Switch to full style
A place where restoration project-type threads can go to avoid falling off the main page in the WIX hangar. Feel free to start threads on Restoration projects and/or warbird maintenance here. Named in memoriam for Gary Austin, a good friend of the site and known as RetroAviation here. He will be sorely missed.
Post a reply

Pre-heating oil in a Stearman

Sat Dec 20, 2014 3:46 pm

Hello chaps!

I have been tasked with the enviable job of 'looking after' a beautifully restored 1946 Stearman. She is kept hangared and the temperature in the hanger never gets below freezing but it does get down to about 5 degrees Celsius in the winter.

A colleague has suggested that to avoid the 20-minute wait after start for the oil temperature to get above the minimum of 30 degrees Celsius needed for the run-ups I install a heated pad to the bottom of the oil tank. Another option seems to be a heated 'dip-stick' that could be temporarily inserted into the tank itself.

I understand the rational of already warming the oil but at the same time I wander if there is any benefit. If I heat the oil to 40 or 50 degrees C, but the engine is at an ambient 5 degrees C, the won't the oil just be cooled back to ambient in the first 5 minutes or so of running the engine?

My questions are these:

Have any of you had experience of using such a system to expedite the warming of the oil system?

Have you had positive or negative results?

Do you have any recommendations?

Thank you in advance for your thoughts.

Tin O' Beans.

Re: Pre-heating oil in a Stearman

Sat Dec 20, 2014 6:08 pm

I use a Reiff hotpad on the sump of my RV-6 (which obviously has a flat, cowled engine). Even on 10F overnights (we get those occasionally), an overnight preheat will get the oil to 100F+ and the CHT's are 80-90F as well. Obviously, the cowl and smaller engine help, but I would think you could drape the engine on a Stearman with a blanket to hold more heat in and get a useful temperature rise.

The good thing about preheating the oil is that it will be thin enough to pump, so the pressure galleries will at least get some oil to lube the crank and other pressure lubed parts. And, yes, the oil may cool off pretty quickly, but at least you've got some oil where you want it.

Re: Pre-heating oil in a Stearman

Tue Dec 23, 2014 8:13 pm

It's very important to pre-heat the engine and oil. The first 500 rpm the engine turns is the most critical for engine bearing longevity. The warm oil flows so much better, remember it's 60 weight oil. Without warming the engine, the fuel will not vaporize and it will wash oil off of the cylinder walls before startup.

Re: Pre-heating oil in a Stearman

Tue Dec 23, 2014 8:44 pm

There's a third time-tested option that no one has mentioned yet.
Drain the oil after putting the airplane in the hangar(Placard the airplane heavily!!), and keep the oil in a heated space until next flight.
Refill the tank before flight with warm (well, warmer at least) oil, and off you go.

If it worked on the Ostfront...

Re: Pre-heating oil in a Stearman

Wed Dec 24, 2014 3:56 pm

The important thing is to heat it with something, anything, somehow. As was stated, that first bit of cold-start engine running does all the damage.

Most radials use 25w60 oil. It's great stuff, but as you may know from adding it to the engine at freezing temperatures, it's very sluggish until it gets to 20C or so. Sure, it's multi-grade, but there is quite a visible difference between adding a quart of it versus 20w50.

So, I preheat anytime the temp drops below 10C. What I use is simple and cheap and effective.

Look at this thread, page 18. I have 2 of them in use, one on the oil tank, one on the crankcase from the front. http://warbirdinformationexchange.org/p ... &start=255


As you can see, it's a $15 hair dryer attached to a tube, held in a simple frame. This blows on the oil tank and also warms up the mags and the back of the engine. After about 30 min, a 3 gal oil tank is up from 5C to 15C.

It works.


Re: Pre-heating oil in a Stearman

Fri Dec 26, 2014 8:23 pm

Thats a nice and simple idea Dave! Might try that myself (if I ever get my project finished!!)
Post a reply