radiator caps, cooling system pressure

[Ashton Crusher]

I was thinking of putting a higher pressure cap on one of my cars to increase the factor of safety against boiling. Looking thru the web for info on the likelihood of changing from 7 psi to 13 psi causing leaks I found little on that issue but did find a couple references to the pressures created by the water pump. One site boasts of a 19 PSI, $25 cap to get you thru your "hard driving".

Thought I'd see if anyone else has heard of this. The claim was that the water pump could create over 30 PSI of pressure. Since that is double the normal operating pressure of most modern cars I find it hard to believe. If the system was at full 15 psi of pressure while the car is idling and then your floored it and ran it up to near redline and created another 30psi of additional pump pressure, or even 10 psi of additional pressure downstream at the radiator cap, you would immediately cause the system to have to vent to the overflow to relieve this higher pressure. I've never seen a car vent due to me revving the engine up while I'm working on it. Thoughts?????

[Tony Hwang]

Hi. There is a over flow bottle for coolant/anti-freeze. Ever cleaned/flushed your rad. and maintain proper level of coolant/anti-freeze in your rad.? If the car is old, messing with cap can spring a leak.

[hrhofmann]

AMEN!

[bob haller]

DONT EVEN THINK ABOUT THIS WITH A CHEVY VENTURE! their engine the 6 cyc one tends to develop super expensive head gasket leaks as is......

some things are best left alone

[Ed Pawlowski]

How often does that happen? If it is frequent, you have other problems that need to be fixed. Last time I had a boil over was probably in the 1960's or so.

This is not the proper thing to do. The engineers have put a lot of work into getting the right temperature and pressures and you think you can do a better job? Really?

[clare]

A water pump cannot produce system pressure because it just moves water from one side of the pump to the other. Expansion due to heat is what builds pressure..

[clare]

I'd never overpressure anything with a plastic tank rad. Actually I wouldn't overpressure ANY system.

[harry]

The only way to increase the system pressure would be to change the thermostat to a higher temperature one so increasing temperature as well as pressure. You would then have to change the radiator cap too. But changing the radiator cap alone wouldn't change the pressure but in the event of engine overheat/pressure would negate the protection it gives.

Very unwise, you may get hoses bursting and engine overheating . If your engine is overheating there is a problem with the radiator (blocked) or the thermostat not fully opening. Possibly slack belt (drives the water pump). Electric fan (or it's thermostat) if it has one faulty. Waterways in cylinder block/head blocked/corroded.

[trader4]

You might want to rethink that one. Water isn't going to move through a system without pressure to push it. I wouldn't expect the pressure to be very high, but there has to be pressure due to the pump.

As for the question at hand, what is unstated is if there is actually a problem, ie is the car overheating? If it is, then finding out the cause of that instead of trying to raise the boiling point of the coolant via pressure would seem to be the better approach. For example, if he has a bad thermostat or collapsing hose, he'd be just covering up the real problem.

[trader4]

Dumb as ever. The current cap releases pressure at 7 PSI when the car overheats. He's proposing changing it to 13 PSI so that when it is overheating, it will not release until that higher pressure is reached. That results in a higher pressure when overheating exactly as he claimed and doesn't require changing the thermostat.

Dumb as ever. When the engine overheats, which is what he's specifically concerned about, having that higher pressure cap will result in higher pressure.

That part is correct. Even a stopped clock is occasionally correct.

[MLD]

"Ashton Crusher" wrote in message news: [e-mail]...

Lots of comments--my two cents: First of all, the water pump is a centrifugal pump and as such the pressure rise across the pump is a function of it's speed. The flow output of the pump is a function of the system characteristics-- Pressure drop vs Flow So changing pressure caps and thermostats will not change the operating behavior of the pump. The purpose of the pressure cap is to raise the boiling point of the fluid. This allows you to run the coolant at higher temperatures (greater than 212F) without causing it to boil. Just because you have a 180 deg thermostat doesn't mean that the coolant at running at 180 deg-----because of the cap, typically, the coolant boiling point is closer to 234 deg F (or higher). That's why they say never to remove the cap until the coolant cools down--if you remove the cap too soon, the system pressure becomes 15 psia (atmospheric). the boiling point becomes 212F and you get a great big flash of steam as the coolant immediately changes from a liquid to a vapor. As the coolant temperature increases, it's density (Specific Gravity) decreases and because it's weight remains constant, the only other variable is it's volume which increases. Because the cooling system volume is fixed the coolant pressure will increase (no room to expand) from atmospheric to whatever the cap is set for and then it is vented to the over-flow bottle. The downside of increasing the pressure cap setting over what's specified is two fold---At the higher cap setting, all the system components will be subjected to pressures beyond design intent--not a good idea. The same applies to the operating temperature. In summer like days the coolant temperature will go beyond normal design intent. In both cases, you're moving in a direction to accelerate component failures. MLD

[harry]

Thoughts?????

One other possibility is you may have a blown head gasket.

[trader4]

The other very real possibility is that harry is the village idiot, as has been proven time and time again.

[clare]

driving".

Harry, you are incorrect on this. The cap alone WILL cause most suystems to run at a higher pressure as long as the vehicle runs at a minimum of 160F. The thermostat only controls the MINIMUM operating temperature of an engine, so even an engine with a 160 thermostat can run at 195F, or higher. The cap allows the pressure to build to a MAXIMUM of the rated pressure - at which point it releases into the overflow to regulate the pressure.

Or bad timing, or bad mixture, or simply overloading the engine. But yes, you got ONE thing right - installing a cap with a pressure higher than the system is designed for CAN cause problems with hoses, radiators, heater cores, etc..

[clare]

Which WILL cause the pressure to increase rapidly if it is causing an overheating problem - and even a 30psi cap would vent under these conditions

[larrymoencurly]

I live in Arizona, and nobody in my family here has ever had an overheating problem that wasn't caused by a burst hose or bad radiator cap, and I know the latter happened in fall or winter. The hose that broke was a flex hose -- never use those if you don't have to. The bad radiator caps were brand new replacements -- 2 in a row gushed out coolant on day one, while the ~5-year-old factory original cap and a replacement from a car dealer worked fine. Also I once bought 3 bad thermostats in a row -- when I tested them in a pot of hot water with a thermostat, one wouldn't open more than 1/4", the other two opened wide at about 150F (rated 195F). So for radiator caps and thermostats, I use only OEM.

[Ashton Crusher]

No, the car is not overheating. It's never overheated. What happened is that I installed an AC unit in this 60 Dodge. That has made it run about 10 degrees hotter then it used to, mainly from just having the condenser there in front of the radiator. So I was thinking about whether it would be a good idea to go to a 13 pound cap instead of the

7 pound one on it. Just to give a bigger margin of safety when the temps here get up to 110. The manual for the car lists the 7 pound cap for non-ac cars and the 13 pound cap for AC cars. Just curious if anyone has ever seen this increase in pressure cause an immediate leak to happen. The Radiator was rebuilt 10 years/10,000 miles ago. The heater core is factory original. Now, on a 95 degree day it's running up to 205 on the freeway and 195 around town. Thermostat is 180.

[Ashton Crusher]

It would just change it to the pressure for AC cars. For it's first

52 years of use it was without AC. I added AC to it.

[Ashton Crusher]

I didn't want to make the original post into a novel but it appears a lot is being read into what wasn't included. That car is not having any problems at all right now. I'm just looking at increasing the factor of safety against overheating because I just added AC to it. Non-ac cars use a 7 pound cap and AC uses 13. But it's a 52 year old car (well maintained) and the downside would be if adding 6 pounds more pressure is likely to create any leaks, like in the 52 year old heater core. Nothing leaks now. I'm just torn between being proactive and getting a higher pressure cap "just in case", or just sitting tight and seeing how the temperatures run as the weather heats up.

[Ashton Crusher]

I'm in Phoenix area and my experience is the same as far as overheating but I've never had this low a pressure cap (7 psi) before. A 13 pound cap would give me another 14 degrees before boil over. I just added AC and that seems to have raised the temp baseline by 10 degrees once the weather is over 90.