Well first the good news. We fired the engine up for the first time today and it worked!! After 3 years building including a complete engine rebuild this a real milestone :-)

However, one small fly in the ointment.....

We noticed that when the engine was revved the coolant level in the header tank increased. As the revs increased the level increased until the tank was completely full of coolant. The instant the revs were dropped the coolant level receeded very quickly.

We can't find any leaks (water or air) in the plumbing and we tried a different header tank cap to no avail.

Also, after letting the coolant temp rise to approx. 100 degrees (to test the fan switch) we suffered from some coolant venting from the header tank cap.

I've included a photo of my cooling system plumbing in case anyone can offer any explanations?


Xflow Cooling System

Thanks
Gary

I would plumb the header tank into the lower pipe going to the rad.Image deleted by owner

You have taken the bottom expansion hose from the heater bypass. As shown, it should go into the return pipe from the rad to the engine.

Gary, I've got my coolant plumbed into the same place and have had no problems at all, mind you, I don't have a thermostat fitted yet, you could try it the same, ie without the stat, this would tell you if you have proper circullation ??

Jason

Basically he has 2 outputs feeding the expansion tank.
Taking the thermostat out is bad news for your engine. It will never get hot enough in cold weather and will run on choke (automatic) or constantly need choke to keep it running.
You need flow through the expansion bottle to bleed off air and for the water to find it's own level.
In other words, the tank is placed either side of the water pump.
The small bleed off from the thermostat is an output from the engine and the bottom hose is the input.
The heater pipe is not the right place for the return.

unless i'm mistaken (and i can't be bothered going into the garage again). the bit plumbed in is before the water pump therefore is part of the return circuit.

Therefore there is no difference between putting it where it is or putting it into the blue pipe next to it.

when the engine gets hot the thermostat will open and water will flow into the radiator. until then it flows from the head via the pump to keep water circulating.

Are you sure you have an air tight expansion tank? I would expect the level to move a little but not huge amounts like youre describing. Once the air inside the expansion is compressed it shouldn't allow the water to rise any higher.

Tip, take off the bleed to the thermostat, lower it to the floor. Water will (should) flow out of it. Put your thumb over it and then reattach to the expansion.

(note, i'm an internet expert. My system is setup the same but has only run for up to five minutes - having said that i never experience the problem you've got.)

I couldn't find any evidence of air of water leaks anywhere in the system.

What I think is happening is this.

When the engine is revved the pressure of the coolant exiting the inlet manifold is greater than the pressure of the coolant in the thermostat housing (when the stat is open). This results in the coolant taking the easist route (i.e. through the header tank) to equalise the pressure difference. But in doing so it is displacing the air that was in the header tank into the main coolant system hence the header tank completely fills up with coolant.

When the revs drop the pressure difference drops and the air returns to the header tank (the highest part of the system).

What do you think?

if the thermostat is open the the pump is also pressing through the themostat into the expansion tank so there should be no increase that way.

If the thermostat is closed then i don't have an answer (ok, i did but i'm not sure it makes sense!)

I believe the Fozz mobile has it plumbed the same way, that's the system I was advised to copy, It's worked well for me, but I don't have my car on the road, it's still only being driven around the garages where I'm building it so the fan doesn't come on too often, saying that though, my carb is nacked so I don't try it that often.
Sorry I couldn't be of any help

Jason

My x-flow is plumbed almost the same as this, BUT I have blanked the outlet from the manifold, 5000 miles and no problem. The only other mod is that I have drilled a 2mm hole in the plate of the thermostat to vent air when the stat is closed. A search on the W_______d site will give lots of discusion on this problem. Baz.

I assume the head gasket is ok?

When the engine is running there should be a continuos flow of water from the small pipe into the expansion bottle and that should be taken away by the larger pipe. This should happen irrespective of the thermostat being open or closed.
The description said that the bottle filled up.
This is telling you that there is no flow of water, so therefore you need to place the larger pipe from the expansion bottle, on the otherside of the pump.
That otherside is the lower blue hose from the radiator.

Why bother with a header tank?
The standard cooling system is well up to the job.
Mine's been to the South of France, stuck in a traffic jam going into St Tropez at 37°c, with no overheating problems.

Guys

Thanks for all your comments.

In the end it couldn't have been simpler.

All that it needed was the T-peice connections changing so the main flow out of the inlet manifold (to the water pump) wasn't impeded (i.e. the header tank bottom connector hose was plumbed in at 90 degrees to the main flow).

Happy bunny again :-)

i'm confused by the answer - don't suppose you've got a picture, heard they're worth a thousand words

Hi Mike

I was going to wait until I had a chance to tidy up the new plumbing with some longer hose and new shiny clips before posting a picture but here's one especially for you!


Revised xflow plumbing

As you can see the path of least resistance for the coolant exiting the inlet manifold is now straight down to the pump, whereas before the T piece split the flow 50-50 and that was sufficient to fill the header tank.

I have read many post that claim some flow through the header tank is acceptable but in my mind it's not a good idea as the displaced air must be being forced round the header tank breather hose into the thermostat housing or even further into the rad which is bad thing surely?

This also demonstrated to me that the flow around the heater bypass circuit is very significant (even when the stat is open) and probably results in less efficient cooling. So i'll be making a 'custom' T piece that restricts this flow but restircts the flow to header tank even more.

Cheers
Gary

I still think that this will not be right in the long run.
The true test will come when you are at full bore on the motorway.
That is when you will find out.......like I did!!!!!!!!!!

Hi Gary,
To be honest your mod should make no difference, my X-Flow is plumbed exactly as your first picture and no problems once the air was expelled from the system, the cooling system will not pump into the header tank unless your header tank is vented, with my cap off the tank the level does rise with revs, but with the cap on and pressurised the level does not move.As mentioned make sure there are no airlocks I battled with high temps untill I finaly removed all the air.

Cheers

Airlocks will occur less if you plumb it into the lowest pipe