Well let me try to catch up on a few replies. I'm on my phone and can't see my Sig but it should say 239 Flathead....I think...lol. Anyway running that and a factory radiator. When I got the truck it had the wrong cap on it and when I posted on here I was told DO NOT put a higher pressure cap for any reason so that suggestion confuses me. It is my first inclination to up the pressure but I'd have to look back and find the discussion on it. Also to answer you Jim, I've been driving it for two years with this leaking. It leaks until it can't anymore I guess. Yesterday all I did was fill the radiator and started the engine....it never gulped coolant into the block like most modern engines do. Normally when I remove a radiator then put it back in I fill the radiator and wait till the thermostat opens and draws coolant into the engine. At that point I finish filling the system. So this one was a little different. I'm going to NAPA in the morning to check the cap and the pressure at the radiator neck.

 

You for sure don't want the cooling system pressure to exceed 4 psi, or you risk ballooning the top tank or splitting a seam. Ask me how I know...

I usually run the engine up to temperature on a fresh fill with the cap just loose in the neck. It may burp and the cap will keep most of the water from spewing out, but let out the air.

As noted in a different thread about adding a recovery tank, flat V8 cooling system capacity is 22 qts, and it expands almost 5% from 70 deg. to 180 deg. That is more than a quart. You have to leave plenty of room in the tank for expansion.

Did you measure your filler neck and the cap?

 

Thanks for the info Ross. I was gone all day today so I haven't measured yet. I'll do that in the morning.

 

The more I read the more I think I agree with Pete, it sounds like air in the system somewhere. Increasing the pressure sounds like a bad idea with your engine and radiator and Ross has a scary story to reinforce that thought.
Good luck Wayne.

Wally

 

Thanks Wally. I'll have a couple answers tomorrow anyway. It will be a start.

 

I hope it is not a head gasket....my gut isn't feeling good about that...
I don't know my flatty's though...but if you get an immediate leak before it warms up it seems pressure is building right away. And in my experience, it doesn't neccessarily have to be pulling coolant into the cylinder on the intake stroke. Hmmmm....I am subscribed...and I hope I am way off here.

 

True. In fact some thermostats already have a 1/8 inch hole in them when new. I only suggested this because it sounds like Wayne might have a back pressure issue. His truck is pushing coolant into the recovery tank even when the engine is cold.

Let's see what he comes up with tomorrow.

 

Wayne, you are right. Something is keeping your system from filling. Thermostats in backwards will cause that and air trapped in the system when parts of the cooling system are higher than the water level in the radiator. Some cars with low mounted radiators used to have bleeder valves on the top of the upper radiator hoses.

 

Ok here's what I've come up with. I'm at NAPA. Napa part number 703-1419 is the cap that it shows for many years of these trucks including mine. That's a Stant # 10281. Picture shows it to measure 1 1/4" from top of cap to bottom of the metal button that is the lowest part of the cap in the radiator. Kinda hard to measure a vague dimension like that since its a compressed dimension. My cap measures around 1.4" uncompressed and the 1 1/4" number compressed. Neck of the radiator measures 1.09" with a digital caliper. Keep in mind the longer number on the cap is to the TOP of the cap. Radiator was measured from top of flange obviously. The cap isn't seating and sealing off. We are all stumped here because we see no caps listed longer. No clue what to do. I went thru every single cap in stock here and none are even close to the length of the one i have in hand. And none are 4# caps either. My radiator is a factory flathead radiator and I know hundreds of you guys are running them just fine. What should I try next?

 

Hmmm . . . I don't understand Wayne. If the radiator flange to seat measures 1.09" and the old radiator cap top seal to bottom seal measures 1.4" then you should have .31" of compression which should be OK. What am I missing or misreading?

 

I just checked the NAPA website. For your 1949 Ford Truck V-8 the correct radar cap is a Belknap BK 7031419.

Here are the dimensions:

 

There is an inner brass piece that is just on the underside of the part of the cap you twist. That brass piece is what sits on the top of the radiator housing. Measuring from that to the bottom of the COMPRESSED cap gets me .844".....so I'm short!! An overflow wouldn't even help because the radiator must seal at the cap.

Pete: Thanks....see my post above that lists that same NAPA part number....

 

I missed that number so yes you had the same number as on the website buut it obviously is the wrong part. I think that I had the same problem at NAPA but the guys went in the back and found on that worked.

 

A quick call to Stant......there are NO caps longer than the one I have. How is that possible!!!!!

And look at this part drawing from Van Pelt....what the heck is part #8067? Looks like some kind of tube sticking into the top of the radiator...which would do what to the overflow tube that is made into the radiator neck?? And how does is connect? Never seen one....anybody?

http://www.vanpeltsales.com/FH_web/F...48-51truck.jpg

 

Wayne, Mac's shows having one made for your rig. Hope this helps. Give them a call with any questions.

Good luck,

Wally