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Discussion Starter #21
heathwebbo : what sort of sound would I need to listen for on the supercharger please, mate? It doesn't rattle, tap, grind or squeak if that's what you might mean?

The tank seam looks a bit ropey but doesn't look like it's leaking - I can't afford to change the tank just for the sake of trying if you know what I mean... The pressure test would have shown if the tank was knackered, right?

I can't tell for sure but I don't think I can smell fuel in the coolant. I do get steam from the exhaust in the mornings when cold and occasionally when I give it some throttle once car is warmed up but it's not constant - just a small puff that disappears almost straight away.

mab01uk : The last time I know the fan was definitely working was the first time it boiled over the first time last month. The loud fan was running even after I turned off the engine.

Since then, the fan hasn't been on at all but that's probably because I've had the OBD set to show coolant temp on every trip. If it got over 90c I'd pull over to check for leaks (all fine)

This has meant I haven't given it the opportunity to overheat and therefore see if the fan works. Today, I know for sure that the first stage fan didn't activate because I checked it while engine was still running at 107c before i shut it off. It won't make it far enough for the second stage fan to kick in as it will boil over by then for sure!

What really concerns me is that coolant appears to start leaking from around 90c which is way too early.

I've even checked the strength of the coolant today with a cheapo Halfords hydrometer which says the strength is fine - I though maybe the coolant was weak resulting in early boil over.

I'm now getting too scared to drive this car and have been carrying around a load of water and antifreeze for the last month!

If it isn't this then it's the proxy airbag light!!!!

Sorry for the long reply.... Pent up frustration hahaha
 

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The supercharger would most likely rattle/tap if the waterpump gear was dry/warn.
Yes the pressure test would have shown if the tank was leaking & I would have thought if the head gasket was leaking between the water jacket & the cylinder that should show up on a pressure test & what you say comes out the exhaust also sounds normal.
The only thing I can think of at the moment is the seal between your expansion tank top & the cap or an airlock in the system as at 90c I wouldn't have thought the pressure should be enough to blow through the cap & it doesn't sound like you have a overheating problem
 

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Discussion Starter #24
Hi heathwebbo, my thoughts exactly. 90c is barely normal operating temperature isn't it?

If I let the car just sit there and idle, it'll happily purr away at a stable 84c. Whilst driving it will typically stay at around 86c and occasionally it may rise up to around 88c if going uphill or something.


In stop/start traffics is where it then goes beyond 90c and coolant starts coming from the rad cap.

So it's not overheating as such, just losing coolant once the system appears to be pressurised at around that temperature range....

The only thing I have now noticed, (thanks to someone else who previously posted a reply)
Is that on the expansion tank itself, at the very top of the filler neck where it should make a tight seal with the rad cap, there is a small "ridge" all the way around which has also created an opposite "ridge" on the rad cap gasket/seal too.

Probably a long shot but do you think that might be contributing? I'm guessing that this raised "ridge" isn't allowing the rad cap to properly seal as it can sit fully flush.

I don't have have the means to check any other minis to compare either haha
 

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Discussion Starter #25
Hi mab01uk, thanks for that.

Yes, definitely no stage one fan. As far as I'm aware it's never worked since I bought the car in May last year. During the summer the fan would come on very regularly in traffic and I just assumed that was normal.

That was before understanding there were two stages of the fan. This was most definitely the second stage kicking in.

My concern is that even if I somehow got the first stage fan working (which is supposed to kick in at 105c) - my car would've already started losing coolant way beforehand if you see what I mean.

It sort of renders the fan useless at this stage until I can work out why the coolant loss occurs when it does...

I've read up about checking the operation of the fan when turning on the aircon. Makes no difference. The fan doesn't operate even after I've had the aircon on for 5-10 mins (when idling)

I've prodded the fan blade itself and it turns freely enough, I noticed the 5a fuse in the engine fuse box had blown so I replaced that last week. The relay (FL9 I think?) looks ok but don't know how to test it so just gave it a few gentle taps in case it was stuck and put it back.

Gonna read your link now so hopefully it might help... Cheers.
 

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Discussion Starter #26
If this helps... I've attached a picture of the old rad cap and the new one I replaced it with a few weeks back.

It's only to show what I mean by the "ridge" being made by the expansion tank.

My new cap now has the same "ridge" indentation on the seal on it.

... Does anyone else have this ridge on their rad cap seal please?
 

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What year is your R53, if its a later one you will have the 3 wires to the fan (single plug) which is easy to do the resistor mod or if you dont have a resistor to hand for now you could wire it without so the fan just comes on at high speed when you reach 105c but like you say if its blowing coolant out over 90c thats not going to be much help.
Mine is the earlier 5 wire 2 plug fan which involved more work to wire in my resistor.
I am sure my R53 sits around 93 94c on normal driving, I will check it out today & let you know.
With the caps getting the indentation in the rubber seal it looks like it is sealing tightly
 

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Re: Expansion Tank Cap seals. The design of the cap means that there is hardly any 'give' in the seal so that if you overtighten it then it does end up with a ridge like impression in the seal and will tend to leak. The trick seems to be not to over tighten it and in fact just tighten it enough so that it doesn't leak!

I'm wondering if fitting a suitable size 'o' ring might actually do a better job.
 

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Discussion Starter #29
Cheers, guys.

ihughes, it was actually your previous comment I was referring to so thanks for explaining again. Looks like I'll be needing another cap then and just make sure it's not too tight even though this one is only just over solid hand tight?!?!?

heathwebbo, mine is an 02 R53. I might have some helpful info that's just become apparent about half an hour ago.

Just been out - driven for about 20 mins and OBD temp was sat between 84-86. Thought I'd try the "aircon trick" again as it didn't work previously.

So, driving along as I was before but now with the aircon set to LO and the temp gauge rapidly rose to 92 and dropped back to 88 then rose up again when I decided to pull over and check - engine and aircon still running at this point and OBD was showing temp at 96c but tank/cap wasn't leaking. I couldn't tell if any fan came on but the aircon was definitely working as cold air was blowing out although there was a constant feint hissing sound from inside the car.

Turned off engine, went back to look again and a smallish amount of coolant began trickling from the cap. I don't know how long that continued for as I had to go to my destination.

Once I'd got back to the car, I wanted to check if it was still leaking - it wasn't but I didn't remove the cap to check fluid level and just drove home where the temp stayed between 84-86.

Got home and left engine running and tried the aircon again. Temp rose up to 93 when I suddenly heard a fan come on for about 3 seconds then off again. Temp dropped to 88 and rose again to 95 and then the fan did the same again.

That continued for about 5 more mins before I decided to call it a day. Turned off the engine expecting coolant to leak from the cap. Stood there for a good two mins waiting but nothing trickled out.

Does that help with anything?

Why do you think the coolant leaked out after I turned off the engine earlier?

Any suggestions would be great!
 

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Discussion Starter #30
Scratch that. Just checked on it and at some point between then and now, the caps leaked again. Can't tell how much as want to let it cool before checking fluid level.
 

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I have just tried mine, my thermostat seems to open at 96c then the temp drops as it lets the coolant in it then goes back to 96 then sits between 92c & 96c
When its hot have you tried squeezing the hoses to see if their is much pressure in them. When mine is hot the hoses are quite firm but can be squoze slightly, just thought you might be able to compare that to yours
 

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Discussion Starter #32
Hi mate, as it happens, I did give the top hose a squeeze when it's hot. It's as soft as you like and I can't feel any pressure build up behind whatsoever!

What could that mean?
 

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Now we might be getting somewhere, it should be pressurised so its obviously not holding any pressure at all (I take it you tried squeezing the hose after it had been run & the cap was still on) if the pressure test was ok then its got to be something to do with the cap & if thats new it only leaves the seal between the cap & bottle. Check see if the threaded part of the expansion tank is cracked/split
 

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Discussion Starter #34
Right! That's nice to hear for a change hahaha!

Yep, gave the top hose a good squeeze yesterday after it boiled over when I was bleeding the top hose bleed valve. The hose itself was SO hot but when I opened the bleed valve, it spluttered out some air and coolant but then quickly just released coolant.

And yes, the pressure check went ok but the only part they weren't able to test was the cap itself which suggested the cap was dodgy hence me replacing it.

That said, are you thinking the tank maybe dodgy on the neck or thread as it would've effectively been covered with the pressure tester?

That would make sense I suppose...

Will look tomorrow when it's daylight.

Really appreciate your help today, mate!

Thanks again.
 

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I would take it for a run get it up to temp then without touching the cap or the bleed valve check the top hose for pressure it should be quite firm but not solid, if its soft then your problem is no pressure
 

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Discussion Starter #36
Morning! Just driven to work - 45 mins via b roads. OBD temp was stable between 84-86. Got to work, left engine running while i checked the cap. No leaks visible at the time.

Next, gave the top hose a few squeezes and it was red hot but still pretty soft TBH.

I turned off the engine and gave it another squeeze and could hear a little water being pushed into the expansion tank - couldn't see though as rad cap was still on.

Im going to go back at lunch to check if it did leak from the cap and check fluid level.

Cheers
 

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Discussion Starter #37
Cant check it. The caps on so tight that i cant get it off!!!

Looking at it just now, the cap cant be tightened any further but i can see there is still some "thread" available on the expansion tank - at least a quarter of a turn...

If this turns out to be just an ill-fitting cap or even more embarrassingly for me, a poorly fitted one cos i aint put the cap on properly i will go and flog myself!!!

In your opinion, if its the latter - would air get into the system via the cap not sealing properly? I guess that would also make it much easier for the water to pour out too, right?

Think ive mugged myself off a bit now haha
 

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The top hose will be hot as it would be around 90c
If the cap isn't sealing it means that the system cant pressurise so once it gets near boiling it will just push air & water out as there is nothing to hold it in. When the system is under pressure it can & will go above boiling point if there is no pressure it cant so will blow it out.
You wont really get air in the system from a bad cap but it will cause the problems you are having as it needs to be sealed & under pressure
 

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If the cap isn't sealing properly, then water will leak out when under pressure. But air shouldn't get into the system unless the header tank is completely empty, as when the system de-pressurises on cooling, the water in the header tank is sucked back into the engine/radiator but air wouldn't get in unless the header tank water level was way down below the level of the bottom tank connection.

Whilst you may have a slight leak on your header tank cap due to over-tightening it (as mentioned previously), from reading all your posts and responses from others it sounds to me like you either have a fan problem which may be caused by a faulty fan temperature sensor, or else you have a thermostat problem. I don't think the header tank/cap would lead to major boiling over problems.
 

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Discussion Starter #40
Just removed the cap and replaced it properly. Still locates at the same point roughly - it looks like there is still a little bit of thread left (still about quarter of a turn) but I literally can't tighten it any further. I've done it good hand tight this time instead of using the rubber strap thing I have.

It's got air in there for sure cos when I undid the cap just now - pretty much soon as I got home after an hours drive, there was no hiss of pressure release whatsoever!

Don't know what to do as I've bled it quite a few times now.

My mate also reckons it's just air locked...

With regards to the fan issue - I definitely have a fan problem as in my first stage doesn't work. The problem is, even if it did work, it operates at 105c whereas my car seems to boil over way beforehand so having a first stage fan makes no difference (at this stage at least)

How can I tell if the thermostat is faulty? It gets up to temp ok and tends to stay stable at 84-86 while driving and only rises in stop/start traffic.

Also, if the stat was stuck shut then I wouldn't get any coolant going into the expansion tank, right?

This is too confusing haha
 
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