Radiator Cap Gen 2

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Johnny O

Johnny O

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I can't find the thread now but based said advice I replaced the 20 lb radiator cap with a 16 lb cap today. Stant #10233. In order to avoid a hassle at the parts store, I scoped out the unit on my son's Mustang. Same size, 16 lb. Tell the parts counter lady I need a cap for a 2000 Mustang, V6. No prob. :banana:
 
A few others were complaining of cracked radiator tanks. A quick look at my other cars revealed that everything else has a 16 lb cap. I believe it was mentioned elsewhere that the newer engines are designed to run hotter for emissions purposes, which is not necessarily the same thing needed for long engine life. However, if an engine is predisposed to run at say 220*, it's going run at 220* regardless of whether it has a 16 or 20 lb cap or a 210* or 190* thermostat.
 
The radiator cap doesn't really have an affect on how hot the engine runs...unless it is overheating. The problem with running a lower rated cap is that they system is designed and built for more pressure and running a lower rated cap you are sooner or later going to be pushing coolant out of the overflow tube, also by installing a lower rated cap you are lowering the boiling point of the coolant which in itself can casue a different set of problems. Just becasue the Mustang 4.0 may run a 16lb cap doesn't mean that the ST 4.0 should run it also...then engineers didn't just put a 20lb cap on it to mess with you.



So is your reasoning behind the lower rated cap simply just to try and avoid the radiator cracking??
 
Yes.

Seems to be running at the same temp so far, just at lower psi in my opinion. The overflow tank seems to have plenty of room.

I also think that in order to save weight and space, automakers are going to smaller radiators and less coolant and just running everything at obscenely high temps. If I recall correctly, my dad's V8 Cadillac only holds 10 quarts of coolant (but it holds a crapload of oil).

I'm not enough of a Luddite to believe that low temps and thick oil are what ALL engines need however. :grin:
 
The radiator cap does not dictate cooling system pressure...it limits maximum pressure. If normally the system runs at 17 psi with a 20 lb cap on it and you put on a 16 psi cap sooner or later it will overheat becasue the coolant is being pushed into the expansion tank and that will eventualy leave the cooling system low. You are asking for trouble by running the lower rated cap..may not happen today but sooner or later you are going to deveolp a cooling system issue becasue of it.



The reason for the higher operating temps, and this is usually only true at idle, is for emissions. If they can keep the engine hotter then the tailpipe emisisons will be less and also the engine becomes more efficent the hotter it gets..to a certain point, but regardless most engines at cruise speed still run the same temperatures today as they did 30 years ago.



The 4.0 ST holds about 3.5 gallons of coolant and the 4.6 is just a tick over that..most Cadillac v8 engines hold right around 3 gallons with the exception of the Catera but that isn't really a Cadillac.
 
How would more coolant entering the expansion tank leave the cooling system low? It is the same net volume of water, just expanded because it became hotter. When it cools, it will draw back into the radiator, only at 16 lb instead of 20 lb. Higher pressure will raise the boiling point of the coolant and allow the engine to run at a higher temperature but if it isn't going to run at that temperature, then I don't see that it matters.



FWIW, I note that my dad's Caddy has an 18 lb cap.
 
Last edited by a moderator:
JohnnyO,6/19/2011 19:24 MT



How would more coolant entering the expansion tank leave the cooling system low? It is the same net volume of water, just expanded because it became hotter. When it cools, it will draw back into the radiator,
Click to expand...



You answered your own question if you think about it. Say you are on a trip and under normal circumstances your cooling system that is designed to run a 20 lb cap is only producing 17 lb, which would be about normal. Now the 16 lb cap that you have on there is allowing coolant to the overflow/expansion tank, at this point the vehicle isn't overheating becasue there is still enough coolant in the actual cooling system to maintain temp. Now you keep driving and your 16 lb cap keeps allowing coolant to the overflow but you haven't stopped and allowed the vehicle to cool down so the coolant can be drawn back into the cooling system so over time the cooling system becomes less efficent because there is less coolant in there, as a result the cooling system temp begins to climb and with it so does the cooling system pressure and guess what..your 16 lb cap isn't designed for this system and next thing you know you are overheating and possibly boiling becasue all the coolant that is supposed to be in the cooling system with a 20 lb cap is in the expansion tank due to you putting a 16 lb cap on it.



Alot of Chrysler products also run 18 lb caps and you would be surprised at the number of them that overheat simply becasue someone put a 15 or 16 lb cap on them and the above scenario takes place...seen it with Caddies also.
 
I don't think that the radiator is really low on coolant, it has just expanded out into the tank. It's not like it's replaced with empty space or air. The radiator is still "full".



Can someone with a Gen 1 take a look at your cap and see what it's rated at?
 
GEN 1 is a 16.......



Honestly I would not mess with it.... ALSO the check valve in the cap will leak the coolant into the overflow then pressure building locks the valve.... IT will ONLY take the coolant from the tank back to the radiator in a no pressure COLD situation....



Asking for trouble is also my opinion...



Todd Z
 
But if the cooling system capacity of the Gen 1 and Gen 2 (4.0L) are the same, then could it be purely an emissions issue that has no bearing on the rest of the cooling system?



Looks like I'm starting to get outvoted.... :smack:
 
It sounds to me that something needs the extra pressure. Either safety or temperature. They gen2 is a carry over so maybe the use of the vehicle, different cooling system, pump, or radiator.



There is a reason its there and honestly i don't think its emissions..... I bet there is a temp issue or ford found in the gen 2 body style, they needed the extra pressure to raise the boiling point a few more degrees for a reason..



Todd Z
 
Uncle, uncle, :smack: I'll put the OE cap back on. Probably time for a new one on my son's car anyway. :grin:
 
Lots of Camaro drivers who took thier cars to the track also thought they would solve their overheating issues by installing a 160 degeree thermostst; after all, if the stat opened sooner, that would keep the car cooler on the track... right? Nope, actually it would heat up faster and the cooling system became less efficient.



Thermodynamics is a subject best left to the engineers.
 

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