Sorry in advance for the long post.

About 4-5 weeks ago I noticed a tiny drop of fluid under the left front end of my car. I traced it down to a leak in the left radiator cylinder. It was extremely slow and over a period of 1-2 weeks I didn't notice any change in my coolant levels. I wasn't having any overheating problems at this point but I thought I'd have it looked at.

My local mechanic suggested that I had 2 options - 1) replace the radiator, or 2) repair the leak. We decided on the repair as they suggested that they have good success with repairing small leaks with sealants. They repaired the leak with some form of liquid sealant. It seemed to work, there was no more leaking under the car. About 2-3 days later I noticed a gurgling sound coming from the engine bay, especially after longer rides (45 min-1hr). Even when I first start the car I can hear a faint sound of liquid flowing - I never noticed these types of sounds before. A day or so later after turning off the car I noticed the fan coming off - sounded like a jet plane. I've owned this car for over 3 years and I've never heard this come on before. I contacted the mechanic and he re-assured me that the fan coming on was normal and not to worry about the gurgling sounds as long as the car isn't overheating. Something had changed and I thought perhaps the sealant messed something up. About 2-3 days later while stuck idling in traffic the car started to overheat - needle moved up to the red zone. I pulled over and shut the car off and checked the coolant (normal levels). I waited a few minutes and drove off. As long as I was driving or wasn't idling for no more than 1-2 minutes the car wouldn't overheat.

I took the car to the mechanic and they told me that my thermostat was stuck / not working properly. They replaced the thermostat and flushed the coolant system. I still noticed the gurgling sounds driving home and the next day during my commute to work the car overheated again while idling. I checked the coolant expansion tank and I noticed some sediments in the bottom of the tank. The mechanics where not sure exactly what was wrong, they pumped the sediment out of the tank (sealant remnants) and they suggested that I could have a bad radiator (flow problem) or a head gasket problem. I decided to do a little of my own research. After checking a variety of threads on this forum I figured out that both my fans where working properly (coming on at the proper temperatures), the water pump appeared to be working (cabin heater is working fine), and there was no white smoke coming out of the exhaust or any water / coolant in my oil.

After reading about radiator sealants clogging up radiators, etc. I decided to have the radiator replaced. They replaced the radiator and after testing the car re-assured me that everything was working perfectly. The next day driving to work the car overheated again while stuck idling in traffic :(

I'm not sure what to do. I asked my mechanic about air in the lines and they re-assured me that they use a vacuum when re-filling the coolant so there shouldn't be any air in the system. I asked them about the bleed valves and they where unaware of any bleed valves for my car but suggested that the method they use would not allow for air to be trapped in the coolant system. I was going to bring my car to another mechanic in town who specializes in radiators to see if they have the tools to test both flow and compression. If I don't get some answers I'll have I'll have to go to the dealer as it's getting expensive to keep replacing parts. I would have brought it to the dealer sooner but it's hard for me to take the time off work in order to make the trek.

It could be co-incidence but I have a gut feeling that the sealant has messed something up - perhaps the water pump, one of the lines to the radiator? The coolant expansion tank doesn't appear to be bolling like a pot on a hot stove would, the bubbles only appear to be shot up from the feed line at the bottom of the tank. I wasn't sure if this was indicative of of overheating, air in the lines, or both.

My cooper has just over 100,000 kilometers.

Any thoughts??

 

Sounds like your having problems with getting the air bled out of it.

 

I'm hoping it's that simple. I plan on picking up some coolant and trying to bleed the system before I bring it to another mechanic.

 

Start with the easy things first. Check here for bleed procedure. It's common for a MINI to not be properly bled. A big for your mechanic for not knowing about the bleeder screws.

 

After doing some research I decided to bring my car to a radiator shop in town for a combustion leak test to rule out a head gasket problem. It would be pointless to bleed the system if the problem was a faulty gasket or crack in the head as the air would simply return. The lady on the phone at the rad shop reassured me that they would do the test and check the car out for me. I got the car back and they told me that they could not find anything wrong with it and that they didn't have the tools to perform a combustion leak test. Nice of them to inform me after the fact, considering this was the only reason why I brought my car to them! They further informed me that some gurgling sounds in the engine bay and having the loud fan come on is often normal. NORMAL They suggested that I take the car to the dealer to have the electronic checked out. ELECTRONIC ??? - why would they even consider this when the fans are working, the ECU is registering the coolant temperatures, etc. I decided to purchase my own combustion test kit and after doing some further reading I also picked up a new radiator cap. The combustion leak test was negative for combustion gases in the coolant system so I decided to install the new radiator cap. It's been about 2 weeks after having installed the radiator cap and there has been no overheating, no funny gurgling sounds in the engine bay, no boiling or bubbling in the coolant expansion tank, and the stage 2 fan stopped coming on.

Just imagine if I would have brought my car to another mechanic or even the dealer for that matter - more parts, more $$

Don't underestimate the role of your radiator cap!