I've built the degas pressure test kit. Hooked it up and would only build about 10 psi. OP, due to your thread here, I called Autozone and see if they could test my cap. They JUST got a radiator and cap test kit. $240 for the kit. What beautiful kit it is. They let me use it in store and my cap wouldn't hold more than 8 psi. I tightened the adapter, got it to hold 13.5 psi at best.

Not sure if that is good enough.

 

That is interesting, these caps say they are good to 16psi, but it seems as though they are not...or are our homemade test kits inaccurate? I will have to run to autozone and see the kit. They are fairly nice locally I will ask if they will let me test may cap without purchasing the kit (my wife ended all my projects till nov-3rd, so that means I can’t buy the kit) and I will post the results...
This brings so many questions to mind...I don’t want to seem dumb, so I will get back with a few more questions...

 

these caps don’t appear to be very accurate with their pressure release system. With that in mind, how accurately does the pressure need to be regulated? are these caps part of the problem with these trucks? it makes me wonder how many people have had unnecessary repairs due to these problematic caps. It seems that we (just this small collection so far) we (as a collective) have spent a large sum of money on just caps.... I think we have a problem.

 

If someone is losing coolant out the cap, then it is only common sense to put on a pressure gauge before rushing to head gaskets. Ford Workshop Manual / TSB requires verification that the cap is working before proceeding to something more serious. Besides a cap problem, the degas bottle can warp and cause the cap to relieve early or to just plain leak. So can gouges in the cap surface. A knowledgeable mechanic would check all this unless they are dishonest and want to get a quick score on a head gasket job.

Also, the forums have been talking about the weak caps for MANY years, so a quick search would find a lot of information on it for the 6.0L owner. Me personally, I have not ever had a bad cap, but I changed it once to have a spare and once after 100k miles. Personally I think the OEM cap is better than aftermarket, but I have no data on it and I know quite a few people disagree with me. They could be right, I could be right - not a big deal in my mind.

Below is a good TSB to read. Also there is a coolant loss thread in the Tech Folder.

https://alliantpower.com/sites/allia...B-09-08-03.pdf

https://www.ford-trucks.com/forums/1...nts-degas.html

The cap is there to hold a certain amoont of back pressure so that the coolant will not boil in the upper ranges of coolant temperature that the engine was designed to run. That (and no leaking) is all that they are intended to do. It is not really all that important if a cap holds 15 psig or 17 psig. They don't have to be that accurate.

When you put a pressure gauge on the bottle, how do you know the pressure gauge is accurate? I think there is AT LEAST as much chance of a pressure gauge being off a few psi as there is the cap having an issue - especially if you get a pressure gauge with a full scale range greater than 20 psi.


Lastly - an oil cooler plugging has nothing to do with this cap. It is identified by the differential between the coolant and the oil temperatures. Also, the degas cap has nothing to do with coolant in the cylinders and "peanut butter" on the dip stick. Tuners and 35 psi boost have more to do with that.

 

Good info right there mark,ive tested several caps in past few yrs from big box stores,2-3 out of 10 may be higher or lower,but what i found was put one on that opens at 16lbs and something makes it degas it no longer holds to 16,it may be 10 lbs now,never open again unless towing so repairs made but with the same old cap thats now opening at 10 or lower and when it keeps opening it gets lower and lower,more repairs made,more parts swapped but with the same cap or a cap that did not hold to 16 from the start, expensive cycle.

 

Ford has stated that every time the pressure relief is actuated, it could weaken it and cause it to relieve at a lower and lower pressure.

 

I am just happy that the problem is solved. You guys have given me a lot of good solid information. Thank y’all very much.more updates to come...

 

Does that mean that every time it vents, we need to replace it?

 

Personally I would test it and only replace it if the relief pressure dropped below 15 psig.

If the cap relief valve is the same as those in industry (hot water and steam service), part of the mechanism to weaken it is exposing the spring to hot temperatures.

 

I would be surprised the OE cap varies in its blow off point more then AM. And in looking back at this thread I wonder if the replacement cap was OE.

The cap on our trucks is exactly the cap used on our LS. Twice that vehicle has overheated due to a failed electric cooling fan and I had to replace the cap due to a lowering of its blowoff psi. I actually pulled the cap from my non-running 6.0 that has been on there for 100k and it works fine on that vehicle. I had replaced my old cap after doing a coolant flush where I had a setup with hoses to use a garden hose to aid in flushing and didn’t moderate the pressure in a well as I should have, so it puked.

So there may be something to a cap only handles one or two blow offs before fatiguing. And maybe it’s only when the cap is hot as that is when most materials are at risk.

I set up a simple 3/8” Tee so I could install a pressure gauge in both vehicles to check how pressure was holding. I only takes a minute to install, but now it takes longer since I installed the gauge in the truck and have to pull it for the LS.

Pressure gauges are most accurate in the middle of their range, so I have a 30psi gauge. It’s accuracy is 1.5%, again middle of the range. Harbor freight it isn’t.

 

Jack,that the gauge ive used for years,even to ck other gauges with,i also have teed into the line and it stays in my trucks, this is realy important if you tow alot building more pressures than not towing.

 

Yep, it’s a good gauge. I used them (in another range) at the facility to run vehicle-stopping distance tests measuring hydraulic pressure before going all electronic. They were a good gauge and we rarely had to recal them against our $2000 calibrator.

And I do the same, used it to check cheaper gauges.

 

I know what my next mod for this truck is.

 

Update: the radiator sprung a small leak yesterday...I noticed it after a 22 minute ride then a 10-12 minute cool down, and on the 22 minute drive back to the house, the truck puked. I am not sure at what point it puked. It did not over heat, the temps was only 3 degrees off, and riding around 192ect and 195eot. When I got out the truck I noticed the tire was wet, and it had not rained. I am not sure at what point it puked, but I imagine it was close to the end of the ride. The radiator leak came first. Will the Leakey radiator have anything to do with the puking? Maybe flash boiling due to pressure loss... I already have a new cap, and I am getting a replacement spare, aswell as replacing the radiator as it’s leaking.
Can one of u guys point me to the transmission line disconnect tool? I had to unscrew the fittings and replace the o-rings last time. I want to do it right this time.

 

$8 on Amazon prime . It's also in a Lisle master kit that local stores might have.
Lisle 39960 Transmission Oil Cooler Line Disconnect
im sure this is correct, I pulled the part number from my Amazon purchase history and used it on my truck.