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K series venting water from expansion tank


p.mole1

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I have just put my engine in with a remote thermostat, I never had problems before but now I am venting water from the header tank and running too hot when stationary.

I think I have discovered why this is happening.

If you are running with throttle bodies you loose the one way valve in the hose that runs into the header tank from the cylinder head.

The bypass hose from the remote thermostat is now forcing water into the header tank and back into the cylinder head forcing the air gap from the tank into the cylinder head and eventually it accumulates in the highest point in the radiator and remains stuck there. This also causes the fan switch to become less effective.

I have refitted the remote stat with the bypass hose uppermost so this is now the highest point in the cooling system.

This seems to have cured the problem,however I may look at fitting a one way valve into the pipe that runs from the cylinder head to the header tank.

 

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p.mole1, it sounds like we have the same setup and the same issue (except for running too hot, my temps are steady).

On reflection I can see why the expansion tank fills up so dramatically; the bypass hose feeds into the hose between the expansion tank and bottom hose. The flow should in theory go with the existing current from the expansion tank into the bottom hose; but if pressure builds it could just force fluid in both directions and force the air that was in the expansion tank somewhere else (such as the radiator)?

What I'm not sure on is how fluid could be forced back through the overflow hose (and in the wrong direction); or am I misunderstanding? Unless your tank fills to the brim (which mine doesn't, quite!) then I can't see this happening.

elie boone, within my diagram I've put together, from where to the top radiator bleed screw would you add another hose? I like the sound of it. Would it also help get some warm water into the radiator before the thermostat opens therefore reducing the chances of thermal shock to the block?

40017835021_626d9ed92e_z.jpg

 

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The header tank should feed the original coolant bypass/ heater feed, the way its plumbed in the 7 stops the head degas being in full flow when the stat is shut. This maybe not quite the same with the remote stat but I still think it's unnecessary on a car with such a short cooling system. I had a vhpd with a small rad in a previous car plumbed in this way and never had any issues 

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From what I understand, my header tank does feed the coolant bypass feed (and ultimately the bottom/return hose)? Sorry if I've misunderstood something; still quite a novice in the field of coolant plumbing!

I'm wondering whether putting the bypass feed from the stat straight into the bottom hose would be better and help attain the correct / most efficient flow.

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Rhauri, why is your bypass hose fed into the header tank rather than the original thermostat housing? The original bypass hose is there to take warming coolant from the top of the engine (during warm up) and feed it back in via the thermostat housing but bypassing the thermostat ... hence the name. This is there so that the engine doesn't suffer the thermal shock from only receiving return feed coolant through the radiator/stat. Is the 16mm inlet on the original thermostat housing now blanked off?

Stu.

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Hi Stu,

It isn't fed into the header tank, it's fed into the outlet pipe from the header tank which then feeds into the bottom/return hose. As the original thermostat housing would have been on the bottom/return hose, in theory this should be equivalent; but I'm not convinced the flow efficiency is there in practice.

I didn't install the QED top hose stat in my car, but according to QED's fitting instructions the bypass should feed the header tank, which then feeds the bottom hose. My setup bypasses the header tank and feeds the hose going to the bottom hose. Not sure if that is better, worse or negligible; but ultimately, it is the same end game.

I'll have to have another look to see if the original stat housing is there for whether a complete new bottom hose has been installed as I just can't remember/picture it at the moment. If the original housing is there, with the 16mm blanked off; I could consider using that for the bypass hose rather than where it currently attaches.

QED fitting instructions if they're of any use:

https://qedmotorsport.co.uk/files/k-series_qed_remote_thermostat_fitting.pdf

Rhauri

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Going through the QED instructions it appears that you must still have the original bypass hose in place, running from the rear of the coolant rail around the back of the engine to the 16mm inlet on the original thermostat housing. This is missing from your diagram.

Stu.

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Sorry Stu, I'm not sure what you think I'm missing. I have a by-pass it's just feeding to a different location as to QED's advised location. They do caveat that their layout is for guidance only and that other configurations may be more appropriate for different applications.

I've had a play with their diagram and made two more which may be clearer still.

Below are three diagrams:

  1. The original QED layout for reference
  2. I converted the original QED layout into a QED Caterham layout, but with all pipes leading from and to the same places.
  3. I have amended the QED Caterham layout to show the QED setup in my car.

Hopefully from the below you will see that my by-pass hose feeds in after the header tank as opposed to before the header tank.

My understanding of the by-pass is to circumvent the stat while it's closed and get warm water back into the engine. In theory, my setup should (and I believe does) do this; just with a negative side affect of the header tank filling up a bit (not to the brim) and blowing pressure out of the header tank cap.

My thoughts are, if I feed the by-pass hose directly into the bottom/return hose (and therefore into the block), it will allow for better flow and circulation and therefore alleviate the side effect my car is experiencing.

Have a look at the below three diagrams anyway and let me know your thoughts *smile*
 

39122172915_de0c057b42_o.png

 

25149593357_be797a6608_o.png

 

40020055031_37cc84f384_o.png

 

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http://www.thecaterhamregister.net/images/SLRs/Superlight%20R%20no.077/enginebay1.JPG

The blue hose that goes round the back of the d/s tower and under the throttle bodies is the bypass hose - it links the rear of the coolant rail to the 16mm inlet on the side of the o/e thermostat housing. Surely you must still have this in place (but omitted from your drawing), it would connect through the heater if you have one fitted, otherwise it's just a long loop of hose.

Stu.

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Agreed elie, not sure I'm happy with it's current location.

The QED installation instructions say the bypass from the QED thermostat ultimately needs to feed to the back of the water pump, so I'm wondering whether feeding to the bottom hose is also a good option? Thoughts on any draw back?

I'm sure I've seen some PRRT setups that by-pass the rad in this way.

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I think my problem is caused by fitting throttle bodies, you loose the one way valve which is fitted to the original inlet manifold. I am going to install a non return valve in the pipe from the inlet manifold. This should stop the air from being cycled around the engine

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If you connect the small connection on the header tank to the hose that draws coolant for circulation in the engine then you will always draw air in the system because this connection will always be higher than the coolant level and you pull a vacuum in the header tank.

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  • 3 weeks later...

I thought the non return valve would fix it, but I was wrong! I have just been out for a drive and my expansion tank has lost the air which is now residing in my radiator? I have been reading the Des Hammall Rover K series book of doom and he mentions the removal of the troublesome ball valve in the inlet manifold. If you remove the the valve you need a 1.5mm restrictor to stop the water flow but allow air to vent into the expansion bottle. 

This seem to make sense as even when the engine is ticking over there seems to be a quite flow entering the expansion bottle from the manifold pipe 

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  • 1 month later...

I have found how the air in the expansion tank is getting into the radiator. I blocked the small diameter hose from the inlet manifold to the expansion tank and the air stays where it is supposed be. What seems to happen with the QED thermostat and throttle bodies are

1 You no longer have the ball valve which only allows air to escape from the head but does not allow the flow of water into the expansion tank

2 You now have a flow water from the QED bypass hose into the expansion tank lower hose.

What seems to happen is water is constantly flowing out of the cylinder head via the manifold hose into the expansion tank and aerating the coolant in the tank and then flowing through the engine and then getting trapped in the radiator.

I am going to try fitting a 1 mm restrictor to reduce the flow, ideally there should be no flow into the expansion tank but I don't like the idea of blocking off this hose.

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