Cessna 170/140 winter block off kit question

For you cold weather guys.

On my 1952 170B the cowl opening block offs cover about half the opening on the inboard side of the opening. This results in covering the air inlet for cabin heat as it is behind that one. On the other side, the inlet for the carb heat is outboard of the plate and works normally.

With the plate installed that covers the cabin heat inlet, there is no cabin heat. (No surprise). So logic says cut an opening in the plate the same size as the inlet. But that doesn’t work, verified by guys in the 170 association and also a guy with a 140 trying the same thing. The 170 forum is does not have a lot of members, so I thought I’d try here.

I have to assume there is something going on with turbulence around there or a low pressure there that is interfering with the ram air going into the inlet. There is no way to reposition the inlet on that side to be unobstructed by the plate.

The first picture shows the opening without the plate. The inlet is hard to see but it is a vertical oval close to the case.

I wonder if anyone here has solved this issue.

Rich

Not on a Cessna but with my Citabria 7GCBC I tried two mods....one was installing a 2" flanged SCAT adapter in similar front winter baffles. Then running a short tubing to another adapter mounted (screwed to temporarily) forward on the existing heater inlet. The second was to drill 2" holes in the cowl below the cooling air inlets and reposition the intake heating air sources. Cosmetically the latter changes things but worked the best.

Gary

If there's not much room from adapter to existing duct opening the flanged duct adapters can be cut down to fit. All that's needed for the hose to grab is the width of the hose clamps, providing the SCAT hose can make the offset bend required.

Gary

Thanks. Not sure I can’t make the bend, but in any case I’m not sure that changes anything. I’m afraid the issue is there is no pressure there with the block plate in place. I like your second solution except as you say, not the best cosmetic solution. By the time I figure this out, it will be warmer!

Rich

Hard to tell from a picture, but it looks like the intake scoop is to far inboard for the early cowl, which you have. That cowl should have the pressure baffles installed over the cylinders, the scoop should be in front of the cylinder head. This would be on S/N 20267-25372. Later B models used a different cowl and baffles with the scoop inboard. Maybe you have some miss matched parts. Check your s/n, maybe some pics with the cowl door open.

The original winter kit covered the inboard cylinder openings, installed with spring hooks, and also had a plate to covered the center cowl vent.

Mine falls in that range and the scoop on the passenger side is in front of the head, but on the pilot side the scoop is inboard as there is no room for it in front of the head on that side as that cylinder is farther forward than the other side. 52 models do have the earlier cowl with the shrouds over the cylinders. I think 53 models started with pressure cowl.

In any case, I will check the service manual to see if there is a discrepancy in the configuration. Can’t see much with the cowl open because everything is under the nose bowl but I will take some better pictures from the front. It may be a couple of days from now as wife and I will be getting our second Covid shot tomorrow

Rich

https://support.cessna.com/docs/custsupt/cessnasupport/IPCFiles/P108-12.pdf

Starting with Fig. 49 which setup do you have that's the closest?

Gary

Gary
That link didn’t work for me. I’m on an iPad. Maybe that’s it. I’ll try to find it.
Rich.

No expert here but it looks to me like the left baffle air source feeds the carb heat and the right the cockpit heater.

Gary

Cessna never could figure out a decent way to “manage” air flow over cylinders AND provide cabin heat.

Take the block off plates off, leave them in your hangar/garage, cover the oil cooler with duct tape and go fly.

Lots of these things have been flown way colder than you’ll see that way with no harm done.

My experience with Cessna “winter kits” is they’re useless except for covering the oil cooler.

MTV

Mike

No oil cooler on C145/O-300
On a 30 degree day I see oil temps of 130 without the plates and 175 with them. I’m not hung up on that. I’ve owned and flown a lot of antique airplanes where I never cared about oil temps. Maybe I’m reading too many forums.

Gary

My set up has the right side (passenger side) muffler providing carb heat. It’s inlet is outboard on the right opening and not covered by the plate. The cabin heat is supplied by the left (pilot side) muffler. It’s inlet is on the inboard of the left cowl opening. And is covered by the plate. This is consistent with other 52 model year C170B airplanes I have seen. There is more to this than the covering of the inlet because even when a hole is cut to allow air to get to the scoop, it doesn’t work. Other 170 and 140 owners report the same. I intend to try it myself but I’m not holding out much hope.

Rich

Rich the figures 49-50 I see show otherwise - left carb; right cabin. Not arguing just looking at available figures in the link. Why not hook it up to feed the right muffler that flows better to the cabin or match what Cessna shows?

Gary

Gary

I wish I could see that drawing. It sounds like it’s mirror image. The firewall fitting for the cabin heat is on the left side. The carb heat inlet to the heat box is on the right side of the box. The battery is on the right (passenger) side of the firewall. If your drawing shows it on the other side, that’s for a later model 170.

When I say left and right it’s as viewed from behind the engine.

Thanks for your interest and effort in helping with this.

Rich.

I tried to post pics above but no luck. I did look up the C-170A Parts Manual and it shows what you describe, not what's in the C-170B Parts Manual for S/N 20267-25372. I'm corrected. The mufflers for the C-170B are round...the C-170A not.

Gary

Edit:

C-170 P/M: https://mrwebman.com/aviation/cessna/manuals/170_pm_pre59.pdf
C-170A P/M: https://mrwebman.com/aviation/cessna/manuals/170a_pm.pdf
C-170B P/M: https://support.cessna.com/docs/custsupt/cessnasupport/IPCFiles/P108-12.pdf

This is on a 1954 170B. Not a great picture but you can see where I cut the plate and then made an air scoop to direct the air through the heater intake. This works good, after the plane picks up speed. Plenty of cabin heat down to 0, at 20 probably only open it half.

Do you realize the 170 with no oil cooler, has an air blast tube pointed at the oil temp probe? That would be the first thing I would block off. Then read what your oil temp. really is. I would be very cautious about blocking airflow over air cooled cylinders. In the past in Alaska, we would block the center vent holes on the nose cowl but not the cylinder openings. That applies to the 140 also. You can also put a cover over the 140’s oil tank, to keep the temp up. I certainly would not block off my cabin or carb heat cold air intakes...

nanook said:

.... we would block the center vent holes on the nose cowl but not the cylinder openings.....

Click to expand...

That's the one that lets air blow in onto the oil sump. Cover it up in cold wx, might help a little.

Good suggestions about the blast tubes. I knew they are there but forgot to consider them in the equation.

Thanks

Rich

Gary

I think the confusion comes is that the 52 170B was the first year and has a lot of 170A artifacts. The Engine install is one, the panel with the piano key switches is another. The major change on the 52 B model is the wing and flaps, being exactly like the 172 of today. The 170B POH (owners book) that claims to be for all B models is focused on the later models. I have not been able to find a hard copy of the strictly 1952 book, but I know it exists.

In any case, you all have given me good advice and I will try the simple things first. I do have the cover plate that covers the hole in the cowl that blows directly on the crank case.

Just to close out the thread, I’ll take more pictures of the front where the intakes are for info

Rich

Another option might be to put an air intake adapter (or another in addition to the original) in that sump cover plate and feed the heater muff. I did that on a PA-11 with a similar opening and it helped the cockpit airflow and heat. I realize there's a factory trough installed behind it to channel cooling air to the sump, but maybe that can be modified some for winter? After 75 years of living with winter plus 56 in alaska I like heat when flying.

Gary

Rich,

How did you resolve your heating issues with the winter kit installed on your 52' 170B?

I also have a 52 170B. Fortunately this winter has been pretty mild but this past weekend it was in the teens and I wanted to go flying so I dug out the cowl plugs and attempted to use them for the first time. While they certainly kept the engine toasty... I was freezing. In my 52 the heater is plumbed from the pilots side and the carb heat is plumbed from the passenger side. Did you decide to swap the scat tubing so that it crosses over? Having just replaced all of the parts of my muffler and heater on the pilots side last winter (it kept trying to poison me) I'm reluctant to mess around with something that is now working happily.

Thanks!

Hayden

Well, I actually gave up after destroying an extra block off plate. Truth is when the temp gets below 25f or so around here I don’t even want to open the hangar. So I use the small block off for the small opening in the cowl and leave the cylinder block plates in the cabinet. For the usual winter temps we get here on Long Island this configuration gives plenty of cabin heat while giving acceptable oil temps at at temps around 30.

In my younger days (I’m in my 57th year of flying) I used to fly open cockpit in December and January. Those days are long gone.

Rich

Rich,

I'm in Rhode Island and have been flying the same way. Until the other day there had not been a flyable day when I was available and it was under 25f.

Last summer I ended up over at KMTP pretty frequently. Hopefully our paths cross this summer, I would love to compare 170's.

-Hayden

I owned a 52 Cessna 170B equipped with an O-360 Lycoming for about 20 years, much of which was in Fairbanks, AK. Granted, it's a different engine, but that cowling is wide open, no doubt. I covered the oil cooler, and left it at that.
When I first arrived in FAI, I was assigned a brand new (1985) Cessna 185, which came set up with a full winter kit.....cowling air inlet block off plates (fairly elaborate gizmos with slits for air inlets and ramps riveted to the back of the plates) and a block off plate for the induction, which had a ~ golf ball size hole in the center, but other wise blocked off the entire induction air filter.

The recommendation from Cessna was don't install this stuff above (I think) -20. My first winter in FAI, I dutifully installed all three of those plates when the bottom fell out, and went flying at -30, headed north. As I climbed through the inversion layer, CHTs and Oil temps both went up alarmingly. So, I descended back down into the cold layer. That whole trip was flown at about 500 feet. ANd, there was virtually NO cabin heat or windshield defrost. Miserable trip.
I got back to FAI and chatted with an old time mechanic. His recommendation: Remove those cowl inlet plates, duct tape about half the oil cooler, and leave the induction plate installed. That worked beautifully for twenty years, operating in very cold temps occasionally. That mechanic cautioned against disturbing the cowl inlet air. His point was that an untested plate could conceivably create turbulence in the inlet air, and maybe create hot spots on cylinders.
The induction block off on the 185 restricted the amount of cold induction air to help prevent the engine from making too much power, based on the very dense cold air. When at high throttle settings, the engine creates a vacuum in the induction, which opens the alternate air door in the cowling induction plumbing, thus mixing warm lower cowling air with that frigid arctic air coming through the induction filter.

At 25 degrees, I really wouldn't worry at all about cylinder temps. After all, those things have fire inside. Oil temps, of course should be around 180 if possible. That said, I've run a lot of hours with oil temps below that range. My C-90 Cub got an insulated cover for the oil sump, and that stupid blast tube on the oil temperature bulb was removed. Temps seems fine, flying above zero.

MTV

Hayden

Would be nice to meet. MTP has been sold and the landing fees are ridiculous. I believe all the hangar Leases have been canceled. East Hampton is worse.

I’m based at KHWV. Brookhaven. There’s a really good diner here now. Closed Monday and Tuesday currently. Other wise open 8am to 2pm. The sectional says *RP. That means gliders use Right traffic. Powered planes use standard left traffic.

What airport are you at?

Couple of pictures of my whole airplane.

MTV

I had a Legend Cub with an O-200 and my buddy had one also. We flew together all the time. In the winter I put the oil tank insulation kit on and the push rod insulation kit. He didn’t. Our oil temps were exactly the same. I told myself that maybe mine retained the heat longer on the ground, but never tested it. Those planes ran oil temps about 100 to 110 degrees over ambient. Never flew much over 1000 feet in 700 hours so the effect of cooler air higher up was not a big deal. Even on 90 plus days the oil temp never hit 200.

The C-145 in the 170 acts in a similar way. I have not blocked the blast tubes so that’s something that might give higher oil temps in the winter. Like you, I have owned a bunch of old airplanes from T-Craft and 65 J3 to a modified Fleet 16B with a W670 220 Continental on it and never cared about low oil temps. Of course, I’m not in Alaska.

Rich.

Richgj3 said:

Hayden

Would be nice to meet. MTP has been sold and the landing fees are ridiculous. I believe all the hangar Leases have been canceled. East Hampton is worse.

I’m based at KHWV. Brookhaven. There’s a really good diner here now. Closed Monday and Tuesday currently. Other wise open 8am to 2pm. The sectional says *RP. That means gliders use Right traffic. Powered planes use standard left traffic.

What airport are you at?

Couple of pictures of my whole airplane.

Click to expand...

That’s a beautiful airplane Rich. Makes me miss my 48 ragwing.

MTV - Thanks! As always you are a wealth of knowledge. The oil temp gauge on my 170 is just a green bar with a yellow strip on the right side. I guess I should just relax and trust that if its in the green all is good. I will keep flying with the oil pan covered and the cowl plates removed. Easy peasy.



Rich - My town beach is currently $40 to park at. The landing fees at KMTP seem like a fair alternative. Besides I don't want the airport to close. I can land and surf the sandbar on Shagwong without a soul around. I've attached a photo of my 170 and my adventure buddies. I have never been to KHWV, I'm always looking for a good fly in diner. I'll message you.

Fishsticks said:

MTV - Thanks! As always you are a wealth of knowledge. The oil temp gauge on my 170 is just a green bar with a yellow strip on the right side. I guess I should just relax and trust that if its in the green all is good. I will keep flying with the oil pan covered and the cowl plates removed. Easy peasy.

Click to expand...

I recommend you calibrate that Cessna stock gauge by removing your oil temperature probe and inserting it in a bath of oil in a Pyrex style container and heating up to 200F while measuring temperature with a quality thermometer. Do this at least twice to catch the temperature on the way up and way down. Helps to have someone ready to mark the gauge with either very fine line tape or a fine line sharpie. The temperatures I have marked on my oil temperature gauges are 100F and 180F. My engines do not go above 1000 RPM at less than 100F oil temp and the 180F is required to remove moisture formed by the process of combustion. If you show 180F on your gauge, there are locations within the engine that are higher, which is a good thing.
TR

TRDunn said:

I recommend you calibrate that Cessna stock gauge by removing your oil temperature probe and inserting it in a bath of oil in a Pyrex style container and heating up to 200F while measuring temperature with a quality thermometer. ....

Click to expand...

An easier way, at least with regards to readings up close to red line, is to put the probe in a pan of boiling water.
Water boils at 212 degrees (100 C).