Low CHT's

[canav8]

Let me admit right-off that I don't have the expertise to solve this on the internet (and maybe not at all) but I did not wish to appear overly-critical of the attempts by others.

As for the last question.... cowl flaps are generally for the purpose of drag-reduction in higher-speed aircraft that, due to that higher-speed, do not and can not utilize all the available air-flow for engine cooling. (For sometimes not-so-obvious reasons...such as the need to reduce the speed of flow within the cowling to allow sufficient time for the air to absorb the engine heat. This is analagous to having a thermostat in a water-cooled engine. Complete removal of a thermostat in an engine which frequently overheats can be self-defeating because the coolant will pass though so rapidly as to not have time to absorb enough heat to make a meaningful reduction.)
Air Flow thru the cowling adds to the overall drag profile of the airplane, and reducing excess airflow not only reduces total drag but also slows the cooling air down to better allow it to absorb heat.

Here's a related "for example" question: When is a CHT gauge required equipment? (Answer: Only in aircraft equipped with cowl flaps.) Therefore my friend's Debonair can legally operate with an inoperative CHT gauge, but my other friends Bonanza cannot.

If your oil cooler is preventing your oil temps from elevating to the normal range...then it's time to suspect the oil cooler verniatherm (Thermostat.) Duct tape is not what the authorities would likely approve because you cannot alter it in flight. (A really elegant solution might be an exit-duct for the oil cooler with a controllable exit-duct flap....properly approved, of course.)

Well George, your absolutely right, but when your vernatherm is still working correctly it does need a little help. Need a vernatherm? I got a few extras used only once. I have used additional cowl sensors to diagnose the problem. Temporary of course but thats the only way you can successfully fly in the summers without killing your engines. Towing Banners or gliders with the Super Cub gives a whole new meaning to the theory of cooling your aircraft engine. I am also a firm believer in airtight baffle setups. When it gets cold outside you would almost need a different airplane, Oh yea, I have a 170. D

[marathonrunner]

I may have missed something but if you are having a problem with low oil temp, which is a problem with this installation, I have seen several field approved shutters that were mounted on the oil cooler and controled by a push pull cable from the cockpit. You do need to verify your gauge is calibrated and most gauges are a wide green arc. Oil needs to get to 180 to get the moisture out which causes a build up and can cause pitting of lifters and camshafts expecially in Lycomings. To calibrate your gauge you can get a hotplate and using a calibrated thermometer which are inexpensive and readily available. Heat up the oil in a pan and watch your gauge as it goes through 180 and mark it, Remove the heat and watch the gauge as it goes down and mark it and that should be the range you need to be in.

For cylinder head temps again, you need to make sure your gauges are properly calibrated and indicating correctly. The best way to lower the temps is to first make sure all your baffling is fitting correctly and that the seals are completely sealing on the cowling. TCM engineers will tell you that a total of one square inch of an undulation in the seal or a hole, will be a 10 percent decrease in your cooling. It also works for keeping heat in. If it is not sealed replace all your seal and cut it or slice it so that you have no U's that allow air to move through. You would not drive around with a hole in your radiator in your car...same difference. Once the engine is sealed correctly and the gauges are verified accurate if you are still low on the temps the best way to increase the CHT at least in most cold climates, is to restrict the opening of the cowlingwhere the air enters. You can add nutplates to the nosebowl and make plates from aluminum with restricted openings. As for creating hot spots the aircraft manufacturers have their own kits that do just this and can be purchased. Unfortunately Avcon is an aftermarket STC and did not make a kit for the 170 conversion. If you look at what Cessna made for their own aircraft for this you will get an idea of how to proceed.

This should be minor and reqire only a log book entry although seriously I doubt any FAA person would even look twice at it. I suppose it would vary from region to region though.

Good luck

[cmsusllc]

I totaly agree with George that too much airflow can cause a temp increase for the reasons he stated, and I've seen the results he mentioned in a water cooled system without a thermostat. Another note, my oil temp comes up to 200 degrees indicated all the time, winter or summer, at all power settings. Also at one time this plane had some type of cowl plugs. It spent most of its life in Colorado before I purchased it.
Scott.....53B

[hilltop170]

Scott-
This is how one owner addresses the cooling air problem you describe. The lip is just a flat piece attached with what looks like PK screws and tinnerman nuts. I have no idea how the approval basis is handled.

170B Lyc O-360 cooling lip

View looking forward

View looking aft

[blueldr]

Richard,
Maybe the owner of the above cowl flap installation just settles for "Owner Approval", which is still available in many jurisdictions.
I always found that to be true where I was. You know, they're very busy down there in Oklahoma City and I always hated to bother them with those type of things.

[Jr.CubBuilder]

My 53B with the pressure cowl was obviously designed for the O-300 and the cooling requirements for it. I have the O-360 Lycoming with an oil cooler which has too much cooling capacity, especially in winter. I personally don't care for cowl plugs as I feel they can cause hot spots. Has anyone tried building a partial plug for the bottom exit which would disrupt the vacume created by the lip? My A&P and I have been discussing it so I thought I'd ask the experts.
The highest temps I've seen in summer is 350 degrees ( #4 single point only ) in climb and 300 to 320 degrees in cruse. Outside temps now in the 30's and 40's only see 265 to 280 in cruise, leaned aggresively. I have a lot of lead fouling issues and feel it's due to inadaquate CHT's.
Your thoughts would be appriciated.
Scott.....53B

Your temps sound typical for this setup, Im running the same engine in mine, Ive talked to a couple of other owners with these, and one of my local friends had the same conversion in his 175. The plug fouling isn't normal though, something is going on there and it probably isn't the just the CHT.
The oil cooler on mine gets tapped over usually around October and stays that way till May or April.
I'm just on the other side of the mountains from you, we could get together in the spring to compare notes if you are interested.

[cmsusllc]

Your temps sound typical for this setup, Im running the same engine in mine, Ive talked to a couple of other owners with these, and one of my local friends had the same conversion in his 175. The plug fouling isn't normal though, something is going on there and it probably isn't the just the CHT.
The oil cooler on mine gets tapped over usually around October and stays that way till May or April.
I'm just on the other side of the mountains from you, we could get together in the spring to compare notes if you are interested.

Where ya at? I get over the hump quite often, weather permitting.
Maybe i'm all wet but I'm looking for someone to convince me otherwisse, the lead deposits will stick easier to a cooler surface than a hotter one.
Someone????
Scott.....53B

[blueldr]

If you guys with lead fouling problems would learn how to operate on mogas, your problems would be over.

[cmsusllc]

If you guys with lead fouling problems would learn how to operate on mogas, your problems would be over.

I know that Dick and would love to but in Washington State there is no more corn liquor free auto gas!
What a waste of good corn liquor!
Scott.....53B

[Jr.CubBuilder]

Your temps sound typical for this setup, Im running the same engine in mine, Ive talked to a couple of other owners with these, and one of my local friends had the same conversion in his 175. The plug fouling isn't normal though, something is going on there and it probably isn't the just the CHT.
The oil cooler on mine gets tapped over usually around October and stays that way till May or April.
I'm just on the other side of the mountains from you, we could get together in the spring to compare notes if you are interested.

Where ya at? I get over the hump quite often, weather permitting.
Maybe i'm all wet but I'm looking for someone to convince me otherwisse, the lead deposits will stick easier to a cooler surface than a hotter one.
Someone????
Scott.....53B

KELN, home of the most expensive AVGas in the US.

[cmsusllc]

KELN, home of the most expensive AVGas in the US.

And the place that makes the Windy City look calm.
My first duel cross country thirty some odd years ago was EPH-ELN-EAT-EPH. After a touch and go and hitting 100 feet AGL my instructer had me go into slow flight and maintain altitude. We backed up the entire length of the runway then turned north for EAT. I'll PM you when I'm over there sometime.
Scott.....53B

[Jr.CubBuilder]

Sounds good, I'd like to check out your installation. That wind does make for some interesting situations.
Chris

[Dooley]

I have the same conversion and have been pulling a glider for ten summers and have never seen 350 on the cht's. I went for years with no CHT guage and didn't have any idea if I was cooking the engine or not. Turns out I am running very cool as well. I never have any fouling problems but I would like the CHT's to run a little hotter. The top half of my cowling has had a pretty extensive makeover and I expect I am taking in too much air and I am losing a couple of knots to cooling drag I don't need. If the only problem is lead fouling you can probably cure it with TCP fuel additive. It does wonder's for my cub when I run 100LL. I could run auto in the cub but I buy gas in bulk and I need it for the Lycoming in the 170 anyway.

[cmsusllc]

I'll try the TCP and see what happens.
Scott.....53b