I'm looking for a brainstorm of ideas or personal experiences with similar setup. I've a 72 454 4spd car with A/C. This car is essentially stock. I've owned it just under 10years and have been slowly improving on it. Always problematic has been the cooling system. Many things have been done, but here's my current sympton.

With A/C off and full coolant system, car cruises at good temps around 170-180 around 50mph. Not much different 10mph faster. However, I was losing about a quart of coolant every 40min of driving. The engine would start to heat up after that,..naturally.

Further inspection revealed the following; In neutral, holding a steady 3500rpm, coolant flows a steady stream out of the expansion hose leaving the cap.

Initially I was thinking poor cap. I didn't pressure test, but replaced with new 16psi cap with no change to overflow problem.

Concerned with sticking (recently replaced) thermostat, I replaced with new failsafe 160temp. This yielded no change.

Additionally, I noticed that with the cap removed and a steady 2500rpm.. (rpm to bring coolant up to cap level) every 10-12 seconds a large splash of coolant blows out and upwards. Concerned I had exhaust gases pressurizing the cooling system via crack/gasket problem, I used a fluid block tester unit.

At idle I showed no color change on the tester unit indicating then that no CO2 was present. I wanted a higher RPM check in case the crack didn't open until then, so I reved her up. However, the littlest RPM increase with the cap removed caused massive coolant overflow. I held the RPM high catching it underneath thinking I'd eventually lose enough to check it with the block tester at higher RPM. I was hoping for a test at 2500rpm. I finally got the coolant low enough including compensating for that 10-12 second big splash. I did a block tester check for CO2 and found no color change at 2500rpm. However, coolant was so low the engine start heating up fast climbing quick towards 250 so I terminated the test.

I am figuring that I've been losing coolant at the expansion area at the cap as I was up-shifting and occasionally exceeding 3500rpm in cruise.

Can I still have an engine crack or head gasket leak that is causing coolant overpressure without showing up on the block tester ?

What else could cause my cooling system to exceed 16psi?

Help????

 

First things first. Do you KNOW you are exceeding 16# of cooling system pressure? A new 16# cap isn't evidence that there is pressure. The lip of the radiator that the cap seals against could be bent or deformed. Pressure could be escaping in any number of other places, including a intake manifold to head gasket. Do a pressure check and if the system isn't holding, find the leak and fix it.

RACE ON!!!

 

Sure...I'm ordering a pressure tester to put on the expansion tank to check that cap's seat. However, there are no leaks except the massive obvious overflow at the cap's relief valve. Its fairly hard to miss.

The cap itself does not leak...its the pressure relief valve. Granted it may be possible for the inner seat where the pressure relief valve on the cap make's contact to not be flat. I'm waiting on a pressure tester to arrive to rule that out.

I neglected to mention that the water pump was NOT stock. Its Edelbrock's Alum pump. I'm hearing that edelbrock's alum pump may put out more PSI than stock requiring a higher PSI system. I've put a question to Edelbrock's tech team and am awaiting a response. I've read in another forum that this pump and maybe Stewart's require PSI cap's around 22psi to prevent overpressuring the stock cap and losing all the coolant.

Any other thoughts???

 

I'm not sure what Edelbrock will tell you but I've been running one of their aluminum water pumps for 4-5 years & have never had it cause any such problems. I've had the same Stant 16 lb. cap on my overflow tank the whole time. Good luck finding your problem. You seem to be methodical in your approach & that can only help.

 

No pump, in a hydraulic system, "creates" pressure. The pump creates FLOW. Absent the heat and the pressure caused by the expansion and vaporizing of the coolant of a cooling system, pressure in a hydraulic circuit, is caused by the resistance to the flow. In other words, your pump is not creating pressure and it is not the cause of your coolant loss.

RACE ON!!!

 

Stories about BB`s overheating is probably due to systems that have over the years been changed from stock. I run a lot of BB`s, and I love um. From 270HP to 550+. 396-454`s with and w/o air conditioning and completely box stock cooling systems and never overheated any of them in all weather conditions and temperatures. 16 lbs is correct for the cap. Heres where the so called authorities get involved. Bench racers with book knowledge from some sucker that wrote about it and has zero practical experience. I do not use a 160 thermostat in any of them. Actually I use a 195 in most of the engines so the water dont circulate too fast for the radiator to recover. A stock cooling system is more than adequate as long as no one screws with it.

 

Yes...pump does create flow...no argument there. As you say removing expansion, etc. and temperature changes only resistance will change the pressure. I agree...however.... the flow of the pump changes with RPM. This would have the same effect as opening your garden hose at a fixed nozzle opening. Our cooling system has a fixed "assumed not plugged" resistance. However, there is a relative resistance change as "FLOW" increases via RPM through the same size hole???

Perhaps I'm a plain ole dummy, but I fail to see how the pump curve does not increase flow as RPM increases through an unchanged diameter hose size?

Be that as it may I'm still not 100% convinced this is the problem, but if not...my only recourse is to prob to yank the motor as I'm getting fairly frustrated. I didn't build it myself and am not sure what may be going on inside the motor's cooling passages. Plus, I'm not sure if a block tester can be fooled so I might still have a blown gasket or crack that won't show up.

 

I know this is a silly questiion but are you sure that the thermostat is in the right way? The round copper sensor should be down into the manifold. A thermostat upside down could cause most of your symptoms.

 

Before you do something dramatic like yanking the motor, try some easier things. My 454 did the same thing when I first fired it up. Water on the ground and high temperatures.

I put in a new chin spoiler, Edelbrock Victor pump, high flow thermostat and a Moroso 19-21psi cap. Now there is no loss of fluid from the expansion tank and the engine runs nice and cool, even in tropics.

 

Basic hydraulics: You have no flow unless you have a "head", which is a pressure differential.

Duke

 

It seems to me, as the pump removes liquid from the inlet side of the pump, inertia of the liquid and the resistance to flow causes low pressure. At the outlet of the pump, the same forces allow pressure to be created. Is that the pressure differential ("head") you are referring to? I know that if I "tee into" my garden hose with a pressure gauge and turn it on for a moderate flow, there is virtually no pressure. If I turn the tap on to full force, there is some, but very low pressure, caused by the "resistance to flow". With a nozzle attached to the end of the hose, the pressure varies with the amount I open the nozzle and vary the resistance. Do I need further enlightenment?

On the subject of the post, I fail to believe that the flow can be so great through a radiator hose, as the restriction to flow, can cause a 16# pressure relief (the cap) to open. And if it some how the hose could cause sufficient restriction (?), the cap is beyond the restriction, where the pressure should have dropped. In short, a better water pump isn't going to cause a radiator cap to bypass coolant.

RACE ON!!

 

A centrifugal pump speeds up the water, but the restriction to flow causes this increased momentum to be converted into increased pressure, and the difference between the static outlet pressure and static inlet pressure is called "head" by hydraulic engineers and is typically expressed in "feet of water" when dealing with hydroelectric power, water pipelines, and irrigation systems. Water pumps work the same as turbochargers. Maybe you've seen a turbocharger performance map. The same chart can be drawn for a water pump, but they are rarely published.

The increased pressure at the pump outlet drops as coolant flows through the system, and the "head" that the pump creates is not large -probably no more than 5 psi at maximum speed. Since the fill cap is always close to the pump suction side, it will not see the pump head.

Duke

 

hmmmmm
slowly improving it for 10 years?
It must have been awful 10 yrs ago
Hint:
i'd do a leakdown test.(bubbles in coolant?)

 

Thank you for the further explanation.

RACE ON!!!

 

my 61 has an intake manifold pressure gauge.
cold start it goes up from 1 psi to 7-8 as the revs climb to 2000. it is a linear climb.
cruising hot it is 14 psi. this is not cap pressure(i don't know what the cap/tank runs, but it never overflows w/15#cap)

 

Lots of good stuff here...

Whatever the prob is...there is only one source of water escaping...the overflow hose off the expansion tank. Perhaps the tank area has some warpage that is hard to see. I would like this to be the answer. Where Murphy is concerned I doubt this would be my problem, but I haven't ruled that out, as I'm working to obtain pressure test equipment now.

However, for all you fluid dynamic nuts out there, Edelbrock seems to think they may have pressure curves for their pumps somewhere and are attempting to help me out. When the smoke clears I'll post the results here even if it turns out I'm a nut.

"rubber side down"
Hawk

 

RACE ON!!!