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K - keep your cool

Hippy Crippy

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K series cooling system - 1.4K 2002


Having read many questions on the site on the difficulty of bleeding the K series and other related topics i.e. head gasket failure, cooling fans not working and anti freeze questions, can anybody explain the cooling system on the K series. It seems to me that it's a little bit back to front. For example, the thermostat is in the bottom of the engine - isn't the hottest part of the engine the cylinder head? There is also a small bleed valve in the inlet manifold that seems to work backwards letting water in but not out - should this valve allow air out of the cylinder head not trap it? Also, the radiator does not bleed back to the header tank.


Most modern vehicles are self bleeding. The K series doesn't seem to be. Has anybody modified their radiator to self bleed, or moved the position of the thermostat. Has this been asked before, is there anything in the archive?


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miraz will come along at some point. he's done exactly what you're asking about just now in his two new engines he's building. the location is abnormal and not what any car in 30 + years of

working on cars i've ever encountered.


miraz? want to disclose what you've done, you tell it better than i.....



210Bhp Sinister Version-VHPD here

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Lots of minefields in here where a first intuitive inspection may not reveal the truth.


First off, being backwards is no inherent problem. The thermostat is designed backwards. It has two inputs and one output. Only one of the inputs feeds the temperature sensing bulb. Unlike a traditional thermostat, there are differences in temperature between the flows. Theory reckons that this isn't a problem (more comment later).


Next bit to be clear about is that the exit flow from the head gets fed via a bypass pipe straight back to the thermostat, so even though it is on the input side of the head there is *NO* temperature sensing difference. Having a heater in circuit confuses this slightly, but not significantly.


The advantages are that the thermostat is always immersed - more than can be said for crossflow thermostats.


The valve in the cylinder head is designed to let air out but stop coolant flow out. It's heart is in the right place, but in practice removing the ball from the valve gives better assurance of self-bleed behaviour without introducing any other problems.


Your point about the bleed from the radiator to the header tank is valid and you can thank Caterham for that particular bit of wisdom.


Miraz's setup is very impressive. I witnessed first filling and switch on and Geoff asked how we would know when it was bled... to which I replied: "wait until the pump goes quiet". 20 seconds later the electric pump stopped pumping bubbles and went quiet. You don't get much better demonstration of bleeding than that.




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Thanks Pete.

Still not quite sure, but sounds as if the water circulates the engine passing through the cylinder head and when up to temp flows throw the termostat, radiator and back into the head via the water rail, but would have to see the engine in the pieces to fully understand. Good idea to remove the ball valve, is it an easy job? and would you know if anybody has modified the radiator to bleed back to the header tank?


Thinking of using a water wetter with the anti freeze. Any views? but I'm going to use the latest Rover anti freeze which is not ethelene glycol.

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The cooling system on the K still runs the normal way round. The way it starts to open is a bit different to the older ways but its a good system for fast engine warm up in grocery getters. Doesnt work so well in mid/rear engined cars such as the Elise and can cause terrible temperature cycling if the pressure drops in the heater and by-pass are wrong.


I take it you have removed and flushed out all of the old coolant before you plan to put in the new Rover organic stuff otherwise the mess you will find in there wont be nice!Unless it was built with the organic stuff in the first place, if so I'll shut up!!



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Experience of many fill ups shows that filling the cooling system both from the header tank and from the bleed hole on the top of the radiator practically eliminates the need for bleeding. The block and head is filled directly via the water rail rather than via any convoluted route and the radiator is then filled completely leaving only a tiny pocket of air in its upper part.



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On build of mine 18 mths ago, I placed a T-piece with a screw topcap on, in the heater hose back to/from the water-rail.


i filled the radiator, the header tank and then held the heater hose up above everything else and kept adding water into the Tee, sealed it, ran engine to move, water, opened it before it got hot, kept adding water until it would take no more - ran until no more bubbles came out - sealed Tee again.


Still fine after loads of nut-screaming runs up and down various motorways (6spd box, low ratio diff, small wheels = nut-screaming!)


Not seen similat Tees over here (but then I've not looked) - bought mine from USA equivalent of Halfords.



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whats the feasibility of putting a threaded hole into the heater valve metal work to use as a bleed valve?

drill a hole,weld a nut on the outside et voila!

I had a FIAT Strada a long time ago which had a bleed valve in the heater matrix for just such occasions.It is the highest point on the circuit.

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