912ul water pump leak

[napierm]

This summer my engine started leaking water I think from the weep hole. Hard to be sure really. Put in stop leak that fixed the problem but don't really trust it. Would like to do some longer cross country flights this spring. Engine is from 1997 and has old style impeller, water seal, old oil seals etc.

Today I got in a $$$ bag of parts and tools to pull the flywheel and rear housing and replace all the seals and the impeller. Will try to post some pictures from the job.

Thought I would give LSAshop a plug. Good (relatively speaking) prices and service from them.

Mark Napier

[jiott]

I thought you could replace the 912 water pump seals by only disassembling the water pump; not have to pull flywheel etc. I must be wrong? I am very interested because I have a very small weepage from my water pump weep hole on the bottom after 300 hours; not much yet but keeping an eye on it.

[mr bill]

I have had my water pump off without disturbing anything else.

[Xengineguy]

If you put stop leak in your cooling system,do yourself a favor. FLUSH your system! Get that stuff out. Flush backwards and do the heater and radiator
Separately . Just my 2cents. Mike

[Av8r3400]

x2 with you, XEngineguy! Flush that system several times.

You should be able to get the water pump apart without pulling the flywheel, but replacing the seals requires taking the whole back end apart. (Heavy Maintenance Manual Chapter 75-00-00 - Free download) Did you buy/rent/borrow the impeller tool, also? Do not try to tighten the impeller without it because they are quite fragile to damage.

(Don't forget the paper gasket on the housing. It's a shim giving clearance to the impeller)

[Dave S]

Mark,

I noticed in your original post that you were not 100% sure where the leak was coming from, but, it seemed to be coming from the weep hole.

"This summer my engine started leaking water I think from the weep hole. Hard to be sure really."

Coolant leaks are notorious for being difficult to locate - ythey often start someplace and show up in another.. Might be a good strategy to consider all possibilities before replacing the waterpump.

Other places to consider include the hose connections above the weephole where drips can form on the bottom of a connection and be pretty hard to see...dripping down to make it look like it is leaking elsewhere. The 1" hose connector at the elbow is a possibility. I don't know for sure if all rotax engines are made this way, but, I believe the bottom water pump bolt penetrates into the coolant chamber creating a possibility of drips past the threads.

Good luck with your search and hope it is something minor.

Sincerely,

Dave S
KF 7 Trigear
912ULS Warp Drive

[Dorsal]

I agree with Dave S as I have had to chase down a number of small leaks over the years. Causes for mine included thread sealant on a pump fitting, o-rings on the cylinder fitting and the hose connections as they got older. The origin of the leaks was usually pretty difficult to detect initially appearing as a drip on the bottom of the engine.

[HighWing]

Years ago, I had a small leak - can't remember where exactly - and called Rotax. I was told to use Bars Leak at a smaller quantity due to the relatively smaller coolant volume in our engines. After that I flew another 600 hours to finish out the 900 hours total. All with it in the coolant with no further drips or other issues. Curious about the urgency of the flushing recommdations. Is this per Rotax?

[Xengineguy]

Years ago, I had a small leak - can't remember where exactly - and called Rotax. I was told to use Bars Leak at a smaller quantity due to the relatively smaller coolant volume in our engines. After that I flew another 600 hours to finish out the 900 hours total. All with it in the coolant with no further drips or other issues. Curious about the urgency of the flushing recommdations. Is this per Rotax?

Stop leak seems to settle out and end up in the inlet tanks of heater cores and
Radiators. (I have disassembled hundreds of heater cores and radiators in the
Last 25/30 years of business.I recore and repair radiators 5 days a week). Given the size of the heat exchangers we use
We don't have a lot of margin on the liquid side of the system.Plugging
Just 9 tubes could be more than 10%???. Don't tell anyone but black pepper
Is probably the best stop leak!

[HighWing]

Don't tell anyone but black pepper
Is probably the best stop leak!

Sad to hear. It just might force me to share my black pepper with the airplane. Just love the stuff on everything.

Seriously, Thanks for the experience heads-up. I can go with that. Still, I wonder if it might have to do with the amount added. In the day, Rotax was very firm on the amount added because of our relatively small coolant capacity. It was just a fraction of the bottle. I had shutters on the radiator and still used them regularly up until the end.