low oil temps

In my RV6A, O360, fixed pitch cruise prop, last Nov/Dec I flew a couple times and did not see the oil temp get above 140. Mostly in the pattern and low power local sight seeing. OAT was 30-45F. I bought an oil cooler shutter to put on the oil cooler to block the airflow for these type situations, but have not yet installed same.

I am now thinking I don't now know enough about what I don't know now to know whether or not I know now how a vernatherm should now work.

About what temp does the vernatherm open.
Just exactly what does the vernatherm do to regulate oil temp?
Since the vernatherm should be mostly closed, (blocking the oil flow to the oil cooler) How much difference will an oil cooler shutter make?

Is the oil cooler actually the culprit here??

vernatherm should open at 185* However, it does not completely block the flow of oil through the cooler. The design does not provide a positive closure of the cooler circuit, presumably to keep some oil flowing through the cooler at all times to prevent thick oil from blocking the small passages at very cold temps.

What you experienced is typical in lycomings. I usually can't get my oil above 140-160 in the winter, depending upon ambient temps.

Larry

Dan Horton posted an excellent schematic diagram and explanation of how the oil flow path, that may be found here:

http://www.vansairforce.com/community/showthread.php?t=45548&highlight=oil+cooler+schematic.

As noted by Larry the vernatherm allows some of the oil to circulate through the cooler even when temperatures are colder. If you live in a cold climate you need to block the oil cooler in winter if you want the oil to get warmer than 140-150?F. Cessna for example actually made a "winterization plate" for this purpose.

Heavy aluminum foil adhesive duct tape works for this. Tape over the side of the cooler exposed to ram pressure. Leave a small opening 1/4" to 1/2" inch and make a test flight. Adjust the coverage as necessary when you're back on the ground.

Calibrate yout OT sensor and readout

I have found all above comments to be true. My winter temps were under 150F. Completely blocked cooler yields no gain in winter and maybe 180 summer. I finally spent the time (and effort) to remove the sensor and put it in boiling water. It was 20F low ! So, The Vernatherm does regulate oil temp pretty well in summer and a blocked cooler helps a little in winter on my 7:1 0320.

In my -4, I used to block the entire oil cooler (before I installed a shutter). Initially, I blocked the cooler on the down stream side (with respect to airflow). It was much easier to install and remove, but only marginally helpful in increasing the oil temps. Blocking the cooler on the upstream side was much more effective. I had sufficient leaks around the block so no special opening was required. It worked ok, but the first warm day of spring, it had to come out.

Later, I installed a shutter from Van's. (Again, on the upstream side.) It's quite effective at moderate temps. At temps to 90F, oil temp never goes above 190F (with the louvers fully open). For cold weather operations, I can maintain 160F down to about 0-10F OAT. Below that, I don't typically fly.

For my installation, I am not able to get to 180F oil temp when it is very cold outside. (And that's assuming I start with pre-warmed oil (60-70F) - warmed by my oil sump pad heater.

Good luck,

Dean Pichon
Bolton, MA

Thanks

Thanks to all for the advise and education. I think I am going to add the shutter, but probably on the downstream side. I think I can get it pretty flush but on the upstream side I would have to trim a bit more off the cooler to go around one leg of the eng mount.

Dewey,
You can save youself a lot of effort by just using HVAC aluminum tape from your local DIY store. As others posted earlier, cover up 1/2 to 2/3 of the pressure side of the cooler.

Its a 10 minute job.

I used to take my tape off in the summer. Did not this past summer and it still never went above 180F on the hottest day.