Cooling system pressure tested

[peejay]

This was a very interesting problem that I had to think around. More specifically, engine is a 385 series Ford.

You should have said that to start with. Slow the pump down and fit a normal shaw or pellet t stat.
385's make a ton of flow at low rpm, designed to keep a low rpm engine in a chock a block engine bay cool.
I have seen these pop/split new heater hoses when revved up. Just slow the pump down relevent to what rpm the engine will see

Ooh, that IS relevant. Particular engine has a multirib belt drive system on it and the water pump pulley looks rather small. As a SWAG, the water pump is maybe 20% overdriven relative to the crank.

Thermostat was a 160 degree unit with a jiggle pin. To be honest, if the 3/8-7/16" bypass from the intake to the water pump is insufficient, I don't see any drilled holes in the thermostat to help any either. I've done that on my personal engines but that is mostly because the engines I build (Mazda rotaries with junk parts, because I don't like spending money) tend to get gassy in the cooling system and if you don't drill the thermostat, air collects there and the stat never gets hot enough to open. Downside is a 180 degree stat turns into a 150 degree stat and you're fighting to get the engine warm enough if it's cool out.

[Kevin Johnson]

With new everything, is it possible that the backing plate for the water pump was left out? I do not have parts in front of me or appropriate pictures to be able to determine if the lack of a backing plate would cause the pump turbulence to resist in-flow from the bypass at increasing rpm.

https://www.460ford.com/forum/37-engine ... plate.html

[peejay]

It's a brand new backing plate, complete with Ford parts department sticker. It's been forever since I'd seen a C9-labeled anything!

Water flow is A-OK with a gutted thermostat in place except for overcooling, of course. Isn't going much over 150 degrees on the street. Going to try out one of those thermostats that doesn't open against water flow, and give March a ring to see if they make different pullies.

[Kevin Johnson]

Per Craig's concern, did you choose this pump ala March's suggestion:

Ford 429/460 Edelbrock Satin Aluminum Standard Rotation Water Pump. Fits all 1970-1992 429/460 V8's in Passenger cars, trucks, vans, and motorhomes. The "super cooling" water pump is computer-designed to deliver more flow at a higher velocity. They're the ideal choice to prevent overheating in any street machine, street rod, truck, or any performance vehicle. Precision cast powdered metal impellers have extra large vanes for the maximum flow rate possible, ensuring adequate pressure and volume even at lower engine speeds. Factory replacement for Style Track Kits and will work with our "Ultra" 2 belt serpentine kits.

[peejay]

Installed the super awesome thermostat late today. We still have a problem though, even with three holes drilled out to 1/4", before the thermostat opens the engine will easily get over 120psi water pressure. That is unacceptable! What are you supposed to do, keep the engine at an idle until it is fully warmed up, and watch the gauge like a hawk and immediately pull over and idle if the temp drops while out on the road?

Next step is going to be removing the water pump to verify 100% that we didn't get some weird one with casting flash blocking half the bypass return or something. If that is all okay, I'm thinking that the best course of action is a restrictor and control coolant temp with the fan. Which I do not like, since there were millions of these engines made that didn't do this. Hell I drove one as my only car for three years and sometimes I might have seen 5000rpm practically by the end of my driveway in the morning

[cjperformance]

Installed the super awesome thermostat late today. We still have a problem though, even with three holes drilled out to 1/4", before the thermostat opens the engine will easily get over 120psi water pressure. That is unacceptable! What are you supposed to do, keep the engine at an idle until it is fully warmed up, and watch the gauge like a hawk and immediately pull over and idle if the temp drops while out on the road?

Next step is going to be removing the water pump to verify 100% that we didn't get some weird one with casting flash blocking half the bypass return or something. If that is all okay, I'm thinking that the best course of action is a restrictor and control coolant temp with the fan. Which I do not like, since there were millions of these engines made that didn't do this. Hell I drove one as my only car for three years and sometimes I might have seen 5000rpm practically by the end of my driveway in the morning

What are you running for a tstat bypass on this? As per factory from intake to w/pump?

[peejay]

Yes. Intake manifold is a Trick Flow unit (needed for the Kaase P-51 heads, I guess - I didn't spec any of it, but it's all beautiful looking stuff) and it's a straight shot from the port in the manifold to the port in the water pump. I can stick a piece of wire from inside the thermostat hole to at least as deep as the front of the water pump, but that doesn't necessarily mean that the passage from there to the center of the water pump is okay.

[cjperformance]

Might be a safe bet to pull the pump and check !!

[gruntguru]

Yes. Difficult to see how you could get such a huge difference in pressure when thermostat closes if the bypass is adequate.

If all else fails - remote thermostat with bypass.

[stock z/28]

Are you sure you dont have cyl pressure leaking into the cooling system?

[peejay]

I'm going to declare the patient cured. Or at least, I feel comfortable that its cooling system is not going to overpressure. (One of the hoses that ruptured had a burst rating of 250psi!!)

The key I think is a combination of an overdriven instead of underdriven water pump pulley (the manufacturer does not offer a larger one, and insists that nobody has ever had this kind of problem before) combined with that Trick Flow intake manifold. The bypass passage on one of these engines is a maybe 2" length of 5/8" hose going straight from the intake to a port in the water pump. In the water pump and in every other Ford manifold I've seen, it is a pressed-in thinwall tube. On this particular water pump the tube had a roughly .550" ID.

The Trick Flow manifold, however, does not have a pressed-in tube, it has a 3/8" NPT female thread, into which was threaded a 3/8" NPT-to-5/8" nipple... which was under .400" ID. Some simple math says that this was about half of the area that it should have been. Opening up that nipple just short of making the threads weak got peak block pressure down to 75psi at about 6000rpm. A restrictor was sized to ensure that the heater core never saw over 30psi. Once the thermostat opens the block pressure never goes over 25-30psi.

Incidentally, I decided to measure block pressure on a 3 liter pushrod Taurus that was available. It would build 45psi at 3000rpm.

The older I get, the more weird sh* I see like this... nothin' you can really do about it but find out exactly what is happening and observe what might be causing it.

[Cubic_Cleveland]

I'm going to declare the patient cured. Or at least, I feel comfortable that its cooling system is not going to overpressure. (One of the hoses that ruptured had a burst rating of 250psi!!)

The key I think is a combination of an overdriven instead of underdriven water pump pulley (the manufacturer does not offer a larger one, and insists that nobody has ever had this kind of problem before) combined with that Trick Flow intake manifold. The bypass passage on one of these engines is a maybe 2" length of 5/8" hose going straight from the intake to a port in the water pump. In the water pump and in every other Ford manifold I've seen, it is a pressed-in thinwall tube. On this particular water pump the tube had a roughly .550" ID.

The Trick Flow manifold, however, does not have a pressed-in tube, it has a 3/8" NPT female thread, into which was threaded a 3/8" NPT-to-5/8" nipple... which was under .400" ID. Some simple math says that this was about half of the area that it should have been. Opening up that nipple just short of making the threads weak got peak block pressure down to 75psi at about 6000rpm. A restrictor was sized to ensure that the heater core never saw over 30psi. Once the thermostat opens the block pressure never goes over 25-30psi.

Incidentally, I decided to measure block pressure on a 3 liter pushrod Taurus that was available. It would build 45psi at 3000rpm.

The older I get, the more weird sh* I see like this... nothin' you can really do about it but find out exactly what is happening and observe what might be causing it.

Good to see it’s sorted! Curious to know what you’re measuring the water pressure with?

[stock z/28]

I'm going to declare the patient cured. Or at least, I feel comfortable that its cooling system is not going to overpressure. (One of the hoses that ruptured had a burst rating of 250psi!!)

The key I think is a combination of an overdriven instead of underdriven water pump pulley (the manufacturer does not offer a larger one, and insists that nobody has ever had this kind of problem before) combined with that Trick Flow intake manifold. The bypass passage on one of these engines is a maybe 2" length of 5/8" hose going straight from the intake to a port in the water pump. In the water pump and in every other Ford manifold I've seen, it is a pressed-in thinwall tube. On this particular water pump the tube had a roughly .550" ID.

The Trick Flow manifold, however, does not have a pressed-in tube, it has a 3/8" NPT female thread, into which was threaded a 3/8" NPT-to-5/8" nipple... which was under .400" ID. Some simple math says that this was about half of the area that it should have been. Opening up that nipple just short of making the threads weak got peak block pressure down to 75psi at about 6000rpm. A restrictor was sized to ensure that the heater core never saw over 30psi. Once the thermostat opens the block pressure never goes over 25-30psi.

Incidentally, I decided to measure block pressure on a 3 liter pushrod Taurus that was available. It would build 45psi at 3000rpm.

The older I get, the more weird sh* I see like this... nothin' you can really do about it but find out exactly what is happening and observe what might be causing it.

Im kind of amazed that a conventional style water pump could generate anything close to 250 psi +. I admit I dont know much about cooling systems (or anything else) but I have always looked at an automotive water pump as more of a coolant circulator than a pressure source. I thought coolant temperature increase was the source of alot of the indicated pressure, as in when a hot engine is off and there is still pressure until the engine cools off.

I have seen a lot of hoses blown off because of extreme coolant temperature , but to see that kind of pressure I would expect to see cylinder pressure leaking into the coolant system.

I used to disable the water pump ( take the belt off, etc.) and fill the radiator full and start the engine, with the cap off and watch the coolant level and for bubbles. If possible load the engine a bit. I found it to be quick test and found a lot of problems that way.

I just cant imagine an automotive water pump generating close to that much pressure even dead headed.

Its very interesting, but I am glad you have it sorted out.

Jeff

[cjperformance]

I'm going to declare the patient cured. Or at least, I feel comfortable that its cooling system is not going to overpressure. (One of the hoses that ruptured had a burst rating of 250psi!!)

The key I think is a combination of an overdriven instead of underdriven water pump pulley (the manufacturer does not offer a larger one, and insists that nobody has ever had this kind of problem before) combined with that Trick Flow intake manifold. The bypass passage on one of these engines is a maybe 2" length of 5/8" hose going straight from the intake to a port in the water pump. In the water pump and in every other Ford manifold I've seen, it is a pressed-in thinwall tube. On this particular water pump the tube had a roughly .550" ID.

The Trick Flow manifold, however, does not have a pressed-in tube, it has a 3/8" NPT female thread, into which was threaded a 3/8" NPT-to-5/8" nipple... which was under .400" ID. Some simple math says that this was about half of the area that it should have been. Opening up that nipple just short of making the threads weak got peak block pressure down to 75psi at about 6000rpm. A restrictor was sized to ensure that the heater core never saw over 30psi. Once the thermostat opens the block pressure never goes over 25-30psi.

Incidentally, I decided to measure block pressure on a 3 liter pushrod Taurus that was available. It would build 45psi at 3000rpm.

The older I get, the more weird sh* I see like this... nothin' you can really do about it but find out exactly what is happening and observe what might be causing it.

Yes just what i have seen re bursting hoses!
And yes thats nonwhere near enough bypass, amazing difference it makes!! Glad its fixed

[peejay]

I just cant imagine an automotive water pump generating close to that much pressure even dead headed.

Most automotive fuel pumps have a "turbine" that looks like a watch gear, and they will easily make their 80-90psi internal blowoff pressure. A water pump is MUCH larger!


I'd like to give thanks to everyone who helped me gain insight into this issue... The thermostat was key to solving the problem of the pressure spiking at operating temperature. I knew that couldn't be the whole problem so more deeper digging had to be done.

The car incidentally is a seriously badass piece of kit. Modern brakes and drivetrain, a rack and pinion conversion out of Australia (the first rack conversion I've ever driven that didn't have awful bumpsteer/Ackerman issues and feel like crap to drive, and was a fairly easy install to boot), and of course that mountain of an engine, which has been opened up to a bore and stroke that Ford would never have ever contemplated