Volvo cap for Renix bottle? 150 kpa=21.75 psi (too high?)

Will the cooling system be over pressurized with this Volvo cap at 150 kpa?

I have been running this cap for a while and just noticed the rating and converted it to psi.

It has been on a Volvo tank that was sourced from a jy, they last a year or so and then start seeping at the built in expansion area.

The Volvo tanks dont crack like OEM type, but they fatigue and start weeping sooner than later.

My question is, has anyone found that this cap is too high a psi rating and over pressuring the cooling system?

my2monkeys said:

My question is, has anyone found that this cap is too high a psi rating and over pressuring the cooling system?

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I switched to the black cap (~10 PSI) for the same shadow of a doubt. My primary concern is the heater core, everything else is relatively easy to replace.

When I first did the conversion, I strapped the reservoir to the jeep bracket. That lasted about a year. My next step was to use the Volvo bracket and adapt it to my XJ. So far, so good...

The more pressure, the better boil over protection, until a line blows

souske said:

The more pressure, the better boil over protection, until a line blows

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True and correct! Raising the pressure raises the boiling point.

Adjusting the ethylene glycol percentage can also raise the boiling point.

souske said:

The more pressure, the better boil over protection, until a line blows

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this

and with old components you find the weak link quickly.

I just swap them all to open system radiators.

Every renix jeep I've ever had needed a new radiator anyway, so I just do the conversion and save myself all the headache. A 91 radiator will still have the bung for the efan switch.

The closed system is more efficient, which is why most new cars have a closed system now.

The only reason I run an open system, is Griffon doesn't offer a closed radiator setup and I like their big blingy radiator. I run it with a 26 psi cap, though..

I'd be very comfortable with the volvo setup. If you find that you have a coolant leak at 21 psi, you had a coolant leak anyways and just didn't know it yet.

Why compromise cooling to mask already broken stuff?

cal said:

Why compromise cooling to mask already broken stuff?

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My stuff is not broken, and I prefer to keep it that way. Far as I know, the heater core is old enough to drink in any bar in the State of Colorado. If it lived this long with its 14 lb.(?) cap, why push the limits?

The first summer we had our XJ, my wife pulled in the driveway and shut it off. I decided to look things over and popped the hood. As the waves of heat rolled past my face, with the sounds of the exhaust cooling down, I noticed the reservoir all puffed up with the pressure. I tossed a rag over the cap and sloooooooooowly bled pressure from the cooling system. At some point I began to hear a percolating sound from deep in the engine block. I tightened the cap, the bottle started puffing up again, and the boiling sound stopped. I wish I had numbers to go with that set of observations. As it is, I have not noticed any boiling sounds since installing the 10 lb. cap.

Sadly, I have seen only one person on this board take a pressure reading on the cooling system. We don't have a lot of data concerning typical pressures in typical operating conditions. Obviously, our stock cooling systems do operate under that 14 lb. threshold, possibly under the 10 lb. threshold, with my 60/40 mix of coolant.

The question is, how much pressure is enough?

And, if you want to live in the "more is better" camp, why not run straight water and a 30 lb. cap?

Hypoid said:

And, if you want to live in the "more is better" camp, why not run straight water and a 30 lb. cap?

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We run a 25/75 mix of bio-safe antifreeze and water because it actually freezes at night.

Peak claims that gives us a boiling point of 221.

A 26 psi cap raises that 78 degrees to 299.

My temp gauge goes to 300...

Didn't see a need to push it further.

Not that its really relevant here, but we have run the motor up over 275 a few times without it boiling over and had it come right back down with no adverse effects.

Anyway. I am just saying 21 psi is NOT too high for our rigs. Myself I would never run less than 16 psi.

Without factoring coolant, a 16 psi cap gives you a boiling point of 260 which is the top of a factory gauge.

10 psi boils over at 242 which isn't much higher than operating temp..

Does 4643 still have a heater core?

Would it matter if it did or didnt? If the heater core would fail at the factory 16 psi it will fail at 10 or at my 26

I know it's up for handling 16 psi, as it has since the day it left the factory, in a different body.

I was wondering if you had actually run it up to 26psi without issues. As far as I know, griffon doesn't make a bling bling heater core.

I stand corrected! After diving into the 1990 FSM, I have learned the RENIX cap should relieve pressure anywhere from 16 to 18 psi. The test procedure says to pressurize the cap to 18.6 psi, and the pressure should stabilize within 1.5 psi of this setting.

I am less concerned about using the green cap. Thanks for asking the question!

On more than a dozen I've installed the green volvo cap on, I've experienced no issues.