have driven 200 miles in last couple days and level hasn't dropped; maybe air void yet not sure if it could have stayed there for 3 months.

 

If she drops again will follow the above advice.

 

Thank you

[perryinva]

Don't know if it ever re-occurred, but I had a similar, though not as dramatic occasional loss of coolant a few years back, and I accidentially located the source as the o-rings on the oil cooler.  Under the right conditions of temperature and pressure, the coolant would slowly seep out, not enough to cause a puddle, but I occasionally got a whiff of coolant in the garage.  While replacing my AOS, I noticed dried red coolant on top of the engine when I removed the main air intake plenum. I replaced the orings probably a year and a half ago or more, and the coolant level has never deviated from the same level in the coolant take, for hot and cold. Its a PITA job, as anything on top of the engine would be, but well worth checking out.  PIctures in this thread: http://rennlist.com/forums/996-forum/730667-changing-out-those-old-motor-mounts-well-worth-it.html