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Overheating Problem

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Best Answer Captain Mainwaring , 07 August 2013 - 01:45 AM

Hey guys, just a quick one: I took he mini for a short drive yesterday and then I took the rad cap off and put a temp sensor in the top of the rad, the temp read 90 degrees and the gauge inside the car was just below he red line. my question is: what is the normal running temp?

 

 

You shouldn't have taken the cap off, though in this case it doesn't matter, the car wasn't boiling. You have however answered your own question and solved your own problem - a car isn't in the red at 90C :-)

 

anything between 82 and 92 degs is quite normal temp

in the cylinder head temp will be slightly higher, so i'd expect the gauge reading a bit higher, when temp outside gets above 30° minis tend to run quite hot, but if temp goes quickly above 95-98 degs while driving, then you have a problem somewhere

 

Well not really once you are above the stat opening temperature. 

The circ water temp will increase once the balancing point of the cooling system is reached - given a certain ambient temp with the engine under a certain operating condition, the circ cooling water temp will increase until their is sufficient differential in the circ water temp and the ambient air temp to effect a change in the heat balance and allow heat energy to flow from the cooling system to the surrounding air. Heat transfer is expressed as W/(mK) so a cooling system water/air will loose 1/(273+new ambient temp-original ambient temp) *100% efficiency for a given change - it won't suddenly get worse at 30C.

 

I don't  reckon an engine is excessively hot at 90C and the gauge certainly shouldn't be in the red - unfortunately these are hardly calibrated instrumentation and I think there may be a huge difference between calibration of gauge head units and PT100's (i'm guessing that they are 100's)

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#1 Pog49

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Posted 20 July 2013 - 09:30 PM

Hi All,

I recently bought my first Mini, a 1986 Austin Mini.

 

On the drive home she started over heating and soon was at the top of the gauge.

I have replaced the engine oil and filter and I have also put in a brand new radiator and fluids but she is still over heating. 

 

Does anybody have any ideas?

 

Pog



#2 The-Womble

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Posted 20 July 2013 - 09:33 PM

Best start by checking the thermostat to see if it's opening. Take it out of the housing (top front right of the engine block where the radiator pipe goes in), put it on some string and put it in some boiling water. You should see it open. If not, just buy a replacement...only a couple of quid!



#3 AVV IT

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Posted 20 July 2013 - 09:37 PM

As above, check the thermostat and also the water pump.



#4 Pog49

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Posted 20 July 2013 - 09:48 PM

Best start by checking the thermostat to see if it's opening. Take it out of the housing (top front right of the engine block where the radiator pipe goes in), put it on some string and put it in some boiling water. You should see it open. If not, just buy a replacement...only a couple of quid!

Thanks, Forgot to mention that I have also replaced the thermostat, I am looking at replacing the water pump but as all the pipes are hot I am unsure if this is the source of the problem as this would suggest to me that the water is being pumped around? 



#5 The-Womble

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Posted 20 July 2013 - 09:57 PM

It might be that the pump isnt pumping the water round the engine at sufficient speed for it to efficiently cool. You didn't mix coolant colours by any chance did you (red with green or blue, for example). I did this once by accident and it turned into a sludge inside the block...took about 6 flushes to get it all out and for it to run at normal temperature again.

 

Did it definately overheat? It's not just a duff temperature switch for the gauges or shorting out somewhere?



#6 Pog49

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Posted 21 July 2013 - 07:39 AM

Ah okay, I'll have a look at replacing it then.
I used only blue + water so hopefully no sludge!

 

The temperature switch looks good and the needle rises and falls so sadly I don't think either is to blame, I will try replacing the water pump and see if it makes a difference. 



#7 bmcecosse

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Posted 21 July 2013 - 08:14 AM

Good block flush is wise. Don't waste money on antifreeze at the moment - plenty time for that when summer blows away.....   Does the engine run well enough?   Not running with retarded ignition timing ?  Try advancing slightly - but don't let the engine 'pink' under load.  



#8 Scoop77

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Posted 21 July 2013 - 08:29 AM

Flush and clean everything. If you're doing the water pump the rad has to come out anyway so inspect and flush. Flush the heater through as well. Then refill with 25% blue coolant/ anti freeze.

#9 Yoda

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Posted 21 July 2013 - 08:30 AM

How quickly does it overheat from cold?



#10 Pog49

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Posted 21 July 2013 - 08:47 AM

How quickly does it overheat from cold?

She goes from starting to being up in the red on the gauge within a 3 mile drive on a straight road.



#11 Yoda

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Posted 21 July 2013 - 08:50 AM

Possibly suspect either the rad cap is not sealing properly or worst case would be a blown head gasket. change the cap first ( borrow one to try ) its a cheap option to try first, If that does not solve it, i suggest getting a compression test done asap which will show up any issues with the head gasket.



#12 Pog49

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Posted 21 July 2013 - 10:42 AM

Possibly suspect either the rad cap is not sealing properly or worst case would be a blown head gasket. change the cap first ( borrow one to try ) its a cheap option to try first, If that does not solve it, i suggest getting a compression test done asap which will show up any issues with the head gasket.

On the radiator, I have an overflow pipe that is open at one end and I am wondering if there should be something on the end of it?



#13 Captain Mainwaring

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Posted 21 July 2013 - 10:50 AM

 

How quickly does it overheat from cold?

She goes from starting to being up in the red on the gauge within a 3 mile drive on a straight road.

 

 

 

As an aside...never by a car when it's raining...and make sure you thrash the pants off it before parting with a penny....if they won't have it....walk away.



#14 Captain Mainwaring

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Posted 21 July 2013 - 10:52 AM

Possibly suspect either the rad cap is not sealing properly or worst case would be a blown head gasket. change the cap first ( borrow one to try ) its a cheap option to try first, If that does not solve it, i suggest getting a compression test done asap which will show up any issues with the head gasket.

 

 

Certainly good advice - but don't mess around borrowing one - just buy a new one. Also check the seat inside the cap.....You can pressure test a system by filling it up and the putting a footpump on the rad overflow and clamping the schrader shut over it - it's close enough to hold pressure.

 

Bring it up to 15 to 20 psi and leave it...see what happens.



#15 Yoda

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Posted 21 July 2013 - 11:25 AM

But isn't the overflow, above the rubber seat for the relief valve? i would use an old cap and drill out the relief valve, install a shreader valve and then fabricate a seal for the top lip of the rad.


Edited by Yoda, 21 July 2013 - 11:28 AM.






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