Was wondering which one is more popular? Here's what I'm thinking about the mechanical gauges:

• You're bringing fuel into the cab. If the gauge bellows cracks, you got diesel everywhere. I had that happen to me with an oil pressure gauge once.
• You have this long tube filled with fuel that never goes anywhere. The fuel that fills the tube tomorrow will be the same diesel 10 years from now. Given the propensity for algae growing in the fuel, wouldn't that be an ideal breeding ground thus contaminating the fuel and clogging the gauge?
• Is there a procedure for "priming" the mechanical gauge so you don't get and air in the line. Air compresses, creating inaccurate gauge readings.

I've heard things about sending units going bad in electrical gauges, so I'm sure which way to go. Any suggestions are welcome.

 

It takes water for alge to grow. If your fuel is clean it shouldn't be a problem.
My mechanical guage has a stainless braided line to feed, and attatches through a $3 needle valve so if there's a problem I would just shut off the valve. It also is shut off until the gauge just starts to register so the flow can't be that dramatic, and as an added bonus also dampens the "pulses" some see with a mech. gauge plumbed at the Inj. pump.
#1 plus for the Mech gauge.....No sending unit to go bad. ;D
If it says no pressure....there's probably no pressure.

 

I have the Di Pricol mechanical guage with an isolator. The isolator is nothing more than a cylinder with a piston inside. It's mounted under the hood tywraped to the firewall wiring harness. One side of the piston a port connects to the fuel. The other side connects to the gauge in the cab. The side going to the cab is filled with antifreeze. I have some air bubbles in the line going to the gauge but that doesn't cause any problems according to Di Pricol. The reason for the liquid antifreeze in the line instead of just air is that the coefficient of expansion of air with temperature changes would cause inaccurate readings depending on the temperature. The liquid doesn't change much in volume with temperature changes. I thought about not using the isolator and just running the line into the cab. Visions of fuel squirting out into the cab with flames and other nasty things happening changed my mind.

 

I just had the same question. Glad I didn't start a new thread.<br><br>I'd be a little leary about putting a fuel line into the cab, but I suppose a braided metal line with such a low pressure would be (gulp) fool proof. I was also thinking about maybe putting in a shutoff valve that could be closed via a cable pull to the top of the dash so I could manually shut it off if something happens.<br><br> A great idea just hit me. how about a hydraulic fuse. I was just looking at one on a plane's brakes today. If a certain amount of hydraulic fluid passes through the fuse, it shuts off so that you don't lose fluid from the whole system.<br><br>Now the hard part. Where to get such a hydraulic fuse small enough for this application. The ones I was looking at today shut off when 30cc of fluid pass through. Maybe one with a 3-5cc limit would work.<br><br>Sorry for the long post, but it posed a problem to me and uncovered a creative solution. Maybe someone out there has some thoughts on this?<br><br>-SFB

 

Running a fuel guage inside a truck is crazy. <br><br>Just buy a kit with a isolator and no fuel will ever come near the truck.. <br><br>Be smart about this.. Mechanical are the best guages without a doubt. It is a exact reading. <br><br>Its like comparing Analog to Digital, the mechanical guages will give u a better sweap but are not dead on accurate.. But lets be real if the guage says 0 psi its says 0 psi and hopefully your truck is not running.. [undecided]<br><br>Spend the extra money and buy a isolator

 

[quote author=wick link=board=7;threadid=7117;start=0#70532 date=1037890788]<br>Running a fuel guage inside a truck is crazy. <br>[/quote]<br><br>I'm going to offer up an alternative opinion here. I personally prefer non-isolated, full mechanical setups, with a line run inside the cabin of the truck. There is virtually no risk of fire from diesel and the KISS rule applies here ;D Should you have a leak, the diesel fuel is easier to clean up than a glycol/water mix (sticky crap, been there, done that :'()<br><br>If you use a quality line, such as a braided stainless with teflon, good swivels and fittings, and a liquid teflon at each join, the risk of leaks is minimal. When doing your gauge install, the first time you fire up the truck, hold the gauge in your hand, outside the cabin of the truck. If your going to get a leak, chances are this is when its going to happen.<br><br>Rod

 

mechanicals are considered 'exact' only because they are perceived to be simpler in nature and measure pressure pressure &quot;directly&quot; without conversion. consider, however:<br><br>a mechanical gauge converts fuel pressure to antifreeze pressure, and then converts mechanical pressure to movement (of the needle). The system is subject to inaccuracies in the gauge movement (expanding metals), the antifreeze isolator, and the length of the line. all of these issues have been thoroughly perfected and are no longer important factors. There are many such gauges in production use today in critical applications that demand reliability and accuracy. <br><br>an electric gauge converts fuel pressure to electrical pressure, and then converts electrical pressure to movement (of the needle). the system is subject to inaccuracies of the sending unit and the needle movement in the cab. all of these issues have been thoroughly perfected and are no longer important factors. there are many such gauges in production use today in critical applications that demand reliability and accuracy. <br><br>even the simplest mechanical pressure gauges convert pressure to movement, which is no different than what an electronic gauge does (it converts electrical pressure to movement). The smarts of a mechanical gauge is in the meter movement. The smarts of an electronic gauge is in the sending unit. Both are subject to inconsequential amounts of degradation over time and vanishingly low field failure rates. <br><br>BTW, if you're concerned about the reliability of electronic gauges, then you need to also worry about your oil pressure, fuel level, and volmeter gauges supplied by DC in your instrument panel. only yours will be easier to get to and service.

 

OK, so when you're looking for a &quot;mechanical&quot; fuel pressure gauge, how can you tell if the model uses an isolator, or is directly piped?

 

[quote author=Commatoze link=board=7;threadid=7117;start=0#70639 date=1037903590]<br>OK, so when you're looking for a &quot;mechanical&quot; fuel pressure gauge, how can you tell if the model uses an isolator, or is directly piped?<br>[/quote]<br><br>by smelling the end of the hose line? . <br><br>I would think, though, that the temperature expansion behavior of fuel (read: gauge accuracy w/ temperature) would be a pretty bad boy to deal with, but I have to say I don't have any experience in that area.

 

the isolator and the guage are seperate. The isolator is usually D shaped... see pic below..

 

[quote author=Doug link=board=7;threadid=7117;start=0#70634 date=1037903125]<br>(of the needle). the system is subject to inaccuracies of the sending unit and the needle movement in the cab. all of these issues have been thoroughly perfected and are no longer important factors. there are many such gauges in production use today in critical applications that demand reliability and accuracy. <br>[/quote]<br><br>In essence, I agree with what you are saying here Doug. There are electric gauges available whose accuracy and reliability appear to be reasonably good, however I haven't seen an affordable one for the light truck market. Apparently SPA's sender is tough and accurate, however you're stuck with a digital gauge. But, a mechanical is still going to outlast even the best sending unit around. I've got mechanicals that are close to 30yrs old and still work every bit as well as the day they rolled off the factory lot. I don't have an electric around that can say that.<br><br>Rod

 

Aha! Mechanical it is. :

 

I had some issues with a connector for a fuel pressure guage with isolator...I noticed a small white line on the connector and paid no attention to it until I popped it into place and started the truck...Glycol and water all over and stains on the dash. :'( Then I tried a braided line direct from the post filter position to the gauge and the darn line did not have a swivel and I needed one for in the dash pod...well...then I had some diesel spill. It sure cleaned up better but it stunk up the truck a bit. :'(<br>So I finally got a braided line and it has swivels on it...works great now. I got rid of the smell too. I just bathed in #2 and that neutralized the aroma. ;D

 

well, 30 yrs ago the electric gauge state of the art wasn't where it is today. Sending units are extraordinarily accurate and reliable now, and the needle movements themselves have been around for about 100 years. I've come to the conclusion that most people will confuse what they understand with some notion of an objective reliability difference. When you work with something week after week you learn to trust it because you understand it. What you don't understand, or are less familiar with, you tend not to trust. <br><br>BTW, an pyrometer thermocouple is an electronic sending unit.