So, my stock 03 MCS was overheating so I changed the water pump and thermostat. Got everything back together (with several bumps along the way) and now it's still overheating. I let it run with the heat on and bled the system (no hot air coming out BTW). The cooling fan comes on at 235f, but it does almost nothing to bring down the temperature. Any ideas on where to go next?

 

Two causes could be a coolant expansion tank leak, or a failed tank cap not holding pressure. Dried coolant on side of tank would be indicative of either.

 

These first gens can be hard to bleed out all of the air. After bleeding with the bleeder on the top hose, have the heater at highest temp, then bleed for cool to warm, you can just crack the bleeder a little (without removing the bleeder), run it to operating temp. Rev it a few time, to make sure coolant is circulating. Shut down, cool off, remove the fill and install coolant to a little more than half fun in the expansion tank. If you are using the original plastic one, it could be split on the seem and still look good, but will cause it to overheat, if it is leaking!
Many of us buy an aluminum tank, that takes the stock cap.
You can see mine in the JCW area in the gen 1 section under Just scored a 06 JCW in the JCW area!

 

I just changed out the expansion tank with a new one. I bled the system twice and it's still overheating and no heat from the heater. I'm at a loss. The only thing that hasn't been changed now is the heater core. Could that one piece keep making it overheat?

 

Couple questions.

1) You mentioned a new tank. I assume a new cap too, correct? Bad caps that can’t hold pressure can cause overheating.

2) When you bled the system, did you bleed from the lower bleed screw first? That screw is steel, and is situated in a coolant pipe below the thermostat.

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The following coolant change and bleed instructions are from
BMW Tech ​Information System, 1982-2004, v6.3.1.23B / ​Series R53, engine W/11 Cooper S

· Elevate the vehicle safely on jack stands.
· Place tarp or plastic sheet under vehicle.
· Remove cap on expansion tank.
· Remove the under body protection panel.
· Disconnect the lower radiator hose, drain and catch the old coolant.
· Crack upper plastic bleeder screw to facilitate draining.
· When it stops flowing, reconnect the hose.
· Loosen LOWER vent plug (10mm bolt) under thermostat housing.
· You already loosened the UPPER vent plug in radiator hose.
· Leave BOTH plugs loose so system vents during filling.
· Slowly pour fresh coolant into expansion tank, watching lower vent screw.
· When coolant emerges from lower vent screw (no bubbles), tighten it.
· Fill expansion tank until coolant stays at the MAX line without dropping.
· Place the heater control on HIGH and fan on LOW
· Start the engine, run at idle, slowly adding coolant if the level drops.
· With the TOP bleeder screw cracked, idle until thermostat opens (196°F)
· Watch the TOP bleeder screw carefully and close when coolant escapes.
· Make sure coolant stays at the MAX line in expansion tank without dropping.
· If it drops, slowly add until it stays at MAX level.
· Take car for a short drive, re-check when cool, and top off (to MAX line) if necessary.

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Expansion Tank Cap Pressure: 14-15psi

For every PSI of pressure the tank holds (the MINI R53 cap holds 14psi), the coolant boiling point raises by 2°F, so if working properly, the coolant can go as high as 240°F (115.5°C) before boiling. If the tank isn’t holding pressure, either due to a failed cap or a split in the tank itself, the possibility of overheating raises exponentially.

 

Thanks for the info! So, I followed the steps above. When the thermostat opened, my level dropped in the tank. I added coolant to it, but I never got any coolant out of the top bleeder port. As it got hotter, the expansion tank filled back up and start sounding like there where marbles in it. All I got out of the tip bleeder was hot air coming out. I tried again with the same results. Do you think there is a blockage somewhere in the system?

 

The "marbles" sound might be your coolant boiling due to the cap being off the expansion tank. Let the coolant come back down in temperature, then try it again with the top bleeder screw removed completely. With a penlight or similar, shine the light in the hole and watch the coolant level in the hose. When the thermostat opens, you should see coolant flowing, then eventually filling, then seeping out the hose. Coolant level should be filled to, and stay at the MAX line, about halfway up the tank.

You mentioned a recent thermostat and water pump change.

Is it possible you installed the thermostat backwards?
The spring portion should be towards the inside of the head.
THIS photo shows proper orientation.

Was the water pump you recently installed an OEM pump?
Some of the aftermarket pumps have plastic impellers and are known to fail in short order.
Are you hearing any odd noises coming from the water pump area?

 

The water pump was after market, but had metal impellers. I'm pretty sure that I installed the thermostat the right direction. What's weird is that this the first time I haven't had fluid come out of the top bleeder. I sucked the fluid out of the radiator when I started the process earlier. I'm not sure if that has anything to do with it. The coolant comes back into the tank and bubble over (I think air being pushed out) at 221f (according to my obd2 reader). It held that temp for a few minutes, which is better than it has before. There are no weird noises coming from the water pump area either.

 

It sounds like the controller, is not setting it to heat mode, or the ac is running. I doubt this is the reason it is overheating. Again, bleeding these cars can be a royal pain in the butt!make sure the heater is on high heat too!

 

The system is likely not bled right. 1st gen is a pain to bleed but I would rebleed everything until you verify the heater core is opening.

 

I, personally have not had difficulty changing coolant or bleeding the system on my R53/W11 if adhering to the protocol I listed previously.

Maybe best plan at this point is to drain all the coolant and start over, using the instructions I listed above.

 

Was the bleed process performed at BOTH bleeding ports or just one.
Fact you now have no heat indicates air in the system.

 

I changed out the heater core yesterday and bled the system again (both bleed ports). The car still overheated, and I still have no heat coming out of the vents. I kept the kick panel off to see if the two heater core lines were getting hot.... They never warmed up. This leads me to believe that coolant isn't getting to the heater core. The thermostat is opening (verified by coolant being sucked into the system rapidly from the expansion tank). What controls the flow of fluid into the core? Could it be something to do with the a/c ****? I have it on full heat every time.

 

I used both ports, multiple times. Now there is no hot coolant going to the heater core, which needs to be happening for me to properly bleed the system.

 

Someone correct me if I'm mistaken, but I don't believe there is a valve that selectively routes coolant into the heater core or not.

The water pump controls all movement of coolant through the system. The thermostat is the only mechanism in the system that can control the flow of coolant, opening only when the engine comes up to temperature, which then sends coolant to the heater core.

The level in the expansion tank should not drop when the thermostat opens. Only change that should occur is coolant moving through the radiator hoses. Before the thermostat opens, there's coolant in the radiator hoses, but it's not moving, since the the thermostat hasn't opened to allow that coolant through the system.

My understanding is if the thermostat is open, coolant is always flowing through the heater core, and getting heat into the cabin is just a matter of the heater fan blowing air through it or not, which of course would depend on (A) the climate controller being on, and (B) the ambient temp in the cabin, which would activate the fan.

Since the heater core is not even warm to the touch, it appears the coolant is not making it that far, which would lead me to believe you have either a (1) thermostat which is improperly installed (backwards?); (2) The thermostat is faulty and stuck in the closed position; (3) A failed water pump; Or (4) a large pocket of air still in the system.

Not sure there's much more it could be, outside of the somewhat unlikely circumstance of a total obstruction somewhere in the system.

 

I have only speed read this thread. I wonder why no one question if OP install the thermostat backward. If I not mistaken, his remark was "I am quite sure I install it correctly". I correctly pointed out a photo of one of the supporting vendor has the thermostat installed backwards. Short of that the radiator can be clogged due to corrosion caused by the use of wrong coolant. This is very rare these days however.

There is no valve to control the engine coolant to the heater core. It always runs. And the other common mistake is the OE water pump has metal (but in fact has plastic) impeller while some aftermarket pumps have "cheap" plastic. There is nothing wrong with plastic if designed and manufactured right. Without plastic most consumers cannot afford a car that we take so much for granted.

 

Probably should have read more carefully, as in Post #7 of this thread, I did just that.

Also in Post #7, I included a link to a photo of a correctly installed thermostat.

I mentioned that in Post #15

Back to Post #7, I mentioned that too...

Speed reading is way overrated in my opinion. Just sayin'

 

Yes. I did note that you had the most exhaustive remarks, but short of more directly question if he is sure he has the thermostat installed correctly. I stand corrected for not giving your replies more credit. My post was more directed to the repeating allegation that the system was not properly purged of air. I have never encounter difficulty in purging out air from the cooling system. The 20-step of how to purge your R53 coolant system is too overrated. My three step technique has served me well each time. Again the OE water pump has plastic impeller while many aftermarket tout the virtues of metal. I will take the OE pump unless the price is way out of line. The chance of a new water pump failed right away is next to improbable now matter how crapy it is - just saying.

Let me just throw these out there to OP:

• When you removed the water pump did you check the supercharger PTO?
• Is there any evidence that the old water pump is the cause of overheating? Most water pump need replacement because the seal leak but slowly leaking water pump does not cause overheating unless excessive coolant is lost.
• If you didn't check the PTO gears and indeed they failed, it would explain your experience.
• If you installed the thermostat backwards, it would also explain your experience.
• After replacing the thermostat did you perform postmortem to verify you alleged diagnose hold any water? I would test the thermostat in boiling pot of coolant to see if it fails to start to open at near boiling point.

I can never stress enough to seek evidence that you diagnose a problem correctly. It is called postmortem. Too many just replace the part and if the symptom seems to disappear then call it good.

 

I thought my question, again, in Post #7, was as direct a question as can be...

I asked...
"Is it possible you installed the thermostat backwards?"

To which the O.P. replied in Post #8 ...
"I'm pretty sure that I installed the thermostat the right direction."

Let's please focus on helping the O.P. (which I've tried my best to do) and not quibble over semantics...

 

My point exactly. If it were me "I'm pretty sure" is simply not good enough in his situation. I would want to know for sure I had it installed correctly. My post was intend to point out the gravity of this simple potential error that is very easy to make.

 

Just took the thermostat out; it's installed correctly.

 

I would almost bet a donut for a dollar that most likely the problem is failed PTO gears, only that I don't like donuts. My Mini is crazy about donut tires that are. If your water pump does not spin by it you will have the symptoms and experience you described. I am not there to witness nor you provide adequate history so don't take very thing I say without consideration.

 

Curious as to whether you performed the 'boiling water/cold water test' with it to check for proper function?

 

I am going to test the thermostat tonight. I hate starting to guess whether or not a new component is bad. I ran a production control office for helicopter maintenance a few years ago. It gets very costly throwing parts at something hoping for a fix. "Most" new parts should be good out of the box. Is there any way to confirm that the water pump is spinning? The old one seemed fine when I took it off. I will have to look into the PTO gears tonight as well.

 

I'm going to tonight. As disheartening as it would be, I hope that the new one turns out to be bad when I run the test.