Oil temperature now is cooler

·         Mark Dunstone

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Now it's cooler here in southern NSW I'm finding my oil temp doesn't get above 67C with an OAT of 10C. I'm running a recent 2200 hydraulic lifter engine. CHTs on climb out reach 150C (70kts @ 3100rpm & 23lph) and cruise 120-130C (90-95kts @3000rpm & 16lph). EGTs on climb out are 650-700C (no.4 the leanest), and on cruise much the same just more spread 640-710 (no.4 the richest). Oil pressure stays on 37psi. In summer (OAT over 30C) oil temps were usually around 80-85C & chts maybe 10C higher on cruise. My question is, should i blank off my oil cooler inlet with a piece of cardboard to get the oil temp back over 80C? Cheers, Mark

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·         Doug Smith

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Hi Mark,
About 80-85 is generally considered ideal but 67 is still warm enough to avoid cavitation in the oil pump and to evaporate most of the impurities in the oil (water, fuel). Personally I find mucking about with cardboard pretty tedious (no sooner would you get it right then the day would warm up and make everything hotter than ideal...) so I would not go there just yet. It's a bit of a judgement call and it depends what sort of operations you're doing, what sort of oil you're running etc, but offhand I'd suggest leaving it until you're running around the 60 mark.
Regards,
Doug.

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·         Mark Dunstone

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Thanks. And each day is different. I've also been noticing that my right bank EGTs on cruise/descent are just touching 740C with the cold weather and I've had a hankering for cabin heart. I've just sent an oil sample for analysis with my 50hrly service so I'll see what the water content is with the lower oil temp.

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·         Doug Smith

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yes, cold air will often tend to lean the mixture out a little, as you say the easy fix is to pull carb heat on.
Let us know how your oil analysis looks!
D.

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·         Mark Dunstone

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Thanks Doug. I've attached the oil analysis. I'd be grateful for feedback on what is normal for a Jab. I'm a bit surprised as my intake system is tight as it's a new installation in a Cygnet SF2A airframe and I've been a maniac at getting the mixture and chts right, and I'm running on 98 pulp. I have upped the oil pressure on Leigh's advice with another washer (is now usually 45psi where it used to be around 37. I have also added a little silastic to the cht probes (they are on the log as per the engine installation guide) to insulate them from the breeze and that has increased the 'indicated' chts by about 10C across the board and reduce d variation. ..i now see 155C max on a long climb out and 135C on cruise. The leak down at the 50hrly showed two cylinders at 70/80 and two at 55/80. Pull throughs show even compressions and the engine is smooth and runs great. ..I'll see how that goes at the next 50hrly. Cheers, Mark

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·         Doug Smith

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Hi Mark,
I'm not seeing the attachment... I'll get in touch via email and see if we can't get it uploaded.
The EGT going a little high in colder weather is due to the way the carby works. It's not usually a huge change and shouldn't be an issue unless you're operating "close to the line" normally - and if it gets higher than you like a change of jet will sort it out.
Good tip on the silastic on the CHT probes!
Regarding the leak downs, I always found that a session of circuits would do wonders for cleaning off valve seats etc before a service: the power cycles seem to blow out the cobwebs.
Regards,
Doug.

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·         Doug Smith

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File attached here. How many hours total are on the engine? If it's still bedding in then elevated iron etc is to be expected and it may explain the lead levels too.
A point often overlooked with air intake is that often the carby heat will draw unfiltered air (depending on the design of the airbox). That can mean the engine gets a bit of dust during ground runs etc. Another thought is that, depending on the airbox, it's not unheard-of for the filters not to seat properly... you can usually pick that with an inspection or use the old dirt bike trick of putting a wipe of grease around the sealing lip of the filter element.
Regards,
Doug.

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·         Mark Dunstone

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Thanks Doug. I'll check the sealing of the air filter. The engine has just done 50 hours. I did find some tests of other Jabs, and my results seem pretty much in the middle. Thanks for the advice.