19 replies to this topic

[BradleyRogerson]

iv had this problem for months now and cant figure it out, my mini sometimes blows water out of the over flow but its not over heating and then my heater goes cold at low revs, so i started with the stat and took it out and flushed the engine a few times then took the heater out and flushed it and no luck so last week i decided it must be the water pump so i changed that along with a new rad cap, at first it blew/dripped a little bit of water out and i thought it was just blowing the excess water out but  today my heaters have gone back to blowing cold at low revs has anybody got any ideas? trying to get it running perfect for london to brighton as im travelling from Cheshire so quite along way.
cheers Brad 

[BradleyRogerson]

oh and iv also done a compression test all cylinders were the same  

[Gremlin]

Take the rad cap off and make sure where the cap seal sits is undamaged

[BradleyRogerson]

its looks okay but as i just checked there was a bubble in the rad so i'll give it another flush tomorrow and see 

[BradleyRogerson]

could it be from having no stat in? would the water pump just pump it back into the rad? although with the water fully topped up the heaters blow fine...

[Austin mini 30]

run it with the cap off and see if the water is circulating or not, running withg no stat i think causes cylinders 3+4 not to get as much cooling as 1+2

[dklawson]

its looks okay but as i just checked there was a bubble in the rad so i'll give it another flush tomorrow and see 

 

I think you might be expecting the wrong results.  The A-series engine and cooling system are not like a modern car.  If you fill the radiator to the top and drive it until hot, it will burp out a bit of coolant when you stop.  That will leave a bit of air in the radiator header tank.  I am not sure why that is affecting your heater... it really shouldn't.  

 

"Modern" radiator caps have two valves in them.  The main valve prevents coolant from coming out until the system pressure exceeds a specific value (typically 7, 13, or 15 PSI).  A second valve on the cap allows the system to draw fluid back into the radiator when it cools and the pressure in the radiator returns to zero.  

 

If you do not have an overflow tube and bottle fitted to your car's radiator, I would start with that.  Fit an aftermarket coolant recovery reservoir.  Make sure the overflow tube goes to the bottom of the overflow bottle so that when the radiator cools it draws the overflow back into the system.

 

EDIT:  For a more articulate explanation, see the link below starting a couple of paragraphs down at the "Car Smarts" heading.  Actually... there are a couple of "Car Smarts" headings... so take a quick scan of the whole article.

http://www.military....e-radiator.html

Edited by dklawson, 26 April 2014 - 12:47 PM.

[classicoop]

Fit an aftermarket coolant recovery reservoir.  Make sure the overflow tube goes to the bottom of the overflow bottle

Does the stock overflow have a hose inside or is it there just to catch the overflow? Always wondered. Might have to modify mine.

[dklawson]

I have no idea what was stock on Minis that have overflows.  My Mk1 does not have one at all.  That's how I know they burp fluid out if the radiator is 100% full.

[surfblue63]

Have you checked your heater valve is working correctly, no slack in the cable, not blocked?

 

On the overflow thing, most Mini radiators have a piece of wire that runs across the filler neck, this is the max level that you should fill it to. Leaving some air in the top of the rad allows for expansion and stops the excess blowing out of the over flow. If your rad does not have the wire then just fill it to about 1/2" blow the rim where the rad cap seal locates.

[Austin mini 30]

could simply be the rad cap. have a look at its condition

[andyapanel]

Is it possible you have an intermittent airlock in one or both of the hoses feeding the heater?

It would account for the symptoms. No hot water can get to the cabin, and I would imagine the air could expand as it heated, causing some loss of coolant.

 

Don't assume new parts work; I recently replaced a thermostat, which did not cur the symptoms. Turned out the brand new thermostat was duff.

[BradleyRogerson]

iv fitted a new rad cap and the heater does blow hot but only if the rad is full im aware it will blow some coolant out once filled to the top but when its cold you can see the cores and i thought that might be abit low, when the water is around that level the heaters will only blow hot at high revs. i know new parts dont always cure the problem but after taking the stat out flushing the engine then taking the heater out and flushing that i thought it may have been the pumps blades not managing to circulate the water at lower revs although it seems to took a while longer for the water level to drop low again since changing the pump which makes me think it needs another flush (maybe its just in my head) 
also can you flush an engine with a stat in? 
cheers for your help so far guys :) 

[BradleyRogerson]

oh and the heater tap doesnt seem to be blocked i dont have a wire running to it cause i only use the heater for hot air i think i may just get rid of the tap anyway, sliced my finger on it the other day! i think its out to get me 

[dklawson]

I agree with you that if the fluid is dropping down to where you can see the top of the core, you have an issue to sort out.

 

You have done a compression test which is good.  If you have access to compressed air, I think you should carry out a leak-down test to rule out a leak of coolant into the combustion chambers.  A compression test may only show that type of failure when it is extreme.