Tips to install an oil cooler

Paul McBride, an expert on engines, retired after almost 40 years with Lycoming.

Q: We have a Citabria 7ECA with a Lycoming O-235-C1 engine. We live in East Texas, where summers are very long and very hot. Even with an external oil filter with a blast air tube, the oil temps push 220°+ on normal altitude flights, even when babying the air speed and climb rate (which means that we need to climb to pattern altitude to get from cruise to landing configuration. Not really, but the old joke does illustrate the point.) We think we need an oil cooler.

We note that the O-235-K2C, which is externally similar to the C-1, does have the requisite oil cooler. American Champion has drawings for oil cooler installation on the ECA so getting the airframe outfitted should be easy. We note that the accessory case on the C-1 has the bosses where the oil cooler lines would attach if one were to be installed as is done on the K2C version. The bosses are, of course, not bored or tapped for fittings like the K2C. We accept that the internals of the K2C differ from the C-1 in sufficient degree to make an engine conversion impractical.

Would it be feasible/practical to change the accessory case to a K2C case and hook up an oil cooler per the drawings? What kind of paperwork drill would be involved?

BILL TALUTIS, Murchison, Texas

A: Here’s a good question for any of you who have a Lycoming engine that does not have the accessory housing machined to accept oil cooler lines. This was quite common on several models of the O-235 series and was primarily done to reduce the cost of manufacturing by Lycoming and a lower purchase cost for the airframe manufacturer.

Remember, it’s the airframe manufacturer who must keep all engine operating temperatures within the limits set by Lycoming, so if the airframe manufacturer could keep the oil temperature within the specification without using an oil cooler, then one wasn’t required. This is just one of many things the airframe manufacturer has to establish during the certification process. If the manufacturer can’t keep the oil temperature within the spec, then a cooler or some device to keep the oil temperatures within the requirements is required.

For those who reside in warmer climates or who may be seeing oil temperatures that come close to the maximum of 245° F and want to install an oil cooler, it is possible even on those accessory housings that are not machined for oil cooler lines. This may be done by installing an adapter, Part Number 62416, which mounts where the pressure screen is mounted on the current accessory housing. I’d suggest getting a copy of Lycoming SSP-885-2, dated February 2003, and refer to page 8 of 12 for a sketch of the components. Depending on the engine to firewall clearance, you can probably even mount a full flow oil filter to this adapter. If there isn’t sufficient clearance to mount the filter, then I’d recommend installing the screen housing Part Number 69510 with the appropriate oil pressure screen and gaskets, which permits using an oil thermostatic by-pass valve (vernatherm valve) rather than the spring and plunger currently used with the single port housing and screen. If you decide to go this route, make certain you remove the spring and plunger from the accessory housing located at about the 11 o’clock position on the accessory housing under the screen housing. Failing to do this will cause the vernatherm to be inoperative because the mechanical spring and plunger will override it.

I think this is a relative easy way to solve the condition you explained and contacting the airframe manufacturer for additional information regarding the specific oil cooler and lines it recommends should be all that’s required to complete the job. Don’t forget to complete all of the necessary paperwork required for our friends at the FAA. Before and after pictures are also good to have with the aircraft paperwork.

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