1990 M20M - Wastegate issue? Has this happen to u

[Dklossner]

While flying my 1990 M20M I experianced the following issue:

During a flight to 16,000 feet,  (34/2400) power, fuel flow, temperatures and performance were normal.  The aircraft was leveled at 16,000 feet and we proceeded to select a cruise power.  I proceeded to reduce manifold pressure to a conservative cruise setting of 26-27 inches.  To my surprise when approaching 26 inches the manifold pressure randomly and quickly fell to exactly 20 inches all on its own.  Easing the throttle forward again did not result in any change as the power remained at 20 inches.  Oil pressure remained constant within the green arc. Turbine inlet temperature fell off scale and we proceeded to immediately lean the engine.  I do not recall if the TIT temperature came up on the gauge scale which starts at 1300 degrees Fahrenheit.  We started an immediate descent and the manifold pressure continued to remain at 20 inches. After descending approximately 2,000 feet I was relieved that the manifold pressure surged to a normal number. 

Other details:

• 
  
• This incident happend in Ohio (12/15/10) and the aircraft was previously based in Florida.
  
• Summer grade Aeroshell 100W50+ oil,
  
• OAT temperature was approximately -30 Celsius
  
• We were flying in clear air
  
• We did not pull the alternate air source and there was no indication that the automatic alternate air opened
  
• Future flights, though not into the flight levels, were normal
  
• TT is about 2,000 hrs
  
• Engine, wastegate and trubo was overhualed in 2006 - 125 SMOH
  
• Lycoming TIO540AF1B engine with the oil cooled valve modification
  
• To  our recollection our oil pressure was close to 50 pounds at time of incident. 
  
  
• Recent oil change - less than 8 hours on oil
  

What I have heard as possible cause:

• 
  
• Something got stuck in the oil supply system either through the controller or the wastegate to cause the wastegate to stick and then let go
  
• Oil should be a changed to winter grade
  
• Air hose servicing the wastegate collapse
  
• Possibility of induction icing 
  

Has any body experianced this situation before?  Other ideas?

 

[Skywarrior]

I have not had this issue, but I noticed your engine has been exercised only 125 hours in the last 4 years.

Correlation?

 

Chuck M.

1991 M20M

[Dklossner]

Chuck,

Happy holidays,  yes, we are thinking it may have something to do with the plane not being flown very much over the last several years.  I just don't want to start changing parts. 

david

[Jerry 5TJ]

I had a (perhaps) similar problem in a T210 about five years ago. At altitude the MP would drop six or eight inches, but it would be OK again after descending 10,000 or 15,000 feet. Turned out (most likely) to be the rubber hose from the inter-cooler to the intake air body. The hose apparently leaked when the differential pressure was higher at altitude. A new hose and new clamps seemed to fix it, but that was not the only thing we replaced during the investigation.

I did not worry that we may have replaced some "OK" parts during the investigation, I changed anything that looked dubious.

[Dklossner]

Jerry,

Thanks for the insight.  I will check out the hose.   Have a great holiday.

[thinwing]

Have you tested the wastegate shaft....this part should be "mousemilked "every chance you get along with all the other exaust slip joints....the lever should move against the spring(I use a crescent wrench on the lever itself)quite freeley..it can bind up and remember its running red hot!!!...kpc

[Dklossner]

Thanks for your tip.  I will look into it.