Oil Consumption and Breather Tube

[rocketbob]

Why not coat the ID of the nipple with a coating that will not allow the buildup to stick. Kind of like spraying Pam on a cookie sheet. Techline Coatings makes several different exhaust coatings that would probably work well in this application.

[DanH]

Originally Posted by bpattonsoa

This is obviously conductive heat from the pipe and perhaps some heating from the exhaust impingement on the small piece that is in the exhaust flow.

Can I talk someone (with a clamp-on exhaust tap) into an easy experiment?

Install a small tee fitting in the accessory-case-to-separator hose in order to connect a manometer. Get a baseline vacuum reading at some selected power setting.

Now pull the clamp-on exhaust pipe tap, file off the small angled protrusion that sticks out into the exhaust stream, re-clamp, and fly again with the manometer. What is the difference in vacuum reading?

Worry not...if you don't like the result, send the clamp-on tap to me and I'll weld the protrusion back into place.

When I added the relief valve after just about 1.0 hours from completely cleaning the coke off the inside of the pipe, there was a very small buildup starting.

It certainly seems like the RV-10 tap location puts temperature pretty close to the middle of the coking zone....say 200C to 300C on Bill's chart. It would be nice to find a similar chart for our motor oils. What search terms might find it?

[F1Boss]

Originally Posted by Mike S

Most of us are flying with all electric panels, there is a vacuum pump pad blocked off on the engine that could be put to use.............

Bennair; Dunnatt. Used an Airwolf wet pump. Worked great & made power, until I sold the plane to another, and he had the nerve to turn it upside down. Large blob of oil tried to get thru the pump, and snapped the shaft. Stopped pump rotation, and outlet flow. With no aux outlet, it let the engine force oil out of the nose case. BIG mess; no damage.

SO!! This *might* work if a very reliable separator was installed between the pump inlet and the case....along with a reed valve sort of emergency outlet in the case to pump line, but this active pump system will not tolerate a slug of oil getting into the pump. No sir!

Carry on!
Mark

[rocketbob]

I had a wet vac pump pulling on the breather on my RV-6. I put a flapper-door check valve with one side vented to ambient on the intake side of the pump so that in the event of the pump failure the breather functioned normally. The limiting factor to the system was the fuel pump. Since it is vented to the crankcase, the pump would quit if a high vacuum was pulled. It worked well but I had to dial back the vacuum, using a simple orifice at the inlet of the pump.

[F1Boss]

Originally Posted by rocketbob

I had a wet vac pump pulling on the breather on my RV-6. I put a flapper-door check valve with one side vented to ambient on the intake side of the pump so that in the event of the pump failure the breather functioned normally. The limiting factor to the system was the fuel pump. Since it is vented to the crankcase, the pump would quit if a high vacuum was pulled. It worked well but I had to dial back the vacuum, using a simple orifice at the inlet of the pump.

A fuel pump that actually flows fuel is important - I did not run into the problem: I had the rotary pump from the turbo setup on the engine with the pump, so crankcase vacuum didn't really matter to it. That flapper door check valve sounds like a good item of the current exhaust systems to have - even if the coking problem is solved. How about supplying a drawing, or a vendor?

Carry on!
Mark

[rocketbob]

It was a Dukes flapper door check valve, purchased at OSH from B&B.

[jcbarnes1]

My O-360 will throw out anything over 5.5.

As for the breather hose, I blew out the prop seal on a real humid, 50-60 temp day running full out, I looked into causes for that. Found a ton of stuff from the canard guys. Learned most oil breather slop is about 95% water.

Most likely cause, icing in the hose. But furthermore...

I deduced my breather hose should NOT be cut facing forward - WHICH CREATES POSITIVE PRESSURE, but instead turned around so the 45 degree cut faces rearward, giving NEG case pressure, better performance, and no blown prop seals. With neg pressure, even if you find your prop seal pushed out of the engine, you won't find you are blowing oil out there. So I turned it facing backward, and got a performance boost.

Just think fuel vent: to pressurize tanks, 45degree goes forward.

Since then I installed anti-splat. 1) Don't test to see what it will do if you overfill your engine... just don't overfill, and 2) every oil change inspect the tube going into your exhaust and scrape out the coke deposits you are forming... if that totally cokes up, your going to get a backup.

YMMV

[DanH]

Originally Posted by PerfTech

...The photos below are of our double walled saddle mount that is currently being tested. This should eliminate this heat transfer completely. The inner tube that carries the blow-by products is welded only at the cooler top fitting and has .025" clearance all around. This insulates it from the hotter outer tube that is perpetuating the buildup or coking.


.
It also seems that any major hard buildup is on systems that the exhaust valve mounting tube was welded into the exhaust pipes and not on the saddle mounts. We are and have been working and testing many different designed parts to eliminate the possibility of this happening and have several in use now, building time. We will report the results when they have accumulated viable, credible information at 20, 40, 60, etc hours and when available. Thanks, Allan

Allan posted the above just before OSH, so it's time to start hearing field reports (coking or no coking) about the double wall tap.

I welded one into my homebrew tap 10~15 hours ago. Had the cowl off last weekend for an oil change and could detect nothing in the tube but a film of the same gray/beige dry deposit seen in the tailpipe. More reporting as the hobbs rolls forward.

[BillL]

Originally Posted by DanH

....say 200C to 300C on Bill's chart. It would be nice to find a similar chart for our motor oils. What search terms might find it?

Here is a little background on motor oil testing. I think the test we would be interested in is weight loss vs temp, or boiling point fraction. The type of oil used can make a significant difference in shifting a curve.

http://www.upmpg.com/motor_oil/motor_oil_testing.htm

I looked around for coking temps of motor oils and did not find anything definitive. 225C coking temp was found for standard oils, but synthetics are higher. Coking takes place in turbos, and in ring grooves. The petroleum vs synthetics coking temps may only be 30-50C apart (guessing) for what we can buy off the shelf. If we have any RVers that work at SwRI in San Antonio, they would have access to some proprietary data (and certainly public) that we would have to pay for. They certainly have data on many oils as they do the qualification testing on single cylinder engines for piston deposits etc. They NEVER would publish, or post, definitive brand data, but might give us a delta for petroleum vs full synthetic temps. A simple toaster oven test would (could) provide some useful data if really needed.

[scard]

Originally Posted by BillL

Here is a little background on motor oil testing.

If we have any RVers that work at SwRI in San Antonio, they would have access to some proprietary data (and certainly public) that we would have to pay for. They certainly have data on many oils as they do the qualification testing on single cylinder engines for piston deposits etc. They NEVER would publish, or post, definitive brand data, but might give us a delta for petroleum vs full synthetic temps.

Wow, blast from the past. Yeah, throughout the late '80s- early '90s the facility at SwRI ran large labs of engines 24x7 for years doing oil analysis. The nuclear physicist that ran those labs was my best friend / mentor / guru, for whom I am forever grateful for his teachings.