So after a little over two years and almost 20,000 miles of trouble-free ownership of my '04 Justa Cooper, I got my first ride on a tow truck today.

I was on my way back from work and stopped at a light. I noticed the temperature needle was PEGGED and the red light was on! Crap! I turned the heat up as far as I could, then pulled into the nearest parking lot and shut down. The temperature came down fast as soon as I started moving again, but I didn't want to take any chances. Aux cooling fan was screaming, and stopped after shutdown when the temperature got below the halfway mark (where it normally sits).

Popped the bonnet and there was nothing in the expansion tank.

My wife came to pick me up, and we went back to my parking spot at work. Sure enough, there was a pretty nice puddle of sticky-sweet coolant right under the spot where my radiator had sat all afternoon.

Even though it was only 5 miles, I wasn't going to take any chances and the car came home on a tow truck tonight.

I read as much as I could find on NAM about coolant leaks and water pumps and thermostats. I took off the plastic engine cover (on the bottom) and it was pretty well full of coolant. It looks like it leaked from somewhere around the bottom, passenger-side corner of the radiator. The water pump is totally clean.

I had filled up the expansion tank with plain water (it's all I had handy) before I drove the car up the driveway into the garage, and it all stayed in the tank. So I ran the car again, for about 10 minutes or so, to see if I could get some circulation and find a leak anywhere. The engine warmed up, and the temperature needle stayed right in its usual spot. The fan kicked on after a while, too. Water stayed in the tank until after I shut down and popped the lid. Then the tank emptied.

Still no leaks. After 15-20 minutes, I ran the engine again for another 5-10. Tank filled up with a water/coolant mix, but still no obvious leaks anywhere.

So I'm stumped. I definitely lost a lot of coolant today, but apparently not all of it. And I definitely pegged the temperature needle and got a red light at one point, but the aux fan is working fine. The pump isn't throwing fluid, and I can't find any obvious leaks, under pressure or not.

Any suggestions?

 

I had similar problems with my 2005 MCS, and it turned out to be a leak around the thermostat housing. After I had the thermostat replaced, the problem went away.

You might want to have your dealer/mechanic check that first. Good luck.

 

This sounds more mysterious than a leak around the thermostat housing.

Are you getting any puddling of fluid under the car again?

 

A got a couple of drops out of it after the second idle run last night, and NOTHING more overnight.

The reservoir emptied itself again. After work tonight I'm going to throw in a quart of straight antifreeze to balance out the straight water I put in last night and run it again. If it stays cool and doesn't leak at idle, I'm going to drive it around the block and see if I can get it to heat up real good and leak again so I can see where it's coming from.

I did notice one thing last night that struck me as odd. When the car was running, the radiator got hot in the top corner on the passenger side, but felt cool everywhere else, even when there was definitely fluid running through it (warm hoses on both ends), and even when the aux fan kicked on. I don't know how much you can tell from the surface temperature of the little cooling fins in the radiator, but it seems like it's not distributing the heat very evenly.

Is there a relief valve somewhere in the system? Is it possible that the coolant was low, I hadn't noticed, and it overheated and relieved itself, which led to more overheating later?

The other thing I'm thinking is maybe there's a crack in something somewhere that only opens enough to leak when it gets good and hot. That's what I'm hoping the road test tonight will help me find out.

I live in Vero Beach, FL, and the nearest dealer is a hundred miles away in Orlando. Parts availability kind of stinks, so I'm hoping it's nothing too serious. Hopefully I'll find out more tonight...

Thanks for the help,

Dave