Expansion tank questions...

[BigB98]

Ok, I've made the shell of an expansion tank. So far I have the filler neck, etc, an the look replicates an original on an MKIV.

I know I need a radiator bleed line that goes basically to the top of the filler. But what else is needed? My cobra has an expansion tank that is fed by the main line coming from the manifold and then goes directly to the radiator and aside from the bleed line from the raidiator, that's it. Is that all that is needed in this case too? If not, what else is needed and why?

Thanks for your input.

Picture of the expansion tank during fabrication. Only real difference now is the filler neck.

 

[Jac Mac]

The line [-4] to the top of the expansion tank [ just below cap in tank ] should come from top & immediately behind T/Stat on manifold, If your engine block is mounted nose down it might pay to run additional small bleeds [-3] from rear corners of intake as well.
Another larger line [-6 or -8 ]should be run from base of expansion tank to heater return fitting on intake side of pump-- I think I read where your intending use of electric pump--- in that case you may need to TEE this line into radiator return line if no other fittings will suffice. In the Mk2 they also ran a small bleed line from rad top tank back to head of expansion tank.

 

[BigB98]

You are one helpful son of a gun.

One thing I forgot is the heater. My pump is electic and mounted at the firewall down at the bottom below and just ahead of the crank pulley. I was "thinking" I would run a line from the manifold directly to the heater, but based on what your saying above, I wonder if I ran from the manifold and then from the base of the expansion tank to the heater and then out from the heater to the radiator return line? Thoughts?

 

[Jac Mac]

When Ford plumb their heater lines they do take the 'hot' from the inlet manifold just behind the T/Stat--""BUT"" the fitting extends right to the 'floor' of the coolant passage. This prevents air bubbles from entering the heater circuit & possibly creating air locks in the heater etc as well as forcing majority of coolant thru radiator, I quite often find with high mileage Mustangs etc that simply replacing this fitting [ which is 'crimped' to make it work as a restrictor, in NZ means making a new one ] cures a whole host of niggling cooling problems-----Soooooo while your idea has merit, I think it might cause more problems than its worth--- might work, but if the heater lines are all going to be 5/8" bore you might find that flow tends to go thru heater rather than radiator as intended.

 

[BigB98]

Sorry to ask silly questions, but I'm out of my comfort zone. So if I ran from manifold to expansion to heater to the line just ahead of the radiator, would that solve the problem of coolant only running through the heater core? Also, if I run from the expansion tank to the heater core, shouldn't any air in the line have been taken care of because of the affect of the tank?

Again, sorry for the basic questions...Just haven't done this sort of thing before. Thanks for your time.

 

[Steve C]

Jac Mac,

Acedemic question re bleed lines.

BigB98's engine is an FE. I have been told that an FE inclined down in front does not have the same issues (that can cause or keep air trapped) that a SB has as the head construction (particularly with an aftermarket head) is different. Additionally the intake in that area has no meat for bleed line fittings?

Be great if you can put us straight on this matter.

Thanks, Steve

 

[Jac Mac]

Sorry to ask silly questions, but I'm out of my comfort zone. So if I ran from manifold to expansion to heater to the line just ahead of the radiator, would that solve the problem of coolant only running through the heater core? Also, if I run from the expansion tank to the heater core, shouldn't any air in the line have been taken care of because of the affect of the tank?

Again, sorry for the basic questions...Just haven't done this sort of thing before. Thanks for your time.

Brent--Slept on this!-- Since you have blocked the 'normal' FE by-pass to work the Electric pump the following which is a rework of your idea should do the job.
1. Dash 6 from top of manifold to top of expansion tank [ this will do double duty as air bleed & heater hot supply- in practice it may need to be enlarged to -8 or even -10 (1/2" or 5/8") to get enough flow/heat in actual heater core, but start small to prevent overheating- make thread fittings in manifold/tank large initially with stepdown AN adapters so you dont have to rework whole system to fit larger fittings later].
2. Dash 8 or 10 from bottom of expansion tank to heater, then same from heater into main radiator return [ you may be able to fit this up front if convenient ].
3. Dont forget the small bleed line reqd from radiator top tank to expansion & the -3 bleeds from rear of manifold if nose down engine mounting.

Steve C.
While the FE head is slightly different in configuration the need for rear bleeds could still be there if a nose down installation.

Other than the air bleeds, the other way air can be purged from these 'spots' is going up an incline that negates the 'nose down' angle or where coolant flow rate is sufficient to move the air.

You also have to look at each situation on its own merits- for a road car it might only occur in traffic & @ slow engine engine speeds where coolant flow is insufficient and the next increase in RPM or slight incline might suffice to 'shift' any air bubble.
A track car @ high power levels can be 'creating air' on a regular basis, so continous purging this by rear bleeds can help.

In the real world, if your pushing coolant out of the expansion tank into the catch tank in sufficient amounts that you regularly have to add coolant to the system then you have a problem & the need for an air bleed system is the first place you should look on these cars.

 

[RichardH]

In the real world, if your pushing coolant out of the expansion tank into the catch tank in sufficient amounts that you regularly have to add coolant to the system then you have a problem & the need for an air bleed system is the first place you should look on these cars.

Yu got me worried there. I have no catch tank and regularly loose about half the expansion tank volume of water on a normal road run. I assumed that this was purely a case of the expansion of such a large volume of water. A catch tank was one of the options I was considering. Does anyone have any drawings or ideas where such a device can be purchased in the UK. I would imagine that it would be best plumbed in so that the system will "suck" the ejected water back when cooling via a one-way valve.

 

[Jac Mac]

Yu got me worried there. I have no catch tank and regularly loose about half the expansion tank volume of water on a normal road run. I assumed that this was purely a case of the expansion of such a large volume of water. A catch tank was one of the options I was considering. Does anyone have any drawings or ideas where such a device can be purchased in the UK. I would imagine that it would be best plumbed in so that the system will "suck" the ejected water back when cooling via a one-way valve.

You should be able to cure that with a recovery type cap [ two seals/one against the 'normal' lower part of the rad/tank neck and another on the upper rim ], then mount your catch tank up near the expansion tank and simply fit your overflow pipe into it [ right to the bottom so it can drawback during cooling ]-makes it easier for the coolant to be drawn back in when the motor cools down------- Dont mount it down alongside the tranaxle like some I have seen here, that just makes it harder for the system to lift it back up when cooling. Catch tank can be anything off a later model car or a bling bling boyracer article if your that way inclined- my thoughts are nobody will run alongside @ 100mph to check it out.

Many people make the mistake of filling the expansion tank right to the top- DONT- leave the level down about 3" or 4" so it can do what its designed for, that alone may cure your problem. Is it always the same amount you have to add, if so you might get away with a larger expansion tank only.

 

[Al Jones]

Jac Mac,will the radiator top tank still bleed off air if, at some point,the level of the bleed tube drops below that of the attachment point on the radiator tank.Kind of like a trap in a sink,only in reverse function. What would induce enough flow to purge the trapped air?Is the pressure differential enough to keep a constant and substantial flow in this line back to the tank? I can't visualize it but maybe you can explain it.
A.J.

 

[BigB98]

Jac Mac,will the radiator top tank still bleed off air if, at some point,the level of the bleed tube drops below that of the attachment point on the radiator tank.Kind of like a trap in a sink,only in reverse function. What would induce enough flow to purge the trapped air?Is the pressure differential enough to keep a constant and substantial flow in this line back to the tank? I can't visualize it but maybe you can explain it.
A.J.

Thank you for asking that...i've been wondering that for a long time.


Jac Mac, thank you very much for your input on this stuff. Very very helpful.

One other quick question: At what point in the system is it no longer on the pressure side and now on the suction or return side and why? Not clear on that. I think you're telling me that coming out of the heater I must go to the return line thereby bypassing the radiator. Why can't it feed from the heater to the inlet line to the radiator (guessing pressure is same/similar and won't flow well).

 

[Jac Mac]

Can get a bit hard to follow---- Remember the bleed lines are small dia, say 3/16" or 1/4" bore, now the return to the pump from the bottom of the expansion tank is either 1/2" or 5/8" bore which is approx three times the area of the combined bleeds, this helps create the pressure differential in the expansion tank ( with the pump turning ) that draws the air [if any] back thru the bleed lines.

Brents [Big B98] system does concern me a bit & I think I would do an out of car trial run in mocked up format to ensure its all going to work before committing to hard metal.

 

[Jac Mac]

One other quick question: At what point in the system is it no longer on the pressure side and now on the suction or return side and why? Not clear on that. I think you're telling me that coming out of the heater I must go to the return line thereby bypassing the radiator. Why can't it feed from the heater to the inlet line to the radiator (guessing pressure is same/similar and won't flow well).

Right- this answer is in relation to Brents proposed electric pump FE setup, so all you MK2 & MkIV belt pump guys switch off for a second or two!!

In this system you wish to have the heater as part of the return line from bottom of expansion tank to the pump- therefore the closer you can connect it to the pump suction side the better it will function- if as you suggest it was fitted to the entry/top side of the radiator the restriction to flow induced by the radiator core might be enough to reduce the flow thru the expansion tank- fluid flow always takes the easy route .

As mentioned in the previous post I think I would try a mock up system first to ensure its all going to work.

It is very hard to be definitive in pressure versus suction side in 'real' terms. In a 'normal' belt drive pump with T/Stat it can be visualised that from pump thru block/heads to T/Stat will have the most pump induced pressure, since the T/Stat in most cases also acts as a restrictor pressure then drops slightly on the way to the radiator, & as the pump is now drawing from the bottom of the radiator pressure is lower again. So while you might have say a 22psi cap, its quite normal to see perhaps 40psi readings at various points in the block/heads, yet 10/15psi in the bottom hose @ higher RPM. Have a look at the bottom hose on say an old Mustang 289- give it a good rev & the bottom hose will try to contract---thats why they have a coiled wire inside them , they will 'suck' themselves shut without it.