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O-360 FP high CHT and fuel flow issues follow up

WingnutWick

Well Known Member
All,

A follow up post from my earlier post: http://www.vansairforce.com/community/showthread.php?t=159504

So after confirming with Dan H via photos, my original baffle seals were "the worst he's seen in a while" haha. So I completely re-did all of the seals, added a washer behind #3 ("washer trick"), and sealed off all the gaps in the baffling with Permatex. Furthermore I adjusted my dual P-Mgas to -1.4 Adv Shift and max advance to 36.

All this improved my CHT's by around 30+ degrees as now I am able to hold my hottest cylinders (#3, #4) around 400 at WOT, full rich, sea level on a slightly hot day. It's still a bit hotter than I imagine it should be but a heck of a lot better than skyrocketing back 430 instantly. I believe I will attempt the "baffle mod" in the near future to attempt to bring those down a little further.

I am still showing my #1 running pretty cool compared to the rest. For example at a normal cruising altitude at 2500 RPM pre lean I will see this: #1-344/1349, #2-372/1314, #3-383/1293, #4-312/1206. As I begin to lean #1 will peak out earlier than the rest at 1390. I will continue to lean to drive #1 LOP. #2 and #3 will peak out around 1410 and, with #1 showing about 30 LOP. Resulting lean from this has: #1 20 LOP, #2 50 ROP, #3 87 ROP, #4 110 ROP (with #4 never hitting peak). Any thoughts on these spreads? Normal?

Finally, cleaned gascolator wire screen (pretty clean) and crimped off a primer line that was no longer being used and broken - still seeing the low fuel pressures on WOP and full rich. Again no noticeable loss in power when this happens or significant change to EGT's though it is often accompanied with a large spike in FF momentarily and then as the FF's drop back down shortly thereafter the fuel PSI will rise a bit. Does this sound like air in the lines?
 
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In that case, not much you can do about the fuel flow/EGT spread per cylinder.

I would agree that it may be fuel vaporization that is causing your random pressure changes. If so, turning on the boost pump should remedy the issue.

Also, if you have a gascolator, remove it if allowed. If the mechanical fuel pump doesn't have a cooling shroud, install one.
 
I do have a gascolator, that was the screen I cleaned. You're saying remove it - as in bypass it altogether for troubleshooting? I cleaned its filter and replaced the O-ring to make sure there weren't any leaks.

The electric fuel pump does return the PSI to nominal.

I don't think there is a cooling shroud on my pump. Is this something I have to fabricate?

Thanks for the help!
 
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I do have a gascolator, that was the screen I cleaned. You're saying remove it - as in bypass it altogether for troubleshooting?

Gascolators have been known to absorb heat when installed under the cowling (typical location), transmit that heat to the fuel and provide little benefit. Most RVs don't have one unless required by the approving authority. Folks in Canada say they must have one installed.
 
Gascolators have been known to absorb heat when installed under the cowling (typical location), transmit that heat to the fuel and provide little benefit. Most RVs don't have one unless required by the approving authority. Folks in Canada say they must have one installed.

Really? Every carbed RV I know of has a gascolator. All running with no issues. Our airport has more than 40 RVs and many are good running carbed models? all running gascolators?- mine included.
 
Gascolators

Gascolators are installed in the low point of a fuel system to trap water. I have yet to see one installed in an RV that is lower than the fuel tank drains. If you drain the tanks during your preflight, then any water will be purged from the system. Therefore, IMHO, a gascolator installed in a RV is no more than a poor filter, and a source for heat related problems. Grandfather worship!

My certified Grumman AA-1A Yankee did not have an installed gascolator for the same reason.
 
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Gascolators are installed in the low point of a fuel system to trap water.

Gascolators are installed in "a" (not "the") low point. They are a local low point and by virtue of holding a few ounces of fuel, allow the fuel's velocity to slow enough so gravity separates the water from the fuel. Kind of like the baffles in some dust collectors. Alternately, it works the same way as how sediment will stay suspended in fast moving water but will fall out once the water enters a slow moving area or lake.

That said, I have a gascolator and have never found water in it. I do suspect it adds to the under-cowl fuel heating problem.
 
Gascolators are installed in the low point of a fuel system to trap water. I have yet to see one installed in an RV that is lower than the fuel tank drains. If you drain the tanks during your preflight, then any water will be purged from the system. Therefore, IMHO, a gascolator installed in a RV is no more than a poor filter, and a source for heat related problems. Grandfather worship!

My certified Grumman AA-1A Yankee did not have an installed gascolator for the same reason.

A gascolator does not remove water by being at the low point. It is an active "separator" (uses cyclonic flow and dwell time) and will separate water from gas and store it at the bottom of the gascolator bowl (the water sinks due to it's higher density), at least up to it's capacity. It does not have to be at a low point to achieve this goal, the same way that a fuel filter can remove debris without being at a low point.

The goal is to backup the tank drain method, as well as to capture liquid saturated gas that has not had a chance to settle, such as filling up at the local FBO. Its takes time for the water in suspension, especially small drops as you find when that saturated gas goes through a high pressure pump like a fuel dispenser, to work their way to the low point.

Water is nasty business with a carb. Any drops that make it to the carb, go straight to the bottom of the bowl and coalesces where fuel is drawn into the jets. It doesn't take much water to create a real problem with a carb. I would think twice about removing a gascolator from a carb'ed engine, as it is a safety device.

Larry
 
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Gascolators are installed in the low point of a fuel system to trap water. I have yet to see one installed in an RV that is lower than the fuel tank drains. If you drain the tanks during your preflight, then any water will be purged from the system. Therefore, IMHO, a gascolator installed in a RV is no more than a poor filter, and a source for heat related problems. Grandfather worship!

My certified Grumman AA-1A Yankee did not have an installed gascolator for the same reason.

No, but if your Yankee was like all of the later Grummans it did have a secondary filter built into the base of the firewall mounted fuel pump. It was the only crud removal between the tank and the very fine inlet filter on the carb.

Wouldn't the filter part of a gascolator be considered a good thing? Even if it is a poor filter? :)
 
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No, but if your Yankee was like all of the later Grummans it did have a secondary filter built into the base of the firewall mounted fuel pump. It was the only crud removal between the tank and the very fine inlet filter on the carb.

Wouldn't the filter part of a gascolator be considered a good thing? Even if it is a poor filter? :)

Any filter is a good thing. A high quality dedicated filter would be much better than the screen in a gascolator. I have one for each tank mounted in the wing roots, a larger filter mounted just prior to the firewall, and finally, the screen in the fuel injection throttle body.

I have seen many RV's with just a gascolator.
 
Update

So launched off yesterday and paid special attention to the fuel situation as the CHT's seem to be under control for the most part. (#1 still running high EGT's compared to the others - valve leak??).

In regards to the fuel PSI, had very low PSI on deck (which is abnormal), sometimes dropping to 0 indicated on taxi. Turning on the boost would return values to nominal. On takeoff used boost pump with full mixture rich, but once I turned the boost pump off when at a safe altitude the PSI would plummet to between 0-1 PSI at which point I noticed a spike in my EGT's and an audible RMP rise as they peaked out indicating a lean condition due to the lack of PSI. FF if anything goes up during this time. I had to turn the boost pump on to keep from running at peak (or potential loss of power).

WOT and mixture rich exacerbates the situation, if I pull the mixture back, reducing the fuel demand, the PSIs improve a bit but that requires me running CHT's above 1350 or higher on climb. At cruise, the PSIs return to pretty much normal as I am leaned out. The problem seems to be worse with lower tank states but I don't have enough data to confirm that.

What are the indications of a failing engine driven pump? Can a failing pump also have indications similar to air in the lines - or possibly cause air in the lines?

Pretty close to buying a new pump, but any other ideas before I pull that $700+ dollar grenade pin is greatly appreciated!
 
So launched off yesterday and paid special attention to the fuel situation as the CHT's seem to be under control for the most part. (#1 still running high EGT's compared to the others - valve leak??).

In regards to the fuel PSI, had very low PSI on deck (which is abnormal), sometimes dropping to 0 indicated on taxi. Turning on the boost would return values to nominal. On takeoff used boost pump with full mixture rich, but once I turned the boost pump off when at a safe altitude the PSI would plummet to between 0-1 PSI at which point I noticed a spike in my EGT's and an audible RMP rise as they peaked out indicating a lean condition due to the lack of PSI. FF if anything goes up during this time. I had to turn the boost pump on to keep from running at peak (or potential loss of power).

WOT and mixture rich exacerbates the situation, if I pull the mixture back, reducing the fuel demand, the PSIs improve a bit but that requires me running CHT's above 1350 or higher on climb. At cruise, the PSIs return to pretty much normal as I am leaned out. The problem seems to be worse with lower tank states but I don't have enough data to confirm that.

What are the indications of a failing engine driven pump? Can a failing pump also have indications similar to air in the lines - or possibly cause air in the lines?

Pretty close to buying a new pump, but any other ideas before I pull that $700+ dollar grenade pin is greatly appreciated!

Lycoming's operator manual says 0.5 to 8 psi at the carb with a desired 3 psi.

No operating conditions specified so this would be for all operational phases of flight.

It sounds like the pump isn't putting out the volume needed and hence the pressure drops. Probably new pump time. :)
 
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