Should I Change my Radiator Cap?

[robfg67]

I have a '90 Renix with the 4.0L and the factory closed system.

 

The original radiator was replaced about six months ago with a NAPA model that had a traditional radiator cap. A 16 cap was installed.

 

Well, I noticed after I got home from a short trip yesterday, antifreeze was dripping from the cap.

 

Since the radiator was replaced, the truck always runs at just under 210-even under load, so it wasn't overheating.

 

Should I replace the cap with a different pressure rating?

 

 

[75sv1]

Someone has done a conversion.  The purge tank looks still set up in the system. 

[gogmorgo]

Is it coming out the cap or puking out the overflow port?

The later radiator with the cap is intended to push fluid out into an overflow reservoir when it gets up to pressure. This is the “open” cooling system. When you shut the engine off and it cools off, the coolant shrinks and gets pulled back in from the overflow.

The original “closed” cooling system is sealed and only releases pressure if it exceeds the reservoir cap pressure, which it should not do under normal operating conditions.

I don’t remember off the top of my head what the original closed cap pressure is, but the Volvo cap Cruiser (RIP) recommended was around 22psi IIRC. You’ll keep blowing coolant out the radiator cap overflow unless you have a cap higher than that or block off the overflow port a little more solidly. 

[RG67MA]

1 hour ago, gogmorgo said:

Is it coming out the cap or puking out the overflow port?

The later radiator with the cap is intended to push fluid out into an overflow reservoir when it gets up to pressure. This is the “open” cooling system. When you shut the engine off and it cools off, the coolant shrinks and gets pulled back in from the overflow.

The original “closed” cooling system is sealed and only releases pressure if it exceeds the reservoir cap pressure, which it should not do under normal operating conditions.

I don’t remember off the top of my head what the original closed cap pressure is, but the Volvo cap Cruiser (RIP) recommended was around 22psi IIRC. You’ll keep blowing coolant out the radiator cap overflow unless you have a cap higher than that or block off the overflow port a little more 

It's coming out from the cap. So, I'll replace it with a 22psi cap.

 

Yeah, the discharge tube was covered with a plastic/rubber cap and it's held on with a small zip tie-not the greatest option, but it's not leaking from there.

 

Thanks

[rokinn]

You need to allow for the hot expanded coolant to exit the radiator into an expansion tank.  Somethings got to give when the coolant gets hot and right now it's the radiator cap.  Best idea is to add an expansion tank some where.  I used the closed system expansion tank but there are multiple ways of doing it.

[Pete M]

I would drop in the 22psi cap and carry on with your system as a closed system.  

[Eagle]

3 hours ago, Pete M said:

I would drop in the 22psi cap and carry on with your system as a closed system.  

 

Just keep in mind that the plastic tank on the firewall is NOT a "purge" or overflow tank -- it is part of the pressurized cooling system. In fact, that tank is where the coolant expands as it gets hot. For that reason, it's super important NOT to fill that tank to the top when cold. Don't fill it more than halfway. There's a post inside to show the correct fill level, but it's awkward to see it.

[robfg67]

Thanks for all responses. 

 

I never overfill the bottle. 

 

I found it weird that it spit out antifreeze now, but the weather here in Massachusetts just turned hot (over 85 for several days) recently, so perhaps that explains it.

 

I'll start with the 22 psi cap and go from there and report back.