Coolent leak
 

So, I get in the car Monday and after about 3 mins of diving the light on the temp gauge "low coolant" light start flashing. I'm not surprised to see this as I can occasionally smell coolant and assumed the tank was starting to leak. Light stops blinking after about 5 more minutes and is intermittent for the remainder of the day. No sweat, I top it off that night on my way home (over filled it unfortunately, but it was dark) figuring I'll tackle it post holiday. Fast forward 4 days to this morning. I'm 5 minutes into my morning commute and the coolant light starts blinking and then goes out again. I park and go into the office. I come back around 10:00AM to a huge puddle on the passenger side just in front of the rear wheel. I check the tank and fill again with the remaining 1/2 gallon of coolant.

So I know I need to get in there and see why it's puking coolant everywhere, but I was wondering if anyone had any guess as to what has failed?

Yea... I know how to spell coolant...:o

Classic cooling tank failure (rear trunk, where you add coolant). Tank is plastic and eventually cracks. It cannot be glued and needs to be replaced.

Don;t fool around with leaking coolant. These cars will overheat very quickly and catastrophically.

Bear with me Jeff as I've not yet seen how the system is routed, but I always thought that cracked expansion tanks typically leaked into the trunk. I guess the back of the tank is located in front of the rear axle.

Best source for the part?

I've already bought one of these:

The puddle you saw is where the car puked coolant out of the overflow tube because the coolant system couldn't hold pressure because of a leak and boiled the coolant.To check if its the coolant tank, you have to remove the carpet and subflooring the trunk to check for coolant under the coolant tank.

218.42 from sunset imports.
order also a new cup.
i replaced the oil filler tube in the same opportunity.

They tend to, but they can also leak near the rear tire as well. Check under the trunk carpeting, which you will need to remove anyway to get at it to change it out. If the trunk is dry, look up from below at where the tank connection hoses go thu the firewall, it could be one of those as well. While under the car, check the overflow line as well for wetness, if you just had an air pocket due to dumping coolant, you should be able to see dampness on the line.

Regarless of what failed, go with Sunset for the parts.

Additional thought: Check the last two digits on your cooling system cap. If they are lower an "-04", you could have a simple cap failure. Both the cap and tank can be pressure tested if you can get access to something like a Stant cooling system pressure tester; but if not and the cap number is low, you would be spending about $100 to buy a tool to test a $17 part. Can it and get a new cap if it is a low number, but be sure to either evacuate or burp the system to get any air out.

Mine has also just done the same thing last night,
As I was parking the car, the fans kicked in then when i got out of the car I noticed it dumping coolant near the RHS rear wheel,
I Let it cool down for a few hours before driving home, had to add about 2-3 litres for the light to go off, drove it home for about 20 mins no sign of over heating,
check it this morning and coolant tank was full

Do you think its the coolant tank? I

I have just recently replaced my water pump & added low temp thermo stat,

Cracked tanks are repair staple on these cars, but as mentioned above, there are diagnostic pathways to determine the leak source. Look under the carpet in the rear trunk for signs of being wet, check the number on your cooling system cap to see if it is an old one, pick the car up and look for where it is coming from. With real hard to find leaks, you can add a cooling system dye that collects at the leak point and fluoresces under UV light, which is very useful in problem cases.

One of the most useful tools any backyard wrench may own is a good cooling system pressured testing system that can pressurize the entire system to check for leaks, as well as test the cooling system caps in a matter of a few min. on any car. You might be surprised how many bad caps we find while doing regular pre-winter maintenance checks on customer cars.

I checked the carpet yesterday, no sign of any moisture, topped up the coolant and bled the system again, let the car idle for about 2 hours no signs of any leaks or over heating at all,

My guess is the cap wasnt holding pressure causing a air pocket, and i didnt bleed it properly when i added some redline water wetter

dsisco...
Did you open the bleed valve (under the plastic cover below the coolant fill cap) for a couple of heat cycles after you installed the pump / 'stat?
If you didn't there is a very good chance you still have air in the system.

yeh i have, im gonna leave it open for a couple of days, and drive the car, to get all the air pockets out

Tested my car again today, was the tank cap, doesn't hold pressure and coolant was coming out from there.

So if the tank cap will not hold pressure, is the overflow diverted out of a drain hose like a conventional cars radiator cap diverts to an expansion tank?

Correct. The system has a drain line that runs downward under the car, where the coolant will blow out. These caps are supposed to hold around 18 PSIG, but often "pop" as low as 8-10 PSIG when they get older. That is why we always test them on any car in the shop.

Can someone in the know comment about this practice. Will this work or will air be drawn in when the system cools? I bled mine based on the Bently book (I think), that has you open the valve for a series of idle-to-5500 RPM cycles, then close it.

Dan, the Bentley manual is correct, but if you leave the bleed valve open for at least 3-4 heating / cooling cycles, you will see the coolant level stabilise, indicating that any small air pockets have been removed.

tested the car again tonight, was definetly the cap, its got to the point where it doesnt hold pressure once it get extremely hot, coolant was spewing out from there,