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It just runs too warm

caryr

caryr

Well Known Member
Patron
I have just about run out of ideas. So I thought there might be a opinion or two here.

first its a -7 ,Lyc O-360 180hp been flying for several years and I have always had to baby it during the summer to keep the CHTs from going out the roof.

Yep. I have checked the calibration on the probes.

This winter, I decided to make a effort to solve it.

I had a few nonstandard RV items. It is now plain vanilla van's RV-7. I replaced the Skydynamics 4 into 1 because I thought it might be distupting the exit air.

I had a not standard intake air box because of the exhaust header shape. have not put the std van's air box on with Vetterman's crossover.

I have a EI on the right and mag on the left. I checked timing on both a couple weeks ago.

I put ramps on both #1 and # 2 cylinders to divert the airflow rearward. I don't have leaks around the baffling.

The between cylinder baffels are in place.

Both back cylinders CHTs are over 400 on any climbout. If its heat soaked in the ramp, takeoff will go over 500 cht. That's just too hot.

the front cylinders are on the warm side too, but they lag along behind the rears.

the egts all run 1300 to 1400, which seems fine.

oil temp will climb to over 200 as the chts heat up.

Last week, I taped a duck tail on the cowl exit to attempt more of a suction at the exit.

I even drained a tank and put 100LL rather than the car gas I normally run this past Saturday.

nothing I have done has changed it at all.

I think my next move to to attempt a manometer on the upper and lower pressure chambers in the cowl.

cary
 
Cary,
Just for additional information. What size oil cooler are you running? Where is it mounted?

I did open up the exit air on my 6-A and it seemed to help some. Since I live in West Texas, I have the large Positech oil cooler mounted on the firewall with a 3" scat tube off the #4 Cyl. I also run an O-360 and my oil temps are running about 185 to 195. They will get a bit higher on a hot day climb, but I usually climb out at around 120K and they stay within range. EGTs and CHTs are well within range. CHTs run around 350 or less in cruise, but rise to about 400 on a hot day climb out.

It appears that you have addressed all the other potential problems. I was just wondering about the oil cooler size and where it is mounted.

On my -7A I will probably get the large Stewart-Warner and see if it does any better.
 
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I 've got the larger Stuart Warner mounted tot he firewall with 3" scat off the #4 cylinder.


I have even blocked about half of that to see if the cylinder will cool off.

The cht's are closely related to oil temperature, I have found.

Thinking aloud here -- seems related to hi angle of attack and hi power.

I have even thought about changing the prop. Its a wooden Aymer Demuth.


cary
 
Are your

fiberglass inlet ramps on the upper cowling sealed so air can't escape and leak across them into the cowling?
 
I put the ramps that came with the cowl in place and seem to have a smooth airflow surface.

the upper baffle seals all seem to be good.
 
caryr said:
I put the ramps that came with the cowl in place and seem to have a smooth airflow surface.

the upper baffle seals all seem to be good.
Click to expand...
It looks like you didn't understand Rooster's post. There is a tunnel underneath the upper inlet ramp. Many builders discover that with the way they ran the upper baffles, that this tunnel connects the area above the engine with the area on the other side of the baffles. This makes a huge air leak, and allows a lot of air to avoid going through the cylinder fins. One solution is to close off one of the ends of those tunnels with fibreglas.
 
Some questions...

What climb airspeeds are you using?

Which EI? Have you tried climbing/cruising on just the mag or just the EI?

What MAP, RPM and fuel flow are you using on the climb?

Also, what are MAP, RPM, fuel flow, IAS and cht's are you seeing after cruise is established?
 
Timing was also my thought. Have you tried running it on just one mag/EI at a time?

I know you checked the timing....probably not the problem.
 
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After Mike had such an issue with timing a couple weeks ago, I determined to eliminate that as a problem.

The mag was a couple degrees off. I adjusted that, but it wasn't enough to cause a major issue.

I went thru the EI proceedure to force it to fire at TDC and put a strobe light on the start gear to check fire at TDC. It was right on the money.



fuel flow, etc.

I run full rich on climbout. I have the GRT box. It indicates 17 gal p hour or so. I lean it in cruise to 2400rpm and 8 gals or so.

fixed pitch prop, so I don't have any control over the prop bite.

cruise temps are 350ish on CHTs




kevin, I'll have to check the ramps. Its been a while since I built them. I don't think they are open on the ends.


EI is a Jeff Rose -- Electro Aire
 
Yes I like the idea of climbing out on one or the other.
Are your cruise numbers ok? meaning at 9gph ROP high throttle setting ~7k' are your chts in the ~360 range?

After all you have already tried Carey, Id be headin for the exit area cut.
And get rid of that stick on the front:p

Best,
 
hey Mike

the cruise numbers are all reasonable. 350ish 360ish on all cylinders

the two rear ones a littler warmer than the others.

The Exit Hole:

I had cut out a semicircle to accomodate for the SkyDynamics trumpet. That was one reason I was suspecting the exhaust. I haven't put a roll fairing on the lower firewall. I've seen these sometimes.

I kinda like the tree limb on the front. I don't have to slow down as fast as you guys do.
 
caryr said:
I 've got the larger Stuart Warner mounted tot he firewall with 3" scat off the #4 cylinder. I have even thought about changing the prop. Its a wooden Aymer Demuth.
cary
Click to expand...

Keep in mind that the air in the plenum is low-speed, high pressure. A 3" scat tube may not conduct enough air to the oil cooler, since first of all, with its corrugations, it is effectively a much smaller diameter. Secondly, to get the required flow though a small diameter tube requires high velocity which then is gradually expanded to the cooler area. I use a SW 10578B cooler on my 125 HP O-235; it requires 20 lb/min in the design center of the graph. At 200 mph, my 2 sq. in. external inlet is flowing 4.07cf, or 18.7 lb/min at sea level. If you have 180HP, you will need about 180/125 X 20 lb/min or 29 lb/min. So at 200 mph that would require an external opening of 2.88 sq. in., about 2" diameter sticking out into the airstream. That's probably about the effective diameter of your scat tubing. You'll not get that kind of flow velocity from your plenum. Does this make sense to you?
 
That really does make since.

I am of the opinion that the oil temp being above normal is a consequence of the CHT being high.

I really haven't had major oil temp problems.
 
Carb?

Cary,
What carb are you using?
I'm assuming you are running a carb, but didn't see any mention of it or FI.
I'm surprised no one has mentioned it so far. I'm betting you have the 10-3878. The 10-3878 is the lean carb and it works fine in cruise but is too lean
in climbout. You want the 10-4164, I think, as I don't have the numbers in front of me right now. You can drill out the main jet in the 10-3878, 3 thousands at a time until you get better cooling. The Carb people, used to be Prescision but I think is Kelly now, sell a "enrighment" kit for about 200+ dollars. The kit is suposed to effectively make the 3878 like the 4164.
Check to see what you have. They is plenty more info on the carb mod if you need to go that way.
Good Luck
 
Cary,

So from what I'm reviewing here - your problem high CHT is 'worst' during low speed climb out, but once into the cruise everything is cool and happy?

Climb on just traditional mag sounds like a great test.

Can you confirm the fuel flow calibration is good - compared with the multiple tank filling?

WAG - Feels like timing / carb jet type things to me if gaps are all gone.

Regards,

Carl

PS: With the GRT you can easily save and review the data. Good for baseline if nothing else - (if you need assistance with GRTDecode PM me)
 
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caryr said:
That really does make since.
I am of the opinion that the oil temp being above normal is a consequence of the CHT being high. I really haven't had major oil temp problems.
Click to expand...

You said in your original post that the oil temperature was going over 200F. Keeping the oil cooler can help keep CHTs low just as in the opposite. The rotarys depend on oil cooling to maintain engine temp.
 
fiberglass inlet ramps on the upper cowling sealed so air can't escape and leak across them into the cowling?
__________________
Rusty "Rooster" Williams - FFI Wingman
Susan "Chick" Williams


Rooster, u da man

You are so correct

I turned the upper cowl over today and the ramps are open on both ends.

That's where all my cool air is going.

I don't guess I have ever had reason the study the underside of the upper cowl. Its always laying over there in the floor while inspecting for air gaps around the baffles and cylinders.

I'm betting that will make alot of difference.

I have struggled with this for at least 3 years.
 
Cary, I don't want to spoil your potential success, but both ends can be open without a leakage problem also. It all depends on how the inner and outer baffle seals in that area are installed. You should be able to run your hand up in there and figure out if they are making contact along the ramp. Or, perhaps there are witness lines.

350 in cruise in the summer is quite typical for many, if not most.

What sort of climb airspeed do you use?
 
Close them up with .025 sheet

caryr said:
fiberglass inlet ramps on the upper cowling sealed so air can't escape and leak across them into the cowling?
__________________
Rusty "Rooster" Williams - FFI Wingman
Susan "Chick" Williams


Rooster, u da man

You are so correct

I turned the upper cowl over today and the ramps are open on both ends.

That's where all my cool air is going.

I don't guess I have ever had reason the study the underside of the upper cowl. Its always laying over there in the floor while inspecting for air gaps around the baffles and cylinders.

I have struggled with this for at least 3 years.
Click to expand...

You don't need to fiberglas. I made my closures out of .025. Make a quick pattern, it will end up kind of kidney shaped, cut them out, and pop rivet them to the the ramp. Seal with RTV, your done. Took less than 30 minutes.
 
More high CHT info

Here is a message a buddy sent to me. I haven't done it but if anyone else does let me know how it worked.

When I first started flying Scooter, I had cylinder issues, as well. My
engine has a carby. I found out the carby was running lean at most
settings. I did a test, as suggested on the RV-list, and found that
it would not lean when the mixture was pulled at several rpm levels.
It would die, immediately. I fixed the problem by drilling the jet hole
from a size 41 to a size 37 hole. Now, I can pull the mixture and see
a rise in the rpms as it leans out. I also see lower cylinder temps.
Mine run in the mid 300Fs. If I ever build another airplane, I'll do
the same test and make the same correction, as needed.

Of course, the suggestion to climb at about 120kts is a good one.
I see no need to climb at any slower speed than that. One can see
over the cowl and keep down temps, at the same time.

Jim Sears [email protected]
 
Cary,

I read recently in one of the RVators that Van was struggling with high CHT's in his new RV-10. One of the things he did was to sand down the inside of the top cowl, apply micro-balloons, sand that smooth and then cover the micro-balloons with a coating of pure epoxy.

Like you I'm struggling with high CHT's in climb but not as high as yours. In cruise, #3 stays about 408, which is 50 higher than the other three.

When I pulled my top cowl, you could see where the air leaks were. Check out these pictures to see what I'm talking about:


Today I smoothed out the micro-balloons and coated them with a layer of pure epoxy so I can't tell you if this was a success or not. With luck I might get a chance to go flying this weekend, if family responsibilities don't get in the way.

Either way, it was very easy to do and won't hurt.
 
lets talk a bit more about the carb modification

I do have the 3878 carb

So, consensus says that I need to change something inside of it.

Man, I hate to take apart a perfectly working carburator.

It looks like there is a kit to improve the climb out temps by richening the mixture.

Have any of you done this modification?

Somebody said to search the archives for info. I don't think we have archives on the this forum, do we??

Guidance Please--
 
I just read thru the Lean/Rich thread that is running right now.

So I have that much information.
 
I know it won't completely solve your problem, but it would be real cheap and easy to replace your scat with skeet hose. Supposedly flows much better.
 
Bill, while your at it....

N941WR said:
Cary,

When I pulled my top cowl, you could see where the air leaks were. Check out these pictures to see what I'm talking about:


Today I smoothed out the micro-balloons and coated them with a layer of pure epoxy so I can't tell you if this was a success or not. With luck I might get a chance to go flying this weekend, if family responsibilities don't get in the way.

Either way, it was very easy to do and won't hurt.
Click to expand...


You might want to close off one side of those ramps. It help me reduce temp on my #2 when I closed off mine.

Kent
 
Is there a link to a good picture of the carb internals??


Or even better, a parts breakdown.


I am seriously considering enlarging the main jet to a 37 or 38



thanks
 
Be careful

caryr said:
Is there a link to a good picture of the carb internals??


Or even better, a parts breakdown.


I am seriously considering enlarging the main jet to a 37 or 38



thanks
Click to expand...

Cary,
Be careful about just drilling to a size.
Measure what you have for a main jet size first with the shank of a drill bit.
than go up 3 to 4 thousands at a time. You will see the temps drop each time. But if you drill too much at once you might miss the correct size and then you will have to either replace the main jet and start over or you will always have to lean on the ground for takeoff. So go slow and watch the temps drop til you get them where you want them. After the first time, you can can do the complete job in about 3 hours.
 
High CHT's

I am running the Aymer Deymuth wood prop on a 0-360A1A and my temps are just fine.

Just food for thought
 
CHT updated

Post inspection, I got the rv back together SAturday and test flew it around the neighborhood.


With the sealed ramps in the upper cowl. it looks like I have picked up an improvement of about 15 deg on the CHT. I still saw 420 on the #4 cylinder and 404 on the #3, but it was after a longer steady climb.

the oil temp is 8 to 10 deg cooler also. I think the added pressure differential helped the oil temp more than anything.

I talked to the guy at Precision Airmotive also last week. They have sold off the carb making business. I asked about a larger main jet. He said to drill the one I had.

His recommendation was 2 drill bit numbers from the existing.

I think I will order a gasket and some nut safety clips and try that later.

For now, its a reasonable improvement I think I can live with.
 
caryr said:
I talked to the guy at Precision Airmotive also last week. They have sold off the carb making business. I asked about a larger main jet. He said to drill the one I had.

His recommendation was 2 drill bit numbers from the existing.

QUOTE]
Your fuel flow will increase proportionately to the area increase, so to get 10% more flow, increase the diameter by 5%. Use numbered drills inserted in the jet to determine its diameter.
Click to expand...
 
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