Radiator cap pressure

Includes fuel system, cooling system and exhaust.

Moderators: reidy, Blacky

Post Reply
strogger
Posts: 498
Joined: Thu Feb 08, 2007 8:39 pm
State: NOT ENTERED
Location: Mount Warren Park

Radiator cap pressure

Post by strogger »

Hi all,
As the topic says, can someone please tell me the correct pressure for an EK Hydramatic radiator cap.
I have a 7LB recovery cap currently and it looses water until the level is approx 3/4" from top. (I dont have recovey bottle fited either.)

Thanks.
Anthony..
FB/EK Car Club of QLD

www.qldfbekholden.com
karsten
Posts: 613
Joined: Wed Oct 17, 2007 6:31 am
State: NOT ENTERED
Location: bungendore nsw

Post by karsten »

mine does that but stops at that level cause they dont have a bottle and when water gets hot it exspands if you check it hot it would probably then be full, and down a bit cold like you said you could get a bottle from the weckers of somthing which may solve the prob
when they start building them like that again i will buy a new car of them
kevin

Post by kevin »

if you don't have a recovery bottle you should change yor cap to normal, because the idea of a recovery cap is to let the water out then suck it back in from the bottle
strogger
Posts: 498
Joined: Thu Feb 08, 2007 8:39 pm
State: NOT ENTERED
Location: Mount Warren Park

Post by strogger »

I am planning to get a normal or non-recovery type cap when the shops open after christmas. Is 7Lb's the right pressure though?
Anthony..
FB/EK Car Club of QLD

www.qldfbekholden.com
FB MAD
Posts: 2725
Joined: Thu Jun 30, 2005 7:59 pm
State: NOT ENTERED
Location: Upper Hunter N.S.W

Post by FB MAD »

Years ago I made a recovery system for my FC wagon I had.I had the same problem as you described.Found that the distance from cap to the sealing rubber ( at end of cap ) wasn't as long as it should have been therefore when fitted to the filler neck, the rubber was actually not sealing to the radiator tank filler hole and was standing proud of it about 3 mm or so.

So when the coolant heated up and expanded it actually filled up the recovery bottle as there was nothing stopping it from coming out and because the system in effect wasn't sealed, it wouldn't draw back the coolant into the radiator when the engine cooled and in addition, because the rubber wasn't sealing the filler hole and the system was now subject to atmospheric pressure, the boiling temperature was lowered as well.

I ended up fitting another cap after modifying it ( can't remember what car it was from ) and the system worked perfectly.

From memory the original Fc cap was rated at 7 psi ( FB/EK would probably be the same ) but I have used heavier rated caps as well when I ended up fitting a 161 Red to the FC wagon.From memory I also used 9, 11 and 13 pound caps ( some I had to modify to fit ).

Cheers,

Terry.
I can't think what to write here so this will do.
rosco
Posts: 2569
Joined: Wed Feb 04, 2004 8:34 pm
State: VIC
Location: Melbourne

radiator cap

Post by rosco »

Hi Strogger,
you have everything right - 7lb's.

There is fundamentally nothing different between a manual and Hydra cooling system except for the plumbing in the radiator lower tank - to cool the trans fluid.
7 lb pressure is identical - raises boiling point to approx 220 degress F.

3/4" -7/8" level below radiator filler neck when cooled is normal - book quotes 1" - but subject to how hot the engine gets previously.
If you keep topping up the radiator, it will continue to overflow and cool again to this level.
If you do not intend to fit an overflow tank - just keep an eye on the level - it should remain constant when cooled without the need for continual filling.
There is no disadvantage in using a recovery type radiator cap other than for posterity.

I understand overflow tanks are not original - but very practical.
Not only to purge air from the cooling system, but also serve to give indication of a cooling system leak - the drop in level between overnight coolings indicating the degree to which leakage is occurring.

It also serves to keep spent coolant from staining your engine bay.

If you want to make use of that recovery cap - you will need to fit a tank somewhere.

I had a stainless one made up to my requirements from
– Rod-Tech, 190-192 Hampstead Road,
Clearview, South Australia, 5085
rodtech@bold.net.au
My application is to a modified vehicle - Igor fitted a factory shelf model in an original application and it works fine.

I did have problems for some time with recovery - sometimes it would work, sometimes not.

Went to local radiator repair centre and had them replace the radiator filler neck with one designed for recovery system - no problems since.

Try to keep any connections as short as possible for (and I am hesitant to use the word - it is false in this application but easy to understand) - vacuum purposes.

Height has little effect on coolant in our systems when they are sealed - the bottom of the radiator tank is our lowest point - I'm not sure with a Hydra -although believe that it is only the trans fluid which does any traveling - of course it is!

With this in mind, gravity will not have bearing on coolant level in your system whilst sealed - bit like siphoning a tank

There won't be issue in expansion - unless you seal the recovery tank - it must be freely vented to atmosphere - best at the highest possible location.

it is in contraction (recovery) where any problems will emerge........any leak will draw the lighter air, not the weight of the coolant into the filler neck- again like siphoning, once the continuity is broken - the weight in both directions from the leak is then subject to gravity.

For the system to work properly, check: seals at :-

radiator cap/ filler neck

radiator cap "vacuum" washer (inner one) - this check is for system pressure failure only - it won't have effect on recovery - ie always open to overflow tank.

hose from filler neck outlet - be careful not to use a silicone sealant - if it breaks loose it will enter your system - and may block the overflow hose at some time.

sufficient coolant in recovery tank above end of hose when cooled.
when it comes to choosing a recovery tank, it is more practical to use one which is tall rather than wide - gives a greater "range" and less chance of coolant escaping the vent hole.

If the hose enters the tank then goes down into the coolant - it need not be sealed, just a good fit to prevent coolant loss due to sloshing around.

If however it runs through a lower point than the coolant, it must have a sound seal.

You will need to provide some "escape" vent from the recovery tank - it works at atmospheric pressure only - expelled coolant from the radiator must be able to freely enter your overflow tank and not face any resistance by pressure - again keep this vent as high as possible.

If you are running additive - whatever brand, you may stain paintwork.
If not, the good book suggests to drain and flush twice a year.

We must remember that the welch plugs are subject to corrosion.
If you ever need to replace these - I would suggest handing over the extra cents and opting for brass.

I vented my recovery tank over-flow outside the engine bay to keep any spent coolant from the area.

Think that's about it - if you need any more - post another message.

Sorry for the big rant on recovery - just thought I'd clear up any misunderstanding of that system for others watching...........

frats,
Rosco
User avatar
Cal
Posts: 2796
Joined: Sat Nov 08, 2008 8:07 pm
State: NOT ENTERED
Location: Sydney

Re: Radiator cap pressure

Post by Cal »

I thought I'd resurrect this old thread rather than starting a new one...

What is the correct cap for an EK.......4lb or 7lb? A few auto shops say I need the 4lb, and there's a guy on Ebay selling 4lb caps saying they suit these cars but reading here, people here say 7lb. Reason I ask is that I fill my radiator to the top, and even if I go for a 10 minute drive, it's lost about 1/2 a litre through the overflow. It'll keep spewing it out until its down about 1lt, then it seems to back off. The radiator cap on it now is pretty rooted, so I'm guessing the spring has had it too, allowing coolant to escape, though it has been doing this since I got the car

The temp light has never come on, there are no other water leaks, and importantly, no water in the oil.
User avatar
Aussie Bob
Posts: 8276
Joined: Wed Mar 14, 2007 12:28 am
State: NOT ENTERED
Location: Sydney

Re: Radiator cap pressure

Post by Aussie Bob »

When I am out at the warehouse next, I will take a look at Steve Jnr's car, and let you know what Strogger put on it. It had no issues driving back from QLD. :D

"7" is the cap we use on all of our FB and EK's ... if we have put them on.

Steve
rosco
Posts: 2569
Joined: Wed Feb 04, 2004 8:34 pm
State: VIC
Location: Melbourne

Re: Radiator cap pressure

Post by rosco »

Hi Cal - correct pressure for FB & EK is 7lb - non-recovery cap (these do not have a neoprene outer seal around the inside of the cap)
The correct cap should hold the coolant under 7lbs of pressure during warm up.
What will happen, however - is that once the engine has reached the operating temperature (167 deg F) it will only be at 7lb whilst at that temperature..... if you go down a very long hill in winter, with the heater on - you will not have 7lb's of pressure in your system... it will recover again when the temp rises back....

Now, in answer to coolant loss...... an absolutely full system of water cannot "pressurise" .... unless there is some form of release - the weakest joint/tube/hose/gasket will fail.... hydraulically....

By fitting a radiator cap with a spring set at 7lbs, it allows this hydraulic pressure to escape......

Sadly, when the system cools out - there is a small neoprene valve in the middle of the cap - and this allows vacuum to be destroyed..... allowing the greater atmospheric pressure to pass through into the system and equalise it ...... if this valve fails - you would crush the weakest component (radiator).... by atmosperic pressure being 14lbs higher than that in the system......

I believe you can now appreciate that the hydraulic release of coolant when temperature rises - together with the contracted level as it falls - amounts to a certain "loss" in the system......

From all accounts, this should be about 1" below the neck of the radiator filler....... any more loss than this suggests it is leaking....

It is probably worthy to note here, that a simple check of your system is to cover the radiator cap with a cool wet thick cloth (towel etc) and turn the cap until the first stop... this is the pressure release stop... the next one allows the radiator cap to come off... and if you coolant is at boiling temperature, it will scald......

The test basically goes - allow the engine to warm the coolant to operating temperature (or take it for a bit of a run), stop the engine, wait around 5 minutes and then perform the "pressure" test... you should still hear/see coolant under pressure come out of the overflow hose.....

At any time you are losing coolant beyond 1" below the neck of the radiator filller - you have an issue - and it requires attention.....

Adding anti-freeze/boil in the correct amount will assist in preventing the coolant from boiling - and freezing to some extent.... the more "glycol" in the coolant - the higher and lower the temps can reach before trouble.....

Most also do not understand that it is not so much the temperature reached with damages an engine..... but the effect of boiling the coolant....
What happens is that boiling coolant creates air pockets - and these air pockets allow the metal to become superheated... that's when the damage occurs....

But - and please read this - I do not like to run my engine over 212 F or 100 C.... I cannot possibly guarantee that the coolant is under pressure at any given time whilst driving......

frats,
Rosco
User avatar
Cal
Posts: 2796
Joined: Sat Nov 08, 2008 8:07 pm
State: NOT ENTERED
Location: Sydney

Re: Radiator cap pressure

Post by Cal »

Thanks Steve and Rosco, I'll buy a 7lb.

Rosco, it does seem to lose more coolant that usual, though would a faulty or low psi cap cause this ?
rosco
Posts: 2569
Joined: Wed Feb 04, 2004 8:34 pm
State: VIC
Location: Melbourne

Re: Radiator cap pressure

Post by rosco »

Cal,
I probably would lean very slightly towards believing a lower pressure relief would cause more loss - but it would be marginal..... and probably no more than an extra 1/4" drop when the system cools down again..... guess you'll be able to tell us.....

I am a little concerned that your level continues to fall.... have you tried allowing it to heat up and cool out a number of times...? if it falls any further on each successive running (without topping up, as you have been doing) from the first time - you definitely have a leak in there somewhere.... it would then continue to fall until you couldn't see water in the top tank..... and you should never run with a level so low.

The critical level in the system is when the coolant level is below the highest part of the motor - ie, the head galleries...... the coolant keeps the temperature in all metal parts fairly constant..... when there isn't any water to draw away heat - the metal expands specifically at any exposed point....
If you look at the level of the water in your radiator - then look across at the engine on a horizontal plane - you will note that the water level has to drop quite some distance before exposing any engine components.

The other danger, is when the water level fails to reach the level of the thermostat - as air will begin to get trapped within the system - a coolant level above this will allow any air in the system to naturally "float" to the top - and out through the top tank/overflow of the radiator.

As I have posted quite some time ago in this thread - I am a strong advocate for a "recovery" coolant system..... it eventually purges all air (even in suspension) and affords the best coolant/metal contact.....
It also will provide a degree of compensation for coolant loss....... by replenishment from the overflow tank......
In such a system, it is possilbe to monitor the coolant level when the system is under pressure - as the overflow tank is always at atmospheric pressure - and therefore can be viewed at any time......
It will also afford a more exacting observation in coolant loss...... as the system will decrease the volume in the overflow tank as the coolant temperature falls........ after a few trips - this should pretty much be obvious if coolant is escaping elsewhere....

This is current practice in modern vehicles (undoubtedly you and all others are aware of this)...... and it can be determined quite easily where the "running" and cold level in the overflow tank should be...

From memory, I believe the red motors went as high as 13lb at one stage.... I was told by an old chap that the higher the engine temperature can be maintained without boiling, the more efficient it becomes... but as stated, I am not comfortable with running any coolant temperature in excess of boiling point ...... 212 F or 100 C (at sea level..... lower boiling temps at higher altitudes)...

frats,
Rosco
User avatar
Cal
Posts: 2796
Joined: Sat Nov 08, 2008 8:07 pm
State: NOT ENTERED
Location: Sydney

Re: Radiator cap pressure

Post by Cal »

Thanks Rosco. The level definitely drops to the point where I can't see any water in the top tank, though it has been like that for years. Mind you this is when the engine is cold, not hot. I'd always presumed the water level drops when the engine warms up anyway, as the thermostat opens.

The car's away getting some panel work done to it, so I'll investigate further when I get it back. Thanks again :thumbsup:
rosco
Posts: 2569
Joined: Wed Feb 04, 2004 8:34 pm
State: VIC
Location: Melbourne

Re: Radiator cap pressure

Post by rosco »

Yes, Cal - you can't do anything for now.... but you've got a few things to go on when you get it back.
They shouldn't ever go so low as to expose the core tubes when looking down the cap opening.
Me thinks you've got a leak somewhere.....
But, be warned - by fitting a higher pressure radiator cap will exaserpate the issue... it will add a bit more pressure to the system to make it leak.......

There are lots of hidden places where it might leak from.... don't panic, I'm hoping it won't be head, head gasket or welch plugs..... they are the most feared.

Could be as simple as tightening up some clamps, replacing a hose because of scale build up - or even cleaning out the radiator cap mount.....

One very good indication that a head or head gasket is leaking is when the engine has thoroughly warmed up... when you accelerate - it blows "white" smoke.... vapour from the leaking coolant. I must stress - the only time concern is needed is when the motor is well and truly warmed up.... not during the warm up period......

We'll know more when you get your bus out and about a bit more, Cal..... don't stress.

frats,
Rosco
Eeek
Posts: 247
Joined: Wed Nov 22, 2006 10:33 pm
State: NOT ENTERED
Location: Adelaide

Re: Radiator cap pressure

Post by Eeek »

Great reading this post. All car parts dealers are telling me that the correct radiator cap is 4 pound. Ill get a 7 pound when i get home. After the restoration of my car, the maiden voyage the engine started boiling and lost all of the water. "angryy: "angryy: New head, head gasket, thermostat, radiator cap and recon radiator. Took the radiator out to find some crap rattling around in the top tank, so its back for another refurb. ( I had it refurbed around 4 years ago then it sat in the shed)..... The mechanic checked the head gasket by crimping the radiator overflow hose and taking the coil lead off. He then turned the motor over. He said that if the head gasket was damaged the water would push out through the filler, which it didnt do. so im hoping a good clean and touch up of the radiator... and a 7 lb cap will sort my cooling issues.
THE BLACK EK SHALL RIDE AGAIN!
Post Reply