[trib]

This may be a silly question, but figured I'd check with those with experience. In looking to reduce oil temperatures during the hot summer months, I plan on blocking the flow from the baffles to the cabin heat muff on the exhaust pipe. Since I don't need the heat, this air is just exhausted into the cowling, reducing the differential pressure from the air inlet and exhaust and reducing the cooling air flow over the cylinders and the oil cooler. I'd like to know if others do the same and check to see if there is any concern for the scat tubing attached to the heat muff, as there will no longer be any air flow through the tubing. The air will continue to flow external to the tubing of course, within the cowling, and I would think this would be sufficient, but would appreciate some confirmation from those who did this already. Design of the scat tubing is for 450F. I just planned on installing a blank plate over the hole in the baffle behind cylinder #3 where the scat attaches to block the inlet.

 

[Kyle Boatright]

Typical advice is that you need some airflow through the heat muff to prevent heat related problems with the muff or exhaust. Maybe you could put a plate over the flange feeding the heat muff then drill a much smaller hole in the plate to allow some airflow.

IMO, the key in reducing oil temps is increasing the flow through the oil cooler and I believe you'll see better results from increasing the size of the opening feeding the cooler than from closing off the flow to the heat muff, although reducing losses to the heat muff will help some.

What oil temps are you seeing and have you compared your installation to another airplane where the temps are to your liking?

 

[Russ McCutcheon]

Hi Tim,

I?m wondering the same thing, what are your oil temps? 225-230F on a climb to 10k on a hot summer day and 200+ in cruse on the same hot day is fine. Don?t block off the cabin heat muff, by all accounts I have heard, it needs air flow to prevent damage.

 

[kevinh]

This may be a silly question, but figured I'd check with those with experience. In looking to reduce oil temperatures during the hot summer months, I plan on blocking the flow from the baffles to the cabin heat muff on the exhaust pipe. Since I don't need the heat, this air is just exhausted into the cowling, reducing the differential pressure from the air inlet and exhaust and reducing the cooling air flow over the cylinders and the oil cooler. I'd like to know if others do the same and check to see if there is any concern for the scat tubing attached to the heat muff, as there will no longer be any air flow through the tubing.

I do this every spring. I take a few inches of aluminum tape and cover the inlet on the baffle 75%. Still has some air going over the exhaust and some heat if I want it. Works great.

 

[erich weaver]

I taped up the hole in the baffles entirely and removed the sheet metal cover to the heater. Pretty simple and fast and I need heat so rarely...

Erich

 

[flyboy1963]

data points fwiw

My engine seem to cool nicely, credit to the builder and baffles?
Actually find it hard to heat up to 150 on the ground in winter, with oil cooler blocked off.
summer, rarely see temps of 200, even in a long climb on an 80 degree day. 2 heat muff inlets, one at the front left, and other at the rear right side, oil cooler top rear left side, just dumps straight back at the firewall.
stock 0-320 carb, FP prop, using Exxon elite 20w-50, no filter

 

[trib]

Still no joy

Well, I did go ahead and block off the heater hole on the right (passenger) baffle. I also disconnected the scat tubing from the heater muff so it wouldn't see any higher temps with no air flow. Checked carefully and found two small gaps in the baffling just above the oil cooler where I installed a sheet metal shield to bridge the area where the baffling bumps aft. I sealed these with red RTV. The cooler is the standard cooler mounted on the baffling behind cylinder #4 per van's plans. I've checked and verified that the oil flow is into the lower portion of the cooler and exits the top. With OAT at 80F at 2500 ft, (and similarly with lower temps) I have to limit cruise power to 2300 RPM to keep oil tems below 215F. Today it was at 213F at 2300 RPM. The cowling seal appears to fit and seal very well, and the inlet ramps were glassed closed at installation. No issues with the ram air seal to the carburator as mentioned in another current post concerning high oil temps. I never noticed any issues during phase I testing, but that was from Dec to March with much cooler temps (initial flight was at 20F). Cruising to Roanoke from Chesapeake last weekend at high power (2600 RPM) and leaned the temps rose to 240F, causing me to reduce to a maximum of 2300 RPM and running full rich. This kept the temps in the 215F range, which I still consider too high.

One post mentioned that using semi-synthetic oils lowers temps. I'm using Phillips XC 20W-50 as recommended by ECi.

I do wonder why the oil cooler is mounted so low. It seems like if it were mounted higher there would be more cool airflow over the cooler. About half of it is mounted below the cylinder fins. Have most people mounting the cooler on the baffle kept it in the plans location, or has anyone moved it higher, and if so, did this help?

Other than relocating the cooler, about the only thing I can see doing is to replace it with the more expensive SW cooler.

Any advice would be welcome!

 

[L.Adamson]

Other than relocating the cooler, about the only thing I can see doing is to replace it with the more expensive SW cooler.

Any advice would be welcome!

For a comparison, my "Van's" cooler is also mounted on cylinder #4, as high as possible. RV6A with Lyc 0360. I haven't seen 200F in the 150 hrs it's flown until I installed the Van's slider on the cooler for this winter. It can raise temps from around 155 - 205F. Before that, I'd block around 2/3rds of the cooler for winter flight.

I just went through a lot of pics that I've took of the panel, during various cross country flights for the last two summers and winters. Highest temp without the slider was 195 degrees F. Temps in the summers here range from the low 90's to 100. Most pics show summer temps in the 185 degree range.

I also have not internally blocked the cowl ramp that's been discussed. But both sides do get blocked tightly with the baffle material ( as Scott from Van's mentioned..... by design)

My temps are generally in line with an RV9A that I often fly with, so I'd say that the gauge is reasonably accurate.

I just seen that an RV owner removed his "slider" door because of high summer temps. My RV has not flown for the last two weeks because of the annual condition inspection. However, the 9A owner said that his temps are still below 200 with the slider in place ( open position). It's been in the low to upper 90's here, for most of the last two weeks. For those who haven't seen the slider, it does block part of the cooler between slotted openings. But the open area is more than the cooler when subracting the passage areas --- so I've heard.

L.Adamson -- RV6A

 

[MrNomad]

My two cents.....

Cooler oil temps is never a silly question. The replies, however, need to be viewed in the context of the airplane's location. I am in Tucson so what happens in San Mateo or BC is going to be different than Virginia Beach or Tucson in July for the obvious reason.

When we built my 9A, we raised the oil cooler to the height that would maximize airflow. I have never seen 240 nor can I even recall a 215 oil temp.

Second, Vetterman told me repeatedly via phone calls to ALWAYS make sure scat was connected to the muff. He didn't care where the output went, but forced air had to go in.

My 9A with O-360 has a FP prop, uses Exxon Elite 20w-50, & filter. I generally run at 1450 egt, lean to below 7 gph, 2400 rpm approx.

When I raced air cooled Corvairs in the 60's, we always had a full sump of oil. I've heard otherwise, but 8 qts of oil has to bear the cooling load better than 6 especially in summer temps like VA & AZ. Bottom line, I try to get my trips started before the heat of the day with temp swings as much as 35 degrees.

 

[Kyle Boatright]

Well, I did go ahead and block off the heater hole on the right (passenger) baffle.

I do wonder why the oil cooler is mounted so low. It seems like if it were mounted higher there would be more cool airflow over the cooler. About half of it is mounted below the cylinder fins. Have most people mounting the cooler on the baffle kept it in the plans location, or has anyone moved it higher, and if so, did this help?

Other than relocating the cooler, about the only thing I can see doing is to replace it with the more expensive SW cooler.

Any advice would be welcome!

As previously suggested, leave some airflow through the heat muff.

Regarding where the cooler is mounted, mine is as high on the baffles as it'll go without interfering with the cowling. Also, it allows a bigger opening in the baffles. Speaking of which, how large is the hole in your baffles? Bigger is better. Originally, I had mine per plans, but I eventually expanded it 25% or so. I recommend expanding the hole in the baffles to as large as practical before you order a new cooler.

 

[yakdriver]

If you have fuel injection balance your injectors so you can run lean of peak. Running LOP lowers my CHTs 40 degrees and my oil temps 10 or more. I also have ECI tapered barrel cylinders with 9.5-1.0 pistons. At 80 degrees OAT my oil runs 205 when LOP and 217 ROP. CHT is 340 LOP and 385 ROP. That's at 23" 2450RPM 6500 MSL. Don

 

[trib]

After sleeping on it last night (i.e. dreaming about it!) I'm pretty sure the problem lies in how I mounted the cooler. I went back through the drawings, and my installation looks just like the plans, but... there is a note that says to mount the cooler as close to the top as practical. Mine is a good 3" lower than the top. Moving this up will expose a significant amount of the cooler to increased air which does not first go through the #4 cylinder fins. I'll relocate the cooler and let everyone know the results.

thanks for the help!