For some reason, the new search criteria won't let me search....What is correct for '84 351W HO..Auto/ 2WD..?...thanks..jv

 

13psi................

 

Yup 13PSI Stant # 10229 for the regualr cap, 10329 for the flip lever style

 

Correct me if I'm wrong, but don't the AC-equipped models use a 16psi cap?

 

Mine has AC...so..13 or 16..That's the question !!!

 

My catalog shows 13 only, no mention of A/C

 

What would happen if you ran a cap with too low of a rating?

 

A 50/50 mixture of antifreeze and water boils at 227 deg F at atmospheric pressure. As you increase the pressure, you increase the boiling point. The pressure vs boiling point looks like this:

0 psi 227 F
4 psi 236 F
8 pis 248 F
12 psi 259 F
16 psi 267 F

So, if you run a lower pressure cap, you coolant will boil at a lower temperature. About the only time you would notice this is when your engine overheated for some reason, or when you shut the engine off and the coolant in the engine block heated up.

I have always run 7 psi caps on most of my cars, including cars with 205 degree thermostats. But, I am willing to live with the possible consequences. For example, if for some reason my engine overheats, it is going to blow off coolant. I keep several gallons of water/antifreeze in my car at all times. I also make sure my overflow line to the overflow tank is in good condition and is not leaking. When I shut the engine off on a really hot day, sometimes some coolant will belch into the overflow tank. When the engine cools, it draws it back into the radiator again. It will only do this if the entire cooling system, including the overflow hose, is well sealed.

The strain on hoses and water pump seals is a lot lower at 7 psi. Since switching to 7 psi caps (20 years ago) I have never had a hose blow out on me or a water pump shaft seal leak.

If you run a lower pressure cap, be prepared for the occasional emergency.

 

Cooling System Pressures:

ALL Engines: 13 PSI

Radiator Cap: E5TZ-8100-A : Motorcraft Number: RS-62

Source: Ford Service Specification Manual.

 

My guy at the radiator shop also told me to run a 7 PSI cap unless you have the real old radiators. The AC on my '86 302 doesn't work, so its not an issue, but I've been running a 7 PSI for several years and have never had a problem.

 

All modern vehicles run the higher pressure caps. As was said earlier it raises the boiling point of the coolant. As was also mentioned, it puts more strain on the components, but that is not a problem since everything was designed to run at the higher pressure.

If my vehicle is in good shape under the hood, I always run the correct cap. If I have a radiator that is old, and I don't have the money to buy a new one right away, I have run a lower psi cap. If you run 7 psi cap, and have a coolant recovery system, you will probably not notice any difference. If you where to study the coolant level in the bottle, with the lower psi cap you will notice the coolant level moves more up and down with the lower psi cap. If you don't run the recovery bottle, you will notice you need more air space in the top of the radiator with a lower psi cap.

 

Finally got a chance to look for a new cap..Always look at my Dad's first !..Found a new 16#.. What would happen if I used it instead of a 13..My truck is Auto/AC..

 

The engine would run 9 degrees hotter before boiling over. The general rule is each pound of pressure on the cap equals 3 degrees higher temperature before boiling. Assuming Jim's previous post is correct and the boiling point of a 50/50 antifreeze/water mix is 227 degrees, with a 13 lb cap the mixture will boil at 266 degrees, and a with a 16 lb cap will boil at 275 degrees. That's pretty hot, but not likely to damage a cast iron pushrod 1980's engine. Do that to one of today's aluminum engines and it would be toast. Keep in mind that radiator caps are not an exact science and the engineering standards for a 13 lb cap are between 12-16 lbs, and a 16 lb cap are 14-18 lbs, so your actual boling points will vary.

 

SO..I probably couldn't tell the difference. I use this truck about once a month..Only put on 2k all of last year..so it's not getting a workout..Would you go ahead with the 16 ?..

 

They're so cheap that I would put the 13 on, but I don't think using the 16 is a huge risk. The risk gets a bit bigger if the 16 lb cap is on the higher side of the engineering standard, and the weak link in the engine is a head gasket. But you should be ok.