So I posted a thread a week ago about my mini overheating. Well I just replaced the radiator fan, the power steering fan, the thermostat and housing and replaced some fuses. The car was running perfectly for a couple days and then today the temp gauge started showing that the car was overheating...this time while moving at a good speed (30+ mph).

I immediately switched it to full heat and the gauge dropped back to normal. then it crept back up to hot again while moving. I switched it back to full cool and the gauge went back to the middle.

Just yesterday I noticed that the fan would turn on full blast after I shut the car off and it has never done this before. After fighting to keep the car cool on my drive home I checked and made sure that the fans were turning on and they were. The gauge would creep to the hot mark even with the fan running at full speed! What the hell is wrong with my car?? This is getting so damn frustrating.

 

Any odd noises?? You bleed the bubbles out when you did the thermostat right? How many miles total?

 

The fan is noisy, tried to bleed as best I could with only having access to the one bleed screw, and the car has 83k miles.

 

If you hear gurlging in the system you could have some air pockets.

Also, just turning the bleed screw is not enough. When bleeding the system, you have to turn the heat controls to high heat. The second bleed screw is by the thermostat, it looks like a bolt head. Just loosen it some if need be until the coolant starts to come out, don't remove it.

If you already did all that. Could possibly be the water pump or the thermostat was put in backwards restricting the proper flow. ( spring on incorrect side )

 

I can't get to the second bleed screw with everything in the way on my S. I don't have a long enough torx screwdriver. How does everyone else get to theirs? Also, I'm pretty sure I put the thermostat in the correct way. Put it in the way it came out.

 

You have to find a way to get to the bleed screw. I had a problem after changing the thermostat housing on my cooper, and went back in and did a careful bleed from both screws. LOTS of air came out (even though I thought I'd done it well the first time).

Today I sat basically stopped in traffic in Boston for 15-20 minutes at a time over a three hour period in 100 degree heat with a/c blasting and the temp never moved above its normal position.

 

Ok I'll give it a shot in the morning, hopefully air is the only problem. Will probably be selling this thing after this.

 

Well I've been bleeding all day and it still wants to overheat. It takes a long time for it to get there, but its 98F outside and once I start driving around the block it will creep past the middle, the high speed will take over and it just keeps steadily moving towards the red before I have to shut it down. What could be causing this? I don't think I put the thermostat in backwards because I drove the car for 3 days and it was running perfectly until yesterday.

 

Ok guys, after 7 hours of bleeding and re-bleeding, I have made no progress. I need the creative minds here to help me out because I have exhausted all of my resources. I have no other transportation and this car has only been usable for 4 days out of the last 14.

 

Take a look at 2 things...just to make sure nothing worse s going on...look at the underside of the oil filler cap, and look at the oil. The cap should be pretty clean...not creamy, and the oil should look like...er..oil...no bubbles, creamyness, or other oddness.
I know when I bleed mine, I had to add 2 or 3 cups of coolant to make up for what I lost comming out the bleed line...I drove it..bleed it..drove it bleed it....and by the second or 3rd time it was bubble free...it does take some time, and you must add coolant to the tank so you don't re-introduce air into the system...
If it seems to be bleed ok, and the fan is running...and there are not any noises.... It might be time to get it looked at.
One thing....is the motor idling quietly? If you have a clanging, kinda like chans dragging or rattling, then there is a different problem...
The problem is the infamous SC water pump gear issue, covered in several threads...but it makes a bit of a rattling, even maybe a hi-pitched noise at low speeds as the gears get ground down to nothing from lack of lube...end result is the waterpump wil stop running...car overheats...and it needs a rebuilt SC and waterpump....but the noise is usually noticable...so it is unlikely it is you problem unless the car suddely changed in sound....

 

If you drive the car enough, and keep coolant in the expansion tank, it will eventually expel the bubbles. Check your fuse box: count 5 fuses back in your engine bay fuse box. It should be an orange 5-amp fuse. Check it.

 

Also, I would add that.....With your car cool, like first thing in the morning, squeeze the upper rad hose. Does it have any pressure pushing back? If so, release the expansion tank cap slowly to relieve any pressure. Top off coolant, reinstall the cap and start the car. Immediately go to the upper rad hose and squeeze it again. It should take a while to build pressure and if it does right when it's started, you have a blown head gasket. That would also explain the constant air pockets. Other symptons would be a skip in a cylinder right at start up that might clear up right away. Good luck...may the shwartz be with you..

Chad

 

Also, keep in mind that a cooling system MUST be pressurized to work properly. Pressure raises the boiling point of the coolant. No pressure = coolant boils in the cooling passages around the cylinders and in the head. And that means micro-air bubbles on the walls of the cooling passages. And that means the cooling passage walls are then insulated and heat can not transfer as easily to the coolant which then results in the engine getting even hotter and the cycle repeats.

Common reasons why adequate cooling system pressure cannot be reached and/or maintained:

Bad seals on pressure cap.
Air in system prevents pressure buildup.
Any tiny pin hole leak. You might not even notice fluid as it might evaporate quickly due to engine heat.

A common way that air get's into the cooling system after you've burped the system is through the overflow system. As the coolant heats up it expands and extra pressure in the form of coolant is expelled from the main part of tghe system and into the overflow tank. Then, when the engine is shut off and the coolant cools and contracts, a vacuum is created and that fluid is sucked back into the engine. But, if there are any leaks in any of the hoses or connections in the overflow system, even though it's not a pressurized part of the system, when the engine cools, it can suck in air through the leak rather than the fluid it should suck back in. So, clean and check all connections and hoses in the overflow system.

Hope that helps.

 

Checked the oil already, nice and smooth and black. No residue underneath the oil cap either.

Now that you mention pinhole leaks, I can hear a tiny whistling from the overflow tank when the car is cooling down. It sounds like air escaping. Could a tiny leak like this really be causing my problems?

 

That tiny leak could be overpressure due to blown head gasket or like the other poster said a faulty coolant cap.

Chad

 

Well I don't know what to do anymore. Tried some more to bleed it and it still overheats. Rented a compression tester but the damn mini spark plug tubes are too small for any of my sockets to tighten the thing down. And now all the shops around me are closed until Tuesday. FML.

 

.....Is there flow? Your heater won't work very well if you don't have good flow. I'm not talking about the heater working after the entire engine is to the point of overheating. Within 3-5 minutes the heater should be getting pretty warm. You can grab the rear heater core hose and feel them. Don't have flow, only one of the hoses will be hot. Did you check for a blown head gasket or an overpressure in the coolant system?

Here is another way to check. http://www.arrowheadradiator.com/hea..._leak_test.htm

 

Heater works great, but car overheats with it turned off

 

IT's not enough that your heater works...read my post again. Are both of your radiator hoses hot, upper and Lower? Again, not at the point of overheating....as the car is heating up. Example, even if you have a working waterpump, but have a radiator that is stopped up, you will have one hose that is very hot, but the other is substantially cooler.

 

so if you drive around with the heat on it does not overheat? If so it sounds like the thermostat may be stuck closed.

 

Ok I decided to just pull the thermostat again and see if it was backwards...thermostat was definitely going the right way. Boiling some water now to test it vs the original one that I pulled out to see if it works.

 

Scratch that plan lol. I'm an idiot and didn't even think that water cannot get to 195F since it boils around 180F in normal pressure. Any other way to test if a high temp thermostat like a mini's works?

 

Ok I just swapped out the new with the old. I know the old one worked so this will tell me if it was the thermostat or not...

 

A candy thermometer in a pot of water on the stove is the way that I have tested the opening of a thermostat.
Just be patient as it takes a while to get close to boiling. The numbers below are from Wiki Answers.

Approximate Boiling Temperatures of Water:
@Sea Level: 212F
@7500 ft.: 198F

Hope this helps...

 

Well I have some good news to report...it seems everything is in working order now. I will knock on wood that it is all fixed. Drove it around, fans never came on, upper and lower radiator hoses as well as radiator was hot, and after 15 minutes of spirited driving the low speed finally came on in my driveway at idle then promptly shut off. Gauge never went above medium. I can't believe I wasted 2 days screwing with this car over a bad, brand-new thermostat.