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Does your engine driven fuel pump become a heat sink when you shut down?

Jetguy

Well Known Member
Yes it does!:D
Here's the scenario. OAT 70 F or hotter, engine driven fuel pump in good working order, carbs balanced and in good working order. You come in from flying and shut down for about 15 minutes while you refuel then you head back out for some more flying fun. But when you throttle up for takeoff the engine runs ruff and you think your engine fuel pump just went bad.:confused: What really happened in this scenario is when you turned your master switch on for startup and fresh fuel from the electric fuel pump entered the engine driven fuel pump it vaporized because the engine driven fuel pump got really hot from heat transfer from the engine case. ;)
Two ways to stop this from happening.
First, if it's hot out side and you are going to do a quick turn, leave you electric fuel pump running while you refuel. This will keep your engine drive fuel pump cool.
Second, during your takeoff roll after a quick turn your engine starts to run ruff at full power, abort, taxi back to the end of the runway, increase power to about 3000 rpm and choke the engine for about 30 seconds. :eek:Then turn choke off and try a full power run up, now the engine should run normally. What you are doing is increasing the fuel flow through the engine hoses and cooling everything down.
We were able to reproduce these scenarios many times today once my buddy and I figured out the problem and how to fix it. There is a time frame after you shut down when the engine heat in your cowl will peak and begins to cool off. If you wait till after this peak (no idea what the approx time would be) then you will most likely not experience this problem. The way you can verify this could occur in your engine is after flying shut down you engine and wait about 3 to 5 minutes, then put you ear next to the cowl opening in front of the engine driven fuel pump and listen for a few minutes, you will hear nothing. Then go turn on you master switch and electric fuel pump, go back and listen again to the engine driven pump. What you will hear is a sizzling sound of fuel vaporizing in the pump. After about 5 minutes the sound will go away as the raw fuel cools the pump. It seems like we never stop learning something new about these engines. :)
 
Heat Issue

I usually pop open the oil door when I shut down for a few minutes or stop to have my $100 hamburger. Helps everything to cool down quickly and avoid the issue that you discussed.:cool:
 
A small louver on the top of the cowling works well too, someone on here did that a few years ago with success. If I recall correctly, Vans sells them as part of the RV10 stuff. Automatic convection airflow when stopped.
 
Thanks John, good info. I think Cubdriver also hit on a helpful tip. I have been through a pair of ignition modules and a voltage regulator. They all went sour at the 250 hr. mark. My thought is that prior to shut down, there is still a small amount of airflow through the cowling, but as soon as the prop stops, things start to really heat up. The engine, radiator and oil cooler are still radiating heat. Lets face it, the Rotax is a hot one. The heat continues without the ventilation and that is when it does get hot under there. I use the same practice of opening the oil door as soon as I exit. Its' amazing how much heat pours out of that opening. Will it make components last longer? Don't know, but it can't hurt. Personally, I think it will. Another thought that I have had, but not completed, is to form a scoop inside the plenum horn to force ram air to the voltage reg.. It could be a simple as a small scoop added to the end of the black conduit that runs from the plenum to the volt./reg. shroud. Of course. this scoop will only help when the prop is spinning.
 
While visiting the Van's booth at SunNfun I noticed the voltage regulator on the SLSA RV12 was mounted in the cockpit under the instrument panel.

I placed a temp sticker on my regulator in the engine compartment and so far the 170 degree tab is dark. Will have to see what shows up in August.
 
I have the temp strips on the ignition modules and the regulator and they are showing 140 degrees.
 
Recent research,

I hope no one here has 170F+ on the ignition modules because that is where these will fail. 170F is the magic bullet temp. (You don't want to be there). I just finished a test (which may be slightly different from model to model aircraft), but on a recent test of a Flight Design the module temps were 130F and the reg/rec which on that plane is mounted in the engine compartment on the right side firewall was only 115F. These temps are well within temp specs. One way to help keep some under the cowl temps down is to use header wrap. Other ways is to allow an opening some where towards the top of the cowl that can allow heat to rise as it sits and no cool air is flowing through as it would during flight. You can buy this temp strips from several places.

You don't really need them to be below 130F, but 140F-220F would work
 
I usually pop open the oil door when I shut down for a few minutes or stop to have my $100 hamburger. Helps everything to cool down quickly and avoid the issue that you discussed.:cool:

Guess you and I are the only ones doing this. Every shut down, I try to face the wind and open the oil door. Instant chimney effect with hot air flowing out. (Makes me feel better, anyway.)
 
We used to do the oil door thing on the Bonanza too. On the RV12, when you say "open the oil door" - mine does not raise fully open and stay there. (Unless you take off with it unlatched but that is another story.) I would have to use a clip or something to keep it fully open - one that would not mar the paint, maybe a wooden clothspin. Is the small gap you are getting by just unlocking it adequate?

I have a battery maintainer pigtail that I leave connected. It holds the oil door open about 1/2 inch when I open the oil door and pull it out and connect the maintainer to it.
 
Just tighten up the bolts/nuts that serve as the hinges on the oil door and the friction will hold the door open. Put a nylon washer between the aluminum parts to reduce the wear. I think that opening the oil door after flights also prolongs the service life of the cowling.
 
Guess you and I are the only ones doing this. Every shut down, I try to face the wind and open the oil door. Instant chimney effect with hot air flowing out. (Makes me feel better, anyway.)

Another good idea, face into the wind always. Saves wear and tear on that canopy.
 
Opening the oil door isn't a bad idea, but really should not be necessary for any over heating issue. I would agree that it would help dissipate heat under the cowl better. Pump temps don't get very high and many times the noise you hear is the pressure in the system bleeding off and not boiling off. Heat from the engine can add to some vapor in hose lines especially ones that aren't in fire sleeve, but it shouldn't be a major concern. This is one reason why all 912's should have a re-circulation line.

For example:
My plane after sitting for 45 minutes after a shut down my exhibit a low fuel pressure on a re-start, but a few minutes of running or taxi to the runway usually has it back up to normal. I have talked to hundreds of 912 pilots and don't know a single one that has ever had an engine shut down or issue at take off because of it.

If this was a real and problematic issue thousands of 912 owners would be screaming about the problem and going down all over the world. Rotax has over 4 million hours and has a pretty good handle on things.

When I get a chance this Thursday I'll run a temp test on the pump. My guess it it never goes over 130F and maybe lower.

I'll report back.
 
Opening the oil door isn't a bad idea, but really should not be necessary for any over heating issue. I would agree that it would help dissipate heat under the cowl better. Pump temps don't get very high and many times the noise you hear is the pressure in the system bleeding off and not boiling off. Heat from the engine can add to some vapor in hose lines especially ones that aren't in fire sleeve, but it shouldn't be a major concern. This is one reason why all 912's should have a re-circulation line.

For example:
My plane after sitting for 45 minutes after a shut down my exhibit a low fuel pressure on a re-start, but a few minutes of running or taxi to the runway usually has it back up to normal. I have talked to hundreds of 912 pilots and don't know a single one that has ever had an engine shut down or issue at take off because of it.

If this was a real and problematic issue thousands of 912 owners would be screaming about the problem and going down all over the world. Rotax has over 4 million hours and has a pretty good handle on things.

When I get a chance this Thursday I'll run a temp test on the pump. My guess it it never goes over 130F and maybe lower.

I'll report back.
It's not a black and white thing. Will there be any observable benefit? Maybe, maybe not. But like I used to tell the operators who would operate *my* machinery back the old petrochem mfg days - heat kills, more heat kills faster.
 
I've never experienced it that bad after a quick fuel stop (and that is in 100+ degree heat around Phoenix and Tucson). I have a switchable electric fuel pump and I do experience start-up problems after a quick engine shutdown for fueling. So I turn on the electric pump while waiting for the SV to boot up, but the engine still runs somewhat faint after it fires up for about 10 seconds. Then the lines seem to have flushed and the engine runs as usual. I have never experienced any roughness or loss of power on take-off after a fuel stop - and would honestly be quite a bit terrified if it was otherwise.
Oh, I should add that I keep my oil door open during the refueling process to promote the chimney effect. For what it's worth... (the "cool" air is scooped up from the tarmac and is probably 120+ degrees hot in the summer).
 
Talk To Me About Header Wrap

Recent research,

One way to help keep some under the cowl temps down is to use header wrap. Other ways is to allow an opening some where towards the top of the cowl that can allow heat to rise as it sits and no cool air is flowing through as it would during flight.

Before taking action to move the oil cooler further away from the muffler, I bought some muffler wrap. I did not install it, but instead, I added about 3/4" of clearance between the muffler and the oil cooler, via a cowl duct mod. My temps have been running well within the guidelines, with both CHT, and oil temp staying just below 200. I am still considering wrapping the header pipes down to the muffler, with the intention of getting rid of some of that exhaust heat, and forcing it out the tailpipe. Is that what you are suggesting? I still have the wrap! Your thoughts??..............Tom
 
I think the header wrap will help and won't hurt. It isn't a cure all, but will enhance what you have already done. I installing header weapon another plane today. I have it on mine. It can make a difference depending on what you are trying to accomplish.
 
Putting insulation wrap on a stainless aircraft exhaust is a sure way to reduce its life.
Larry Vetterman is adamant that people don't wrap the stainless systems he sells. The insulation greatly raises the temp of the pipes and they burn away from the inside out.
The wall thickness of the pipes on the RV-12 exhaust are thicker than it is for the Lycoming exhaust, but it still applys.
 
I recommend against it.

This is what my exhaust looked like after about 18 month of header wrap. If you moved your oil cooler forward then you will be fine.:D if you live in a high humid area then the rust would be much worse.:(

0eb43b907bb30a1e48bee02ab95ae043_zps9f05d6bb.jpg

7cd1cbb47d034e87b870f495bbbd4571_zps0bc7101b.jpg


While were on the subject I heard a rumor that Synergy is thinking about changing the oil cooler location, any truth Scott?:confused:
 
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Wow!! I sure don't want my pipes looking anything like the above pictures!! As I said, I am pleased with my operating temps, with both CHTs and oil temp under 200, even with 80 degree OATs. I do notice that the upper cowl gets pretty warm after shutdown, which I attribute to trapped heat. I just open the cowl oil door, post flight, to let it out, which seems to work just fine. Thanks for the heads up................Tom

Correction: My original post said EGT, and it should have been CHT, which I corrected. By the way, my EGTs run closer to 1400 degrees. Sorry for the typo.....Tom
 
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These are stainless pipes. Many aircraft have had wrap on for 10+ years and have never had an issue.
In my years around Rotax I have seen broken exhaust pipes, both wrapped and bare pipe. More bare pipe just because there are more bare pipes out there. These usually break because they were not properly stress relieved when welded or are under some tension in their mounted position. I just did another wrap yesterday on a CT. Mine has had it on there for 7 years. Standard iron composition exhaust pipes are subject to carbonization (makes them more brittle) where stainless is not because of the nickle and chrome. There are 18 different types of stainless. If yours looks like the above picture it is because they have been subjected to moisture. The discoloration won't hurt anything and isn't visible with the wrap on. If the wrap is applied correctly and not over wrapped by more than 3/8" on the edges then no appreciable wear should come from the wrapping. Over wrapping by 1/2 the wrap or more can cause excessive heat, but for our short 15" run isn't usually a problem either. I don't see many wrap the muffler. Many RV12's and other Rotax engines have exhaust leaks at the knuckles where the muffler and pipe meet. Sometimes and adjustment can fix this, but many times it can't. A wrap down and over the knuckle can stop the hot exhaust blow-by from causing problems in that area. (i.e. burnt wires, dried out engine mounts and exhaust residue on everything around it and excessive wear at the joint from the hot gas leak jetting out). The exhaust temps will not change, but the advantage of a wrap is a greatly reduced radiated and convective heat to wire insulation, hoses and under cowl temps. The wrap MFG claims a 70% reduction in heat (?), but even if it isn't that much it's huge. If you land would you put your hand on the exhaust port bare pipe. Not and keep any skin, but with the wrap on you can.

Bottom line color on a pipe is nothing, but cosmetic and the gained advantages far out weigh some coloring on the pipe.
 
p.s.

Exhaust springs per Rotax should be safety wired through the spring. Springs do break and even though with a tractor prop won't go through they prop fall out on taxiways, runways and fall into populated ares as bombs. The safety wire is to keep the spring on the plane in case of a break. They do break as I replace them from time to time. The springs shouldn't be filled with silicone. This procedure was abandon long ago due to excessive heat build up from filling the spring and it can't dissipate the heat. The silicone should only be down the side of the spring. When the spring is filled it can not stay air cooled and the excessive heat will cause premature failure and you can't run a safety wire through the spring. After many hours of use the small amount of silicone on the top hook won't hold anymore as it doesn't have a good enough purchase point and the heating will loosen its hold. I called Vans about this and I'm surprised they haven't verified with Rotax and made the change. It's a simple easy change. Here is a picture as an example of a more proper way. There are some variations to this.

http://ctflier.com/index.php?/topic/2817-exhaust-spring-and-header-wrap-picture/
 
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I'm sure this debate is just like the ethanol one and it's a lot like the Chevy and Ford likes and dislikes.

You may like one, but not usually the other, but they both get you where you're going. Just a matter of preference.


"Larry Vetterman is adamant that people don't wrap the stainless systems he sells. The insulation greatly raises the temp of the pipes and they burn away from the inside out.
The wall thickness of the pipes on the RV-12 exhaust are thicker than it is for the Lycoming exhaust, but it still applys."

"Larry Vetterman is adamant that people don't wrap the stainless systems he sells.


You may have hit the nail on the head because without knowing what metal composition he uses he could have issues. This may not be apples to apples comparison. I don't know, but it isn't a Rotax exhaust.

Different stainless composition does matter. Too much iron content and it can become more brittle and when wrapped properly raises temps marginally. Over wrapping can cause the excessive heat. There is a line right on the wrap so you know exactly where to wrap and no further and it says it right on the packaging. If it was a serious problem no aircraft or race cars would use it. The racers use it many times to help keep the exhaust gases hot all the way down the pipes (long pipe runs) as this causes less back pressure from cooling exhaust and allows a small jump in HP. Our 15" of pipe won't make any difference in anything because it's too short a run. Just don't over wrap. I have seen many RV AB with header wrap and several at my field and they have been wrapped for years without issues. It's all about knowing your metal and proper installation. I have a friend with an LSA Rotax powered aircraft he uses for instruction. He has right about 2000 hrs. now and the pipes have been wrapped since the day he took delivery.
 
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I don't think it is common knowledge out side of where the RV-12 exhaust is manufactured (Van's welding shop), what material it is made of either, so I think generalizations comparing it to other 912 powered LSA is not valid.

Interesting that a parallel thread just popped up in the forums. As posted previously, I recommend caution regarding wrapping the RV-12 (or any RV) exhaust.
 
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