Q: May I ask a question regarding our engine in a Cessna 152? When we shut down from flight, there’s a foam or steam inside the engine and it will come out at the breather like water. What is the cause of this and what is the remedy?
Also, what is the hottest cylinder in an IO-540 Lycoming engine?
Mario Bedayo, Italy
A: Here’s a question from an old friend in Italy and it’s interesting to learn that the technical issues we see are quite common worldwide.
Mario, I can tell you from my past experience that the Cessna 152 engine installation does run very cool and this is what I suspect is causing the foaming in the oil filler tube and what appears to be steam or vapor coming from the breather tube.
My suspicion is that the oil temperature is not getting high enough to cook off the condensation inside the engine. As you know, this is not a good situation and steps should be taken to correct this condition.
My suggestion is to confirm the exact engine oil temperature by using a known accurate instrument or by confirming that the aircraft oil temperature gauge has been calibrated. You can confirm the true engine oil temperature by using a glass bulb type laboratory thermometer. These are usually about 18″ in length and have a small eyelet at the top end. This method requires extreme caution or you could end up with a serious problem. Using the small eyelet, attach a piece of safety wire or string so that you can retrieve the instrument safely from the oil filler tube.
First, you must fly the aircraft until all operating temperatures are normal for the aircraft. As soon as possible after landing, remove the engine oil dipstick and very carefully insert the laboratory thermometer down the oil filler tube until you feel it touch the bottom of the oil sump, then pull it back about 1″, allowing it to rest there for about 30 seconds.
Then very carefully remove the thermometer from the oil filler tube and check the temperature of the oil and compare it with the aircraft oil temperature gauge. This information will confirm the accuracy of the aircraft engine oil temperature gauge and also confirm, hopefully, that the oil is not hot enough to cook off the condensation that’s causing the situation that you reported.
Now for the cure, I’d suggest that you begin with closing off a good portion of the oil cooler using some material like duct tape or, better yet, fabricate a piece of aluminum and secure that to the oil cooler. With the current temperatures in Italy, I wouldn’t hesitate to cover the entire cooler this time of year, but not during the hot summer months.
At this point, fly the aircraft and monitor the engine oil temperature closely so as not to exceed the maximum oil temperature of 245° F. I’d like to see the oil temperature during normal operation read 180° F or higher.
I hope this will lead you to the cause of the problem and you can correct this situation by getting the oil temperature in the range that it needs to be.
With cold oil temperatures, we expect to see bad things in the engine like internal corrosion, which can cause things like excessive wear on the camshaft and tappet bodies. If the aircraft is flown infrequently, there could be corrosion on the cylinder walls causing excessive piston ring wear.
With regard to your second question, I cannot give you a specific answer as to which cylinder is the hottest on a Lycoming IO-540 engine. The hottest cylinder is always determined by the specific airframe manufacturer, such as Piper or Cessna.
The reason behind this is simply because each aircraft has a different cowling design and different cooling aspects. The aircraft manufacturer during certification flight testing determines which cylinder is the hottest for that particular installation.
I will tell you that normally on the IO-540 series Lycoming, the number 5 cylinder in most installations is the hottest. Possibly you could confirm this by viewing aircraft installations at your local airport.
Try using speed tape to cover at least half of the oil cooler allowing the oil to get warmer, I’m guessing your oil temp is constantly running cooler than usual, specially during colder months. Please keep in mind this only a suggestion always consult with your mechanic.
I could do is change oil every 25 hours in hopes of getting rid of some water.
Thank God for your comment Henry, I was thinking of buying
a C 152 But now I have second thoughs
Thanks again
Well, all our 152s were flight school ships and piled the time on rather quickly, so all the nasties showed up much quicker than they would for some private owner.
Miami Mike,
Textron did not buy Cessna until 1992. I believe Cessna was a stand-alone company until they were bought by GD who sold it on to Textron. Most likely the switch was done for the extra power/higher TBO/100LL compatibility. But I agree the early engines were a mess and they are still harder to start/require more careful management than the 0200.
The O-235L2C in the C152 IMHO has matured into a more or less bulletproof engine. 2400 hour TBO (though it’s pricey to overhaul compared to O-200) and the extra horsepower is noticeable. The 152 did have a few improvements over the 150 including a bit more room in the cockpit and better performance overall.
Henry, very interesting about your solution to the hard-start/oil temp/lead fouling issues, and innovative.
Thanks,
Don
I think the O-235-L2C was developed from other tried and true 80/87-eating O-235 engine models for the reason that Big Oil was phasing out 80 /87 red AvGas. Very few airports had it. So, the L2C was designed to eat 100/130 and 100LL. Sort of. If you wanted to fly, you bought 100 gas or nothing. No MoGas STCs had yet been developed.
The phase-out of 80/87 caused a load of problems. TCM engines from the A-65 up to the O-300 started burning intake valves. I was yanking O-200 jugs off about every 250 hours, where as before, pulling the jugs was a rarity. You can grid an intake seat only so many times! The O-320 started eexperiencing stuck valves and bent pushrods. I had a “field fix” for this, but you had to hold your mouth right when doing it. The C182 O-470 loaded up with lead and carbon, and burned more oil. The L2C was a nightmare, as I described in a prior missive. No amount of Alcor TCP (was that what it was?) or Marvel Mystery Oil helped.
The difficulty arose when they switched from the wood-burning steam engine (as in my 150) to the coal-burning steam engine in the 152. They never did get the steam pressure (or something) calibrated correctly.
The reason for the switch was that Textron owned both Cessna and Lycoming, and some junior assistant blame shifter noticed that Cessna was buying engines from Continental, a direct competitor of a business they owned (Lycoming). They also made the switch to 24 volt electrics about this time, in the interests of commonality across the product line. The fact that the 24 volt parts cost far more than twice as much as the 12 volt parts (and didn’t work any better) was of no concern to them, the customers would pay it anyway, and thus increase Textron’s bottom line.
(The big iron is 400 volts AC, when you have miles and miles of wire in an airplane, if it was all 12 volts, the wires would be so big and so plentiful that there wouldn’t be anywhere for the passengers to sit. Higher voltage means you can use smaller wires, 12 volts at 10 amps is 120 watts, 10 amps means you need a big, fat, heavy wire, 400 volts at .3 amps is also 120 watts, .3 amps means you can use a skinny, little, light wire. On the 152, the change to 24 volts might have saved one pound, but at a cost to the customer of probably several thousand dollars.)
I do know that there were a number of changes made to the O-235 to tame it (or at least housebreak it slightly), there were different cylinders and special spark plugs (RMB35Y, I think), and eventually the engine became manageable and tolerable.
Then Cessna stopped making single engine piston airplanes, and the answer was, sorry, we haven’t made that product in a while (two whole hours) so you are on your own.
It seems there are other inputs to aircraft designing and production besides the engineering department. In this case, accounting and legal had a lot to do with the problems in the O-235 in the earlier 152s. (I also have to shake my head in amazement at the early 152 cowling which required removing the propeller to take the cowling off the engine.) Further, I wonder just how they were able to get that engine through FAA certification in its original form.
Best Regards,
Miami Mike
What a mess the O-235-L2C in the Cessna 152 was!
At our Cessna dealer and flight school, we took delivery of our first three C152 aircraft in late 1977, if memory serves.
Almost immediately I noticed water droplets coming out of the crankcase vent tube, but I considered this normal, given the cool weather.
The next surprise was finding the lower spark plugs packed with lead during the initial 100 hour inspection. This certainly didn’t seem normal. I began cleaning the lower plugs at 50 hour intervals, finding what seemed to be the same copious quantity of lead. Soon, I began cleaning the lower plugs every 25 hours, in an effort to forestall calls from students on cross country flights reporting “bad mag”.
The third surprise was hearing what sounded like a movie theater popcorn machine coming from inside the cowling immediately after shut-down. At the first valve adjustment, the culprit was evident…..water. The inside surface of each rocker cover was rusted.
It was obvious that the oil temperature was not hot enough. The panel oil temp gauge was a “best guess ” at best, as the green arc had no temperature values noted….one was “in the green”, or not.
I made a call to Tex Francine at Lycoming, and he suggested making a plate to cover the oil cooler air inlet, which I did. The popcorn machine was still there, even after changing the oil and filter! On one engine, I connected the oil cooler inlet and outlet hoses with a union, bypassing the cooler altogether. No real improvement. The only thing I could do is change oil every 25 hours in hopes of getting rid of some water. The issue was never completely eradicated.
What I did next was illegal, but desparate times call for desparate measures. The 152 was hard to start when cold, as the carb had no accelerator pump, and the engine only had priming to a single cylinder. So I fabricated lines to prime #2, #3 and #4 cylinders. I shortened the inlet checkball spring on the primer pump so it would fill faster. I installed a second impulse magneto, and set the lag angles back 4 degrees. Then I rerouted the spark plug leads so each mag sparked two upper and two lower plugs. Lo and behold, now I could get a coldsoaked engine started, and a mag check didn’t have the engine trying to jump out of it’s mount, and a stranded student jump out if his mind !
The water and the lead problem persisted, but at least I think I made my life a bit easier!