Fuel pressure in hot weather

[JerzyGeorge]

I have another question:

 

About 2.5 years ago on taxing back to hangar I noticed fuel pressure fluctuating widely . It was very hot summer day in NSW , Changed the engine pump for new one and never happened again even in hot weather.

 

Until yesterday , While flying about 3,500 feet and filter air box temperature about 30 deg C I noticed fuel pressure dropping slowly. Was not happy at all , switched on electric pump , pressure came back where usually is on engine pump only. After short time I switched electric off and pressure started dropping again , was not brave enough to wait and see how far will drop. Turned electric on and was good . It happened a few times with time in between anything 10-15 minutes. In the end left my electric on for a duration of the flight 1.5 hours. I am thinking of replacing the engine pump with the new one again.

 

Any comments from you guys?? I cannot provide any numbers because my pressure is only indicated by green field with no numbers , but I know where usually is or where should be.

 

 

[facthunter]

You have done the right thing with the indications you had. You are either getting vapour lock (are you running on mogas?) or there could be an air leak on the suck side of your engine pump. Have you retensioned the screws on the engine pump diaphragm? Don't overdo it but sometimes they take up a bit. Insulate your fuel lines where they might be subject to heat also. Nev

 

 

[JerzyGeorge]

Thanks a lot Nev,

 

Bolts are tight, checked them as checking others, all the connection on fuel lines tight, but do not have red thermal insulation on fuel lines. It runs on mogas 98 UL Jerzy

 

 

[facthunter]

Mogas is a bit good at vapour locking. It can also cause bubbles in the float chamber and loss of bouyancy of the float leading to flooding. I think I got the last lot of insulating cover from Aviall. The more of this you do the luckier you get. Nev

 

 

[Yenn]

Would loss of buoyancy of the floats cause loss of pressure? I would have thought it would cause flooding. The engine driven pump is pulling fuel within the hot engine space, a lot of electric pumps are pulling it from a much cooler area and pressurising it before it passes the firewall.

 

 

[facthunter]

Flooding gives a higher fuel flow. Nev

 

 

[jetjr]

Could also be clogging filter?

 

 

[JerzyGeorge]

Thanks guys,

 

My electric pump is in the engine compartment but on the fire wall, the engine pump is at the front on Rotax and fuel lines run on the top of engine where can get hot , filter is before pumps just on the outlet from header tank , inspected every week. So I reckon I will get the fuel line thermals on the lines to engine pump.

 

 

[RichTee]

Hi Jerzy,

 

Have a look at my thread http://www.recreationalflying.com/threads/fuel-ambient-temp.142031/

 

Your snag may be due to other factors (as suggested by other responses)....but I have certainly seen high temps leading to dropping fuel pressure & increased fuel flow.

 

With us at no time did the 912ULS cough or show any signs of being unhappy BUT at 300ft doing anti-poaching work, watching one's fuel pressure drop and fuel flow increase sure gets one's attention !!!!

 

In our case its was / is definitely ambient temp with a few other factors thrown in. Our thoughts on the matter are that:

 

1. MAKE SURE your lagging on the exhaust manifolds and pipes are adequate and intact.

 

2. Make sure you don't have any leaking welds on your exhaust system....we had 4 small holes at various points, hidden by lagging. VERY scary

 

3. We are considering drip trays / heat shields (see http://contrails.free.fr/temp/912_installation_3.pdf)

 

4. If ambient temps are going to be high then AVGAS is the way to go.

 

5. Set limits on temp above which we don't fly .....not due to density altitude / PA issues but rather because the fuel system is not happy.

 

Hope this helps,

 

Rich

 

 

[Kyle Communications]

There is also a rubber bung in the back of the fuel pressure gauge...remove it

 

 

[JerzyGeorge]

Hi Jerzy,Have a look at my thread http://www.recreationalflying.com/threads/fuel-ambient-temp.142031/

Your snag may be due to other factors (as suggested by other responses)....but I have certainly seen high temps leading to dropping fuel pressure & increased fuel flow.

 

With us at no time did the 912ULS cough or show any signs of being unhappy BUT at 300ft doing anti-poaching work, watching one's fuel pressure drop and fuel flow increase sure gets one's attention !!!!

 

In our case its was / is definitely ambient temp with a few other factors thrown in. Our thoughts on the matter are that:

 

1. MAKE SURE your lagging on the exhaust manifolds and pipes are adequate and intact.

 

2. Make sure you don't have any leaking welds on your exhaust system....we had 4 small holes at various points, hidden by lagging. VERY scary

 

3. We are considering drip trays / heat shields (see http://contrails.free.fr/temp/912_installation_3.pdf)

 

4. If ambient temps are going to be high then AVGAS is the way to go.

 

5. Set limits on temp above which we don't fly .....not due to density altitude / PA issues but rather because the fuel system is not happy.

 

Hope this helps,

 

Rich

Thanks a lot , it crossed my mind and I checked manifold and muffler but did not find any cracks or holes . My Rotax exhaust pipes from cylinders are bare with no lagging , have you got some photos of yours and material type. It is scary to put any insulation on hot exhaust pipes , midfilght fire is not my favorite option. I have drip trays under carburetors to shield them from heat.

Jerzy

 

 

[RichTee]

Hi Jerzy,

 

I'll take some photos later this week and get them too you. I agree be very careful with the material used. We got a registered guru (AMO) to do it for us - he used the approved GA insulating material.

 

Can I ask you to send me some pics of your carb sheilds.

 

Many thanks,

 

Rich