Like many others, I had noticed that my coolant reservoir always seemed to be low. Since the reservoir looked OK, and after hearing about so many failures of the t-stat gasket, I ordered a new thermostat, housing, and gasket. My car does have 53K on it, so it seemed a possibility.

Put it in yesterday (a real PIA) but didn't bleed coolant system because I just did that 3K miles ago. I finished late, and figured today I'd check for leaks, bleed out any air that got in, etc.

First, I checked, and I didn't see any fresh wet spots under the car. So, as per the DIY on thermostat replacement instructions elsewhere on this site, I took the cap off the coolant reservoir, and loosened the top/front bleed screw. During all this time, the temp gauge seemed to be operating normally - it started out low, then sort of paused a bit at around 140 degrees, then when it got to just over 200 or so, the coolant began to seep out, so I closed the screw. Left the car running till the coolant fan came on, and turned it off. Temp never went to max.

Decided to look and see if there were any new leaks. I saw a LITTLE wetness on the ground below the bleed screw area. Figured that this was just from the seepage. But there was some wetness that accumulated under the edge of the engine shield below the car, and when I pulled down on the lip of the edge, more water came down - maybe a quarter cup or so.

Hmmm. Maybe I have a leak around the thermostat. Looked with the flashlight and didn't see any. I actually went to the trouble of taking out the airbox, ECU, etc. to where I could get a better look. I didn't mess with the thermostat bracket or unplug the O2 sensor or the MAP. I did readjust the clamps on the two hoses going to the thermostat so that they were in optimum position, to ensure a good tight fit. I saw no wetness in the area, though. I put everything back together.

Now, by the time I finished all this (since it took me about and hour and a half), the car was completely cooled off again. I start the car again - and WHOOOSH - the temp gauge shoots to max and the cooling fan immediately kicks on!!! Turned the car off, and the fan kept running - I had to go back and disconnect the battery to get it to stop!

Checked the coolant reservoir - and though there was plenty of coolant before, now it is dry. I fill it to the max line on the reservoir.

Reconnected the battery (cooling fan now off) and turned the key in the ignition. At position 2, the temp gauge needle pauses - for a second - at what I would consider the normal spot for a cold car - the first line on the gauge - then immediately shoots up to max and the fan kicks on again.

I have to go back and disconnect the battery again, to get the fan to stop.
No, as I go to the back of the car, I see a BIG area of wetness which had migrated down towards the rear of the car - under the entire car (I am on a very slight incline).

WTF??? Did something blow? A head gasket? Water pump? Is there some connection between my replacing the thermostat and any of these possibilities?

Now I am totally bummed because my car is not driveable and I don't know what's wrong..

Please help!

Melanie

 

More likely the new housing isn't on right. Did you scrape all the old gasket off? Are the hose clamps all tight? I wouldn't go assume it was anything except what was worked on (and what is right next to what was worked on)

 

I did clean where the old gasket was, there was really nothing to scrape off. I double-checked the hoses and clamps. There was nothing wet in the vicinity of the thermostat... that's why I am puzzled - also the weird behavior of my temp gauge - shooting up like that right upon starting the car...

 

Did you unplug the temp sensor or possibly break it off while in doing the thermostat? I would check that also. as default if it does not have a temp sensor reading the fan will come on and the needle goes straight to the top.

 

It's most likely something you did while replacing the tstat. Look under the front of the car. If it is dripping from the differential cover on the trans, it's probably the tstat that's leaking. If the coolant is coming from the front of the car, you may have a leaky radiator, or cracked hose flange. But check the stuff you messed with first. Also, it's good to make note of how much coolant came out of the car when you changed the tstat. You should have replaced about the same amount of coolant.

 

I haven't seen a t-stat from a Mini, but on some vehicles it is possible to install the t-stat backwards. Was it installed correctly?

 

I think you can fit this in backwards, but I doubt it would cause a leak. Could be wrong...

 

That sounds possible... I found a pic of where the sensor is located on the real OEM page.. What you describe as default setting describes exactly how it is acting now - the car is cold, yet the temp gauge shoots to the max and the fan comes on...

Before I start taking everything apart again, is it possible that a blown fuse in its circuit would cause it to go into default mode? Just trying to think of the easy stuff first!

Also, I am having a devil of a time trying to find a diagram that shows where the coolant temp sensor is located, relative to the area where I was working...

Is THIS the coolant temp sensor?

 

I can verify that it is possible to put the thermostat in backwards in my 02 S. I changed the thermostat and housing this weekend and found that the thermostat had been installed with the spring side away from the block, according to the Bentley manual, that is back asswards! Unfortunately, the thermostat will fit into the housing in either direction, that is probably why Bentley clearly states that the spring side goes toward the block.

I can report that the only issue I noticed with the thermostat installed incorrectly was that the heater was considerably slower to warm up this past winter than it had been in previous years. I had a local shop replace the thermostat last fall (my bad). I'll be doing my own thermostat work from now on...

Oh, by the way, your picture does correctly indicate the temperature sensor location.

 

Yup.

 

I recently had my t/stat replaced. Turned out the leak was falling right on to the sensor connecter, causing corrosion. The sensor had to be replaced also.

Jim

 

It is possible to put the thermostat in backwards. It will still open some as heat is passed to the other side.

When bleeding the system, you didn't mention whether or not you turned the heat on.......?

 

When you giys say "backwards" do you mean with the spring side facing out? I put it in with the spring side facing into the block, and the smaller pyramid-shaped part facing outwards into the engine bay...Does that mean that I installed it correctly?

I did NOT put the heat on when I replaced the coolant afterwards - I should have, in retrospect, but would air in the system alone account for the weird gauge readings everytime I turn the key on? With the exception of a 1 second hang at the correct number, the needle jumps all the way to the MAX and the fan comes on right afterwards...

I suspect it's the sensor, and will check that out when I take it all apart again this weekend... <sigh>

 

Thanks - this was the bit of information that really helped me nail the problem.

Today, I took everything apart - for the third time - and discovered that the socket/holder for the coolant temp sensor had been pulled back slightly - so it was not making full contact. That explains why it worked at first, and not later. When I went back in the second time, partially disassembled everything to get to the hose clamps, I must have knocked against the plug - just enough to partially pull it out! (I was really surprised that the socket doesn't click into place to prevent this, but it doesn't!)

Your comment about the default setting for the sensor was very helpful. After I put everything back together (triple-checking that the socket was pushed in all the way) - I started the car, and all was well!

Now, I have to just be sure that there are no leaks (I didn't see any when I checked in the area of the t/stat with my flashlight) - and bleed the coolant system a few times to get rid of any air pockets...

to be continued...

 

good to hear!! glad it helped. Happy Motoring!!

 

I recently replaced my t-stat along with flushing the system. Decided to do this since I had easy access while I was refreshing the super charger oil. Another story. I have a 06 S, 97k on it with the Alta CAI and 15% pulley. I have owned the car since I drove it off the lot with 17 miles on it. Since I did the flush I have noticed that the area where the heater core is seems exceptionally warm. (inside the car, middle, by the gas pedal, the plastic cover is very warm to the touch) When I bled the system I had the heat on and used the 2 bleed screws till coolant was flowing out of them at which time I tightened everything. I do recall having drained the system a couple of years ago and having a problem getting the heater to blow hot air after I refilled everything. That corrected itself.

According to the temp gauge everything is normal. Once its up to temp the needle is dead middle with very little movement. Any thoughts?