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View Full Version : Coolant leak in summer but not now



BikerBill
10-18-2011, 05:38 PM
During a few hot (low 90ís) days in July my 2000 A4 was losing a significant amount of coolant after a modest drive. Thereíd be a puddle the size of a sandwich plate underneath the car pretty much in the center of the car near the firewall. I looked for leaks in hoses, connections, etc. but didnít find any. I assumed the heater core had gone and bypassed it. That stopped the coolant leak.

Itís getting time for heat here in New England so I hooked up the heater core again to verify it was leaking before I tried to repair or replace it. I no longer have any coolant leaking. Not a drop. The only difference I can point to is temperatureówhen it was leaking it was hot out, and now itís not (50ís in the daytime). Iím wondering if I have a bad cap on the coolant expansion tank and the system got overpressurized and forced coolant out somewhere near the heater core, possibly where the heater hoses connect. I checked for stains on the carpeting below the heater core and couldnít find any so Iím not sure the core was ever leaking.

Is it possible I have a bad expansion tank cap? Do they usually fail by releasing pressure too soon (low pressure) or too late? The car has 195,000 miles on it. Does someone have another explanation as to what might be going on? Iíd really, really rather not replace the heater core if I donít have to.

SS92
10-18-2011, 06:13 PM
During a few hot (low 90ís) days in July my 2000 A4 was losing a significant amount of coolant after a modest drive. Thereíd be a puddle the size of a sandwich plate underneath the car pretty much in the center of the car near the firewall. I looked for leaks in hoses, connections, etc. but didnít find any. I assumed the heater core had gone and bypassed it. That stopped the coolant leak.

Itís getting time for heat here in New England so I hooked up the heater core again to verify it was leaking before I tried to repair or replace it. I no longer have any coolant leaking. Not a drop. The only difference I can point to is temperatureówhen it was leaking it was hot out, and now itís not (50ís in the daytime). Iím wondering if I have a bad cap on the coolant expansion tank and the system got overpressurized and forced coolant out somewhere near the heater core, possibly where the heater hoses connect. I checked for stains on the carpeting below the heater core and couldnít find any so Iím not sure the core was ever leaking.

Is it possible I have a bad expansion tank cap? Do they usually fail by releasing pressure too soon (low pressure) or too late? The car has 195,000 miles on it. Does someone have another explanation as to what might be going on? Iíd really, really rather not replace the heater core if I donít have to.

If it was in the center of the car or on the sides of the tranny bell housing, my first guess would be the Coolant flange on the back of the head. Have you checked that? Its a common failure on our cars.

Just my guess... mine just epic failed in my apartment complex the other day... Gone through a jug of coolant already. Need to get a new one in.

BikerBill
10-19-2011, 07:41 AM
Does my 2.8L V6 have that coolant flange or is that only the 1.8 turbos?

SS92
10-19-2011, 07:49 AM
Does my 2.8L V6 have that coolant flange or is that only the 1.8 turbos?

I had assumed you had a 1.8T. I'm not sure about the 2.8's. Thats a question for someone else.

seanj130
10-19-2011, 08:06 AM
Maybe you are just out of coolant?

Colorado_Mike
10-19-2011, 08:45 AM
It sounds like your heater core has/had a leak because you said your coolant was leaking but then stopped when you bypassed the heater core. Two possibilities come to mind. Either the (pinhole) leak in the heater core calcified and kind of sealed itself while you had it bypassed, or you didn't properly 'burp' the system when you hooked it back up and there's an air pocket in the heater core now.

BikerBill
10-19-2011, 09:18 AM
Sean,

Coolant level is fine.

Colorado Mike,

I'm not lucky enough to have the core self-heal. The core did just "sit" in the car for about 3 months with coolant and no pressure in it though . Your other suggestion about the core having an air pocket is worth some follow up. When I reconnected the heater core I didn't spend a lot of time getting air out of the system. I will do a more thorough air purge today. I do get plenty of heat out of the heater, though. So I don't think it's what you'd call air-bound.

Thanks for the suggestions.

Colorado_Mike
10-19-2011, 12:42 PM
Another possibility, however remote, is that one of your hoses was leaking a little bit and through the process of disconnecting/reconnecting them, you've resealed it. The bottom line though is that if it's not leaking now and it's blowing heat - drive it!

BikerBill
10-19-2011, 05:11 PM
I repurged the cooling system today. I'm going to to exactly what you suggested--drive it and see what happens. Perhaps fiddling with the hoses "fixed" a marginal connection problem. Thanks for your help on this.