80 VS 100 OCTANE

100LL vs 80 OCTANE... (12199)
From: Don Cumpston <>
My swift has a C145 in it that at overhaul had 6 new superior cylinder asy's installed. We only have 100LL at AXQ. Should I use TCP in the fuel? When I am at other airports that have 80 octane available should I use the 80 or 100 ? Don Cumpston <>

Use TCP whenever you use 100LL. The 7 to 1 compression ratio of the O-300 will not scavenge all the lead. Buy 80 whenever possible.

The following discussion regarding TCP is from the Yahoo! Globe Temco Swift Club message board...

When everybody was fueling up for the trip home from Westover this year I saw a couple guys put in TCP with the 100LL. What was interesting about it was that they had Cont. 210's. Why would you need TCP in an engine designed to run on 100LL? Keith Bracht <>

The short answer is: It can't hurt! TCP scavenges lead out with the normal combustion. Even using TCP with 80/87 keeps the engine cleaner, especially when an occasional load of 100LL is used. -- Jim

Swifter Steve Roth <> adds...
Right Monty, even Alcor TCP supports your statement. Alcor has the measuring syringe graduated for 80 Octane proportions. TCP makes a difference. I have seen it with my own eyes. For a long time while I was in Tampa (TPF), the airport had two separate compartments in the fuel truck -- 100LL and 100LL with TCP. I was driving a 1959 C-172 with O-300A. I got the TCP version all of the time. I know what my plugs looked like. Then, they quite putting TCP directly into the fuel trucks; I was lazy and did not use TCP on my own. My plugs started getting "rocks" of lead deposits inside the plugs. Made a difference. I tried to tie the use of TCP to my problem of valve sticking in that O-300A but it seems there is a "God of Valve Sticks" and only he decides when a valve will stick. Using TCP can't hurt, for sure. That's a whole nuther subject, though, fraught with voodoo. Steve

The following was posted by Swifter Steve Wilson on the Yahoo! Globe Temco Swift Club message board. Most of you know Steve's credentials but for those of you who don't, Steve's day job is with a group you might just be familiar with that has the initials NTSB...

Tricresyl Phosphate (TCP) works like Monty and Steve say, but a word of caution. You should be aware that the substance is noxious and is transdermal with serious complications for your innards. This means that you don't want to get it on your skin, eyes, etc., at any cost. Fumes are a serious health risk also. Not to mention that the stuff has the potential to be extremely explosive under certain conditions. Sooooo, what worries me is carrying it in an airplane. In fact, if you read the label Alcor warns against carrying it aboard the airplane. Actually, that recommendation came about due to a can exploding inside a C-172 with two fatalities. Using it in your hangar, with latex gloves, maybe a respirator, and good ventilation, it works as advertised, but the potential hazards must not be ignored.

I use Marvel Mystery Oil (MMO)in my Avgas. It is NOT FAA approved and it has NO scavenging properties, but adds a little upper cylinder lube which works well against the ravages of 100LL in the low compression engines designed for 80/87. As for the safety aspects of MMO, you could probably take a bath in it (that's a joke...not recommended, but at least you would smell like wintergreen). While carrying it in the airplane it presents no more hazard than an extra can of oil. --  Steve

From: Ron Natalie <>
Just looking through your article on OCTANE. I should point out that there is some dangerous information in your part marked "Dark side of TCP." Latex gloves are entirely inappropriate for TCP, it will go right through them. Nitrile gloves are what is recommended.

MONTY LIKES TCP... (050200)
Subject: TCP
From: Alan Dicker <>
Hi Jim, Do you recommend TCP for a C145 engine? I haven't been using it in 80733 but wonder if I should. What about for a O300? Thanks. Alan

Oh definitely! Every small Continental, from A-65 thru C-145 should have TCP added to the fuel when using 100LL. I even use few ounces every other tankful or so when using 80. O-300 is the same thing. I don't think TCP hurts anything even on the "big" engines designed for 100 octane.  --  Jim

From: Richard Aaron <>
Subject: Re: TCP
I just read the comments on TCP from Ron Natalie. I've always found it difficult stuff to handle without dripping or spilling, even with the plastic syringe that you can get for it. The syringe eventually deteriorates too. The latest scheme that I've tried, which seems to be working out well, is to use an old fashioned metal oil can (straight spout, no pump) filled with the TCP and a small graduated plastic beaker. I'm using a nail in the tip of the spout as a closure but am looking for a suitable plastic cover. Once the TCP is in the can, it can be dispensed quite neatly. Regards, Dick Aaron N2405B

Subj: Re: N77759
From: Jerry Swartz <JSw7211963>
Jim:  Prior to the new TCM cylinders installation, I had been running Marvel in the gas. What is your feeling on the continuation of using it? Is there some other additive that would be better?? Jerry S.

It won't hurt anything. TCP scavenges lead deposits out of the cylinder. Marvel seems to add to the top oiling of the cylinder as well. TCP is FAA approved, Marvel just seems to work, although its benefits are largely anecdotal. Marvel has been around since the '20's. I had an FAA inspector ask me once, "Tell me, man to man, do you use Marvel Mystery Oil?" He replied in the affirmative. He said, "Yeah, me too, I wouldn't run an O-300 without it. Any big aircraft supply place has TCP. Aircraft Spruce has it for around $44/gal + shipping. I looked in TAP on Pg.11 and Aircraft Supply has it for $44.80/gal. Many FBO's have it also. -- Jim