Ok, I give up. truck is a 95 F250 with the 460. I am having issues finding a radiator cap that is CORRECT for this truck. Both the twist on, and the lever style from Duralast are WRONG. Neither one is sealing at the neck, and therefore the radiator is not pressurizing. I know it is leaking here, because from cold, my overflow bottle level continues to rise, and the coolant gets HOT in it. The upper hose is NOT getting hard to squeeze, so no pressure. No loss of coolant, except when the overflow bottle overflows..

is there a preferred cap for these trucks. I have the aluminum core radiator with the plastic tanks and neck. there IS NO DAMAGE to the sealing surface inside the neck. its just like the radiator caps are too damn short to get to the neck, and therefore there is no pressure seal.

 

HOW ABOUT SOME PICTURES OF YOUR CAP AND THE NECK? HAVE YOU CONSIDERED THE NECK MAY HAVE SOME ISSUES, IS IT CLEAN/SMOOTH/NOTHING SUSPECT?

DO YOU HAVE ANY BLOCKED HOSES LIKE HEATER CORE OR IS THE COOLANT DIRTY. HAS THE OVERFLOW LINE BEEN BLOWN THROUGH TO MAKE SURE ITS CLEAR?

 

I do not believe the 7.5L trucks use the extra coolant lines for the throttlebody but the nipple for the supply line is probably there on the neck. This post from the Bronco sub-forum appears to be very similar to your issue: https://www.ford-trucks.com/forums/4...flow-tank.html

The short story is verify the over flow bottle hose is on the correct output port of the radiator neck.

 

ok. Sorry for no pics, it was dark out last night when I was working on the truck, so no pics. The issue is that the seal to seal distance on the caps is 3/4 inch, yet the seal to seal distance on the neck is 13/16 or so. Just for ****s and giggles, I put 2 lower gaskets (that seal the pressure spring assy to the neck) and lo and behold the system pressurizes as designed. IOW, the neck is about 1/16 too tall for the caps. I dont really want to run it like this long term, as the small valve in the center that allows coolant to return to the radiator as the system cools is not able to properly function. This however seems a smaller issue than boiling over due to not pressurizing at all.

I have verified that the reservior is attached to the neck between the two sealing surfaces. there is a bypass hose that goes to the "lower" port below the sealing surface that leads to one of my heater hoses.

The radiator was advertized as "new" when I bought the truck, and as clean as it is, I have to believe this. there is no abnormal wear on the neck, either internally or externally, and the upper gasket seats and seals just fine. the only issue is that the radiator cap (as designed) does not properly seal the system below the upper gasket, allowing pressure to build.

 

 

what do the tabs on the cap look like? can you show me that too? Also what does the plastic "ridges" look like on the neck which the cap grabs to(like the ps pump cap is the same concept, just not as critical)

 

Well theres your first problem, buying **** from autozone. Now you know Duralast = deadlast.

 

Ok, Sorry it took so long to get back to you, been busy in Court all day (freaking jury duty....). Radiator neck ridges are good. The tabs on the cap are good, its just that the neck is made too long it seems. Here are a few pics, dont know how well the ruler pics are going to turn out, but the distance on the cap from seal surface to seal surface is 3/4 inch, while the neck depth is about 13/16 inch. The cap I was replacing was about 3 months old, and there is no sign that the gasket was touching the inner neck sealing surface...


upper hose on neck to overflow, lower to heater hose

doubled gasket on lower surface. In this configuration, IT WORKS. the coolant from the overflow even returned when the engine cooled last night. I think Ill leave this well enough alone for right now, until I figure out why the seal surfaces are so far off

inner neck, no damage.

seal to seal height on the new cap. set up like this, it works great. its a bodge, but it works....

this is the cap I robbed the extra gasket from. Its about 3 months old, so shouldnt have issues. The tabs on this look proper, even bending them wouldnt help, it would just tighten up the upper gasket surface.


I know, problem is, their stuff doesnt seem any better/worse than anywhere else for this truck.... I havent been able to get anything but crap parts for it.... I wont mention fuel pump modules, lest my blood pressure spike again.....

 

why does it look like there is an entire build up on one half of the flange of the neck? I use the same cap(presumably same on my engine as same overall size, same psi)

And Did you follow the caps instructions to install it with the lever up


much older pic to see the inside of the neck a bit
r up

 

cap installed lever up. as for the buildup, its likely just my crappy iphone camera with low light...... water level is right to the top of the neck, and the overflow is about 3/4 full from its little overheating temper tantrum a few weeks ago. When running with the cap off, there are NO bubbles coming to the surface, just expansion of the coolant as it warms up. I need to put a manual water temp gauge in this thing though, even when boiling over, the temp never went above the "N" on the idiot gauge..... if I hadnt stopped for fuel, I never would have known it was cooking off....

quick synopsis of symptoms

No coolant in oil
no oil in coolant
no bubbling while running
no consumption of coolant
able to make expansion tank level surge with engine off and dead cold just by squeezing upper hose
system not pressurizing when hot (with stock cap).
no signs of gasket contacting lower sealing surface


Either I got a crap radiator with an out of spec neck (I wouldnt discount it..) or the cap is just too damn short to seal.

 

do you notice anything about the thermostat here. anything at all. side to side(hint) twisty twisty


See the stuff on the rim? Under the ledge, across the very top of rim, on the outside perimeter. All I see is a clear as hell neck that your cap should fit in if you clean those parts up and check out your cap being distorted.
do you have all your heater core hoses routed right, any restrictions in the system that may push way to much pressure to the cap,
To bleed requires that being highest point, the thermostat working right, the engine has to be reved up for parts, the heater has to be on full hot, the hoses/interfaces cannot leak water pump has to be working, not slip,

 

I think I have the same problem on a 351w.
I've determined that the metal rad cap has been on and off so many times, that the tabs on the cap have worn the plastic radiator neck, causing a loose fitting.
I have to put the cap on carefully, overtightnening will cause it to spew, has to be just right.

My fix is going to be buying a new radiator.