I know this sounds a bit strange, but I would like to know if this has happened to anyone else.

I had a coolant leak a while back that only leaked when the car stayed at high temp for a while. I usually only drive 10 minutes to and from work etc so it took a while until I got stuck in traffic for 10 minutes. As I am getting home, the clutch petal feels funny and I can no longer get into gear. It happened instantly, from one shift to the next! I check under the hood when I get home and there is no coolant in the reservoir! I figured out that it was the master cylinder and replaced it (that master cylinder only had about 300mi on it). I filled up the coolant and monitored it every day looking for coolant under the car etc. It did not fluctuate at all. I drove the car with absolutely no problems for about 3 months. I checked the coolant before I went to work and the reservoir was full. On my way to work, I got stuck in traffic for about 10mins. I left work that night and noticed that the car got to temp a bit faster than normal, but the temp gauge did not go above normal operating temp. I got stuck in traffic for about 10 minutes. As I am pulling into my parking lot, the clutch goes out on me again and I can't go into gear. Fortunately I had enough momentum to get to my parking spot. I open up the hood and the reservoir is empty! I found out where the leak was coming from...the thermostat housing was cracked and I guess the engine had to build up a lot of pressure for it to leak and that only happened after being stuck in traffic.

Obviously there is no connection between the clutch hydrolic system and the engine cooling system, but this happening at the same time on two separate occasions seems a bit strange to me.

My theory is that the increased engine temps caused the brake fluid to get much hotter than normal and this blew a seal in the master cylinder causing the fluid to bypass the cylinder. BTW when I tried to bleed the system before I replaced the master cylinder, I could not bleed it. It would just pump the fluid back into the brake fluid reservoir. As I pumped the clutch pedal, it would just go up and down in the reservoir.

Is this an isolated situation or has anyone else had this problem?

 

I don't know how the coolant can be low and the M/C has to be replaced. When you bleed the barkes and clutch, leave the key on to activate the ABS and then bleed systems. Clutch and brakes have same M/C. Coolant is another reservoir. The M/C is seperated from the engine by the air cleaner which should keep the brakes from being affected by the heat.

 

I know they are different reservoirs...the coolant was low from a leak, it just all leaked at once for some reason. I am wondering if the increased temp from losing a lot of coolant has caused a clutch master cylinder failure on anyone else's car.

You have to bleed the brakes and clutch separately. They are fed by the same reservoir, but have their own separate cylinders.