Radiator Cap Specifications

[rock2610D]

Was wondering if altitude can affect the radiator cap performance. I am at 8000 feet and water boils at 195 degree F here. Not sure how my antifreeze and water mixture is affected. Air pressure here is about 11 psi vs the 14.7 at sea level. Can I also assume water freezes at a lower temp?

Can anyone suggest a radiator cap psi for my condition? Should psi be lower on the cap or higher or should I just stick with my existing cap.

I have noticed that when temps get above 70 degrees my overflow bottle will fill pretty quick, but if I let it idle for 30 seconds the overflow bottle empties quickly.

I want to make sure its not a radiator cap issue before I decide to replace an expensive radiator just to find I could have put on a different cap.

INFO 2610D with a Fresh 3T80 3 cylinder motor.

 

[Box]

Was wondering if altitude can affect the radiator cap performance. I am at 8000 feet and water boils at 195 degree F here. Not sure how my antifreeze and water mixture is affected. Air pressure here is about 11 psi vs the 14.7 at sea level. Can I also assume water freezes at a lower temp?

Can anyone suggest a radiator cap psi for my condition? Should psi be lower on the cap or higher or should I just stick with my existing cap.

I have noticed that when temps get above 70 degrees my overflow bottle will fill pretty quick, but if I let it idle for 30 seconds the overflow bottle empties quickly.

I want to make sure its not a radiator cap issue before I decide to replace an expensive radiator just to find I could have put on a different cap.

INFO 2610D with a Fresh 3T80 3 cylinder motor.

This sounds similar to one of the issues I was having earlier this year. How full is your over flow bottle when cold? I found that my system worked best when I filled it to the low level when cold. When it was filled to the high mark when cold it would push water out the over flow bottle after a while. Once I started only filling it to the low mark I have not had this problem again and the engine seems to be cooling fine.

Just my .02

Box

 

[rock2610D]

Yah, I know but by bottle does not overflow. I fill it to the low mark and if temps get above 70 and I am working tractor hard bottle will fill up to within about 1 inch of top. If I let it idle for no more than 30 seconds the water level in bottle returns to about 1 inch above cold low mark....

 

[Tom_Veatch]

Was wondering if altitude can affect the radiator cap performance.

Depends on what you mean by "performance". The radiator cap is designed to maintain a particular gauge pressure within the cooling system. It should maintain that gauge pressure regardless of the outside (atmospheric) pressure. In that sense the performance is unaffected. However, the absolute pressure determines the boiling point of the fluid. Therefore, the absolute pressure inside your cooling system will be about 4PSI less than it would be at sea level. In that sense, the preformance of the cap could be said to be reduced.

Can I also assume water freezes at a lower temp?

No. There will be a difference in the freezing point with pressure changes, but that difference will be negligible unless you're talking about pressure differentials measured in hundreds of atmospheres.

Can anyone suggest a radiator cap psi for my condition? Should psi be lower on the cap or higher or should I just stick with my existing cap.

I don't know what the "stock" cap pressure rating is. I've seen the figure "13 PSI" mentioned in one or more posts in this forum, but can't comment on the validity of the number. Whatever the correct number is, in order for you to have the same boiling point as you would have at sea level, your cap would have to have a PSI rating about 4 PSI greater than the rating of a cap at sea level.

I have noticed that when temps get above 70 degrees my overflow bottle will fill pretty quick, but if I let it idle for 30 seconds the overflow bottle empties quickly.

My first impresssion is that it's a radiator cap effect. The fact that the overflow is pulled back into the radiator so quickly tells me that the temperature of the coolant falls rapidly when you reduce power. If the radiator wan't working properly, that wouldn't happen.

 

[BobRip]

Yah, I know but by bottle does not overflow. I fill it to the low mark and if temps get above 70 and I am working tractor hard bottle will fill up to within about 1 inch of top. If I let it idle for no more than 30 seconds the water level in bottle returns to about 1 inch above cold low mark....

As long as the system (radiator and bottle) do not require additional fluid, you are OK. Fluid is supposed to flow back and forth between the bottle and radiator. When the fluid in the radiator gets hot it expands and it has to go somewhere or the pressure would go way up and break the radiator, hoses, or whatever is weakest. Prior to having the bottle it was lost and you had to add fluid periodically. With the bottle its pulled back into the radiator when it cools down. The good news here is not needing to add fluid and air (with oxygen in it) is kept out of the radiator. This air would cause corrosion in the form of rust. No air means much less corrosion.
If you put in a cap with a higher pressure then the radiator has to withstand more pressure difference. It was probably not designed for this and may fail earlier.

 

[CoyPatton]

This sounds similar to one of the issues I was having earlier this year. How full is your over flow bottle when cold? I found that my system worked best when I filled it to the low level when cold. When it was filled to the high mark when cold it would push water out the over flow bottle after a while. Once I started only filling it to the low mark I have not had this problem again and the engine seems to be cooling fine.

Just my .02

Box

Those marks on your overflow bottle are for cold (a tractor that has no been ran in several hours) and hot (operating temps) conditions. As coolant heats it expands. Thus the higher mark is the ‘hot’ level while the low mark is the ‘cold’ level.
Also you should not add outside temp coolant to a warmed radiator system, as you likely have a 100 degree or more diffenence in temps and have the potential to cause issues. It may be a slight risk, but cool the system down (spraying water on the radiator can be done in a fine spray. You may wish to cover your battery first.