LOP - too cold!

Phase 1 is finished. During phase 1 I had oil temperatures that were higher than I wanted. I replaced the Niagra oil cooler with the SW 8406R and got some relief. I also opened the cowling exit area slightly. Other than that, I decided to let the engine get more time on it and not make any more changes until next summer -- if I need to. OATs during phase 1 were 55-80F.

So imagine my surprise when I went flying the other day with an OAT of 35-40F. I found that I couldn't operate LOP very long because it made the engine too cold! With CHTs all in the 280-290F range, the oil temperature stabilized at 165F. Yeah, I know that's in the green, but it's lower than "optimum". I now have visions of having to install a cockpit-controllable oil cooler air-flow blocker -- even though there should be very little oil flowing through the cooler below 180F.

I'm beginning to think our modern engine instrumentation might be a tad bit excessive in some instances. The old "lean until rough, then enrichen slightly" and "as long as the oil temp is in the green band it's okay - if the gauge is even accurate" methods sure seemed to work fine for a lot of years on a lot of engines...

-Geoff
RV-8, 44 hours

P.S. 35F OAT in a plane with no insulation is a little chilly, even with the heater running full blast. I don't know how you people who live in cold, snowy places do it!

[petehowell]

Geoff,

Seat warmers built into the cushions are really nice. With heat, some sun and the tushy warmers, flying at 0F is ok until you need to get out an push the plane in.

The oil cooler on my O-320 is completely blocked in a Minnesota winter.

[Guy Prevost]

Geoff,

Thanks for the updates! Since engine setups are almost identical, your site was a big resource for me. At least until it went away . Any chance you'll get it back up?

Cheers,
Guy

[Geico266]

What were your EGT's running LOP? You could keep it warmer by running hotter?

[Geico266]

I'm learning how to run LOP on a new (to me) RV-10 IO-540. Seems to run okay LOP. EGT's around 1300, CHT's a comfortable 300F. Oil is 180F, OAT was 3F or less. Fuel burn was under 10 GPH.

Originally Posted by Guy Prevost

Geoff,

Thanks for the updates! Since engine setups are almost identical, your site was a big resource for me. At least until it went away . Any chance you'll get it back up?

Cheers,
Guy

It's back up. Comcast did a royal screw job on all their customers with respect to personal web pages, and they still haven't sorted out the mess. I think everything on it works -- please let me know if it doesn't. http://home.comcast.net/~n70ge

Originally Posted by Geico266

What were your EGT's running LOP? You could keep it warmer by running hotter?

Maybe a little bit, but not much. I probably could have increased the power another 10%.

EGT absolute numbers don't mean much because there are too many variables with respect to probe installation. However, here is a sample data point from near then end of my LOP that day:

OAT 33F
20" mp, 2400 RPM
Oil temp 168F
Fuel flow 6.4 gph

C1 - 276
C2 - 286
C3 - 286
C4 - 262

E1 - 1314
E2 - 1356
E3 - 1352
E4 - 1342

Contrast that with the same power setting but running approximately 100F ROP:

Fuel flow 9.0 gph

C1 - 312
C2 - 314
C3 - 320
C4 - 308

E1 - 1300
E2 - 1312
E3 - 1310
E4 - 1304


My CHTs always have a much bigger spread when running LOP. Strangely enough, the coolest LOP is always #4, which has the oil cooler hanging on it. That probably doesn't help the issue of having cold oil when running LOP in cold OATs.

I've also noticed that running wide-open throttle reduces the spread between the absolute EGT readings to almost zero, regardless of whether I'm running ROP or LOP. Something about a partially-cracked throttle plate messes with the EGTs.

-Geoff