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For the first 25 hours of my Phase 1 flight testing (over the span of about 15 months) I had been adding TCP lead-scavenging additive to my fuel. I was having a constant battle with a sticky turbocharger throughout those hours. The issue was almost like clockwork... if the plane sat for 10-14 or more days after the last flight, I'd find the turbo stuck and would need to free it manually by removing the intake hose and spinning the compressor either with my finger or a socket.

3 months ago I decided to stop adding TCP to see if that made a difference with the Turbo getting stuck. There is a theory that suggests that while the TCP may be keeping my spark plugs clean, the resulting deposits (lead bromide forming hydrobromic acid with moisture) may end up in the turbo and cause corrosion resulting in a sticky turbo. This may be the reason that TCP is not recommended in Continental or Lycoming turbocharged engines.

Well, 3 months, 5 flights and 6 hours later, I haven't had a single instance of a sticky turbo. I'll update this post if anything changes, but I'm inclined to believe that it was the TCP that was causing my turbo issues and I won't be using it for the foreseeable future.

Keep us updated this is very interesting to me considering the sticky turbos are one of my concerns with engine choice.

Using TCP - the sludge is Lead Phosphate not Lead Bromide.

My chemistry is then not good enough - but I suppose it forms Phosphoric acid?

I'm not sure Graeme, you're probably more correct than I am on the chemistry. My evidence so far is only anecdotal and flight/mx logs, and so far I'm on the side that TCP may not be great for the Turbo. If I don't have any more sticking issues going forward I can only think of 2 reasons it would be the case: 1) my turbo is finally fully broken in (and happened to coincide with when I stopped adding TCP), or 2) TCP was causing the sticking. Or both.

Just to add a bit more context to the "sticking", basically the turbo is essentially siezed in place before flight (NEVER in-flight.) Easily detectible during a quick throttle-up during a runup (manifold pressure wouldn't go above 30".) I was having the problem so consistently that if the plane sat more than 2 weeks before a flight I'd pull off the cowling and check the turbo manually by removing the intake manifold hose (I got really good at it, could pull cowl, disconnect hose, check/free turbo, replace hose/cowl in under 15 minutes.) Sometimes it would free with just my finger, but usually I had to put a socket on it to get just enough force to break it free, then spin it with my finger a dozen or so times and it would be totally freed up. If it was a week or less between flights the turbo was always free. This, to me, was an indication of a rust deposit versus oil coking or whatnot. Once it was free it was totally free and flew great.

My piece in the Camguard thread - It was the Camguard inventor put me onto it being Lead Phosphate instead of Bromide.

If you are two weeks between flights - I could see the tolerances rusting up. I wonder if Camguard would help at that point?

I used to run a turbo on a Ford marine diesel that had a specific process for making sure it was OK after a week of non-activity. As we ran it every day - it was a non-issue.

To the best of my recollection the issue was oil coking going "hard" if not cooled down properly after a run. A 15 min idle after hard use to allow the turbo to cool, the oil impregnated carbon bearings to shrink back a touch and a "thicker" oil film to get re-established kept things OK there. If it coked slightly and then was left it went "hard" and the turbo wouldn't spin. There was actually a shielded hex on the end of the shaft that was outside the turbo that you wrenched prior to starting to be sure the turbo was spinning freely.

I'm not a motorhead but aren't there thousands, or tens, or hundreds of thousands of cars driving around with turbos in them? My wife's SUV has one. I never hear of those sticking. There must be something different with the one on the AeroVee thats causing some underlying issue. I seem to remember them saying it was from a commercial truck? I also seem to have read a few people took them out of airplanes and went back to NA version. I haven't done a lot of research but what does Sonex say? You would think this would have been solved by now.

Scott,

I think there are 2 big basic differences (1 of which has been addressed by Aeroconversions) between automotive applications and ours in the Aerovee Turbo.

The first is liquid cooling. Our turbo didn't have it initially but now it does through recommended service bulletin for a post-shutdown liquid cooling add-on (which I have installed.)

The second is the fact that I'm running leaded fuel (as I think most Aerovee Turbo users are.) Cars/Trucks these days don't use leaded fuel. TCP is an additive that directly relates to leaded fuel. And while TCP may be a good product to use in non-turbo engines running 100LL, it might not be good for the Aerovee Turbo, is my point. I agree with you that IF this is true (I'm still gathering my own data), it should be/have been addressed already.

The answer to the question of TCP in an Aerovee Turbo may lie in the fact that the TCP documentation states that it is intended for non-turbocharged Continental and Lycoming engines. I have not been able to determine WHY the documentation reads that way.

For what it's worth, the Aerovee Turbo manual does not make any statement on TCP (i.e. it's not recommended or discouraged.) I was using it mostly due to testimonials on this forum and elsewhere to the benefits of using it when running 100LL in our various engines.

Thanks Ryan. Good stuff. I use TCP in my 912 on my Kitfox. I've been running an AeroVee on my little Biplane for many years but just run it on straight Avgas. Its WAY overpowered so I always have it pulled back. I usually flight plan 3 gal/hour so its REALLY loafing.

The lead makes sense I suppose. I wonder if there is any published results of disassembly and close inspection of frozen ones? That could reveal a root cause. But then the Rust theory also makes sense due to it appearing more of a problem after sitting a few weeks. Hmmm...

Its such a simple solution for more power. I hope we get it sorted.

I'm showing my age here but what the heck. Back in the 50's and early 60's Shell advertised TCP was added to their gas, for I would assume lead scavenging. I also remember reading that the TCP caused a byproduct that rotted exhaust systems, back then you needed to replace every couple years or so. Same thing could be happening today in your Aerovee.

I believe the additive Shell used was HTA.
The jingle was: “it’s that funny little let down when you put your foot down. That’s what HTA is all about.”
Or something to that effect...