Ask Paul: Why is the temperature so high on my left engine?

Q: I overhauled my PA-30 IO-360 fuel-injected engine five years ago. I have flown around 560 hours since overhaul, but have a high temperature on the left engine.

During climb out/cruise the engine temperatures are in the green. The minute I throttle back on downwind, flap and gear, the temperatures increase. On final approach, it starts to go into the band of red and when I land, it’s fully into red and the pressure drops.

I have changed the oil cooler. I have redone the baffles. I have changed the vernathern valve and the oil adaptor and I have overhauled the fuel injector unit.

I am basically pulling my hair out and don’t want to take apart the engine as I have new superior Millenium cyclinders on overhaul and don’t want to upset any seating.

Shakil 

A: Shakil, I’m going to be honest with you and admit that this situation may be a real test of my troubleshooting abilities.

First, I’ve got to ask, if you have a Twin Comanche with a pair of Lycoming IO-360 engines on it, is this a J.W. Miller conversion? The reason for my question is that the standard PA-30 Twin Comanche from Piper Aircraft was powered either by a pair of Lycoming IO-320-B1A engines on the normally aspirated version or a pair of IO-320-C1A engines on the turbocharged version.

The only Lycoming IO-360 powered Twin Comanches were done as a conversion by J.W. Miller in Texas and, if I recall, they offered it both as a normally aspirated or turbocharged version.

Now that we’ve got that out of the way, let’s see if we can’t help you with your situation.

My best guess is that we do not have an oil temperature problem, but let’s see if we can find the problem.

First, I’d like you to swap the oil temperature wires on the back of the cockpit instrument from left to right. If this shows us that the higher oil temperature stays with the engine, then we’ll go to the next step.

I remember years ago while at Lycoming and working with Piper Aircraft in Lock Haven, Pennsylvania, we had a PA-23 Aztec that was doing the same thing you describe. The aircraft flew great with oil temperatures normal in flight, including climb and cruise, but upon descent, the right engine oil temperature would increase and actually get into the red portion of the gauge.

After several days of troubleshooting — swapping the instrument wires, changing the oil filter housing, which included a new thermostatic bypass valve — we hadn’t made any progress.

We also checked the oil temperature in the oil sump by using a laboratory quality glass bulb thermometer — with extreme caution because we didn’t want it to break — which would have caused us to remove the sump in order to remove the glass and mercury and that’s enough to make a grown man cry.

Failing to find the problem, the Piper technicians dug a little deeper and eventually discovered the oil temperature gauge wire that passed through the engine firewall had chaffed through on one side of the wire (very well hidden) which, apparently due to the downward angle of the aircraft, the wire would ground out the gauge, causing it to go full scale.

Since you are dealing with an older aircraft, I’d suggest you conduct a very close inspection of the complete instrument wiring.

Again, if the indication of high oil temperature stays with the engine when you’ve swapped the wires on the cockpit instruments, this also may be a clue there is a grounding problem somewhere in the wiring harness.  

I wish I could have offered more specific corrective action to take, but this sounds like one of those elusive opportunities for your maintenance facility to see how good their troubleshooting skills are. The secret to troubleshooting something like this is to be patient and only do one thing at a time.