What is the procedure for a hot engine start?

Q: I have a Grumman Yankee Model AA-1 with a Lycoming O-235L 108-hp engine. What is the procedure for a “hot engine” start? When I shut down the engine, I run it lean at 1,800 rpm for about 10 seconds before I pull the mixture. Then, when the engine is cold, it starts right away. However, if I stop to refuel on my way to the hangar, it is very difficult to start and I don’t like cranking for a long time for obvious reasons. Would you be kind enough to advise me as to the proper procedure?

CARY MATHIS, via e-mail

A: Cary, this subject usually causes me to ask more questions about specific situations before I even attempt to provide an answer. I’m somewhat at a loss because you didn’t provide your engine age or history, which may provide a few clues, but let me throw out a few thoughts on the subject to see if they might help.

First of all, I’d recommend you review the airframe manufacturer’s Pilot Operating Handbook (POH) for specific “hot start” procedures. These, as well as normal starting procedures, may vary from aircraft to aircraft, making the POH the best source of information for any specific aircraft. However, some of the POHs may not explain why certain procedures are used in the starting process.

Your shut down procedure is fine and should cause no problem in restarting the engine.

You failed to detail the starting procedure when the engine is hot, but let me offer some thoughts. Since the engine has been run and is probably close to its normal operating temperature, you may not need to prime it. However, if you feel there is a need to prime the engine, it can best be accomplished using the primer system versus the throttle.

This brings up another question: Is your engine equipped with a carburetor that incorporates an accelerator pump? Not all O-235-L series engines have them and this, again, is airframe manufacturer specific. If your engine does have an accelerator pump, then this may be used to prime the engine by pumping the throttle two to three times from idle to full open, then back to 1/4 throttle while turning the engine through using the starter.

You must use caution because excessive priming using the throttle may cause flooding of the carburetor and airbox, which could result in a fire in the induction system. If you suspect there is flooding, then open the throttle and close the mixture and turn the engine over several times with the starter to clear it, then begin again with a normal start procedure.

There are a few more things you may also consider just in case they have not been checked recently. Check magneto to engine timing and spark plug condition and gap. Is there a possibility that the magnetos are not of the latest configuration? I’d suggest you ask your maintenance facility to research any and all Service Letters, Instructions, and Bulletins that may apply to your magnetos. Another thing that comes to mind is Lycoming Service Instruction 1068A and its Supplement No. 1, dated March 17, 1997, regarding tappet clearance, which is often overlooked but, none the less, important for the O-235 series engines.

I also recommend you contact the Grumman American Yankee Owners Group at AYA.org to see if other owners have experienced the same condition. An organization like this can be a wealth of information and, since I believe you are not the only person to experience this, the answer may be one e-mail away after contacting this group.

Hopefully, this will get you “started” and it will end up being something simple that may have been overlooked.

Paul McBride, recognized worldwide as an expert on engines, retired after almost 40 years with Lycoming. Send your questions to: AskPaul@GeneralAviationNews.com.

Comments

  1. Steve Lewis says:

    I have a fuel injected Continental, notoriously difficult to hot start, but quite a bit different from the O-235. When I talked to my mechanic about the hot start difficulty (he has an aircraft with the same engine) he told me, just start it, don’t mess with it.

    Here’s the hot start process that works every time – I’ve hot-started several strangers’ engines to get them going at the fuel pump the same way. Use normal shut down, from idle, with mixture to lean cutoff. Mixture – leave it alone at lean cut off, don’t move it at all until the engine fires. Throttle – 1/4 open. Crank engine. When engine first fires, quickly advance mixture to rich. Engine running with 10 seconds of cranking. So much for the old-wive’s tale that a properly shutdown engine won’t fire when turned.

    I’d warn against the fuel shutoff technique. Running the fuel pump out of fuel is hard on it – fuel is it’s lubrication.

  2. John Mackay says:

    With an injected IO-520 I always assume the lines will be vapor locked, so I intentionally flood the engine, then crank with mid-throttle and mixture cutoff until the engine starts to fire, adding mixture to complete the start. Works every time, but I’m going to try the fuel selector-off prior to shutdown mentioned above…

  3. John Weiland says:

    About the hard starting Lyc 0-235. I had the same problem on an older model 0-235. When it got hot it would not start until it cooled down. The problem we found was the mag. coil in the left mag. It would change resistance when hot an not provide a hot spark.
    Thanks

  4. Robert Towe says:

    SlickStart by Unison solved all of our hot starting problems in our TIO-540 Lycoming w/7.3:1 compression. Also, replace points and re-time mags at every annual. Also, Skytec NL149(EC) starter works great…

  5. Andy Reinach says:

    I’d like to offer my response to a hot engine start. If I know I’m going to have a quick turnaround after engine shutdown, this is what I do.

    I throttle up to about 1,500 rpm then I turn the fuel selector to ‘off.’ By doing this, you use the fuel in the line and, when that is gone, the engine will shut off. This basically eliminates any vapor lock on restart, the typical cause for hot start issues.

    Hot start procedures using this shutdown method should proceed as if the engine was cold. It’s worked for me countless times.

    Have you ever tried this method? Thanks.

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