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Old 10-02-2011, 07:53 PM
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My Coolant Pressure Ok?

I tow a 35' fifth wheel and I blew out some coolant about 2 weeks ago when pulling a really good hill. So I decided to build something to able to pressure check as well as check pressure when running.

I pressured up the coolant to 17 psi and the cap bleed down to 15 psi, then it held there for some time. I've done this a few times to check.

With a stock tune, when I'm driving normal at 55 mph, I get a 3-5 psi reading. But It doesn't go over 5 psi. However, if I drive WOT (really pushing it hard), it slowly goes to 10-11 psi and stays there.

Stock tune;
@ 55 mph : 3-5 psi
@ WOT(hard): 10-11 psi

With an aggressive tune, when I'm driving normal at 55 mph, I get a 4-6 psi reading. Now when I'm driving WOT(really pushing it hard) over and over again, I can get it up to 18 psi. But the coolant doesn't blow out.

Aggressive Street Economy(Spartan);
@ 55 mph : 4-6 psi
@ WOT(hard): up to 18 psi

I don't blow coolant when I'm empty and out driving hard with the aggressive tune.

When I'm towing a fifth wheel (20,500 gcvw), I don't blow coolant on the flats, only when I have a really good pull on a hill (5-7 percent grade).

I want to make sure the truck is good. I had the ARP studs and heads done awhile ago with the EGR cooler deleted. I might be overpushing the truck. Maybe I'm overboosting @ 25 psi.

When on the hill pulling;
Boost: 25 psi
EGT : 1000-1100 degrees
ECT : 190-215 degrees (It goes up to 215(slowly) then the fan kicks on and beings it down to 190.)
Trans: 170-190 degrees (Depends on the outside temps.)

I have noticed that the ac unit would be on without me turning it on sometimes. But otherwise it's been running good. I talked to a ford tech, he said that higher pressure would happen when running an aggressive tune at WOT like that. But I want to see what others have seen or done to find out.

I would like to know what the range is for the coolant pressure is good and bad.

Thanks!

Last edited by Pipewelder71; 10-05-2011 at 09:14 AM. Reason: changing
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Old 10-03-2011, 04:55 PM
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Doesn't anyone have any experience dealing with this? Any diesel techs on here?
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Old 10-05-2011, 09:13 AM
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Old 10-05-2011, 10:33 AM
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The coolant system pressure will change based on the temperature of the coolant. As the coolant heats up, it will start to generate steam, which will pressurize it, therefore increasing the temperature needing to boil it. It will continue to do this until it hits 16psi, at which point the cap is supposed to vent the coolant.

So, the pressure will vary depending on coolant temperature. At 190, you'll probably see a little pressure, but once you hit 210-215+, it should start building rapidly. IIRC, the boiling point of coolant at 16psi is about 250ish, so you should not see 16 PSI until you hit about that coolant temperature, after which, it should vent out the cap.

The pressure itself is what keeps the coolant from boiling, which is why, if anything in a coolant system gives when hot, you get RAPID conversion from liquid, to boiling, to gas. The leak causes the pressure to drop, which lowers the boiling temperature, which causes more boiling, which causes rapid expansion of coolant and the blow-out.

Where are you measuring the pressure? That makes a difference.

If you are seeing 16psi before your ECT sensor says you hit 250, then your coolant is boiling somewhere, away from the ECT Sensor, adding pressure to the system. The ECT sensor is right below the thermostat. It is possible for the Coolant near the ECT sensor to be one temperature, and coolant returning to the water pump, or going elsewhere in the engine to be a completely different temperature. Pressure is funny like that, a hot spot somewhere in your engine can raise the entire system pressure, without raising the entire system temperature, since it takes time for that heat to disperse. Your water pump may not be moving coolant as well as it should, you could be having hot pockets of flash boiling in your engine channels, you could be having cavitation issues, etc.

So to answer your question, anywhere from 0-15 PSI is an acceptable range, depending on the temperature of your coolant. Don't worry about the pressure so much, but rather, whats causing it. If your coolant is too hot, if your coolant is flash boiling somewhere, etc. Pressure is a byproduct of heat. You have to examine the source of the pressure, not the pressure itself. Check your coolant, make sure it is 50/50, if you're running a 50/50 mix. Too much water will make it boil easier inside the engine channels.


It's things like this that make me even happier that my coolant doesn't boil until 370 degrees, and runs at 0 pressure

Street tunes are known to run the engine leaner & hotter, which means higher cylinder wall temperatures, which can cause hotter coolant in the channels. I do hope you're not attempting to Tow on your street tune. That is definately not recommended. Street tunes are for unloaded driving, if you're towing anything more than a few thousand pounds, you should either go back to stock, or use a Tow tune specifically designed for towing.

25psi is not overboosting if it's holding it steady. Overboosting will generally surge and be unpredictable due to VGT issues.

Last edited by Dicion; 10-05-2011 at 10:51 AM.
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Old 10-05-2011, 01:09 PM
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I'm measuring at the degras bottle, off one of the hoses.

I know that once my cooolant hits 215-220 the fan kicks on and brings the coolant down to 190. However on the flats, it may go up to 210 at the most. But it usually between 190 and 200.

I understand the point of boiling. But I would like to know the average operating range for coolant pressure. Range for cruising, range for towing heavy, and pulling up hill with a load. I just wanted to make sure that there isn't some else wrong with my ride.

I've been thinking of adding an expansion tank with an preloaded bladder. So there's someplace for the coolant to overflow into. It's the same kind of system as a water heater, most industrial water heaters I have seen have that kind of expansion tank on top or to the side.

Last edited by Pipewelder71; 10-05-2011 at 03:16 PM.
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Old 10-05-2011, 09:38 PM
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Warning, math and science content!!

I hate to hi-jack this thread, but I have seen quite a bit of discussion over the coolant system pressurizing with the suspicion being that leaking headgaskets are the culprit for pressurizing the system. I thought that there may be other reasons for the system to become pressurized. I reached back into the chemistry and engineering parts of the old brain and here are my thoughts. Go ahead and pick this one apart, I figured this out in 10 minutes, so I may have messed it up somewhere....

There is air in the degas bottle. If it starts out at 60*F and is subsequently heated (by the coolant passing through the bottle) to 190*F, the air will want to try and expand due to being heated. If it cannot expand, it will become pressurized. This is governed by the ideal gas law PV=nRT (pressure x volume = # of moles [constant] x R[constant] x temperature). Temp must be measured on an absolute scale (Rankine or Kelvin). You can use the equation to determine the change in pressure given a change in temperature (all other terms remain constant essentially).

So if you go from 60*F = 520Rankine (460 +*F = Rankine) to 190*F = 650Rankine, you should see the pressure change by the ratio of 650/520 = 125%. I am at 6,300' elevation so atmospheric pressure in 12 psia, so I would expect to see a pressure increase in the degas tank to go from 12 psia to 16 psia, which would show up as 4 psi gage pressure.

The other thing is that liquids expand with increased temperatures. This will also cause an increase in pressure. Water will expand at the rate of 207x10^-6 /*C. This means a temp increase of 130*F (about 72*C) will cause the water (I dont know the coefficient of expansion for glycol) to expand to 1.015 times its volume. This expansion causes the water to press on the air in the degas tank (that is why heated water systems need an expansion tank). In a PSD with 7 gallons of coolant, that coolant now takes up 7.1 gallons of space (or another way to look at it is the air in your degas bottle has 0.1 gallons of less room and is squeezed. Estimating that the freespace in the degas bottle is only about 0.25 gallons and using the ideal gas law mentioned earlier, this means that the pressure in the tank will increase by 40% because the volume has been reduced by 40%. Soo... the 190*F air in the degas bottle that was exerting 16psia (at my elevation) due to heating is also now being squeezed and will show increased pressure of another 40%, now it is at 22.4 psia, or 10.4 psi gage. I am assuming that none of the coolant passges or hoses will expand when they get hot (obviously they will), so you may expect the "hot" pressure to be somewhat less than what I calculated, but it is a good starting point.

The bottom line is heating the fluid and the air on the bottle will cause pressure even without a head gasket leak. The best way to run the pressure test on the system is to run it when the fluid is cold and punch it. If the pressure rises immediately to over 15 psia, you likely have a headgasket leak. If you wait for the fluid to warm up, you will see a steady slow rise in pressure as the system comes up to temperature.

MikeB

Last edited by PSDMikeB; 10-05-2011 at 09:42 PM.
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Old 10-06-2011, 01:27 AM
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Quote:
Originally Posted by PSDMikeB View Post
The bottom line is heating the fluid and the air on the bottle will cause pressure even without a head gasket leak. The best way to run the pressure test on the system is to run it when the fluid is cold and punch it. If the pressure rises immediately to over 15 psia, you likely have a headgasket leak. If you wait for the fluid to warm up, you will see a steady slow rise in pressure as the system comes up to temperature.

MikeB
A headgasket leak won't always show up at low operating temps. I have had to diagnose many headgaskets(not psd) and many do not show up unless the engine is hot. It would be a bad hg leak to show much pressure build in the cooling system when the engine is cold. But this is my experience with the really big engines I work on. I would assume it would be the same for a psd
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Old 10-06-2011, 04:56 AM
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PSDMike, You are absolutely correct on all of that. Cooling systems are designed to self-pressurize like that, as the pressure in the system raises the boiling point of the coolant. Being that most coolants used today are 50/50 water/coolant mix, and the boiling point of water is 212 degrees, you need something to raise that point, or else many engines would boil over very quickly. Pressurizing the system does that. Also, having a sealed system that pressurizes, prevents coolant loss through evaporation.

PipeWelder, Being that the OEM cap is designed to vent at 16psi, as I said before, any pressure up to that would be considered 'in operational range'. If you're constantly venting out your cap, and the cap is opening at the proper pressure, then that could be a problem.

If you're generating 18psi at WOT, as I said before, I am of the opinion that either the tune you're running is not designed for towing, causing high cylinder temperature, and microbubbles and flash boiling within the engine channels, raising the pressure, or, as mentioned above, you could have HG issues. I doubt the second one though.

If you remove the tune, and you don't have that high pressure anymore, then it's obviously the tune that's causing it, either through increased temperature generation from the higher power, creating hotter coolant, and more pressure (Which I believe is the cause), or through increased cylinder pressure, causing HG failure/leakage, and pressure entering the cooling system that way. (Which I don't think is occurring, as you'd see more puking of coolant in this situation IMO)

Now, that being said, I don't see any IMMEDIATE problems that will occur if your coolant reaches 18psi, other than the fact that the system is designed to max out at 16. Higher pressures increase the likelyhood of a hose, hose clamp, or fitting failing, and of you possibly losing coolant faster than normal through evaporation and venting of the Degas cap.

If you inspect all the coolant fittings and hoses, and keep an eye on their health, then this is no different than running any other performance mod on your truck that exceeds the standard operating parameters. Our trucks are built to run at 20-25psi boost, some tunes up that to 30. Can it be done safely? Sure, does it however increase the likelyhood of any sort of boost-related failure? Yes. It's all about mitigating risk and knowing how things work.

Last edited by Dicion; 10-06-2011 at 04:59 AM.
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Old 10-06-2011, 08:50 AM
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I understand the thermal expansion of water and air, I'm a Steamfitter and work with these kind of systems. But I'm just trying to find the standard operating range (cruising, towing, pulling a hill). Something that I can follow and monitor.

I tested the cap, it's within specs. Then I tested the coolant system, but there were no leaks (pressured over a period of 2 hours at max pressure, 16 psi.).

We have to remember the engineers who designed the 6.0 thought that having TTY bolts for the heads were good. I noticed that engineers went with a bigger (30%) radiator, bigger degas bottle, and better head bolts in the 6.4. That tells me something.

Thanks for all the replys.

Last edited by Pipewelder71; 10-06-2011 at 05:17 PM.
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Old 10-06-2011, 07:00 PM
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Along with all of the great and very well thought out replies above I will include my own , so here goes. The comon cause of your expecience is that the oil cooler is plugged up and starving the EGR cooler for flow causing it to become a superheated steam generator and it is puking the steam and coolant back to the d-gass tank. Need to check the temp delta between the oil and coolant.


Q: Wrench light when towing and engine looses power

A: Some newer PCM flashes monitor EOT vs ECT delta and when it exceeds 15 deg the truck will go into limp mode. Your oil cooler is obstructed and needs to be replaced. This is a good
time to do a cooling system flush and an EGR delete.


Q: Do I have a blown EGR cooler?

A: Remove the EGR valve and look down the hole, if you see any wetness, wet gooey soot, or it looks steam cleaned, your EGR cooler is bad. This is a good time to do a delete if you can, if you can't I would recommend a new cooler from bullet proof diesel. You may need an oil cooler also as the failures go hand in hand.


Q: Do I have a blown head gasket?

A: Generally if there is a slow gradual pressure increases in the cooling system over 16 PSI then this points to an EGR cooler / oil cooler failure. If the pressure in the cooling system tries to head to and exceed 20psi pretty fast in a cool motor then this points to a head gasket failure. Put a Tee in one of the rubber lines going to the de-gas tank and attach the line for your gauge to that. Or buy new hose and make a test rig to use for now and then loan to all your buds later on. This is as simple as a 3/8 hose barb Tee,5 clamps, 30 PSI gauge and some 3/8 air line. Cut 2 short stubs out of the air line to span the gap between the manifold and the de-gas tank. Next since you saved the end of the air line that has a 1/4 FNPT fitting crimped to it, the free end goes to the tee and your gauge attaches to the factory crimped on FNPT fitting. You will use a gauge with a 30 full scale reading. The cap on the De-gas tank is a 16 lb relief, this is why 16 psi is the magic number. The pressure you reach is not as important as the rate of climb. The reason for the slow increase in pressure for the EGR cooler/ oil cooler failure is as follows. The oil cooler plugs up and starves the EGR cooler for coolant thus turning it into a superheated steam generator. This point source of heat and excess pressure will lead to the EGR cooler failure. In this condition some have reported the melting nipple on the de-gas tank the attaches to a rubber hose that vents steam from the EGR cooler.

The rapid rise in pressure associated with a head gasket failure is caused by combustion gasses entering the cooling system and raising the cooling system pressure until the vent on the de-gas tank cap opens and the puking starts. I think NAPA has a test strip you can use to detect combustion gasses in the coolant.

OK so with a quick check of a saturated steam chart this is what we know.

15.3 PSIg steam equals 250 degF

20 PSIg steam equals 259 degF

What this mean is that if you take a cold truck out and run the heck out of it and it builds pressure to 20PSI or more and the coolant isn’t 260 deg then it’s a safe bet that combustion gasses are entering the cooling system because you have a bad head gasket.

Water boils at 212 deg at zero PSIg. In a closed system there is a very predictable relationship between steam pressure and steam temperature. This is why cooling systems are pressurised. This way you can have 248 deg coolant that is at about 15 PSIa and you make no steam because the coolant isn’t it’s boiling temp for that pressure, it is however saturated. Now at addition of ethylene glycol raised the boiling point too but for what we are taking about we can use a table for water-based steam. If the system doesn’t get hot enough to the point it should make steam and its building pressure you know that pressure is from a different source like combustion gasses entering the cooling system. From ---- wait for it ------ BAD HEAD GASKETS.

Q: What is the delta between EOT and ECT?

A: Delta refers to the difference between the oil and coolant temperatures. This delta should not exceed 15 deg F , if it does once the truck it up to operating temperature going straight down the highway your oil cooler is plugged up.


Q: The nipple melted off of my de-gass tank.

A: Your oil cooler is plugged up and starving the EGR cooler for coolant turning it into a steam generator. The superheated steam is going to the De-gass tank via the hose from the manifold that runs to the nipple that just melted off. You need a coolant flush, new oil cooler and an EGR delete.


Q: What’s the white crusty stuff around my coolant tank / de-gas bottle

A: Your engine is suffering from a condition called coolant puking. Two scenarios cause this.

#1 Your oil cooler is plugged up and starving the EGR cooler for coolant turning it into a steam generator this flash boiled coolant is entering the de-gas bottle from the rubber hose that leads from the manifold and puking out as it over pressurized the de-gas bottle.

#2 You have a blown head gasket. Combustion gasses are entering the cooling system and over pressurizing it causing puking out the de-gas bottle cap which should vent at about 16 psi.
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