Help me understand rad cap

[S15_Spec_R]

OK, I have my own theory on this but if someone could tell me the advantages or not of changing the rad cap from a 1.1 bar to a 1.3.

For the cap to relief on a 1.3 that would mean hotter coolant right? The hotter means a raise in pressure. So If I stick with my 1.1 bar it open earlier and would keep coolant cooler than 1.3?

I'm trying both at the moment to see what differences I get from my defi but if someone is in the know that would help.

 

[Yakozan]

I think its' just a safety feature. 1.1 opens earlier to relieve pressure when the system is overheated. This is to protect the radiator, coolant lines and stuff from cracking from high pressure. has nothing to do with cooling except that a 1.3 cap will open at a higher pressure (higher water temp).

Edit: So in my mind there will be no difference unless you cook your engine.

Edit2: But I don't know if added coolant capacity will get you higher pressures.

 

[StarletRick]

its a bit more than that.

water under pressure has a higher boiling point. the higher the pressure, the higher the boiling point. the theory is; that the coolant will sustain a higher temperature before boiling, and the difference between that and the air running through the rad is greater. the greater the difference in heat, the more heat is transferred to the air.

unless you run drift or circuit HARD, you wont notice a difference. imo you should never get the coolant hot enough to open the cap.

 

[S15_Spec_R]

Thanks. So really if the car is running 90 centigrade then the pressure is less than 1.1, and even under hard street driving it shouldnt rise above it? If so a 1.3 cap helps?

 

[Yakozan]

Thanks. So really if the car is running 90 centigrade then the pressure is less than 1.1, and even under hard street driving it shouldnt rise above it? If so a 1.3 cap helps?

It helps to keep the coolant in your system for higher temps and will continue to cool for that higher temp. as starletrick said above. The only thing a new rad cap will do is raise the boiling temp.
If you can get the stock rad cap to open, I would look into other solutions than a new rad cap. Upgrading the cooling system with a new race radiator or an air diversion plate is the first things that pops up in my mind.

This is just what I think.

 

[gunner93]

Also a water surface tension reducer is also helpful.

 

[S15_Spec_R]

Also a water surface tension reducer is also helpful.

Sorry, what is this? Water wetter etc..?

 

[DeanS15]

careful with uprated caps, if there are any weak points in your coolant system it could cause them to spring a leak. i had this on my old car and of all places to go - the cam belt driven waterpump seal$$. this was a day or two after fitting the cap.......

 

[StarletRick]

Sorry, what is this? Water wetter etc..?

yup, hes talking about a water wetter. it lowers the surface tension of th water and allows more heat to dissipate.

you shouldnt have to run all of that though on a street car. decent coolant is enough.

i use toyota premix (gasp!) its the best coolant you can get IMO.

 

[DeanS15]

what about nissan 4life coolant, do many of you use that? supposed to warn of head gasket failure too by a change of colour???

 

[S15_Spec_R]

I use water wetter, aluminum rad about 2 inch core and coolant that warns me of head gasket failure by going from red to yellow (i think yellow).

So the coolant tank that is filled doesnt get dragged through the cooling system as the rad cap is not letting coolannt in? Could test myself after warm and see if the reservoir is warm too.

 

[StarletRick]

the coolant in that bottle is mainly there so air cannot be drawn into the system.