engine quit on idle after change to 2F

I did my final flight of the season today, and everything ran fine. After the flight I changed the oil to Aeroshell 2F (plus as quart of Vanguard) and did a 15 minute ground run. The oil got up to about 120F. When I pulled the throttle back to idle, the engine quit. I re-started, turned the boost pump on and then idled it with the boost pump on and it didn't quit.
My hypothesis is that the higher viscosity of the 2F provides more resistance to the engine and this resulted in the engine quitting on idle.
Does this seem like a plausible hypothesis, or is it likely I have an issue that will need to be addressed in the spring?

Did it behave as expected during the run up while doing a mag check?

yep, everything was normal other than it suddenly quitting when I pulled back to idle. When I re-started and idled with the boost pump on there was no issue.

I doubt the boost pump changed the viscosity of the oil much. Seems to me that after a 15 minute ground run the undercowl temps could be high enough to cause a little vapor-lock at really low fuel flow (i.e. idle).....the boost pump cured that with a little extra pressure.

Thanks... the plane was actually un-cowled (both upper and lower cowls removed) during the ground run. CHT never got above 350 and EGT barely to 1100... is the vapour lock theory still likely given that data?

prkaye said:

Thanks... the plane was actually un-cowled (both upper and lower cowls removed) during the ground run. CHT never got above 350 and EGT barely to 1100... is the vapour lock theory still likely given that data?

Click to expand...

Yep. Case (oil), barrels, & heads are hot, no cowl, limited airflow - works only with boost pump on - you answered your own question. I would not call it vapor "lock", but certainly hot fuel affecting proper metering.

A 15 minute run uncowled seems excessive, as proven by the 350 CHT. With no organized airflow over the head, I'd expect you got some areas of local heating that went beyond that.

Why so long?

I doubt very much if it was the thick oil.
When you get it cowled... and run again. Report back here how it behaves.
And if the oil viscosity becomes an issue later... put an oil pan heater on it.
I activate mine by Switchbox (cell texting) from home.