Aeromotive FPR and liquid-filled pressure gauges - underhood heat durability

[NewZed]

Does anyone out there know FPRs and fuel pressure gauges? I have a general question, I'm hoping someone with experience can answer or just comment on the topic.

 

I recently replaced my stock FPR with an Aeromotive 13301 adjustable regulator (maybe overkill for a stock engine but it was $45 on CL), after my gas mileage dropped, my exhaust smelled like gas more than usual and I noticed my fuel pressure was sitting 2 psi higher than normal.

 

I mounted it on the intake manifold and it gets pretty hot. Does anyone know how the Aeromotive regulators hold up to heat? I have a message in to Aeromotive but have not heard back yet.

 

Also, I have an inexpensive (cheap ~$18) liquid-filled JEGS fuel pressure gauge mounted on the fuel rail, in place of the cold start valve. Aeromotive recommends a dry gauge due to accuracy drift with temperature on the liquid-filled gauges. There is also some internet info about cheap gauges falling apart under high heat due to soldered joints, poor materials, etc. Has anyone ever heard of a gauge leaking or falling apart? How about accuracy of the liquid-filled gauges? Are they permanently damaged with heat or just inaccurate when they get hot?

 

The new FPR works great and the gauge makes me feel good, checking pressure occasionally to confirm all is correct, but I have visions of my car burning to the ground if something fails.

 

Thanks for any insights.

Edited August 25, 2010 by NewZed

[Tony D]

" Has anyone ever heard of a gauge leaking or falling apart? How about accuracy of the liquid-filled gauges? Are they permanently damaged with heat or just inaccurate when they get hot?"

 

Lots of questions which are not really related. I work in general industry on Rotating Equipment and have seen liquid filled gauges costing $1000's of dollars fail. Same with the dry ones. The liquid is generally put in there to stabilize the needle movement and keep a sensitive movement from wearing itself out. They usually last longer where vibration and pulsation is an issue, compared to non-dampened, non snubbed dry face gauges.

 

"Accuracy" and "Longevity" are mutually exclusive terms when dealing with gauges. Accuracy is only achieved through regular calibration...read some of the comments from the precison calibration guys in the 'Balancing your L6 Valvetrain' thread to see what I mean.

 

The gauges with glycerin fill generally are oriented to be 'vent up' so that the dampening fluid will not leak out. Generally you install them, run the machine up to pressure and temperature and let the dampening fluid expand and weep out. But the back remains open to atmosphere so the dampening fluid's epansion or contraction will not put a stress on the internal tube or mechanisim. It's not the heat, it's where you calibrate it to be accurate that counts. It can be accurate at 15C or accurate at 55C, but not both. There will be some error and that is what calibration is: the art of compromise. Generally you want it accurate in operation so that would mean calibrate it hot. It doesn't matter how it came, that is just a gauge, it still needs calibration before installation. A check against a good known reference source. 2psi on a 100psi reading gauge is 2% of full scale and is considered generally to be well within acceptable deviation. If you want accuracy and not something that looks good under the hood, then you will be spending a lot more than what you did on your Jeggie Meter!

 

What permanantly damages them is overrange conditions, it expands the tube and can damage the movement permanently after one event if the excursion is severe enough.

 

My FPR gauge is a 6" Diameter Ashcroft Test Gauge with a mirrored face and 270 degree sweep, with a 0-120psi range. You don't want to know how much one of those costs. But when I get my cheapies, I manifold them both together, and note on the face of the cheapie the correction factor to use (-5 or +3 for example, meaning the gauge reads 5psi high, or 3psi low repsectively...and those are good numbers for an example!) Do it cold, do it hot. Then you know.

 

Right now you have a guessing gauge. "Guess it's right." Better to have KNOW gauge, or NO gauge at all! Never want a "Guessing Gauge"!

[NewZed]

That is a lot of good information. Thanks for sharing.

 

In the meantime I had a chance to look at the gauge hot and cold and then insert a big bulky inline auto store gauge (of dubious quality also of course) to check against. After a long drive and 15 minutes sitting, the gauge read 32 with fuel flowing, compared to 36 cold in the morning. After cooling off, it matched the 36 that the second gauge measured. Confirming what you've said and what Aeromotive recommended against (using liquid-filled gauges to tune with).

 

It read 38 hot when I was having rich running problems with my 33 year old original FPR so I was probably actually closer to 41-42.

 

It was $18 well-enjoyed for my cheap Jeggies gauge (it doesn't even have a vent that I can find). Now I know something more about gauges in general. At least it gave me another clue that something was wrong with my regulator (the engine runs much better and cleaner with the new FPR). I'll just leave the JEGS gauge on and only look at it cold, until I can upgrade. It seems like a Schrader valve, a high-quality dry gauge and some fittings might be the way to go.

 

The Aeromotive guys responded and said essentially what you said. They also said that the electric gauges were probably the best way to go for a full-time application, since the dry ones are not that durable if used full-time.

 

Thanks again.

[Tony D]

They do make buffered gauges--a sensing line that goes to a diaphragm, and then glycerine fills the line between the firewall and the in-dash gauge... That is pretty accurate.

 

The schrader valve and EFI Tester would be more accurate for sure.