Q: Hi Paul, I’m wondering if you’ve ever come across Aztecs with the right engine oil temperature running warmer than the left. I’ve had mine 11 years. The right side oil temperature is usually 190°, while the left is 160°. CHT is usually pretty even.
Mine came with louvers on the right side cowl, and I’ve seen other Aztecs with right side louvers, which made me think this is possibly a chronic Aztec issue.
Now I have two new engines, same numbers. Gauges and probes have been calibrated, bench checked, etc. Any ideas?
A: Now here’s a question that could end up almost anywhere, so let’s give it a shot with the information Don has provided. While I sure could use a lot more specifics regarding this situation, I’ll just take a shotgun approach to some troubleshooting tips that hopefully will lead us to clues to solve the issue.
Before getting started though, I’d like to point out that I’d be pretty happy if both of your engine oil temperatures were around the 185°-190°F mark, providing you’re confident of the oil temperature gauge accuracy.
As a matter of fact, Ben Visser has a great article in the Dec. 20, 2015, issue of General Aviation News that I’d recommend you take a close look at. The article, “Two things you must do to get your engine to full TBO,” offers some excellent advice on how to achieve reaching the TBO goal. The overall information should be of interest to you and how it might relate to your situation.
So, let’s begin and, as I said previously, I’m taking a shotgun approach using typical troubleshooting methods. I’m certain other folks may approach your situation differently, but what I’m going to share will offer some tips that just may help someone else should they encounter a similar situation.
In my book, probably the easiest thing to do first would be to confirm the actual oil temperature in the engine and we can do this by using the old farmer’s method. The old farmer’s method is to simply take an 18-inch glass bulb laboratory grade thermometer and attach a piece of safety wire through the loop at the top about 10 to 12 inches long.
I’d like to have you fly the aircraft and bring the engine operating temperatures to where they normally are during a routine flight. Once you get the aircraft back on the ground and to the nearest ramp where you can safely shut down the engines, remove the right engine dipstick.
Using extreme caution, insert the glass bulb thermometer down the oil filler tube until you feel it touch bottom. Then, just pull it up about 1/2 inch for approximately 20 seconds. Then again, using extreme caution, remove the thermometer and check the reading in comparison to the instrument gauge. The next step is to do the same thing on the other engine.
I can’t caution you enough about using extreme caution when inserting and retrieving the glass bulb thermometer. Failure to follow this caution will allow you to expand your vocabulary and technical skills by learning how to remove and clean your engine oil sump in order to remove the glass and mercury from the thermometer!!
The next thing I’d suggest is simply swapping the oil temperature gauge wires on the gauges behind the instrument panel. This should tell us whether the higher oil temperature stays with the engine or moves with the wire swap to the opposite engine.
If the higher temperature moves to the other gauge, then we at least know which engine is going to require a little closer look to solve the problem.
I’ll take your word for it that the gauges and the oil temperature probes have been checked and calibrated as a system. If so, maybe by swapping the gauge wire, we’ll see some different results if the left gauge is now reading the right engine temperature probe.
Assuming we don’t see any change here and the high temperature stays with the right engine, we’ll move on to our next step. This gets a little more involved. I suggest we swap the entire oil filter adapter housings, including the temperature probe and the thermostatic bypass valve (vernatherm), from engine to engine.
I do not want to remove the thermostatic bypass valve from the oil filter housing it’s mated with because it’s established a mating wear pattern and we don’t want to disturb that. This may tell us whether the thermostatic bypass valve on the right engine is forcing all of the oil through the engine oil cooler or allowing some of the hot oil to bypass directly back into the engine, resulting in a higher oil temperature reading.
It is absolutely required that the thermostatic bypass valve seat a total of 360° against its mating surface in the oil filter adapter. Lycoming Service Instruction 1316A addresses this subject.
One thing that you didn’t mention was whether there is a difference in the engine oil pressures. While I realize the engine oil pressure is adjustable, if they are very close at start-up at idle, I’d expect that we may see a difference during flight when the right engine oil temperature runs 30° hotter than the left engine. Remember, the typical rule of thumb is as the oil temperature rises, the oil pressure will usually decrease. Have you noticed this at all?
You mentioned something about the right side cowl having louvers. I spent a lot of time at the Piper factory in Lock Haven, Pa., where all of the Aztec aircraft were manufactured and, since that’s been a long time ago, I can’t recall whether the louvers were standard or not. I might be able to believe the Turbo Aztec may have had louvers in the cowl to deal with the additional heat from the turbochargers, but I’m sorry Don, I can’t offer any help here.
I think I’m going to quit here on this one, but I feel there is enough information to get you started in the right direction to solve your problem.
As I said early on, other than seeing the 30° difference on the gauges, I wouldn’t be concerned about the oil temperatures because they are well within specification.