Cessna 150j mogas STC needed?

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Neal Wilkinson

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I fly a 1969 Cessna 150j with the continental o-200. Is a mogas STC, such as the Peterson required? I've *heard* that if the engine was originally certified for a lower octane fuel, a stc isn't always needed, if the original fuel placards around the fuel caps are there and not ones staying 100ll.

I've got a *Lycoming* service bulletin(I know I know, a Lycoming isn't a Continental) si1070ab, that shows engines such as the I0360 and I0540 being approved from Lycoming to run on 93 octane automotive gas, but haven't been able to dig up a similar service bulletin from Continental. I know there are stc's available, but I don't feel like that necessarily means one can't run mogas without it. Any input?
 
Neal Wilkinson said:
I fly a 1969 Cessna 150j with the continental o-200. Is a mogas STC, such as the Peterson required? I've *heard* that if the engine was originally certified for a lower octane fuel, a stc isn't always needed, if the original fuel placards around the fuel caps are there and not ones staying 100ll.

I've got a *Lycoming* service bulletin(I know I know, a Lycoming isn't a Continental) si1070ab, that shows engines such as the I0360 and I0540 being approved from Lycoming to run on 93 octane automotive gas, but haven't been able to dig up a similar service bulletin from Continental. I know there are stc's available, but I don't feel like that necessarily means one can't run mogas without it. Any input?
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George's answer is correct...you need a Supplemental Type Certificate to deviate from the TCDS. As far as the Lycoming service bulletin, the bulletin authorizes the *engine* to burn auto fuel, but the STC is required for the airframe as well.

Ron Wanttaja
 
Your insurance company or FAA may inform you of the error of your ways at a most in opportune time.if the fuel has no approval basis then it’s not approved.

Stickers , tags and 337s relieve the mfg of much of the liability; if any.
So the STC is sort of a CYA for all concerned.

There is more to fuel than just octane. Certain refinery practice can result in some contamination of mo-gas that does not happen with av- gas. Since mo-gas in your car has a high turnover rate it can be readily diluted and not noticeable.

Since the STCs have been with us about 40 years there are folks that are probably operating with technically unapproved fuel. The original STCs specified use of a PARTICULAR fuel meeting ASTM D-439 iirc . I don’t believe that product is available in 2022. I believe the STC Holder will provide new stickers but I’m not sure if there is a charge,

That still leaves the 337s showing a non-available fuel. Do they have to be redone or is it ok to use a superceding product?

The very last line of every Mo-gas 337 I’ve done or seen states;
“ It is the OPERATORS RESPONSIBILITY to assure the fuel meets ASTM xxxx”.

There is no free lunch here. If you are going to use mo-gas please familiarize yourself with the needed testing, handling requirements and storage limits.

Good & bad; it’s not av-gas.
 
Avgas has a lower vapor pressure than Mogas. To get that, the mix is different. That Mogas mix was found to be incompatible with some of the older polymers used in aircraft fuel systems, so that ASTM spec was necessary to avoid having the fuel eat your rubber lines and seals. And ethanol is definitely out.

The higher vapor pressure of Mogas raises the possibility of vapor lock and engine failure, especially in low-wing airplanes where the engine-driven pump pulls on the fuel to lift it. Pulling on it lowers the pressure on it, which lowers its boiling point, and if it boils you get vapor lock. So approval for the airframe is also necessary.
 
Thanks all for the input. I'm aware of the chemical differences between mogas and avgas. I'll look into what standards the STC requires the fuel to meet. If I did eventually get an STC, it would definitely be ethanol free. I've also heard that some stc's will come with a few fittings that need to be replaced due to fuel comparability.
 
Neal Wilkinson said:
Thanks all for the input. I'm aware of the chemical differences between mogas and avgas. I'll look into what standards the STC requires the fuel to meet. If I did eventually get an STC, it would definitely be ethanol free. I've also heard that some stc's will come with a few fittings that need to be replaced due to fuel comparability.
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No.

All the STCs available require ethanol free. Nearly all the STCs are purely paperwork. The only one that requires any fuel system changes it the one for the Cherokee (which requires a new fuel pump, not just "fittings"). I spent a lot of time talking to Peterson about Navions. Just because an engine is approved doesn't mean the airframe is and vice versa. Vapor locking with autogas is a significant problem.

There's been some research into allowing ethanol as a fuel purely as an experimental thing. These indeed require you to worry about things like aluminum fitting corrosion (ethanol is hydroscopic) and rubber swelling.
 
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