So I swapped a 16 lb radiator cap for the 20 lb...

[Berf]

So does the lower pressure cap prevent radiator failures, and does the truck still run at the same overall temp in 100 degree weather with the AC on?

 

[DILLARD000]

So does the lower pressure cap prevent radiator failures, and does the truck still run at the same overall temp in 100 degree weather with the AC on?

ThermoStat rating dictates the steady running temp, typically 192f for stock Ranger\Explorer V6~4.0L~SOHC.
RadiatorCap rating dictates the maximum coolant running pressure, typically 16psi for this same engine.
If engine\coolant overheats, the RadiatorCap is a safety release, preventing more serious component damage.

 

[Berf]

When you lower the operation pressure by 4 psi, you reduce the boiling point by about 12 degrees to around 250, which can result in overheating more easily. Obviously Ford chose 20 psi for a reason. I just wonder if anyone running a 16lb cap has had any overheat issues in summer with the AC on.

 

[user 64972]

I added one when I replaced the leaking original radiator and have had no issues with it and it has been on there maybe a year and a half as best I remember!

 

[Todd Z]

No one has had any issue, I have not had issues, both V8 and V6.

 

[DILLARD000]

When you lower the operation pressure by 4 psi, you reduce the boiling point by about 12 degrees to around 250, which can result in overheating more easily. Obviously Ford chose 20 psi for a reason. I just wonder if anyone running a 16lb cap has had any overheat issues in summer with the AC on.

The radiator cap does NOT CONTROL the coolant system pressure\temperature, it ONLY REACTS to pressure;
opening to relieve pressure to the overflow tank when its PSI rating is exceeded. It's a safety relief valve.

 

[user 64972]

The radiator cap does NOT CONTROL the coolant system pressure

Seems to me that if you lower the pressure at which the cap opens to release pressure then you would be, in fact, control the system pressure and thereby lower the pressure on the plastic radiator. Just my non-expert opinion! I hate plastic radiators on any car. Not one of the better changes made on newer vehicles as I see it.

 

[DILLARD000]

Seems to me that if you lower the pressure at which the cap opens to release pressure then you would be, in fact, control the system pressure and thereby lower the pressure on the plastic radiator. Just my non-expert opinion! I hate plastic radiators on any car. Not one of the better changes made on newer vehicles as I see it.

True, RadiatorCap does limit the maximum coolant system pressure,
though the ThermoStat is the real controller\modulator in the coolant system.
Critical that ThermoStat is working proper & Radiator has both good Coolant+Air flow.
Truely amazing how many drivers are in LaLaLand, go 15+ years,
have never even refreshed\flushed the coolant,
much less replaced the ThermoStat, flushed+backwashed the Radiator, or replaced the FanClutch,
then engine overheats & they start changing the RadiatorCap rating
because in their simple world it's what caused the problem.

Ditto on PlasticTanked Radiators, they're total junk.

 

[Berf]

It's good to hear that enough folks have tested the 16lb cap and not had any negative effect, I'll probably swap mine out as well.

I would like to mention that it's incorrect to think that the operating temp is totally controlled by the thermostat. When discussing cooling systems it's important to remember that every component of the system plays a role and has an impact on the overall systems efficiency. The thermostat does not totally control the operating temperature, and once the full open temp of the thermostat has been reached, it no longer has any control at all on the upper limit that the system will reach. That will be determined by the overall system efficiency. One of the main things the thermostat does do is control the time it takes for the engine to heat up when cold, because it has the most control over the system when it is closed or only partially open. In higher operating temps with the AC on the thermostat will most likely be running full open.

And as the internal pressure increases it lowers the boiling point of the coolant, so pressure is an important factor in preventing boil over. This is why I asked how the system work in 100 degrees with the AC on and in traffic, because this is the upper extreme that will tax the system. Now throw in uphill towing and you may approach the limits and experience boil over with the lower pressure cap. I'm sure Ford did endurance testing to determine what cap pressure, radiator size, and thermostat to select. (Fun fact, many manufactures use Death Valley for this type of testing.) Other things to consider are the cleanliness of the radiator fins, age of the coolant, airflow, speed, proper water pump flow, and a thousand other factors that all come into play to determine what the engines final operating temp will be.

 

[Todd Z]

Pressure cooker theory is the best way to describe it.

 

[Johnny O]

When you lower the operation pressure by 4 psi, you reduce the boiling point by about 12 degrees to around 250, which can result in overheating more easily. Obviously Ford chose 20 psi for a reason. I just wonder if anyone running a 16lb cap has had any overheat issues in summer with the AC on.

My opinion is that the higher pressure is so the engine can run at higher temperature for emissions reasons. I replaced the 20 lb cap with a 16 lb about ten years ago and no issues since. Engine seems to run at the same temp but remember the thermostat only controls the minimum temp, not the maximum.

 

[Johnny O]

So does the lower pressure cap prevent radiator failures, and does the truck still run at the same overall temp in 100 degree weather with the AC on?

1. Yes. Also helps to keep the thermostat housing from cracking.
2. It seems to.

 

[Paul Fithian]

I recently had 3 of the 4 screw type hose clamps leak on the upper and lower radiator hoses. Replaced all 4 with Smartseal SAE 28 from Advance:

https://shop.advanceautoparts.com/p...tion-over-360-degrees-372150028058/11854977-P
No more leaks, these clamps have a more uniform circumferential clamp and seal better. They can be installed without disconnecting the hose

I have a 16 PSI cap on order.

 

[DILLARD000]

@Paul Fithian
Interesting, like a basic worm clamp with additional InnerSlipRing;
should help to prevent the clamp from digging into the rubber.

 

[EddieS'04]

Years ago advance auto had 2 different stats listed for the TRAC. A 192 and a 180. I chose the 180. My scangauge show 184. Unless I idle for along time in summer with AC on. Then I climbs into the 190's.

 

[DILLARD000]

Ran many years 192f ThermoStat FactoryOE FordMotorCraft# 2L2z-8575-aa\rt1167;
in 95f+ weather idling, temp would rise & be forced to shut off AC, turn on Heat & rev engine.
Experimented with several TStats from 190f down to 174f; any below 180f were unstable opening+closing.
After replacing junk Plastic FactoryOE ThermoStat Housing with Alum ThermoStat Housing
& junk PlasticTanked FactoryOE 1CoreRadiator with AllAlum 4CoreRadiator,
settled on 183f 84c ThermoStat Stant# 14748 with LowerBypassDisc ground narrow slightly
so to not stick open in Housing BypassThroat & provides longer stroke = higher flow.
CoolantTemp 183~185f steady, both summer >95f & winter <20f, both idling & uphill drag.

 

[Todd Z]

I also run the wider clamps.... More area to bite...

 

[Paul Fithian]

New RS-76 16 PSI cap installed

 

[Paul Fithian]

I can report zero coolant leaks since changing the clamps and radiator cap a month ago.

 

[antny024]

I purchased my 08' 4.0 Sport Trac last Saturday and drove it home 100 miles with no problems, no nothing. Popped the hood, checked all fluuds, all good, no leaks.
Went to Autozone, purchased a 16 lb radiator cap, swapped out the 20 lb cap in a cold engine and started it. At operating temperature (gauge needle @ slight less than mid way) and I smell antifreeze. Look under the hood and behold, small leak in top of radiator (plastic). Attachment shows where leak was.. An @ 2" crack in the middle two squares (I epoxied beyond the crack either side an additional couple of inches for what I couldn't see was a crack but expected to be a crack at some point.

Thing is, when I got the cap the store had two versions, one with no pressure spec stamped in the cap, and another with pressure relief valve and 16 lb stamped in the head of the cap. I bought the latter.

Shame on me, I should have tested the cap unfortunately my Stant coolant tester did not have the correct adapter and 0'Reillys wanted $200 bucks plus tax (rental) for me to test the cap even though I could test it over the counter and hand the tester back to them.

Went back to Autozone, had them pull out the other cap and three of us tested physical pressure pushing the springs for comparison. We all agreed the unmarked cap definetely required less pressure.

So now I am doing a repair (see pic) to see if it actually works while I search listings for an all aluminum radiator. Btw, I'm using JBWeld Plastweld for the repair (all I could find locally otc). Pic shows first application, I plan a second, final coating after the first cures.

Anyone recommend a reasonably priced all aluminum radiator for the 2008 ST 4.0? I see one on Fleabay for @200 shipped. From California so I'm sure it's off the slow boat from China..

I purchased my 08' 4.0 Sport Trac last Saturday and drove it home 100 miles with no problems, no nothing. Popped the hood, checked all fluuds, all good, no leaks.
Went to Autozone, purchased a 16 lb radiator cap, swapped out the 20 lb cap in a cold engine and started it. At operating temperature (gauge needle @ slight less than mid way) and I smell antifreeze. Look under the hood and behold, small leak in top of radiator (plastic). Attachment shows where leak was.. An @ 2" crack in the middle two squares (I epoxied beyond the crack either side an additional couple of inches for what I couldn't see was a crack but expected to be a crack at some point.

Thing is, when I got the cap the store had two versions, one with no pressure spec stamped in the cap, and another with pressure relief valve and 16 lb stamped in the head of the cap. I bought the latter.

Shame on me, I should have tested the cap unfortunately my Stant coolant tester did not have the correct adapter and 0'Reillys wanted $200 bucks plus tax (rental) for me to test the cap even though I could test it over the counter and hand the tester back to them.

Went back to Autozone, had them pull out the other cap and three of us tested physical pressure pushing the springs for comparison. We all agreed the unmarked cap definetely required less pressure.

So now I am doing a repair (see pic) to see if it actually works while I search listings for an all aluminum radiator. Btw, I'm using JBWeld Plastweld for the repair (all I could find locally otc). Pic shows first application, I plan a second, final coating after the first cures.

Anyone recommend a reasonably priced all aluminum radiator for the 2008 ST 4.0? I see one on Fleabay for @200 shipped. From California so I'm sure it's off the slow boat from China

I purchased my 08' 4.0 Sport Trac last Saturday and drove it home 100 miles with no problems, no nothing. Popped the hood, checked all fluuds, all good, no leaks.
Went to Autozone, purchased a 16 lb radiator cap, swapped out the 20 lb cap in a cold engine and started it. At operating temperature (gauge needle @ slight less than mid way) and I smell antifreeze. Look under the hood and behold, small leak in top of radiator (plastic). Attachment shows where leak was.. An @ 2" crack in the middle two squares (I epoxied beyond the crack either side an additional couple of inches for what I couldn't see was a crack but expected to be a crack at some point.

Thing is, when I got the cap the store had two versions, one with no pressure spec stamped in the cap, and another with pressure relief valve and 16 lb stamped in the head of the cap. I bought the latter.

Shame on me, I should have tested the cap unfortunately my Stant coolant tester did not have the correct adapter and 0'Reillys wanted $200 bucks plus tax (rental) for me to test the cap even though I could test it over the counter and hand the tester back to them.

Went back to Autozone, had them pull out the other cap and three of us tested physical pressure pushing the springs for comparison. We all agreed the unmarked cap definetely required less pressure.

So now I am doing a repair (see pic) to see if it actually works while I search listings for an all aluminum radiator. Btw, I'm using JBWeld Plastweld for the repair (all I could find locally otc). Pic shows first application, I plan a second, final coating after the first cures.

Anyone recommend a reasonably priced all aluminum radiator for the 2008 ST 4.0? I see one on Fleabay for @200 shipped. From California so I'm sure it's off the slow boat from China..

When buying parts like radiators you're better off getting them locally. If do have an issue you won't have to ship it back and wait days for a replacement. I just put a Murray radiator in mine from O'Reilly's. I did that because a Motorcraft wasn't available locally. ALWAYS replace caps with the correct pressure. Why anyone would waste time or money to test a radiator cap makes no sense, they cost $10-$15... BTW There is nothing that will repair a cracked radiator side/top tank. No glue or epoxy will adhere. As soon as it gets hot and builds pressure, it will leak. 100% of the time.