Marvel Mystery Oil and TCP: A cure for valve sticking?

Dennis Corsi recently sent a note, detailing his problem: “”We operate a 1980 Cessna 182 RG with a Lycoming O-540. Recently, the number one exhaust valve push rod bent. We have been adding Marvel Mystery Oil ever since, but I sense that we are not quite solving the problem.”” He went on to state that the engine runs rough on startup and then runs normal after warming up. His main question was what is TCP and would adding TCP to the fuel cure the problem?


Dennis Corsi recently sent a note, detailing his problem: “”We operate a 1980 Cessna 182 RG with a Lycoming O-540. Recently, the number one exhaust valve push rod bent. We have been adding Marvel Mystery Oil ever since, but I sense that we are not quite solving the problem.”” He went on to state that the engine runs rough on startup and then runs normal after warming up. His main question was what is TCP and would adding TCP to the fuel cure the problem?

First, I feel that Marvel Mystery Oil will have no effect on exhaust valve sticking. I have no data, but have heard from many pilots that Marvel Mystery Oil has reduced incidences of intake valve sticking. As Marvel Mystery Oil is just very light oil, I would assume that it is burnt in the combustion process and therefore would have no effect on the exhaust valve and guide.

TCP is Tricresyl Phosphorous. It reacts with lead during the combustion process to form a dry, white, flakey deposit that can be sloughed off by the mechanical action of the exhaust valve opening and closing. Without TCP, the lead deposits are much tackier and can build up and eventually lead to valve sticking.

In his note, Corsi described a condition they call “”morning sickness,”” which probably is caused by deposits in the exhaust valve/guide area. If the deposits are present, then TCP will have little or no effect. TCP works primarily in the combustion process and will not react with lead that is already in the guide area.

So what should he do? To answer that question, I am going to sound like my good friend, Paul McBride, GAN’s engine expert. Lycoming Service Bulletin 388C will tell you how to inspect your engine to determine if the problem is exhaust valve sticking. If it is, then Lycoming Service Instruction 1425A will tell you how to ream out the guide to return your engine to proper operating condition.

Once your engine is up and operating properly, Lycoming Service Letter 197 gives several recommendations on how to prevent future recurrences of the problem. Lycoming does not specifically recommend the use of TCP as a preventive procedure for the company’s engines. However, TCP is approved by the FAA for use in all non-turbocharged aircraft piston engines.

I do not know of any statistically significant data proving that TCP will prevent exhaust valve sticking. I have heard from a large number of pilots and fleet operators who have added it to their fuel and claim that their valve sticking problem went away. My recommendation would be that adding TCP to the fuel should help reduce the occurrence of exhaust valve sticking. I also would recommend that you follow the operating and maintenance recommendations outlined by Lycoming.

Unfortunately, there are very few simple, inexpensive solutions to problems in aviation. I would say that the solution to almost every problem is basic maintenance and proper operating procedures.

Ben Visser is an aviation fuels and lubricants expert who spent 33 years with Shell Oil. He has been a private pilot since 1985. You can contact him at Visser@GeneralAviationNews.com.

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