Hey folks - so i recently replaced my broken/leaking at-the-seam coolant overflow tank with an aluminum one. this was prompted by the engine temp hitting red line last week on my way home from work and finding the coolant tank to be bone dry. I immediately re-filled the coolant tank and waited for the temp to go back before driving home. Did not drive the car until i replaced the overflow tank a few days ago.

After installing the new tank, i just filled it up with ~1/3rd gallon of coolant (the level was a little less than halfway filled). Note: I did not bleed the system.

I drove the car for a few days and it was working fine - no leaks, no issues 0 i thought my coolant leak days were over! Sadly not. My wife called me after running some errands last night and said she noticed the temp gauge starting to rise (i'd advised her to keep an eye out for that and leaks). She was around the corner from my house so she just drove the car home. When i checked on it about 30 min later, there was a fair amount of coolant on the floor and it looked like the tank had boiled over. The tank was empty.

I spent a few minutes inspecting for other issues and found in addition to leaking from boiling over, the hose that runs from the upper part of the overflow tank and connects to another larger hose near the thermostat housing? had broken off!

So here are my questions:

1) Which part do I need to replace here?
2) What could have caused that to break?
3) Is the boilover related to this breaking?
4) Do i need to bleed the system properly?
5) What else should i be checking?

Thanks all!

 

Looks like this is the part that broke (https://www.ecstuning.com/b-genuine-...r/17127518614/). It's the t-connector that connects the overflow to the water pipe?

Any chance this is just a coincidence or could this have broken off due to air in the system since it wasn't bled?

 

Maybe but overheating, ruptured coolant reservoir, then a burst hose would indicate to me that you may have a) bad thermostat b) bad water pump c) bad head gasket. Suggest you replace the burst hose, refill, bleed the system then perform a pressure test on the cooling system. If it passes, bring the car up to temperature and check your upper and lower hoses to see if the thermostat is opening. If the cooling system passes, then do a compression test.

 

Thanks rat - so a few followups:

1) it looks like just the connector broke not the hose - should I I just replace the connector or both?
2) when I refill/bleed the coolant do I need to do a whole flush?
3) don't I need a special tool to pressure test the coolant? Does autozone let you use theirs?
4) what does a compression test entail

 

Oh and would you mind explaining what you mean by the thermostat opening/closing? How does the system work?

 

The tstat has a spring that will expand/open with heat and shrink/close when the car is cold. After you get everything back up and running be sure to check the oil to see if you have any coolant in it (will look like chocolate milkshake). Need to be sure the head did not warp.

 

Do I need to replace the spring hose clamps? Seems there is a mixed opinion as that and whether or not you should replace with normal screw in clamps

 

As I recall, the hose assembly includes the connector. I don't know if you can buy just the connector from MINI. If your coolant has been changed recently, then just add the correct coolant, bleed. Most auto stores like AUTOZONE will loan you the pressure tester as well as a compression tester but, if you've never done a compression test before, leave it to a professional. It requires removing the spark plugs from a warmed-up engine. With a MINI, it requires a long reach adapter. Also, get the parts counter guy to show you a thermostat and explain its operation. Since none of your OEM clamps have blown off, it tells me that they are in good shape to re-use. Obviously, you have other issues to solve.

 

There are a few things I would point out but may not be the root of your problems:

If you bought a cheap aluminum tank, it might come with a dead AL cap that has no pressure relief. If you don't know that I mean, go find the cap off the plastic stock tank and look at the inside. This may be the reason the plastic T-connector broke due to excess pressure from the overheating. The properly designed cap is there for this precise reason so no dangerous explosion.

Your original overheating may due to various reasons, including the thermostat failed. Go find a Youtube video on how does a thermostat work - I am sure there is one.

There could be other causes of your original overheating, like water pump, broken supercharger power take off if S, or just pure ownership neglect.

When it comes to coolant hoses and clamps, the factory ones are the best. Stay away from aftermarket sneak oil variety. Never throw away the factory spring clamps. They will last the life of the car.

Please search on this forum for how to bleed the cooling system. It is very easy.

 

Thanks pnw. Couldn't the original overheating have been the result of having not enough coolant?

 

hey folks so - made good progress today. replaced the broken t-connector, however, I lost one of those pesky spring clamps in the engine bay somewhere. i spent like 2 hours looking or it and couldnt come up with it. what should i do?

 

This is the only time that you should buy a crap worm-screw clamp.

 

I bought these from Amazon. I bought the cheapest as I am cheap.

 

In a sealed cooling system, coolant doesn't just get used up. If it was originally full, then one of two things happened: 1) A hose, coolant recovery reservoir or coupler failed due to age 2) A mechanical component in the system failed (as mentioned above), the thermostat, the power take-off that drives the water pump, the water pump itself, a blown head gasket.

 

After you get everything buttoned up, I would get a block tester and test your system for exhaust gases in your cooling system. If you have a bad head, pressure could be building in your cooling system causing hoses, expansion tanks and a bunch of cooling related items to burst....Even if you've changed everything and it seems fine now, it takes time for those replaced items to weaken from the exhaust pressure before they go bad again. This did not happen to my Mini, but it did in my Jaguar, two radiators later, I realized my head was bad, leaking exhaust gas into my cooling system.

 

I'm assuming it's a good idea to flush the coolant with distilled water before refilling? Do inneed to run the engine at all do this? Should I?

 

I don't see any benefit. I think there are way too much fear mongering about coolants. Just be sure to use the right coolant. Follow the money.

 

Normally, you would need to run the engine to bleed the system however, you can bleed without the engine running by squeezing the upper and lower hoses while allowing air out of the two bleed screw fittings. I also use my pressure tester on the reservoir while opening the bleed screws. The pressure tester forces the coolant into the system while expelling any trapped air pockets out through the bleed screws.