Fuel Vacuum Gauge

[Gulf Comanche]

What would be an ok reading on a fuel vacuum gauge? I did a search here because I know this has been discussed, but no luck. At the end of a 6 hour ride home this weekend my gauge was reading 3.5 to 4 inches vacuum. Filters were changed maybe 20 hours ago, fuel was clean when I changed them. What passes for a normal reading? Engine is a Perkins 4-236.

 

[DavidM]

Racor, the fuel filter people, sells a vacuum gauge specifically for this purpose. It is marked with three vacuum ranges: 0-7" is normal, 7-10" is yellow, and 10" and above is red.


See https://www.marinepartssource.com/v...trMevKrq9bMTV834sPqwICZh8ARWU7DhoCKP4QAvD_BwE


David

 

[Comodave]

What was the reading right after you changed the filter element? I would be concerned about the amount of change. If they read 0 shortly after the change then your reading is showing that something is going on. How bad it is may depend on your system. I would watch it and see what your normal is.

 

[caltexflanc]

How high are your fuel tanks in relation to the filter? If they are below the filter, such as the molded-into-the-hull centerline on our old Hatteras, the vacuum gauge will automatically read a little higher, in our case a couple inches. What RPMs were you running vs max RPMs when you looked at the gauges?

 

[Comodave]

How high are your fuel tanks in relation to the filter? If they are below the filter, such as the molded-into-the-hull centerline on our old Hatteras, the vacuum gauge will automatically read a little higher, in our case a couple inches. What RPMs were you running vs max RPMs when you looked at the gauges?

Absolutely. That is one of the reasons you need to learn what your normal is. Check the vacuum after about a half hour after the change and make that reading your baseline. Then watch the increase and change it after maybe 6 to 8” rise.

 

[syjos]

Mine sits on 0 for about 50 hours after changing the element.

I change the element when the needle reaches the yellow.

I have Racor 500's with the gauges mounted in the T handle holes.

I use 2 micron filters. Engine is a Lehman 120

 

[Martin J]

to those who are interested you can pay $80 for a racor gauge, or pay $9.70 from the Surplus store for the same basic thing correctly marked for fuel filter use.
https://www.surpluscenter.com/Hydra...r-Gauge-Use-On-Suction-Line-Only-9-4544-G.axd. I might add this is the same store I get my Engine room fans from. https://www.surpluscenter.com/Elect...C-Rotom-R7-522-Centrifugal-Blower-16-1541.axd

 

[Crusty Chief]

A suggestion, spend a few more bucks and get the good gauge that is oil filled, less fluctuations and I noticed more accurate reading. Anything over 7” and my Cummins starts to surge, this in turn might be causing unnecessary load on the lift pump.

 

[Gulf Comanche]

The tanks are part of the hull, one aft, one midship, one forward. I use the midship tank all of the time, have never used the other 2. The filters are maybe 10’ from the tank, and 2-3’ above it. The RPM on the day I checked was about 1650, which is where I run the engine 90% of the time.

 

[Gulf Comanche]

Absolutely. That is one of the reasons you need to learn what your normal is. Check the vacuum after about a half hour after the change and make that reading your baseline. Then watch the increase and change it after maybe 6 to 8” rise.

That’s a great idea, I usually just change them, crank the engine to make sure there’s no air in the line, and go to the next project. Seems like it takes awhile to go from 0 to 3.5/4.

 

[kchace]

Just as a point of reference, my fuel tanks are about at the same level as my engines and my vacuum gauges read about 0-1 with clean filters.


Ken

 

[jleonard]

Just as a point of reference, my fuel tanks are about at the same level as my engines and my vacuum gauges read about 0-1 with clean filters.
Ken

Same for me.

 

[Boat]

This might be a contentious remark so take it as my opinion.

I like a water separator and a screen (strainer) on the suction side of the lift pump and a filter on the discharge side of the lift pump. Rational is that generally, lift pumps push well but don't pull well. The screen provides protection for the lift pump. It is good to be able to quickly and easily see what is getting caught.

There was a good thread recently about fuel plumbing with an electric pump on the side to bleed the system easily. Don't remember if it mentioned vacuum.

 

[caltexflanc]

This might be a contentious remark so take it as my opinion.

I like a water separator and a screen on the suction side of the lift pump and a filter on the discharge side of the lift pump. Rational is that generally, lift pumps push well but don't pull well. The screen provides protection for the lift pump. It is good to be able to quickly and easily see what is getting caught.

This is standard, with the "screen" in most cases being a primary filter like Racor or Fleetguard. After the pump comes the secondary filter. On my old Detroits, there was a pressure gauge after the pump, as well as a pressure switch which triggered the engine hour meter. On the suction side in line with the primaries are the vacuum gauges being discussed here.

 

[sdowney717]

Clean filters flow easier, but the other thing is volume and suction the pump is drawing, its power. A pump that is drawing greater and harder against any restriction like any filter clean even, is going to create a greater vacuum drop on the supply line than a weaker pump.

 

[jleonard]

Also take note that is not only a filter that will cause high vacuum readings. It could be a hose collapsing internally, a plugged tank vent, et al.
Next time take the fuel fill cap off and see if the vacuum goes down.

 

[Ski in NC]

If filter is 3' above fuel level, that alone is worth about 2-3"Hg. SG of HG I think is what, 13 and diesel is 0.9(??). I know this, vac won't go over 30"Hg!!

And make sure your gauge works. Can't tell y'all how many times I had one of those T-handle gauges in my hand while changing filters and the dang thing read like 10"Hg!! Cal fail!!

One trick is if you have a ball valve on your Racor suction, get engine running and close valve. Watch gauge. Should sweep up to at least 20"Hg, then open valve and see the gauge return to normal. Lots of POS gauges out there. Amazing how many flunk this test.

Just gut feel if you read 3" with clean filter I'd change it before it got to 10".

 

[rgano]

And what is your filter body and micron rating of the filter you are using? Not that that makes a lot of difference, but might help more fully understand your system. Is this gauge on the first filter from the tank?

I replace filters at a 5 inch rise in vacuum.

Coming in the pass off a rough day, I once saw this fuel hungry Yanmar of mine running at 10 GPH get a vacuum of 15 inches, and I almost choked because it is normally ZERO. I quickly opened the valve on the standby Racor 500 (both using 2-mic filters). I was situationally aware because my vacuum gauge reading is taken from a tee in the fuel line after both Racors and before the engine-mounted fuel filter, and the gauge is at the helm via a translucent hard plastic line like you use for an ice maker water line. I did this same arrangement for both engines and generator on my trawler - it's about an hour long job including cutting the hole for the gauge.

 

[rgano]

Photos of tee and vac gauge at helm.

 

[Martin J]

Like that idea Rich!!. It's on my "to do list" As you may have noticed in my previuos post I've just fitted vacuum gauges on mains and Gens. But the addition of vac's on the main bridge I would see as absolute positive step.

 

[smitty477]

Like that idea Rich!!. It's on my "to do list" As you may have noticed in my previuos post I've just fitted vacuum gauges on mains and Gens. But the addition of vac's on the main bridge I would see as absolute positive step.

FWIW - we had our vac gages mounted on the fuel lines near the engines so that fuel 'paths' were not led outside the engine spaces.
A camera was placed so that we could see the vac gage readings at either helm for both mains and the genset.

 

[smitty477]

A suggestion, spend a few more bucks and get the good gauge that is oil filled, less fluctuations and I noticed more accurate reading. Anything over 7” and my Cummins starts to surge, this in turn might be causing unnecessary load on the lift pump.

Most any decent gage will have the ability to fill it with glycerin available for about $2 per bottle. That or you can use a 'snubber' which will alleviate the needle bounce caused by the pressure changes in the line.
We used both a snubber and glycerin in our vac gages mounted on the fuel lines - about $30 each from the gagestore online.
Having gages mounted to the "T" handle necessitates the removal and re-installation of them at each filter change with the possibility of damaging the gage unnecessarily.

 

[syjos]

Having gages mounted to the "T" handle necessitates the removal and re-installation of them at each filter change with the possibility of damaging the gage unnecessarily.

I don't think so.

I've had the 2 "T" handle gauges on my Racors for 19 years and never had any issues.

Had them on my previous boat for 15 years without damage.

The gauges replace the "T" handles. The gauges spin on easily. How will they get damaged?

 

[smitty477]

I don't think so.

I've had the 2 "T" handle gauges on my Racors for 19 years and never had any issues.

Had them on my previous boat for 15 years without damage.

The gauges replace the "T" handles. The gauges spin on easily. How will they get damaged?

If your thoughts are that mounting fuel vac gages in the fuel lines and never touching them again are the same as mounting them where a "T" handle would go on a Racor so that you need to wrench them off and on ….then we disagree.
The gage then gets taken off and 'placed' wherever when the filters are replaced before re-installation at every filter change.

Not a big fan of Racor filters in general either.

 

[syjos]

If your thoughts are that mounting fuel vac gages in the fuel lines and never touching them again are the same as mounting them where a "T" handle would go on a Racor so that you need to wrench them off and on ….then we disagree.
The gage then gets taken off and 'placed' wherever when the filters are replaced before re-installation at every filter change.

Not a big fan of Racor filters in general either.

I don't use a wrench to take the Racor "T" handle gauges off. It spins off by hand just like the original "T" handle.

I take tha "T" handle gauge off and place it on an absorbent pad while I replace the element and top off the fuel. About 2 minutes.

I reinstall the ""T handle gauge, by hand.

I don't see your issue with the "T" handle gauge. Thousands are sold by Racor without consumer complaints. Unless you are clumsy and drop the gauge, or knock it into the bilge, there is no possible way the gauge will get damaged.

I'll repeat;

I've had the 2 "T" handle gauges on my Racors for 19 years and never had any issues.

Had them on my previous boat for 15 years without damage.

The real truth is you don't like Racor.

What do you use to filter diesel?

 

[dhays]

FWIW, on my Cummins 5.9 QSB engine with clean on-engine 2 micron filter and clean 10 micron Racor, my vacuum gauge will max out at 1.5 mmHg with engine operating up to 1,900 rpm.


Typically when I have changed the Racor at a year and the on-engine filter at 2 years, the drag needle is reading between 2-3 mmHg.

 

[smitty477]

I don't use a wrench to take the Racor "T" handle gauges off. It spins off by hand just like the original "T" handle.

I take tha "T" handle gauge off and place it on an absorbent pad while I replace the element and top off the fuel. About 2 minutes.

I reinstall the ""T handle gauge, by hand.

I don't see your issue with the "T" handle gauge. Thousands are sold by Racor without consumer complaints. Unless you are clumsy and drop the gauge, or knock it into the bilge, there is no possible way the gauge will get damaged.

I'll repeat;

I've had the 2 "T" handle gauges on my Racors for 19 years and never had any issues.

Had them on my previous boat for 15 years without damage.

The real truth is you don't like Racor.

What do you use to filter diesel?

I see no reason to attach a gage where it needs to be handled.
There is no fuel system and filter that will read 0" of vacuum even when new.
I have not heard of any manufacturer of engines of fuel filters that recommend 2 mics as a first filter.

I have used many Racors and other filters over time - I find the Racors more
prone to problems, harder to replace, have less filter area ,and more expensive.

 

[syjos]

I see no reason to attach a gage where it needs to be handled.
There is no fuel system and filter that will read 0" of vacuum even when new.
I have not heard of any manufacturer of engines of fuel filters that recommend 2 mics as a first filter.

I have used many Racors and other filters over time - I find the Racors more
prone to problems, harder to replace, have less filter area ,and more expensive.

Wow! Where have you been hiding?

There has been a huge number of discussions on forums and Passagemaker magazine regarding 2 micron filters in the last 20 years. It 's old news.

There is a large number of Racors installed on every type and style of boat. If Racors are "more prone to problems, harder to replace, have less filter area, and more expensive", why do the majority of boat owners choose Racor when adding fuel filters. Why would boat manufacturers install Racor if they are expensive? There are knock off Racors for less money.

Quite a number of boats have crossed oceans and circumnavigated the globe with Racors protecting their engines.

The other fuel filters on boats are Separ and Fleetguard. Neither is as easy to service as the Racor Turbines.

And as for my gauge on my Racor 500 feeding a Lehman 120 which flows minimal fuel since it does'nt cool the injection pump, it reads 0, needle slightly up off the stop. How about I say .0365 instead of 0

 

[trawler joe]

I put a Tee with a small ball valve and nice oil filled vac gauge after the racor to check the vac, u have to check after clean filters installed and if u have any head pressure acting on the gauge too,,any restrictions: lengths of fuel lines to filter, turns, valves, etc add vac too...they are a good tool, someone closed one of my fuel valves and the gauge read 20" or so on clean filters and almost stalled the engine out, but I saw the gauge reading and had the valve opened and engine running ok. smooth sailing

 

[Simi 60]

I have one of these type on ours
Never had any idea where it should read but I have never seen it go any higher, or is that lower, than what is shown in the picture.