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Old 05-23-2012, 10:01 AM   #1
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Default Anyone had problems with liquid filled fuel pressure gauges in the heat (ex. Summit)

I have been chasing my tail with this fuel pressure dropping off after the car gets hot (mostly happening when the car gets hot and I park it, then restart it hot). Started wondering if it could be air in the line from the reg to the gauge in the cowl area since my pump has no check valve, but that led to a few post I found about these liquid filled gauges being pieces of **** and reading low (or zero) when they get hot. Something about the gauge compares line pressure to atmospheric and since they are internally sealed as they get hotter the pressure inside the gauge it self increases thus lowering the pressure reading shown on the gauge.

This would seem to make a lot of sense in my application sense the car doesn't seem to run differently when the gauge is reading sometimes as low as 20psi (vs. 43 base), and typically will get better after a few minutes of driving after a hot restart (probably the gauge cooling off a little from the heat soak of sitting in the cowl with no air flow).

Anyone else had a problem with this? I am thinking about just pulling the little plug and letting the liquid bullshit flow out. Upside is this is the cheapest fix I can think of!

Here is a video of a guy putting a heat gun on his gauge (granted it is a carb'd application so the fuel pressure is much lower anyway).

[youtube]ZdkWbRV5JyU[/youtube]

Here is what my car was doing:


Started it up today from dead cold in the garage. Fuel pressure was normal. Drove it up to Firestone (had a weight on one of my front runners come off). Restarted it 10 min later after they finished and the pressure was low (should be ~37psi at idle, was around 30psi per gauge. About 10 minutes into the drive the pressure was back up to ~37psi and stayed there for the rest of the trip (another 20-30 minutes).

Got home. Killed it, waited ~5 min, restarted it and pressure was ~25psi.

Seems like either the gauge is getting heat soaked or the pump doesn't like being restarted hot. Unfortunately I don't have an easy way to use my diagnostic fuel pressure gauge on this car since it hooks to the schrader and all I have on this is the 1/8th NPT on the side of the regulator.
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Old 05-23-2012, 01:57 PM   #2
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Originally Posted by dville_gt View Post
I have been chasing my tail with this fuel pressure dropping off after the car gets hot (mostly happening when the car gets hot and I park it, then restart it hot). Started wondering if it could be air in the line from the reg to the gauge in the cowl area since my pump has no check valve, but that led to a few post I found about these liquid filled gauges being pieces of **** and reading low (or zero) when they get hot. Something about the gauge compares line pressure to atmospheric and since they are internally sealed as they get hotter the pressure inside the gauge it self increases thus lowering the pressure reading shown on the gauge.

This would seem to make a lot of sense in my application sense the car doesn't seem to run differently when the gauge is reading sometimes as low as 20psi (vs. 43 base), and typically will get better after a few minutes of driving after a hot restart (probably the gauge cooling off a little from the heat soak of sitting in the cowl with no air flow).

Anyone else had a problem with this? I am thinking about just pulling the little plug and letting the liquid bullshit flow out. Upside is this is the cheapest fix I can think of!

Here is a video of a guy putting a heat gun on his gauge (granted it is a carb'd application so the fuel pressure is much lower anyway).

[youtube]ZdkWbRV5JyU[/youtube]

Here is what my car was doing:


Started it up today from dead cold in the garage. Fuel pressure was normal. Drove it up to Firestone (had a weight on one of my front runners come off). Restarted it 10 min later after they finished and the pressure was low (should be ~37psi at idle, was around 30psi per gauge. About 10 minutes into the drive the pressure was back up to ~37psi and stayed there for the rest of the trip (another 20-30 minutes).

Got home. Killed it, waited ~5 min, restarted it and pressure was ~25psi.

Seems like either the gauge is getting heat soaked or the pump doesn't like being restarted hot. Unfortunately I don't have an easy way to use my diagnostic fuel pressure gauge on this car since it hooks to the schrader and all I have on this is the 1/8th NPT on the side of the regulator.
Doesnt matter who makes the gauge, Liquid filled gauges will change pressure based on temp. the fluid expands and causes pressure on the internal membrane thus causing low pressure reading. Change to a non liquid filled gauge or only check fuel pressure after the car has cooled down (not the best for trouble shooting)
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Old 05-23-2012, 09:30 PM   #3
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I have this one, and haven't had a irregularities with it.
It's been very steady, although it hasn't had a torch put to it.
http://www.summitracing.com/search/?...d=800199&dds=1
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Old 05-24-2012, 10:15 AM   #4
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I have this one, and haven't had a irregularities with it.
It's been very steady, although it hasn't had a torch put to it.
http://www.summitracing.com/search/?...d=800199&dds=1
that is the one i am running. i don't put a torch to it either, but it is mounted in right in the cowl area under the hood pointing towards the windshield and between my t6 turbo and the air conditioning the heat coming out of that area is pretty crazy.
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Old 05-24-2012, 12:10 PM   #5
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that is the one i am running. i don't put a torch to it either, but it is mounted in right in the cowl area under the hood pointing towards the windshield and between my t6 turbo and the air conditioning the heat coming out of that area is pretty crazy.
Yeah, mine is mounted up front, and the hood leaves alot of room for airflow.
Maybe that's the difference.
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Old 05-25-2012, 01:07 AM   #6
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hi dville, there should be a rubber fitting on the side of the gauge. remove it, dump the liquid, and call it good.
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Old 05-25-2012, 01:07 AM
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