Warning about Decalin

[kevin814]

In the interest of possibly saving someone from engine damage or a dangerous situation, I just wanted to let others know about my experience with Decalin (used with avgas to help prevent fouling and lead build up in the cylinders). I bought a bottle and added it to my fuel tank before refilling. During full throttle climb out it seemed the power was down and the engine seemed to miss. Also while I was trying to diagnose the problem I would open the throttle during level flight, and the engine seemed to miss and the EGT's went through the roof! I thought it may be running to lean, so I also tried pulling the primer (Rotec TBI) during full throttle. Hmm.... even with extra fuel it was still "missing" and EGT's shot up. I thought this may be due to a fuel restriction or clogged jets, and flew it a few more times trying to diagnose it. Then I remembered it started about the time I used the Decalin. I pumped the fuel out, and put in straight avgas and the problem disappeared. In hindsight the engine (Jabiru 3300) was severely detonating (pinging). The information I've read about Decalin says it won't reduced octane, and that it only becomes active during the moment of combustion, but in my case the detonation was extreme. Hopefully I didn't do too much damage to the engine. I've tried Techron fuel system cleaner, and that also caused detonation. Now I avoid fuel additives like the plage, and have also had good luck with Mogas.

Just wanted to share my experience....

Kevin K.

[DCASonex]

Kevin,

Thanks for the heads up on this. Have never used it, but was just thinking of starting to.

David a.

[kmwoody]

I have been using Alcor TCP fuel treatment for the last 50 gals. or so and have not had any problems.

Ken W

[vigilant104]

I just bought some and haven't started using it yet. I'm surprised by Kevin's report as Decalin is fairly widely used and I'm not aware of a ot of other folks having detonation trouble. The USAF uses it in their ROTAX-powered UAVs, and the same active ingredient is in TCP, which is approved for use in Lycoming and Continental certified engines to reduce lead fouling.
Kevin, thanks for the input. What mixture rate were you using (ounces of Decalin per gal of fuel)? And what is the compression ratio on your engine?

[LarryEWaiex121]

Been using decalin in my 3300 for the last 350 hrs and seems to be doing what it says. Tops of pistons are beige colored with egt's fully in the normal range.
I seriously doubt that the reported readings have anything to do with the Decalin. I'm not suggesting what the problem is, just that I really, really doubt the decalin is the issue.
By the way, the recommended amount per gallon is very small. Being at work I can't tell you the amount but its like maybe a quarter ounce in 10 gallons or so .

Larry
Waiex 121YX 385 hrs.

[Ray Krause]

From Ray Krause.

The recommended rate for Decalin is .5 oz per ten gallons of fuel! Please read the label, do not use a whole bottle per tank!

I have been using it at the recommended rate for maybe 300 hours and it works great. My cylinders are clean, as evidenced by boroscope inspection. At 32 Ozs/17 gallons, you are lucky the engine did not stop! I hope it was not detonation, as that would damage your engine.

Good luck,

Ray Krause
Waiex N51YX, 430 hrs, Jab 3300.

[kevin814]

I believe my compression ratio is 8.5 to 1, but I'm not sure on that, I remember seeing that Jabiru did lower the compression on later engines. I had mixed the decalin as directed using the measurement on the bottle, I think I used less than an ounce. Its possible that it wasn't due to the Decalin, but it did start running properly again when I changed the fuel to pure avgas again. Perhaps my engine is more sensitive to octane, I had hoped to use it to reduce deposits. Lately I've been using auto gas, and the engine seems to run well.

Kevin K.