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4/09/2013 9:32 AM  #1


radiator overflow - cap related??

I am experiencing boiling and excessive rad fluid spitting out the overflow tube on my 68 302 with a stock rad. ( Almost constant. )

The engine is not overheating, it was only just reaching normal operating temp.

When it cooled down I squeezed the upper hose and could get air gurgling in and out of the overflow tube with the cap on tight.

At first assumed a bad cap, but put a good new cap onto rad from my other Stang and could still get air movement in and out when squeezing the upper hose. It was greatly reduced though.

Is it possible the rad top opening is too deep for the cap and can't seal tightly? How would I choose a cap that is "deeper" to tightly seal the rad until it reaches the overpressure release point? Do they make caps of different depths?

It is a stock 68 V8 Ford rad. The opening does not appear to be mis-shapen, and cap seams to pull down tight

Any thoughts or suggestions?

 

4/09/2013 10:01 AM  #2


Re: radiator overflow - cap related??

How many miles on the 302?  Any possibility that you have a bad head gasket.  That would certainly give you those symptoms.

As far as I know, radiator necks and caps are pretty universal.

Last edited by boomyal (4/09/2013 10:02 AM)

 

4/09/2013 10:26 AM  #3


Re: radiator overflow - cap related??

boomyal wrote:

How many miles on the 302?  Any possibility that you have a bad head gasket.  That would certainly give you those symptoms.

As far as I know, radiator necks and caps are pretty universal.

 
I bought it used, described as a zero miles motor after a rebuild.

You should not be able to get air flow through the overflow tube/cap when the rad and cap are cold should you? I would have thought that is when you should have the tightest seal on the cap.

If it was a blown head gasket, how would I determine or confirm that?

     Thread Starter
 

4/09/2013 12:33 PM  #4


Re: radiator overflow - cap related??

Normal water level is 1" below the filler neck of a Mustang radiator.  If you fill it any more than that, it will self-correct until it gets to that level.  Usually will not go any lower than that point if you just leave it alone.  If it starts to uncover the coils, then YES, you may have an issue to deal with.  Use a stock 13psi cap NOT designed for an overflow system.  If your engine is not overheating, the water level should remain constant dor a long time.


Money you enjoy wasting is NOT wasted money... unless your wife finds out.
 

4/09/2013 2:34 PM  #5


Re: radiator overflow - cap related??

I wasn't even aware that you could still get caps that did not have the top and bottom seals on them.  A non-overflow/recovery cap would only have the top seal, correct?

 

4/09/2013 3:23 PM  #6


Re: radiator overflow - cap related??

I believe it has only the lower seal.  When pressure is exceeded, the rubber seal lifts up allowing the water to move upward and out the vent tube.


Money you enjoy wasting is NOT wasted money... unless your wife finds out.
 

4/09/2013 4:19 PM  #7


Re: radiator overflow - cap related??

MustangSteve wrote:

I believe it has only the lower seal.  When pressure is exceeded, the rubber seal lifts up allowing the water to move upward and out the vent tube.

Duh!  Of course that is what it is.  The top gasket only seals to allow a vacumm on the overflow tube if you have a recovery system.  Otherwise that tube sucks in air as the radiator cools.

 

4/09/2013 8:24 PM  #8


Re: radiator overflow - cap related??

So just to clarify. Is it normal to have air flow through the vent tube into the rad on an open system and no recovery bottle when the rad is cold? In other words, not a sign of a bad cap if I squeeze the hose and I get air moving back and forth in and out of the tube?

The cap I had was 16lb, and I believe it to have been for an open system. I am changing it to a 13lb designed for a open system. I topped rad off, so I guess I should not be surprised if it vents again to find it's level.

I should only be concerned if it continues to vent to a low level, or I have overheat issues?

     Thread Starter
 

4/09/2013 9:40 PM  #9


Re: radiator overflow - cap related??

Let it find its own level and see how long it stays at that level.  They work quite well if you put the right cap on it and leave it alone.  It should drop to about 1/2" below that lower ring in the filler neck. or at least 1/2" above the tubes.  Mine stays there for years without moving.  If you top it off, I can guarantee it will puke out the water until it has the proper amount of airspace in there.

You can hear gurgling after the engine is shut off and cooling down as water flows back through the thermostat.


Money you enjoy wasting is NOT wasted money... unless your wife finds out.
 

4/17/2013 1:12 PM  #10


Re: radiator overflow - cap related??

Just an FYI update. Problem must have been with the cap.

Even after topping off rad again, it does not seem to be loosing fluid any more with a new 13 lb cap installed designed for an open system.

I added new overflow hose as well. The old one was about three inches too short and made a mess. The new one is not spitting anything. Only saw a drop on the tip, but it will now carry overflow safely onto the ground outside of the engine compartment should it need to.

     Thread Starter
 

Board footera


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