Sport Pilot Talk

If a Rotax 912 coolant expansion tank got topped up with 1 cup of tap water for a several hour flight how bad is that? If the tap water is removed after the flight. Does the water hardness of the utility matter if it happens only once?

Tap water contains minerals which can promote corrosion inside your cylinder heads and water pump. Always dilute your polyethylene glycol coolant with distilled water. You can buy a gallon of distilled water for under a dollar in just about any grocery or convenience store, so there's not really any excusevfir risking the health of your engine by using tap water. If someone put tap water in my cooling system, I would want to drain and flush out the entire system as quickly as possible.

I know that it should only be distilled water. If it's not my plane for example but the owner who put tap water in said it was fine to do once or twice. Is that true and is the damage slow and cumulative or could it cause it to seize after just a few times?

Tap water BAD !!!

Why not just buy the Prestone DEX-Cool 50/50 premix coolant? It's $13 on the aviation isle at your local Walmart. Ready to use, premixed, extended life
up to 5 years and you simply pour it in, no fuss no muss.

https://www.walmart.com/ip/Prestone-DEX ... 0/16889202

Tap water is not the same everywhere. The severity of possible damage depends on the source of the tap water. Here in the shop I always add Dexcool 50/50 pre mix, at least for the airplanes that are using Dexcool. On the average Rotax installation the capacity of the cooling system is about 3/4 of a gallon. A cup of water is 8% of the total capacity.

Soft water would be better than hard water.
Are we talking a couple ounces?
When is the next 5 year due? The coolant will be changed then.
If it was mine and a few ounces of soft water had been put in the reservoir “accidentally” I think i would remove it from the reservoir and reinstall 50/50 premix dexcool.
More likely if hose change time is close.
I could maybe talk myself into that with mildly hard water.
I am a 40 year plus retired auto mechanic.
I used soft water with antifreeze in cars the whole time.
I also saw clogged radiators and heater cores from people using hard water.
But those are cars. And with a gallon or two of water in every system.
I know that cars with more buildup used to leak less.
Of course, the most important thing here in Minnesota is the freezing point.I’ve seen much more damage from freezing than from buildup.
Same with oil. Brand didn’t matter much. Running low was a big deal.
So... can you sleep at night knowing that water is in there?

I was told by a long time mechanic around here that our water was okay for cooling systems and batteries if you didn't have distilled available. Our water comes from a rain filled lake. I have seen some well water fairly close to here that I wouldn't want anywhere close to my engine.

Type47 wrote: ↑Sat Mar 13, 2021 6:07 pm So... can you sleep at night knowing that water is in there?

Well it's not my plane.

Type47 wrote: ↑Sat Mar 13, 2021 6:07 pm When is the next 5 year due? The coolant will be changed then.

Coolant isn't changed on the same interval as the 5 year rubber chage, Rotax states "Coolant must be replaced as per manufacturers instructions, at the latest during overhaul or when the engine is replaced". This of course varies between coolants but it's not exactly every 5 years. Owners should read their coolant label to determine the time limit for their specific coolant. I do a complete coolant flush of my 50/50 premix DEX-Cool every other condition inspection or every two years as it only costs $13 and it's cheap insurance.

ShawnM wrote: ↑Sat Mar 27, 2021 3:59 pm

Type47 wrote: ↑Sat Mar 13, 2021 6:07 pm When is the next 5 year due? The coolant will be changed then.

Coolant isn't changed on the same interval as the 5 year rubber chage, Rotax states "Coolant must be replaced as per manufacturers instructions, at the latest during overhaul or when the engine is replaced". This of course varies between coolants but it's not exactly every 5 years. Owners should read their coolant label to determine the time limit for their specific coolant. I do a complete coolant flush of my 50/50 premix DEX-Cool every other condition inspection or every two years as it only costs $13 and it's cheap insurance.

For this engine the owner just adds more coolant whenever there's a leak (which happens from time to time because it's an old engine past TBO). The leak gets fixed and the coolant stays there until a new leak pops up. I'm sure it'd be different for a brand new engine.

ShawnM wrote: ↑Sat Mar 27, 2021 3:59 pm Coolant isn't changed on the same interval as the 5 year rubber chage

True, but I find it impossible to change the coolant hoses without all of the Dexcool leaking out! So, at the very worst, coolant is going to get changed at least once every five years.

drseti wrote: ↑Sat Mar 27, 2021 7:40 pm

ShawnM wrote: ↑Sat Mar 27, 2021 3:59 pm Coolant isn't changed on the same interval as the 5 year rubber chage

True, but I find it impossible to change the coolant hoses without all of the Dexcool leaking out! So, at the very worst, coolant is going to get changed at least once every five years.

Do you know the cheapest part on an airplane?

3Dreaming wrote: ↑Sat Mar 27, 2021 9:23 pm Do you know the cheapest part on an airplane?

I sure do, Tom. Pilots are notoriously cheap!

drseti wrote: ↑Sun Mar 28, 2021 6:06 am

3Dreaming wrote: ↑Sat Mar 27, 2021 9:23 pm Do you know the cheapest part on an airplane?

I sure do, Tom. Pilots are notoriously cheap!

And it wouldn't surprise me if some would drain the coolant and put it back in during the hose change.

drseti wrote: ↑Sat Mar 27, 2021 7:40 pm

ShawnM wrote: ↑Sat Mar 27, 2021 3:59 pm Coolant isn't changed on the same interval as the 5 year rubber chage

True, but I find it impossible to change the coolant hoses without all of the Dexcool leaking out! So, at the very worst, coolant is going to get changed at least once every five years.

You have to be a little faster with the clamps Paul and you'll barely lose a drop.

My point was that it is possible, depending on the coolant type, that it's changed more often than every 5 years and yes of course at 5 years with the rubber. I did a whole write up with pics on my coolant flush procedure on our SportCruiser forum. It's a rather detailed flush that takes me about an hour but I get every drop of the old coolant out. I do this every other condition inspection and DONT reuse the coolant. I can't imagine anyone reusing old coolant but maybe there's one pilot out there who's more thrifty than I am who might.

Also everyone, check the gaskets on your radiator cap, there are two of them. During a preflight a few weeks ago I noticed a few small cracks in the large gasket and decided to order a new cap. The old cap was installed in 2014 and lasted 7 years. I just installed a new one. For the record the cap is not a Rotax specific part, they are standard radiator caps that also fit BMW motorcycles among other vehicles. You can buy the exact cap, 1.2 bar, from your local BMW motorcycle shop for about 1/3 the cost. This is my second one. Part number 17112345074. I told you I was thrifty.