Somewhere in a textbook "Handbook of Instrumentation and Controls" by Kallen......there is a reference to what I'm getting ready to type.....will do my best to look it up if necessary.....

Basically, most mechanical pressure and vacuum gages that we are likely to find at a reasonable price will be of the "Bourdon Tube" type...Bourdon Tube manufactured from Phosphor Bronze.....I'm not gonna go into how and why it works.....but as the tube tends to straighten out under pressure, or contract under vacuum....the end of the tube is connected to a gear train that ends up operating a pointer.....to prevent the tube from operating at it's designed limits (the max pressure on the gage face).....one should select a gage that will operate somewhere near it's midrange....(if you wanna measure 15psi, buy a gage that reads 30psi).......prolonged operation at or near the gage's maximum range will eventually damage the gage, the Bourdon Tube will take on a set.......

Digital gages are a totally different subject......but basically the same rules apply regarding range selection, of the sensor or transmitter element...no matter how the digital onformation is sensed.....

Trust me.....I have replaced many pressure gages in my lifetime ......

SB

__________________

Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG

I have been thinking about using the Gasser Economy Gage for/as a Vacuum Gage.....it will be operating in a range that it was designed for......Economy=Manifold Vacuum.....I have wondered why MB did not do this, instead of manufacturing a different instrument cluster for Diesels??

SB

__________________

Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG

I finally got the needle off the shaft. I ended up using a fork and pulling it straight up with my thumb on the pointer head.

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A diesel doesn't operate at the same manifold pressures. With a diesel more Manifold vacuum = blocked air filter = poor economy.

Higher manifold pressures, to a point, give BETTER economy with a diesel.

__________________
Ron Schroeder
'85 300 Turbo Diesel 2 tank WVO
'83 300 Turbo Diesel 2 tank WVO
Some former WVO vehicles since ~1980:
'83 Mercedes 240D
'80 Audi 4000D
'83 ISUZU Pup
'70 SAAB 99 with Kubota diesel
'76 Honda Civic with Kubota diesel
'86 Golf
Several diesel generators
All with 2 tank WVO conversion
LI NY

I think he is thinking of using it as a gauge to monitor the vacuum system, not economy.

__________________
1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

Is it normal for the gauge to react really slowly? It's pegged at exactly 13psi but it takes 3 seconds to return to the other peg when boost goes away.

My VDO gauge works pretty quickly...boost won't go away instantly, it takes a while for it to simmer back down if you are in 3rd or 4th gear. Boost will go away quick I suppose if I goos it in 1st gear and let off. But your gauge should be pretty responsive. I've got the 85 CrAp emissions model, can't remember which turbos those have.

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1985 CA 300D Turbo , 213K mi

I guess I should have said it responds slowly going up and down. By the time my normal boost gauge is at 13psi, the cluster gauge is barely half way.

The pointer is probably overdamped for use as an absolutely real time boost gauge. Ask mj_sid if he notices the same thing in the SDL boost gauge.

Sixto
93 300SD

Just a possibility on the slow responding gauge. Is there any chance you have carbon plugging the line, or a crimp in the line to the gauge?
Either of these could add damping to the movement without cutting pressure, if they were not completely blocking airflow.

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-Josh
Testing the cheap Mercedes axiom, one bolt at a time...

i have a pillar pod guage on my truck with boost exhaust temp and tranny temp But i tow 10-12000 lbs down the road isnt this overkill on the car?

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commercial fisherman diesel in my blood in my boats trucks and Dear old Dad has had me drivin them since i got my first license in 1968
1986 300 SDL 427654
1999 Chevy Crew Cab Dually 225423
1986 300 SDL 287000 Dad's
1987 190 Turbo 158000 Mom's (my inheritance)

Some gages have built in "Pressure Snubbers"........if you look at the inlet connection, and there is a screw inside, back it off a half turn or so.....

Pressure Snubbers are to minimize pressure fluctuations, and keep the pointer from vibrating (sort of!).......and by keeping pointer fluctuations to a minimum they prolong the life of the moving parts within the gage.....

FYI......always select a gage that will read normal operating pressure at it's midscale....so if you wanna read 15psi....use a 30psi gage....

SB

__________________

Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG