Radiator cap part numbers

[Tom F&L GoR]

Some cooling problems arise from the use of drop center radiator caps. The metal disc on the gasket side is simply hung on a pin, seats under pressure, drops open to allow coolant to be sucked back in. Problems arise when coolant and crud dry out on the gasket or disc while hanging open and it loses it's seal. Typical is that coolant is pushed out to the overflow but never sucked back; car overheats and you panic because it's so low on fluid.

The fix is a spring center radiator cap. Same pressure, just that the metal disc is lightly spring loaded closed. It still allows coolant to be sucked back in, but the seal stays clean. If I compared part numbers correctly, here is the "system" for Stant radiator caps.

#10231 plain cap 16 lb drop center
#10331 safety lever 16 lb drop center
#10230 plain cap 16 lb spring center
#10330 safety lever 16 lb spring center

 

[Steve-Indy]

As always, THANKS, Tom...you da man

 

[95Viper]

Tom, FYI...my OEM 95 cap (drop type) was one number off on pressure than the 2001 OEM cap (spring). I think it was 15 and 16 lbs. I went with the 2001 anyways and it is perfect.

 

[luc]

Tom,

For once,I disagree with you, those 2 radiator caps,not only do not work the same way but they serve different pupose.

The closed type (what you call the spring center) is used in constant pressure cooling sytem.

Meaning that since the valve is closed (up to it's pressure rating) by a spring, when the engine is started and beging to warm up,the system pressure start to built up right away due to the expension of the coolant.


The open type (what you call the drop center)is used in pressure vent cooling system.

Under light operating conditions, the cooling system operate under no pressure.
It's ONLY if fast heating or overheating cause a FAST expension of the coolant that the valve close and pressure built up.

In another word, on a closed type, you can put your hand on the top radiator hose and you will feel pressure building right away when on open type there will be no pressure at all until the temperature rise close to overheating.

Since on the open type valve,the metal disk hang down from the rubber seat/gasket, logic dictate than the pressure is equal all around this disk and consequently no force push the disk upward to close/seal it.
Only when there is a very fast and violent increase in pressure v(usually caused by steam) will the disk move upward and close.

Luc 00GTS

 

[Tom F&L GoR]

Luc,

The caps do not work the same, which is why in our application, drivers may want to switch.

Your description is technically correct, and I would only add that the normal sloshing of coolant in the radiator would wet the radiator rubber gasket and the metal disc would "stick" to it and close the system far sooner than when pressure builds up. If you took your cap off right now, odds are it appears closed. I believe this has to happen for two reasons; first it would be a little unnerving to think that sudden steam formation would be the event that closes the system; hopefully the cap has closed before that and you avoid the steam. Second, under slow heating conditions the coolant would slowly expand or evaporate and the vapors or liquid would continually leave the system. Under the extreme and unusual circumstance of continual low heat, you could drive off amounts of coolant without ever closing the system, resulting in a low coolant level.

I think we agree that when up to thermostat temperature, both caps are holding pressure, and that the different operation is for some amount of warmup time.

In my little exposure to coolant hardware, the drop center cap was used on systems where the overflow reservoir was remote or distant so that returning fluid (when the engine was cooling) would have less to overcome. Obviously, the reservoir in the Viper front fascia met this application. However, as GM showed the automotive repair world, the drop center disc also collects debris, get dried material on it, and generally provides a poor seal over it's lifetime. A spring center cap is closed and stays sealed better.

My own experience was that the coolant level would drop and drop over time, and of course, I worried about head gaskets. But it turned out that the drop center disc wasn't sealing, and therefore not raising pressure and increasing the boiling temperature. In this cycle, it would therefore kind of overheat, blow steam and liquid, but never **** back the same amount. Do this a few times and the coolant level could get pretty low. A new cap fixed it, and arguably a new drop center cap might have also. But from reading about GM's problems (see this link) a spring center cap should greatly help prevent the problem, which is why I have switched and think others should consider so also.