Purge engine at oil change

[Rick_A]

My understanding is that you don't need to perform a pressure purge if you don't let the oil drain out of the lines.

Please correct me if I am wrong but I thought the procedure was.
1. Burp engine
2. Drain oil from tank
3. If cleaning tank because you use 100LL
__a. Disconnect oil lines and keep them above the level of the tank
__b. Remove tank and clean
__c. Re-install tank & lines
3. Remove & Replace oil filter
4. Replace oil
5. Re-check oil level after rotating engine/circulating oil

So my understanding is that as long as you don't disconnect the lines and remove the oil filter at the same time, the oil will stay in the lines and a purge is not required.

Also, use a new crush gasket when re-installing the tank drain

[rvbuilder2002]

Edit
I was looking through Line Maintenance today for something else and took a look at the tank cleaning procedure.... Confirmed that after tank cleaning it specifies a purge procedure be done.
I think Rotax specifies doing a pressure purge if the system is broken open for any reason. So I assume this would include removal of the oil tank.

But the recent post in this 1.5 year old thread wasn't asking about pressure purge. He was wondering about the chance of emptying the tank while turning the prop to get oil pressure (a requirement after an oil change, even if you don't open the system).

[sergioam2009]

Most Rotax 912 operators in Brazil (and there are many here) prefer using Premium 91oct mogas instead of avgas. My own engine is relatively new at some 350 hours, so there's not much I can say, but I know more than one owner that have run 912ULS to the TBO with no problems. Our premium mogas is 25% ethanol.

[RFSchaller]

Don't forget to check the magnetic plug for metal.

[Sink]

The manuals do say to do an oil purge after a tank cleaning because they assume you will drain oil from the hoses. If you want to do the purge by all means do it.

If done properly you don't need to do an oil purge and here is why.
COMMON SENSE NEEDS TO APPLY.

When you normally drain oil from the tank during a normal oil change all the oil in the tank including the two metal tubes inside and up to the fittings at the top of the tank all drain their oil. If you disconnect the oil lines on top they will be empty at the fitting. Either place these hose in an upright position or place a rubber stopper in them so no oil gets lost. Never rotate the prop once the system is void of oil or you will be doing a purge for sure. So long as you do not drain any oil out of the hoses you have not drained any more oil than a normal oil change. Once the tank is back in place and the fittings are attached then fill the tank. Now rotate the prop with the spark plugs in place approx. 20 times. This not only fills the oil filter, but will help charge the metal tubes and hoses to the tank. The key here is to lose no more oil in any hose line other than what is normally done in a standard oil change. Replacing the oil filter dry like we have to do introduces more air than a tank clean ever will so long as you do not lose any of the oil in the two hoses.

Rotax wants the purge because many don't understand the system and it covers them for any liability and makes sure the owner is in good shape should someone do it wrong.

Once you pull an empty tank off and break the lines you'll see what I mean about a normal oil drain dumping all oil up to and including the tank fittings.

As soon as I can get to it I will post what 100LL and using the wrong oil does to an engine. It isn't pretty.

[Driftdown]

Thank you Sinker!

[Piper J3]

Originally Posted by Sink

As soon as I can get to it I will post what 100LL and using the wrong oil does to an engine. It isn't pretty.

I'm anxious to see this... My engine has 58TT with first 50 hours using 100LL avgas.

Now switched to 93 octane auto fuel and Mobil 1 Racing 4T 10W-40 Motorcycle Oil.

Piper J3

[RFSchaller]

At the ROTAX course the instructor said he has found the oil tank cleaning to be a pretty much useless task. Has anybody found anything bad while doing the tank cleaning? I'm at 400 hrs on the Hobbs and haven't touched the tank. Sometimes I think preventive maintenance becomes causal maintenance!

[JBPILOT]

I never use 100LL. I use to take the tank apart. Never found anything, and stopped doing it. If you use 100LL, then it might be worth cleaning out tank. However, I do remove the cooler and drain it EVERY time. I also only change my oil at 100 hours since I only use premium auto fuel. There is too much dirty oil in the hoses and cooler to leave in my opinion. If you change more often, then it might not be that much of an issue. I am at 840 + hours now, and my system works well for me.

[Rick_A]

Originally Posted by RFSchaller

At the ROTAX course the instructor said he has found the oil tank cleaning to be a pretty much useless task. Has anybody found anything bad while doing the tank cleaning? I'm at 400 hrs on the Hobbs and haven't touched the tank. Sometimes I think preventive maintenance becomes causal maintenance!

When I attended the Rotax class at Lockwood they said just the opposite, if you run 100LL. They showed pictures of lead sludge in oil tanks after just 25 hours of running 100LL. There was more than 1/4" of lead sludge in the bottom of the tank.

Their message was: When using 100LL change the oil at 25 hours and clean the oil tank. If you run auto gas, change the oil at 50 hours and you don't need to clean the tank.