Running cool....

Not long ago I was worrying about high CHT on climb out at full power. (I can easily control this by reducing power.) Now, with about 40 hours on the engine, and unusually cool autumn weather in the UK, I am becoming much more concerned about getting the temps up in the cruise! I understand RV4 do tend to run cool, so there must be lots of ideas/experience for bringing the temps (CHT and oil) up. My oil cooler is about 80% shut off. My questions are these:

1. What is considered a realistic lower limit for the CHT in the cruise? (Steady state in the cruise the hottest #4 is at 300F, and the coolest #1 at 290F. with the oil at 140F. Letting down its easy to see these drop back to 250/260 despite trying to keep heat/power in the engine.)

2. What are the pros and cons of reducing the air going in at the front of the cowl .v. reducing the exit to increase CHT?

3. Is there any experience of just blocking one air intake behind the prop completely, with gaffer tape? Does this lead to very asymmetric cooling, or does it in fact provide a very practical low cost solution?

I have looked at the 'Alan Judy' thread - marvelous - but really don't want to redesign the front end of the cowl!


Thanks.

Hi Steve....

....Alan Judy has removable carbon fiber inserts of differing sizes that he uses as the weather dictates. Right now, we have 30 degree temps in the mornings, warming to the upper 60's and the low CHT's are of no concern. The oil is harder to get up to 180 and you might need to block off even more of your cooler. There is also a vernatherm in the rear of the engine that is supposed to not let the oil go to the cooler until a certain temp (not sure what it is). Perhaps Mahlon or the other engine guys will chime in.

Regards,

cool is ok

Steve,
One of the GAMI guys commented on this question a while back and said that there is nothing wrong with "low" chts.
Anything much over 200 is fine......

I am running (in the fall) around 285F on #3 in cruise. My oil temps are around 175 with my oil cooler completely wrapped in alum tape.

I have also thought about making some fiberglass plugs for the cowl inlets. But it just hasn't bubbled up to the top of the list.

John

Heat is the enemy of anything mechanical. You will have longer cylinder life with lower temps. The lower the better.

Friends of mine have done extensive experimentation with reducing the size of the cowl inlets and outlets, with negligible gains in speed.

Oil temp is another story however, you need to have 180 degrees to boil off any water in the crankcase. A simple oil door will fix that.

Well this is good news indeed. If the cyls running below 300F is just fine, a simple oil door is all I need to think about. Thanks for the inputs.

Cessna use plugs to decrease the intakes when it is cold. Very simple, and works perfectly.

Just as an FYI, when I ran Van's oil temp probe/gauge my oil temps always showed cool and I was blocking the cooler to bring them up, when I switched to the EI gauge and probe the temp went up 20d easily. Now they always run between 170 on the coolest day to 210 on the very hottest when climbing. Granted low temps for Texas are around 40d on a cold day, anything below that and I stay home!

rocketbob said:

Heat is the enemy of anything mechanical. You will have longer cylinder life with lower temps. The lower the better.

Friends of mine have done extensive experimentation with reducing the size of the cowl inlets and outlets, with negligible gains in speed.

Oil temp is another story however, you need to have 180 degrees to boil off any water in the crankcase. A simple oil door will fix that.

Click to expand...

Rocketbob has it right. I like to see the oil temps get to 210 once a flight, but I settle for what I can get during the winter. My IO-540 has a door on the oil cooler and it works great to get the oil hot. The 0-235 is a different story. 180F is all I can get, and it doesn't even have an oil cooler.

140F is not good. Install a oil cooler door.

We have this issue with our RV8, the oil is not warming up on cool days. Ours has an oil cooler door, and it is closed all the time. Looks like we'll need to wrap our cooler in alum. tape to hopefully bring the oil temps up to 180 (or higher). Any special technique to this or just start adding strips of tape to the cooler?

Cold blooded...

Guys,
I operated my RV4 in the cold of SD and heat of FL for 12 years and learned alot in both places. The South Dakotans taught me to pre-heat on starts below 32F and run multi-vis oil. (I used a JC Whitney Auto Dipstick heater) They also used alot of electricians bundling tape (leaves no goo) to block off air intakes and aluminum tape over oil cooler fins to make sure they got a minimum of 180F oil temps to remove moisture trapped in the oil as Bob mentioned above. We placed the tape across the front and back of the cooler. You can also remove the Vernatherm on Lycomings and replace with a plug which effectively removes the oil cooler from the system. One RV3 guy simply unhooked his cooler in winter and plugged the holes. At -25F my RV4 would still show 180 oil and 300F CHT's with a little help from aluminum tape. My HR2 runs very cool CHT's, below 300F even in summer at LOP. The IO540 book doesn't show a minimum CHT for operation. I use a minimum of 200F for takeoff.

Now for abuse: When I was a new Comm Pilot I towed banners behind Scouts and modified Cubs. One of our Scouts (0-360) ran warm,especially when towing a 30X50 flying billboard. 230 oil, 430 CHT, all day long, 6 hours a day, 7 days a week, Memorial Day to Labor Day for 5 years with regular oil changes. Went to TBO with no worries. Lycomings are tough! I always thought the Hammerhead Sharks I flew over all the time were patiently waiting for a bad Lycoming day...

Smokey
HR2

Kas Thomas has shown that the highest engine wear is during start before oil gets on the cam, lifters and cyllinder walls. When you prime for start you wash off residual oil that would otherwise have lubed the pistons and rings. Up in AK pre-oiling is fairly common in wintertime and Danny King has a typical AK system installed on his "Beautiful Doll".

From Sacramento Sky Ranch:

Minimum Desirable CHT and Oil Temperature for Lycoming or Continental Engines

Operating Limitations are contained in the Type Certificate Data Sheet for the applicable model engine, or the Engine Operators Manual, or the Aircraft Operators Manual. If not otherwise published, the following reference:

According to Lycoming as published in their Lycoming Flyer

Minimum in-flight CHT: 150 degrees F. (65 degrees C)

Minimum in-flight oil temperature: 165 degrees F.

Maybe not...

I was flying today at 45F (on the ground). My 4 does not cool very well on the ground. I had 340F CHT before takeoff and loads of heat coming into the cockpit. After about 40 minutes of flight, my CHT was down in the 270F range with oil at 170F(cooler completely blocked) and the heat was lukewarm at best.

Maybe it's time for some tape over the inlets just to raise the temps of the whole engine. I must be gettin' old. I don't like being cold .

John

Running Cool...

I ran cool also in my -4. My fix was to add Van's cable controlled shutter over the oil cooler. Could run completely closed except for very warm days or lots of hard climbs. Was finally able to get my oil up to recommended temperatures. Great and easy fix.

Pat Long
Sold RV-4

need photo of a OIL DOOR for RV7

would someone please send a photo and/or details on the oil door for cold weather opts on an RV7 w/ IO-360

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