Coolant loss mystery in Barco DP2K-19B

[Leo Enticknap]

Just completed the annual maintenance "C" checklist on a DP2K-19B. While doing it, I found that the level in the coolant tank was only just above the minimum mark. I've spent the last hour and a half trying to figure out why, with no success. Unless I'm missing something, the loss can only have been caused by leakage or evaporation.

This isn't an unknown quantity projector that might have gone for years without a coolant flush. It's in the theater of one our service contract customers, and I've been looking after it since 2017. It has had coolant flushes and refills every year without fail, and pump replacements when maintenance D comes due (the last was in 2023; the next will be due next year).

Obviously it's important to find out how and why the coolant loss happened, because if any leaks onto a formatter, that's a $15K light engine buggered.

There is no sign of any telltale stains to indicate leakage around any of the hose clamps, or in fact anywhere at all. I even removed the light engine and the radiator/pump/fan assembly from the projector, just in case some coolant had leaked and pooled in a sadistically invisible location. Nothing. Totally clean and dry. While I had that assembly out, I turned it upside down, to invert the tank to check for leakage out of the cap. Not a drip. The gasket in the tank cap looks good to me, too. I fail to see how any coolant could have evaporated out of the tank, either. The cap wasn't loose when I first noticed the low level. Maintenance A and B are done by site staff, and they tell me that no-one had noticed a low coolant tank level before I did.

Has anyone experienced this before, and can suggest somewhere to look that I didn't? Many thanks in advance.

[Jim Cassedy]

Assuming it might be leaking very slowly and evaporating, would that
coolant residue be visible under UV or IR light? I found a liquid leak in
something once because the coolant residue it left behind was visible
under UV light. So I knew the leak was originating from the area above
where I could see the 'stains'.

[Mark Gulbrandsen]

Also check the pump seal! Also the hoses may be somewhat dried out after 15+ years and not sealing as well as they would.

[Leo Enticknap]

Thanks Jim. I have a UV flashlight that I use for drying out the last bit of resin stickiness of stuff that comes out of our 3-D printer. I'm back at this site on Monday to work on another projector, and will take it with me.

Whenever I've seen serious coolant leaks in the past, there has been a very distinctive blueish white stain/residue around the problem area, that will yield to nothing except acetone. It was a very familiar sight in Series 1 Barcos, thanks to their pressurized liquid cooling systems and the material they used for the hoses (the brown stuff) starting to decompose after a few years. They changed the hose material for Series 2 and it seems to have held up a lot better: in my experience, coolant leaks are very rare, and usually only happen if a projector goes for many years without a coolant flush, the old coolant starts to coagulate inside a DMD heatsink, pressure builds up, and then a hose bursts.

But there was no sign of this in the projector I was working on this morning. The new coolant went through the light engine without any problem or unusual resistance felt through the bicycle pump. After filling up the radiator part of the circuit and running refill mode, agitation in the tank looked normal, and I could feel coolant flowing through the hoses between thumb and forefinger. Where almost half a quart of coolant disappeared to I'm still at a loss to explain.

I'm wondering about swapping the tank cap with one in another projector, to see if the coolant loss follows the cap, just in case it is evaporation through that.

[Marcel Birgelen]

Jim's idea is a good idea, it's often used to find leakages in cars, but then a UV dye is added to the coolant, so I doubt the default coolant you're using will light up under UV light. It's easily enough to test though, just shine your UV flashlight at a bottle or can of your coolant of choice. UV dye is readily available on-line, if you dare to use it in the system, I leave up to you. It's generally considered safe for car use, but the cooling system in a car has far less exposure to UV light.

The white residue you see from coolant is probably the glycol that was left after the water evaporated. It has a bit of a chalky or waxy kind of composition.

[Leo Enticknap]

I was back there yesterday, and drew a complete blank. The UV flashlight didn't cause any distinctive glows or reflections, either from a little bit of coolant in the bottom of a glass, or any surfaces of the light engine compartment of the projector. Noting Mark's suggestion (check the pump seal), I pulled the pump/radiator/fan tray out a little bit to get a view, but the entire pump was bone dry with no sign of any stains. The projector appears not to have lost any coolant from the tank since Friday (the tank level still looks to be on the max line); but there again, I wouldn't have expected it to from a microscopic leak somewhere in only three days.

So, in the absence of any other ideas, I swapped the tank caps between this projector and the one I worked on yesterday, and put a reminder in my calendar to check both in a month's time. If an imperfect seal between the cap and the tank neck is the cause and House 3's projector loses coolant at the same rate that 2's did, I would expect the level to be visibly below the max line by then.

Thanks for everyone's suggestions.

[Ryan Gallagher]

The related industry of PC coolers with their sealed AIO type coolers is maybe a good data point for coolant loss rates. Seems "permeation" is the technical term. On this one I trust the AI result to have summarized the copious amount of subjective commentary and research on the subject.

Coolant loss through slow permeation in sealed All-in-One (AIO) coolers takes 5 to 7 years or longer to impact performance, which matches the typical lifespan of the pump. Liquid loss happens in tiny amounts (low single-digit milliliters per year) as vapor escapes through the microscopic pores of the rubber or plastic tubing. [1, 2, 3]

Factors Impacting Coolant Retention

• Tubing Material: High-grade rubber or sleeved polyethylene tubes resist fluid loss better than cheap plastics.

• Operating Temperature: Running continuous coolant temperatures above 50°C–60°C speeds up the rate of liquid permeation.

• Build Quality: Premium factory seals keep fluid stable longer, whereas budget units may dry out or fail within 2 to 3 years. [1, 2]

Signs of Coolant Loss

• Gurgling Sounds: Hearing bubbling or rattling means air has replaced the lost liquid volume inside the loop.

• Higher Temperatures: CPU idle and load temperatures rise by 10°C to 15°C compared to when the cooler was new.

• Reduced Pump Efficiency: The pump RPM drops or sounds strained as it tries to push air instead of fluid. [1]

A sealed AIO literally only has a couple feet of tubing. A cinema projector probably has much more and a higher permeation rate. But is it fast enough to notice such a huge difference between service windows? Probably not intended to be that fast? As you noted it was bizarrely low comparatively.

[Phil Ranucci]

Any chance someone in the theatre checked the level after 90 days and left the cap off until the next check?
I accidentally did this once and the coolant level did drop to near the minimum when i returned for the next check.

[Leo Enticknap]

They haven't admitted to it, but it's entirely possible and fits the known timescale.

[Marco Giustini]

Christie series 1 was prone to cracking the lid of the coolant which would then evaporate. However, that would then result in a gel-like substance left behind as water does evaporate but other chemicals do not.

Did you find the leftover coolant to be blue-er than the new one, Leo?

[Leo Enticknap]

Not that I recall from eyeballing it. Neither did I find any goo on the inner surfaces of the tank cap. As you note, this is the smoking (or should that be steaming?) gun evidence for evaporation having happened, especially if the goo is concentrated within the recess into which the gasket is seated. In the past I've had to remove the gasket with a spudger to be able to clean evaporation deposits out of a Barco coolant tank cap properly. But this one was clean.

[Steve Guttag]

If one merely tops off coolant (Christie or Barco)...they are thickening it. As noted, the water evaporates out...so on the top-off one is adding a diluted mix to a concentrated remains. I tent to advise, on a top-off, use distilled water (replace what evaporated.

I have not had Leo's mystery evaporation, however.

[Hong Sung Hyeok]

The first reason is that the lid wasn't fully closed. The second is, strangely enough, that certain projectors tend to have the coolant evaporate unusually quickly.
In my experience, this applies to all Christie Barco projectors. It’s just more reassuring to top it up during every maintenance season.

[Dave Macaulay]

I've had ones where the coolant level drops more than expected. No signs of leakage. Just gone. Possibly whoever did the last change didn't wait and top up after the pump run to eliminate air? I don't know. Series one Barco projectors never seemed to retain the coolant pressurization for long either, that's about 75ml of coolant that went somewhere.

[Leo Enticknap]

In many cases agreed. I've frequently done flushes on projectors previously serviced by others and found the level low. But in this case, the projector was serviced only by Yours Truly for the last nine years, and I always ran refill mode to purge the bubbles and then topped it up to the max line afterwards.

I'm starting to think that Phil's theory is the most likely one: that site staff doing one of the three monthly level checks opened the cap to see the level (which you really can't through the sight glass, because it just reflects your flashlight back at you), and didn't fully close it afterwards.