Mine will read correctly when I start it and then when warm it will go to zero. Chico at Moon told me to crack open the rubber cap on the side and it would release a vacuum and would then read again. This was correct but it released some of the liquid fill oil. I had to keep doing this while checking fuel pressure because it would continue to go back to zero. Does any one else have this problem? I think it is a gage quality issue my self. Here is a shot of how my gage is mounted.
Yes, I've had this problem. As the liquid expands from the heat it skews the guage reading. i'm not saying they all do this,but every one I tried did. ANymore I learn to ONLY read them when the motor is cold - otherwise they will get you into trouble. This was especially fun to learn at the racetrack!!!!
I had the same exact problem you speak of. I think that peice of **** is still laying behind my tool box after I bounce checked off the wall. I just ended up setting my pressure regulator at 1 IB and its been working great sence. I think I have to set it that low because I am running a stock model A tank which puts a pretty good head pressure on the fuel before it ever gets to the pump.
I'm sure its the same gauge made by Marshall that most everyone sells. I went through 3 gauges on my car... Chris 50 changed his out as well. Getting a good quality gauge from Autometer... would help. I swapped my no-name for a Barry Grant and its been fine for 4 years.
Yup, me too! I think it is a heat problem, has anyone tried running one of the remote moon fuel gauges? P.
I have one on my fuel block and it seems to work properly.....have had it for maybe 3 years.......liquid filled......no problems here... Brucie
I have a Summit gauge on my Chevy and the thing just ****pola on me last week (lasted maybe 6 months or so).
If it's a remote read, the new ones use antfreeze in the line instead of oil. Maybe the oil gets hot and thins out. Try an Autometer remote and keep the Moon gauge.
Try shaking out all the liquid, you may get a better reading. The liquid filled ones seem to work better at higher pressures.
I've heard the same thing on liquid filled gauges when hot. Where exactly is yours mounted? Curious since I just replaced a bad non filled one on my fuel log with a liquid filled Marshal.
Commonly available liquid filled gauges are very susceptible to changes in temperature and barometric pressure. Our tech line advises customers to remove the gauge, walk to the garbage can, remove the rubber plug, and drain the liquid in the garbage can. You then have the option of either throwing the rubber plug away as well, or attempting to drill or poke a hole in the rubber plug without doing the same to a finger. The plug works well to keep bugs and other debris out, but to work properly, the gauge needs to be vented.
Side-Valve has it right dump the juice out of it and it will work ok.especially at lower pressures. .....Bob
Mine is bolted on a stand off bracket which in turn is secured to the head of my Big Block. What has got me thinking is, if the oil in the gauge is getting hot enough to create a false/zero reading how hot is the fuel getting? As this is the second Moon gauge I have tried, both having the same issue, I will take the advice of draining the oil out and seeing how it functions then. Still worried about the fuel temprature though.... P.
My Moon gauge is on the firewall and has been on the mark for four years. I've thrown away at least a half a dozen of the ****py pressure regulators with the dial on top.
I spoke to Moon again yesterday. I told them I took their advice and vented it and it worked just momentarily. They said it should not do this and for me to send it back and they would replace it. I just have to dig through my paperwork and find the reciept for the gage first. I am tempted to try to drain the oil first before sending it back to them.
Checkthe picture in the beginning of the thread to see where it is mounted. It is in line going to the carbs in front of the valve cover.
Here's a couple Marshall's I've been running for quite a while. Non-oil filled. They work fine and hold pressure for quite a while after the engine is shut down - two days after shutdown will still show pressure. I've used oil filled gauges in shop air compressor systems with no problems. There's a mechanical Mooneyes fuel pressure gauge in the dash. It's maybe ten years old, no problems. It does have an isolater and I use ATF in it. Some guys use mineral oil and others use anti-freeze. Trick to get a good read on a dash mounted FP gauge is to get all the air out of the dash side of the isolater. You can make it self-bleeding if you put a "T" fitting at the high point and make sure the line from the isolater and the line from the gauge run uphill to the"T". Just fill it and let it sit for a while and all the air bubbles are out.
Duh.... Ive got mine on the back side of a fuel rail that is pretty high. A nice cool spot even with the top of the cowl. I haven't had a chance to take her out and see how it'll work since I put it on though.
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