Hi Gang,

One of the many items I'm inspecting this winter is the cooling system on my car.  I already found a non-stock thermostat and restrictor plate, and the caps on the system tanks may be another possible deviation from stock...

But first and foremost, how can I tell if the filler necks on my tanks are US spec or European spec?  There must be a measurement I can make, no?

Meanwhile, here's a photo of my leaky main tank:

IMG_7029

It has a older Stant 13 PSI cap on it now, it's obviously not sealing well.  Before I try a new 16 PSI cap, I'd like to be sure I've got the US filler neck installed.  I do believe these are aftermarket tanks in my car, as they are not in the OEM locations, and the main tank does not have a temperature sending unit bung.

Regardless of the pressure rating I end up choosing, should the cap on the smaller tank be 'vented', or 'non-vented'?

https://www.coolcatcorp.com/Ra...ps/Radiatorcaps.html

Looking at the larger tank in the background, I noticed that it also has a pressure rated cap.  It's got a 14 PSI lever vent cap installed now, but from what I've read, this should be a non-pressure rated cap from NAPA or equivalent.  That will allow the large tank to function as a recovery tank, correct?

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Original Post

Hi Larry,

Thanks for the link, I hadn't found that thread in my previous search....very enlightening.

I read it, and re-read it again, and now I'm VERY seriously considering George's auto-bleed conversion for the two tanks.  It sure would be a lot easier to do with complete access to the entire system.

It may be a moot point if I do the conversion, but I'd still like to know how to tell the difference between US spec or European spec filler necks.  Anyone know?

The difference between European and US filler necks is, a European neck is deeper, from the top of the neck to the sealing surface. Accordingly, a US spec rad cap is shorter than a European rad cap. If you put a US cap on a European neck, it doesn't seat with the pressure the cap was designed for. That reduces the "release" pressure (or temperature) by a significant amount.

To answer your previous question, in an OEM cooling system, the shorter (pressure) tank requires a pressure rated rad cap and the taller (coolant recovery) tank uses an un-pressurized, vented cap.  

Last edited by davidnunn

Thanks for the reply David.

Assuming I stay with my existing tank scheme (unmodified), I'll configure the caps as you suggest...

Mike

davidnunn posted:

The difference between European and US filler necks is, a European neck is deeper, from the top of the neck to the sealing surface. Accordingly, a US spec rad cap is shorter than a European rad cap. If you put a US cap on a European neck, it doesn't seat with the pressure the cap was designed for. That reduces the "release" pressure (or temperature) by a significant amount.

To answer your previous question, in an OEM cooling system, the shorter (pressure) tank requires a pressure rated rad cap and the taller (coolant recovery) tank uses an un-pressurized, vented cap.  

Or maybe just get a European Cap?

I am running this mod.  I believe the tanks are generally mild steel, and you can have a good welder/fabricator TIG or braze in bungs, and seal up the top of the swirl tank.

I have not seen any of the vendors carry the modified tanks, but I may be wrong.

RockyTanks [5)Tanks [2)Tanks [9)

 

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Hi, Mike. Your leak may not be because of the cap as much as the tank neck. Any radiator shop can desolder the stock tank neck and resolder a U.S-made neck for a few bucks if there's any doubt. This solves TWO problems: first, the factory neck soldering was typically rough- to the extent that the rubber sealing washer on the base of any rad cap could not reliably seal for long. The stock vented cap on the long tank is only a loose cover to keep any liquid inside from splashing out.

The Euro small tank pressure cap is rated 0.9-bar FIM (14.7psi x0.9=13.2 PSI U.S.)  Running a 16 lb U.S cap is safe & will help raise the system boiling point a bit more. But do NOT take this idea to its logical conclusion and run a 22 psi NASCAR thermostat! Street radiator cores are only tested to about 15-16 psi and higher pressures may swell the transfer tubes and crack the soldered fins, thus ruining the whole radiator beyond repair.

Besides a 13-lb U.S thermostat actually releasing around 11 psi and reducing the pressure & boiling point in your system, your leakage appears to be coming out between the cap & tank neck. It runs down the tank (see the stains on yours), across the welded surge tank bracket, down the inner fender panel and right inside an oval frame hole. I've also seen the overflow hose spigot crack on the underside, using the same leakage path. The  frame is normally sealed so cap/spigot leakage doesn't always hit the ground to alert you there's a leak. Instead, leaking coolant stays in the frame doing what water does best- it rusts the frame from the inside-out. So fixing that cap/tank problem is worth doing.

Couple of other points: my September '72-build L model Pantera had nickel-plated tanks inside and out, under a coat of flat black radiator paint. This was factory-done on L models to counteract tank rusting for owners that don't change antifreeze yearly. Earlier tanks were unplated; not sure on GT-5 & later.

It's also worth drilling our 3 recommended 3/8"-1/2" dia drain holes in the bottom of both rear frame rails, and in the extreme bottom of each leg of the horse-shoe shaped stampings that support the upper rear a-arms. Driving in the rain will throw water into that same frame hole; I've seen that frame rail full-to-the-brim after a rainy club run. Drilling drain holes prevents that from happening.

Dig around inside the oval hole with a long wire or something: I found broken spark plugs, rocks and old bolts in mine. Possibly the source of odd rattles you may hear at low speeds. The horse-shoe stampings are usually full of rust and dirt, ground by vibration to the consistency of tan baby powder. It holds moisture and rusts inside at the welds to the frame. Good luck.

Happens me 2 x that the soldering between the fill cap neck and tank was leaking.

Both times first was thinking that the cap was the problem .

Simon

bosswrench posted:

Hi, Mike. Your leak may not be because of the cap as much as the tank neck. Any radiator shop can desolder the stock tank neck and resolder a U.S-made neck for a few bucks if there's any doubt. This solves TWO problems: first, the factory neck soldering was typically rough- to the extent that the rubber sealing washer on the base of any rad cap could not reliably seal for long. The stock vented cap on the long tank is only a loose cover to keep any liquid inside from splashing out.

The Euro small tank pressure cap is rated 0.9-bar FIM (14.7psi x0.9=13.2 PSI U.S.)  Running a 16 lb U.S cap is safe & will help raise the system boiling point a bit more. But do NOT take this idea to its logical conclusion and run a 22 psi NASCAR thermostat! Street radiator cores are only tested to about 15-16 psi and higher pressures may swell the transfer tubes and crack the soldered fins, thus ruining the whole radiator beyond repair.

Besides a 13-lb U.S thermostat actually releasing around 11 psi and reducing the pressure & boiling point in your system, your leakage appears to be coming out between the cap & tank neck. It runs down the tank (see the stains on yours), across the welded surge tank bracket, down the inner fender panel and right inside an oval frame hole. I've also seen the overflow hose spigot crack on the underside, using the same leakage path. The  frame is normally sealed so cap/spigot leakage doesn't always hit the ground to alert you there's a leak. Instead, leaking coolant stays in the frame doing what water does best- it rusts the frame from the inside-out. So fixing that cap/tank problem is worth doing.

 

Hi Bosswrench,

Since I made that initial post a few months ago, I converted my two tanks to George P's auto-bleed scheme, like Rocky did above.

The filler neck on the tall tank is in much better condition that the filler neck that I cut off of the swirl tank, so that's a plus.  It seems that the filler neck on the tall tank is also the U.S. style, so my new pressure cap should seal properly.  I'll start with a 13 lb. cap and see how it works.

I will double check for the drainage holes that you mentioned, if not present I will add them.

Thanks,
Mike

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