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Radiator cap Ford 5000

J

johnofnewhaven

Well-known Member
Need the professionals help. 13psi or 7psi radiator cap for 1974 Ford 5000 diesel,8spd? No oil cooler if that makes a difference. I think 13psi but I have seen 7psi listed and 13psi listed. Thank you for your help!
 

I'm not a professional but all of my tractors had 7 lb caps when I got them, I have changed the one on my 6610 cab tractor to a 13 lb cap.
Most times just as they start to get hot on the gauge they'll start pushing coolant out the over flow.
I look at it as kind of a early warning system.
With a 13 lb cap when it pushes coolant out it's hot.

If you live down south I go with a 13 lb cap.
 

kinda of fuzzy but I believe the higher pressure cap was only used on turbo charged or a/c tractors... It been too long since I read that in the ford service manual so take with a grain of salt.
 
From a boiling perspective I think the lower pressure caps are fine, but on a Diesel, I think the higher pressure should reduce cavitation.
 

Would higher pressure stop the sound waves from causing cavitation?? Had not seen that ideal before.
 
No, not the sound waves, but the sound waves create an area that boils, just my theory that more back pressure on the surface should help.
 
(quoted from post at 16:43:20 07/27/18) From a boiling perspective I think the lower pressure caps are fine, but on a Diesel, I think the higher pressure should reduce cavitation.
Click to expand...

If a 7 psi cap isn't overflowing when you run it then it makes no difference whether you have a 7 or 13 psi cap. The back pressure is less than 7 lbs. either way.
 
You bring up a valid point.

The pressure will almost instantly rise to the cap pressure if the radiator tank is clear full.

The pressure can rise up to the cap pressure as the air is compressed by the expanding water if the radiator tank is not full.
 
(quoted from post at 21:36:12 07/27/18) You bring up a valid point.

The pressure will almost instantly rise to the cap pressure if the radiator tank is clear full.

The pressure can rise up to the cap pressure as the air is compressed by the expanding water if the radiator tank is not full.
Click to expand...

Liquid doesn't expand much as it heats up. Gas (air, water vapor, etc.), on the other hand, does try to expand when it heats, and that is what causes the increase in pressure, so you have to get it hot enough to have the liquid start to try to convert to vapor before the pressure builds.

The reason that the pressure will rise sooner if the fluid level is near the top of the tank is that you don't have a lot of volume of gas to begin with so it doesn't take much conversion of fluid to additional gas to cause the pressure in the small gas volume to increase. When the fluid level is lower there is already a lot of gas volume, so it takes much more additional gas to increase the pressure.
 
I like to research a statement I make, and can find no evidence proving this, so must be debunked.
 
You bring up something I did not think of, yes the air expands in the tank linear relating to temperature difference.

Assuming starting temp = 70F, ending temp = 180F

Should be P = (460 + 180) / (460 + 70) = 1.2 times 14.7 rise - 14.7 for compensation to PSIG = 3 PSIG rise due to expansion of air in the tank.

Please check my math, has nee 35 years since college.
 
(quoted from post at 12:58:01 07/28/18) I like to research a statement I make, and can find no evidence proving this, so must be debunked.
Click to expand...

Were you replying to my last post when you posted this? If so, I have the following question for you...

If it doesn't build enough pressure to boil over with a 7 psi cap, then how can adding a 13 psi cap increase the pressure?
 
I do not know if you are talking to me, but if so, I am concurring the system may not reach 7PSI, let alone 13PSI.
 
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