Cold Starts on TCM IO-550s: Should I Believe the POH?

[Jeff_S]

So here's one I just ran across, thinking about the colder temps coming eventually. Atlanta isn't a real problem area in this regard, but we do get the occasional evenings into the teens in the mid-winter time.

 

The general guidance I've always seen is to pre-heat below 20°F.  Some folks argue doing this even below 40°F. But the Ovation POH says, and I quote: "For engine operation at outside air temperatures below -25°C (-13°F), the engine and engine oil should be preheated to at least -25°C (-13°F) before the engine is started."

 

Wow! Mooney is saying that it's okay to start these engines at sub-zero temperatures. Does anyone have an explanation why the POH would use guidance that seems much more liberal than even the engine manufacturer?

 

Just curious...

[Hank]

I suspect a typo. When I lived in WV, everyone preheated in the winter. I bought a cellular preheat switch from Philip here [look in Vendor Forum] so that I could stop driving to the airport to plug in the night before, then sometimes drive back an unplug for a canceled flight. Normally started around 40ºF/5ºC. Or I could plug in and wait for an hour . . . but I have a Lycoming, not a Conti.

[carusoam]

100LL doesn't evaporate well, when below 20°F.

People with a C know this because their arm tires from pumping the throttle so much on cold days...

The POH is written mostly for operations.

MS is most often written for handling properly for our economics.

With a dial up preheat system, turn the heat on when it is 40°F because you can.

Any time below 20°f is because you have too.

-25°C? They must have been confused by the metric system.

Scan the page, send it to Stacy? This way he can get it put it in the system for updates...

Best regards,

-a-

[Txbyker]

100LL doesn't evaporate well, when below 20°F.

People with a C know this because their arm tires from pumping the throttle so much on cold days...

The POH is written mostly for operations.

MS is most often written for handling properly for our economics.

With a dial up preheat system, turn the heat on when it is 40°F because you can.

Any time below 20°f is because you have too.

-25°C? They must have been confused by the metric system.

Scan the page, send it to Stacy? This way he can get it put it in the system for updates...

Best regards,

-a-

 

I do as Anthony says and just start normally after preheating.

 

Russ

[Cruiser]

my 1999 POH says the same thing. 

 

The Continental engine manual says; "Engine preheating and an auxiliary power unit (APU) are required to facilitate engine

starting when the engine has been exposed to temperatures below 20ºF (-7°C) for more

than 2 hours. Refer to Section 4-5.1.1 and the AFM/POH for specific instructions. At

ambient temperatures between 20º and 40ºF (-7º and 4ºC), refer to Section 4-5.1.1.3.

WARNING

Failure to properly preheat a cold-soaked engine may result in

oil congealing within the engine, oil hoses, and oil cooler with

subsequent loss of oil flow, possible internal damage to the

engine, and subsequent engine failure."

[kortopates]

Clearly a typo since -25C does not equal -13C. I'd check with the factories Pubs list to see if your POH has all of its updates/revisions. Then go from there to get a missing until date or ask them.

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[aviatoreb]

Don't do it!  Preheat below 40f.  For longevity of your engine.  Remember your POH doesn't care about longevity.  It also says your redline is CHT 475F.  That is not good for longevity - it just says your engine won't melt down on the spot or detonate.

[Guest]

Scuffed piston skirts and spalled valve lifter faces should be all the proof required for pre heating the engine. I use 40 degrees as the threshold.

Clarence

[Jeff_S]

Clearly a typo since -25C does not equal -13C. I'd check with the factories Pubs list to see if your POH has all of its updates/revisions. Then go from there to get a missing until date or ask them.

Sent from my iPhone using Tapatalk

 

I have sent a note to Stacy and haven't heard anything yet. I will check to see if there are any updates to the publication. But just for the record, the calculation for F to C is actually correct:  -13 - 32 * 5 / 9 = -25.  So they didn't get their math wrong, but perhaps the whole philosophy is misguided.

 

I will keep digging into this and report back what I find. Thanks all.

 

Jeff

[kortopates]

I have sent a note to Stacy and haven't heard anything yet. I will check to see if there are any updates to the publication. But just for the record, the calculation for F to C is actually correct:  -13 - 32 * 5 / 9 = -25.  So they didn't get their math wrong, but perhaps the whole philosophy is misguided.

 

I will keep digging into this and report back what I find. Thanks all.

 

Jeff

You're right of course on the math - my mistake. Yet your POH is clearly very wrong on this. Mooney is obligated to follow TCM's technical guidance - they provide a Operations Manual and issue service letters to clarify and expand on many issues. In this case, TCM issued SIL03-1 back in 2003 for their detailed guidance which is really the authority on this topic. You can get it here: http://www.tcmlink.com/pdf2/SIL03-1.pdfYou'll see as Cruiser already pointed out, they advise using pre-heat from 20F and below but many pilots, especially those paying the maintenance bills, will be far more conservative and start considering pre-heating at below 40F. 

[Jeff_S]

So I got a reply from Frank Crawford at Mooney Support, and he acknowledged that the POH also points to the TCM owners manual for guidance, and sent me a copy of what we already knew, namely, TCM says to preheat below 20dF.  He did also say they were looking at whether they should remove or revise that part of the POH.  So I wonder if this is the first time anybody ever looked at it, or if they just forgot about it.

 

Anyway, we have debunked the -13dF recommendation as a clerical error.