Time for an Engine Monitor?

[JC150]

I've noticed on takeoff, I'm only getting 27 inches of MP and I've been going through a lot of oil. The oil is coming out of the gaskets, and the plugs at the last oil change were wet. I'm burning around 1 quart every 5 hours. I've also noticed a reduction in cruise speed recently, around 5 knots.

I fly it full MP/2700 rpm in the climb, and full MP/2400RPM 10.5gph in cruise (always cruising above 7,000 feet lately). Full MP/2400RPM 10.5gph gives me ~130KTAS around 8,000 feet.

I'm wondering if the 2700rpm during climb is causing additional stress on the engine?

Anyway, the aircraft is an Arrow III with 1400 hours since overhaul. I want to use an engine data monitoring program so I've schedule an EDM-900 install. As I was talking to another aircraft owner about it, he told me I should wait until I have the engine overhauled before doing it. One reason he mentioned was the engine may not be putting out 100% power on the ground, so when they go to calibrate the power %, it could be off.

Can I have some of your opinions on this? Should I hold off on an engine monitor?

 

[coloradobluesky]

The symptoms you describe could be from an engine that is not producing as much horsepower as it used to. Aircraft engines actually never produce 100% power though for a number of reasons (altitude and exhaust).
One useful measure of engine power is do you make as much airspeed at full throttle as you used to? Good one to monitor.
What's your compression? What altitude do you get 27" at? What manifold pressure did you used to get? You are aware that manifold pressure varies with density altitude (altitude, temperature and pressure) and you will never get as much manifold pressure as it reads on the ground with engine off.

 

[dell30rb]

A worn out engine would not produce lower manifold pressure. A clogged air filter would. Or that could just be a normal value. What altitude is your home field? I think I get upper 27's or so and we are near sea level.

A quart every 5 hours is kind of a lot. Are you filling the oil all the way up, to say 8-9 quarts? Many engines will kick out excess oil and like to run near the lower end of the oil level. For example if the level is 6-10 quarts, don't add any oil until the level is clearly below 6 on the first flight of the day (oil has a chance to fully drain into the sump)

I would start by replacing the gaskets to fix those leaks and getting a compression check.

You don't need to wait until overhaul to install an engine monitor. Now is as good of a time as any! I would get your engine a clean bill of health and address the oil consumption before spending any money on the monitor though. Setting the % power function is done by you, in flight. Its easy and can be reprogrammed at any time.

 

[farmerbrake]

Our Arrow II likes to sit pretty right about 7 qts of oil (8 is max). We don't add any until it dips below 6, otherwise as mentioned above it just gets blown out on the belly. It takes us about 8 to 10 hours to burn through a quart.

 

[MAKG1]

Get the compression checked. Know what's up with your engine before blowing money on instrumentation.

27 inches MP is excellent at 3000 DA, and impossibly good higher than that. What altitude are you working at?

Oil leaking externally has nothing to do with engine performance, unless it's getting blown out the vent from excessive blow-by. A bad gasket doesn't do a damn thing. Bad rings might.

 

[JC150]

The airport I'm based out of is at 100' MSL, so pretty much sea level. This morning the altimeter was 30.21",14*celcius, and the MP gauge read 27.5" with full throttle and 2700RPM. I thought it was supposed to get up to 29" at sea level?

I keep the oil around 6-7 quarts. Am I running the engine too hard by running it at 2700 RPM until cruise?

One useful measure of engine power is do you make as much airspeed at full throttle as you used to? Good one to monitor.
What's your compression? What altitude do you get 27" at?

It will usually stay at 27" until I get to around 3,000 feet or so. I used to get 135 KTAS around 8,000 feet using Full MP/2400rpm and 10.5gph. Now I've noticed it has dropped to ~130KTAS.

I had the mechanic do compressions today. They were all between 74 and 78. The ring around the one of the spark plugs was wet with oil.

 

[coloradobluesky]

Sounds like you are understanding it to me. Interesting. Good luck with it.

 

[farmerbrake]

Am I running the engine too hard by running it at 2700 RPM until cruise?

I mean I've always done full power on takeoff and then back to 25/25 at about 400 ft agl. And take that to cruise where I'll do 23/24 or lower if I'm not in any hurry (21/24).
I'm no mechanic by any means so I can't say as to whether or not how you or I run the engine affects the longevity.

 

[MAKG1]

Naturally aspirated and it stays at 27 inches to 3000? You have a restriction somewhere. If the rings were blowing by, they would do it at 3000, too.

Either that or your MP gauge is wrong.

 

[JC150]

Naturally aspirated and it stays at 27 inches to 3000? You have a restriction somewhere. If the rings were blowing by, they would do it at 3000, too.

Either that or your MP gauge is wrong.

"if the rings were blowing by". Can you explain that a little further?

I mean I've always done full power on takeoff and then back to 25/25 at about 400 ft agl

I used to do it that way but saw how my CHT's rose when I did that because of the reduction in fuel flow. Would there be anything wrong in climbing out at full MP and 2500rpm instead? I'm concerned 2700 RPM may be running the engine too hard.

 

[Chip Sylverne]

Compression's good. If your oil is not turning black quick, I wouldn't worry about blow by. Ask your guy about the valve guides in the wet cylinder.

As long as you 're operating the engine within book parameters, you're not going to hurt it.

When was mag timing checked last, both internal and to the engine?

You will never regret installing an engine monitor.

 

[dell30rb]

"if the rings were blowing by". Can you explain that a little further?

I used to do it that way but saw how my CHT's rose when I did that because of the reduction in fuel flow. Would there be anything wrong in climbing out at full MP and 2500rpm instead? I'm concerned 2700 RPM may be running the engine too hard.

You will need to check the manual but I have flown behind what I think is almost the exact same engine in an M20J (4cyl 200hp angle valve lycoming) and yes, you can climb out at 2500 and full MP. On most normally aspirated GA engines, 2500 and full throttle is fine. 2700 rpm is no problem either, but you are making a bunch of unnecessary noise. I like going back to 2500 for climb.

My typical engine management on that plane would go something like this. Everything forward for takeoff (throttle, mix, prop). At 400' AGL bring the prop back to 2500. FF will be about 19gph. At 3000' or so when MP reaches 25", lean to a more reasonable fuel flow that is still well ROP, maybe 13gph. At normal cruise altitude (6000-8000 feet) bring the prop back to 2400 RPM and lean to either 100 ROP (about 11.5gph) or 20 LOP (9gph). Throttle stays wide open the whole time.

I think 27.5" is a tad low for sea level but it would not be an indicator of an unhealthy engine and unrelated to your oil problem. If anything, clean/replace your air filter. Make sure the throttle cable is letting the throttle body open all the way when you push the throttle in. That is about all you can do. The stock system might just be restrictive and you are missing out on a little power. Or your MP gauge is slightly off. Not worth throwing a ton of money at.

You mentioned the "oil coming out of the gaskets" - you should explain this a little further. It sounds like your engine may be healthy, and just has an oil leak somewhere that can be fixed with new gaskets.

"The ring around the spark plug was wet with oil" I can't tell if you mean the crush washer or the end of the spark plug that sits in the cylinder. If it is the crush washer, It may be wet because of an external leak.

If the end of the plug that sits in the cylinder was black and wet with oil, then you have an issue, probably a leaky valve guide. I would get that fixed.

 

[SCCutler]

You cover a lot of territory here.

First of all, a digital engine monitor is good to have no matter what; and I certainly would not wait until I bought a new engine to put one in, because what the monitor tells you will go a long way to you being able to keep your engine in happy operation for a much longer time. In addition, if you run your incorrectly, the monitor can help you save so much fuel that it will have been, in effect, free. You should look up some of the Mike Busch articles on engine management; very informative. See: http://www.avweb.com/news/savvyaviator/

Her description regarding oil sounds like it is on the outside of the engine; the grease and clean the engine completely, and take it for a short flight, so you can identify where the oil is actually coming out. Top suspects should be rocker box cover gaskets and pushrod tube seals. As noted above, leaking oil and poorer engine performance are rarely related.

My policy (learned from some of the top engine experts) is to NOT reduce RPMs until top-of-climb, unless compelled otherwise by noise-abatement, or an extended interim level-off imposed by ATC. The engine at max power is introducing a little extra fuel to keep cool, and you'll tend to climb at either a higher rate or higher airspeed, both of which will (ultimately) lead to less time in stress for the engine. The engine's certificated to run at that RPM continuously, so no reason not to do it.