Coolant Recovery Tank

[Raleigh]

So I brought this up in another thread and though maybe it needs its own.

Has anyone installed a coolant recovery tank after the factory coolant tank?

I was thinking about coolant and its relationship with the heat and pressure in the sealed system.
I have read that these blocks and heads are prone to steam pockets and hot spots.
This IMO is due to the low pressure in the sealed coolant system.

A liquid at a given temp, say 200* and under 10# pressure it will never boil.
Take the liquid and temp and place it in a vacuum and you boiling.

That said I think this is a design and engineering problem with the cooling system in our trucks.

The lack of pressure is what causes the steam pockets and hot spots in the engine.

With no recover tank (the factory tank is NOT a recovery tank, it is part of the sealed system) once the system reaches pressure the coolant is expelled and lost.
And it will do this everytime it gets up to pressure, soon there is no pressure in the system and the coolant is allowed to boil.

By adding a coolant recovery tank I have captured that coolant, now when the engine cools it will pull in that coolant rather than air.
Now the engine is always full of coolant, even when it cold.

I replaced the 15# cap with a 13# cap to prevent too much pressure in the system.

Any thoughts on this idea, good or bad?

 

[THEFERMANATOR]

There is no need what so ever for it if the cooling system is functioning properly. Also go back to a 15 or 16 PSI non vented cap as the 13 is a tad low and can CAUSE overheating. The factory system uses the coolant reservoir that has several functions. It stores coolant, is at teh highest point for air in teh system to collect at, and it also holds an air charge in it that allows for a steady amount of pressure without discharging any coolant out of the system while preventing air from entering the system. IF you are burping coolant out of the pressure tank, it is because air is being introduced into it from the compression side of the engine and maens you need to fix it ASAP!

 

[Raleigh]

Well I was not losing coolant out of the reservoir, but I also had little to no pressure in the system, even at 205*.
This makes no sense to me, how can a system cool properly with no pressure?

From what I can tell my head gaskets are good, I am not loosing coolant, no white smoke, no oil in the coolant and no coolant in the oil.

The level of coolant in the factory reservoir was about 3/4 full and still no pressure. I have not found a good reason why this is the case.
First I though maybe it is the cap, so I replaced it, no change. Next, maybe it is the thermostat, no change.

I just cannot understand why this system would be different than every other system I have worked on in the past.

I am just trying to figure this one out, seems odd to me!

 

[WarWagon]

Parts of the engine exceed the boiling point under pressure. This is one of the reasons water wetter works. There is a lot of steam bubbles that come out of the engine and get re-condensed in the radiator. Heads are the #1 source of bubbles. And now the pure water vapor follows it's own rules for temp and pressure to condense rather than the 50/50 mix rules for boiling.

In general the system isn't going to boil over from this.

The old systems would build 15 PSI then pop the cap just from fluid expansion. Without a recovery tank they would make their own air cushion in the radiator.

Most diesels since 1994 have this air cushion type pressurized recovery tank. Rather than water hammering everything the air gives things a cushion before the cap blows pressure off. may be other reasons for it, but, look at how complicated and expensive it is vs. the 1993 cap on radiator and overflow bottle systems. GM doesn't spend money unless there is a good reason for it.

 

[WarWagon]

Well I was not losing coolant out of the reservoir, but I also had little to no pressure in the system, even at 205*.
This makes no sense to me, how can a system cool properly with no pressure?

From what I can tell my head gaskets are good, I am not loosing coolant, no white smoke, no oil in the coolant and no coolant in the oil.

The level of coolant in the factory reservoir was about 3/4 full and still no pressure. I have not found a good reason why this is the case.
First I though maybe it is the cap, so I replaced it, no change. Next, maybe it is the thermostat, no change.

I just cannot understand why this system would be different than every other system I have worked on in the past.

I am just trying to figure this one out, seems odd to me!

Put a pressure tester on the cooling system and see what happens. Possible bad cap sealing surface or cracked bottle? Otherwise something is up.

 

[THEFERMANATOR]

Or your using the wrong style cap. Are you using a vented or non vented cap?(Is the little metal flapper on the end of it spring loaded to hold it closed or not) The coolant tank style systems MUST use a non vented cap, or the one where the little metal return portion is spring loaded closed. Otherwise it will not build any pressure until the coolant comes flying out of the system and slams the flapper closed.

 

[Raleigh]

Hmm, I will take a look at the cap, it was the cap that was called for at Napa to replace the OEM.
So the vented caps are held closed by the coolant, and the non vented caps are held closed by a spring....
Now that makes sense about how pressure is built in the system, but it is an OEM cap (according to Napa anyhow).

I was worried about the no pressure and the high temps causing the coolant to flash, I did get a Heath fan and clutch so that will help out.


I did a pressure test and it held pressure with no issues, but I have had one in the past that tested fine, but would leak occasionally from the cap. Turns out the mating surface had a hair line crack in it.

Thanks for the info guys!

I will look into these and see if I can find a solution..

**Edit** I looked at the cap I have and the small disc on the bottom is spring loaded. The spring is not real strong, but it holds it closed. So it is the correct cap.
I will disconnect the overflow and see what happens I guess.

 

[Raleigh]

Checked the other cap, the 16# cap and it IS vented. They gave me the wrong 16# cap which is why I had no pressure until I put on the 13# cap!

So would the recovery reservoir hurt the system if I were to leave it in place?

 

[great white]

Checked the other cap, the 16# cap and it IS vented. They gave me the wrong 16# cap which is why I had no pressure until I put on the 13# cap!

So would the recovery reservoir hurt the system if I were to leave it in place?

Nope.

Won't hurt it.

Where did you plumb in your "recovery" bottle? the overflow line on the OE tank?

What you've essentially made is a "catch can", the stock system will "burp" and then seal once the pressure is relieved. It won't "suck" it back in, which is the purpose of a coolant recovery tank.

But if you find it's getting fluid in it you have a problem in your system.

The OE tank is designed to hold the required amount (hot or cold) unless you have a severe overheat and boil over.

You catch tank is only going to save you the cost of the little bit of fluid lost on a boil over...at least until it fills up and starts puking fluid also....

Pressure is a big part of localized coolant boiling, but so is coolant composition and flow.....

 

[Raleigh]

Yes, I plumbed it from the overflow line.

So this may actually be a way to monitor whether I am having issues with the cooling system, like head gaskets.

Interesting....

No I have to just find a 15# non vented cap, install the Heath fan and clutch, and the 190# AC Delco t-stat and I should be good on the cooling system.

thanks for the info guys!

 

[great white]

Yes, I plumbed it from the overflow line.

So this may actually be a way to monitor whether I am having issues with the cooling system, like head gaskets.

Interesting....

No I have to just find a 15# non vented cap, install the Heath fan and clutch, and the 190# AC Delco t-stat and I should be good on the cooling system.

thanks for the info guys!

Oh, you'll know if you have a problem with compression sneaking into the cooling system toute suite.....

 

[Raleigh]

That is more than true I am sure!

Nothing right now just some mild to moderate blowby and I want to keep it that way until I am ready for a complete rebuild...:agreed:

 

[schiker]

Wasn't the newer style non vented systems started with the newer Poly Propolene glycols ie Dexcool coolants. The newer coolants react with air and can cause corrosion and crystaline buildup problems if vented or has air leaks. The older vented style was used with the old green Ethelyne Glygol (the green stuff) and was more stable with air interface. Forgive the spelling of chemicals.

I had a leak at my heater quick connect and the dexcool crystalized at the leak. Whenever I've had a "green coolant" leak its just leaked and left a slick slimey residue that never seemed to crystalize.

 

[Raleigh]

Well this being a 94 it uses standard coolant, thank God! haha

 

[THEFERMANATOR]

Wasn't the newer style non vented systems started with the newer Poly Propolene glycols ie Dexcool coolants. The newer coolants react with air and can cause corrosion and crystaline buildup problems if vented or has air leaks. The older vented style was used with the old green Ethelyne Glygol (the green stuff) and was more stable with air interface. Forgive the spelling of chemicals.

I had a leak at my heater quick connect and the dexcool crystalized at the leak. Whenever I've had a "green coolant" leak its just leaked and left a slick slimey residue that never seemed to crystalize.

The 94+ 6.5's all use a NON vented cap as they use a remote reservoir system taht has coolant and air in it. In 96 when GM went to the new dex-cool anti-freeze they started chaging everything over to the closed cooling system with the reservoir like the 6.5's use because of the problems associated with dex-cool.

 

[Diesel -T]

Wondering why the air interface with dexcool in the remote reservoir doesnt create a problem?

 

[schiker]

Wondering why the air interface with dexcool in the remote reservoir doesnt create a problem?

Its not vented so the amount of air (oxygen I guess) is limited and the reaction is limited. What causes the problem is when fresh air is "turned over" in a vented system or coolant is exposed to fresh air. Similar to how most things last longer in a sealed container.

A vented system usually doesn't have an air pocket to compress and expand depending on temp. So it expels some coolant when warm and draws it back in when cold. This exposes the coolant to more air each time you drive it and park it long enough to get cold.

 

[THEFERMANATOR]

Wondering why the air interface with dexcool in the remote reservoir doesnt create a problem?

It more so comes down to it is a limited oxygen space, and the air in the bottle will be basically teh same temp as the coolant. That cold air hitting the hot dex-cool wil lset off the coolant sealer in it.