Hey all.

After tediously searching NAM forums for similar issues, I can only post a thread to try to get this puzzle out of the way and to do things right.

About a month ago, I bought a 2002 R50 with now 189000kms on the clock. So far, it ran without an issue.

About two weeks ago or so, I got back from work and parked on my (fresh) underground garage spot. I noticed a curious kettle like sound, opened the hood and found that bubbles were going up in the coolant reservoir (which isn't part of the pressurized circuit, as far as I know).

I left the car cool for the night and checked the coolant levels in the morning. It was sitting somewhere halfway between min and max.

It is at this point that OBDFusion and my OBDII scanner get in the game. I logged the coolant temperature and turned the ignition on. On idle, the car went up to 94ish Celsius degrees. Nothing happened. So I started reving a little bit, and the temp went up to 106ish °C. At that point the fan kicked in (presumably on low speed), but the coolant was already boiling.

Inspected the system as much as I could without taking much things apart, couldn't find any trace of leaks. Next morning, the coolant was at a normal cold level.

Fast forward yesterday. Went on a 50k ride with the girlfriend. Next thing you know, on arrival at the beach the coolant reservoir was sputtering and overflowing like crazy. Didn't have the OBD scanner, so couldn't check temp (and gf was hungry as).

Two hours later, before leaving the beach, the coolant had almost disappeared from the reservoir. Luckily I had 50/50 mix in the boot "just in case". Topped it up gently, drove back home. This morning, cold level is just fine.

So I turned the ignition on after checking the coolant level and left the car idling for a while. Just for the sake of it, I tried to see if turning the a/c on or the heater on did anything. The reservoir level didn't bulge.
Car went up to temp (94°C ish), and minimal expansion happened in the reservoir. I started reving the engine slightly (2k-3K) and the coolant expanded. At around 103°C bubbles were seen inside and the reservoir was full and sputtering the poor PS tank nearby. Turned the ignition off, the bubbling/boiling/sputtering lasted a few more seconds and then the reservoir remained full, and still. I haven't checked yet if the level has gond down again.

So here is the summary if you're still bearing with me :

- Fan seems to kick in at the right temperature, on low speed.
- No traces of leakages anywhere. No traces on the garage floor.
- No water off the exhaust, no milky coolant, seemingly no traces of coolant in the engine oil
-Thermostat seems to open correctly at 91°C.
-Pump seems OK, for the radiators heat up and carry heat in a seemingly normal fashion.

Here are the things I want to check in that order :
- Expansion tank cap
- Circuit bleeding : I can't seem to find the third (deep) bleeding screw, didn't look too hard for it though
- Circuit leak : unfortunately in France you can't rent a manual pump and put the system under pressure. Will have to go to a mechanics to get that done.
- Coolant age : I have no idea how long it's been there. I suspect it is cooked, but I don't have jacks to proceed with a full purge.
- Head gasket. :(


What are you guys' thoughts on this ?

 

How do you know your t-stat is good? This was the exact symptom of a buddy's R50 & a new T-stat solved it.

 

The thermostat seems to open at the right temperature. Here's how I deduced it (may very well be wrong). When the car is completely cold :

Turn the ignition on. For a while, only the engine would heat up, radiators are cold. At about 91°C (seen on the OBD scanner) there is a very subtle click and then one can feel in the upper right corner of the radiator (when facing the mini) heat coming in. This led me to think that the thermostat does open the circuit at 91°C, give or take a degree.

Did your mate get his housing and cap changed along with the thermostat ? I am really suspicious of my cap.

 

Unlike the R53, the R50's reservoir cap isn't supposed to hold pressure. My buddy just swapped a new thermostat in & solved the boiling.

 

Agreed! I was thinking of the pressure cap sitting on top of the thermostat housing. I guess I'll order a complete set and see how that goes.

 

That's the one on the R50. Bleed your system properly.
This might help:
http://www.pelicanparts.com/techarti...ant_Change.htm

 

Do you hear or see the cooling fan running?

 

Yup. I'll order the thermostat + housing + cap kit today. I still have to find OEM coolant 'round here :/

I couldn't get it running with the aircon method. However, I did rev the engine gently up to 105-106°C (per OBD scanner) and then the fan kicked in (checked visually). It stopped when the temperature got down to 100-ish degrees. I figured this was the low speed.
I didn't try getting it into high speed, as at 105-106ish degrees there is boiling and/or overflowing in/from the coolant overflow tank.

 

Since so many mini's have neglected cooling systems.....could be a few things...

First off...did the coolant ever get VERY low....these systems are a pain to bleed...and a bubble can cause overheating....some shops even use a pressure bleeder on the non-s....
Next off...it is old enough...wounder if the prior owner used some sealant (mechanic in a bottle) to seal a leak of some type....
This might have gotten a thermostat stuck....or pluggedca dirty radiator...often folks overlook the 36 month fluid change interval ...can lead to corrosion...heater core get plugged...block rusts, head gasket fails....
Working backwards from there....you can try to figure it out...heck...look at the water pump...look at sighns of failure...the car is getting older, that is possible too.

 

The coolant never got very low on my watch, but I can only guess that the previous owner may not have been that careful.

My guess is that they totally overlooked the fluid change interval. I guess the heater core is alright (I get finely warm air if I trigger it).

How could I assess if the previous owner used sealant ? Will there be traces ?

The way it is going, I think I'll do start by bleeding the system later this evening. Then when I get the parts and the time, I'll replace the whole thermostat + housing + pressure cap assembly, for the sake of it (and purge the coolant, and bleed, AGAIN). Then in a last resort I'll go for the water pump (it seems to be operating, and the belt tensioner tool is not really easy to find so...).

FYI, I just checked the cold coolant level. Was sitting happily between min and max.

EDIT:
Done today :
- Bled both plastic bleeding screws I could find (one under the PS tank, the other one at the front above the alternator). I couldn't be damned finding the third bleeding screw mentioned by Pelican Parts. If anyone has info on that.. Bleeding was uneventful, no hissing, no bubbles, coolant from the get go.
- Inspected the pressure cap. It wasn't looking its best, lucky I ordered another one.
- Did a cold start to 90°C test, car idling all the time. Utterly uneventful.
- Gathered some courage and rode off to get the girlfriend off from work. Car went up to temp at 93-94°C, didn't go much higher than 97°C. Coolant level was fine on arrival, and on the road the temperature was very cell regulated between 90 and 95°C.


This all leads me to think the thermostat is doing fine, and that it wasn't an airlock. The pressure cap is looking more and more like a liability to me, I suspect it can get stuck partially open and so it backflows in the overflow tank.

 

Gents,

More info on this. The phenomenon mostly occurs after stopping the car or during long standstills.

We reviewed the thing with another engineer pal, here is our analysis of it :

- During normal operation, there are hardly any issues. So it does rule out a water pump failure, a shut thermostat failure or a rad failure.
- Fan does operate correctly.
- It could be that the thermostat doesn't close properly.
- It could very well be the pressure cap that isn't holding pressure anymore.
- Nothing seems to indicate a head gasket failure
- Last but not least, the coolant may be cooked or have a biased water/antifreeze ratio.

Course of short term actions :
- Weight-test coolant, just for the sake of knowing the ratio
- Flush coolant, replace with OEM. Take that opportunity to replace t-stat housing, pressure cap and t-stat itself.

If problem persists :
- Check water pump ( I have seen someone having similar symptoms and a partially failed water pump impeller )
- Check head gasket
- Sacrifice virgin to coolant gods.

EDIT :

Also, for the sake of simplicity... has anyone thought of modding the lower radiator hose to add a drain for faster coolant flushing ?

 

When I drain mine...I just undo the lower radiator clamp, and drop the hose....just change it to a Screw type clamp...will take you about one minute to undo/reconnect..

One thought...
SOME mini water pumps had plastic impellers if I recall right...
Subsequently they were changed to metal....believe the plastic ones were wearing from Caviation (vacuum bubbles that form at higher rpms due to the viscosity of the fluid)....it is an 2002....so I WOULD HOPE the original pump has been changed....
One more thought...
Not sure how coolant is sold in your area...
In mine it is either sold pure, needing dilution, or sold prediluted to a 50%-50% mix....if straight coolant was added..could be too thick...but again...a simple flush would solve this...just like if it is partially plugged with sediment if the prior owner was adding plain water...that evaporated, making scale (hard mineral buildup)...
Since the history is unknown...
My take..change the pressure cap on the rad.....and I would FLUSH/DRAIN and fill the system.....maybe toss in a new thermostats...they are KNOWN to leak around the gasket (integrated with the thermostat) ...and run it...if it still has issues...next step is a new waterpump....some might do them all at one time...depends if you are diy'ing it or having a shop do it....if in a shop...doing all at once will save having to re-do steps like bleeding...but DIY'ing it is easy to do the drain/fill/thermostat...many MIGHT do the waterpump...or pay a 3rd person to do it...
Guess no MAGIC solution....just gotta try something...it is 10+ years old....with an unknown history...

 

Gents !

I received my thermostat + gasket + housing + pressure cap assembly from fine folks in the UK (surprising to hear that from a Froggy ). After spending a whole packet of work hours in the hydraulics workshop, I was in the mood for some hoses.

Put in a nutshell, I eagerly dismounted the pressure cap (pretty much the only thing I could remove at 11pm, the day before a 400 miles journey). So while the girlfriend was running amok seven floors higher, I waited a good 20 minutes for things to warm up (car-wise). At 20 minutes, during a temperature up-cycle at 99°C, I couldn't resist and revved the car in a very gentle manner : temp went up to 106ish °C and the low speed fan kicked in.

Usually at that stage (more precisely, 102-103°C and higher) I should have all my overflow tank raging with the wrath of damned souls from Hell.

And nothing happened. Not even a tiny diddly-o bubble. The level in the tank hardly bulged.

So voilà, I am not sure this is the end of this issue, but the problem does seem to be solved. I'll see during tomorrow's journey.

End note : pressure caps do cycle and wear off more than can be suspected.

Also, I will purge everything and eventually replace the t-stat and gasket, for the sake of it. Maybe the water pump as well if I can find a cheap one.

 

Grats for catching it & thanks for sharing the simple fix!!!!!

 

So 800 miles later... no bubble in sight!
But on the other hand, I discovered the previous owner had fiddled with the right headlight connector, which broke off... also, my a/c definitely needs a refit, recharge etc. Leather seats by 38°C outside are NOT nice things.

 

Gents !

So... all went smooth for a while.

And then it came back. Sort of.

After switching the old pressure cap for a new one, all my cooling issues went away. However, since the cap now allows the system to go up to operating pressure (1.1bar), that means that the rest of the elements are also getting more pressure.

I had the good idea to keep an eye on the coolant level, for it as started lowering again. It turns out, after careful inspection when I changed my front wishbone bushings, that there is a leak somewhere near the right (passenger) side of the radiator. Not quite sure today if it's a hose issue or a radiator issue.

So this message is just a quick heads up to anybody changing their pressure caps : keep an eye on the coolant fluid level for pressure-induced leaks.

 

So is there any news on what the leak turned out to be? Was it a water pump, a hose, or a radiator? Please tell us.

 

My bad ! I was certain I had made a follow up on this.

So here are the key points :

- If you buy an old second hand cooper, look for the bubbling noise, then for leaks near the bottom of the front bumper.
- CHANGE COOLANT EVERY TWO YEARS. This helps mitigate corrosion in the front radiator, and thus greatly reduce risks of leakage there.
- Check your pressure cap. These guys DO fail.

So yup, in the end it was a radiator leakage, on the car far's side (passenger side) of the radiator, at the very bottom. Gunk and dead flies had piled up in the padding foam there, between the AC intercooler and the radiator.
That place therefore kept humidity much better than the rest of the radiator. Time did its deed, and it sprang a microscopic leak.
Of course, I was smart (or not so) to scrub the gunk out to check it was coming from there... which accelerated the leak rate.

A quick go on PelicanParts, and the radiator was changed (for a Valeo one, 100€) and coolant purged and replaced in under 4 hours with minimal tools.

By the way, glycol based coolants are very oily/slippery. If anyone wants to change their radiator or anything, please wear gripping gloves. And all safety equipement relevant.