I was playing with a fuel/temp/oil pressure gauge pod from a gasser that had the fuel economy gauge. I thought it was a pressure gauge, but it's for vacuum. It ranges from 0-20 psi, so it's perfect for a turbo boost gauge.

Is there any reason I can't drop that whole pod in my car. It says "use premium unleaded only" on the face, but it's not like I'll forget and make that mistake.

I thought I've seen this discussion on here, but i searched and I can't find anything.

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1987 300D - Frybrid - sold
1985 300SD

Try google search. IIRC you pull the needle off, pull the gauge from the back, rotate the gauge unit 180 degrees and reattach the needle.

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http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

Vacuum isn't rated in psi -- it's rated in inches (or mm) of mercury, as in in/Hg. Thus, it isn't a 0-20psi gauge.

Post #27
Turbo boost guage advice needed

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

It will not work as a primary boost gauge. The needle can be relocated for it to used as a boost gauge instead of an economy gauge but the it's reaction time is FAR too slow.

I have one installed. It's a nice thing to look at but it's not useful as an accurate gauge.

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There's a limited range of sensitivity between the pegs. About 7 psi in W126 gauges. You can set it to read 0-7 psi in which case it will react quickly or 7-14 psi in which case you'll see when you hit max boost. Where exactly you place the pointer based on jba's 10 o'clock guideline will determine the range you get. You can't see everything unless you limit the turbo to 7 psi. What fun is that?

In the case of my SDL, I set the range to 5-12 psi. 5 psi hits at about 2200 rpm at which point you can feel the turbo earning its keep. It doesn't feel like the turbo is doing much below 5 psi. I don't spend time beyond 12 psi, or beyond 10 psi for that matter, other than to blow out the cobwebs. Your eyes learn to see graduations in the gauge. Or you can paint them in.

Go for a gauge set from an 86 or 87 gasser. In W126s there was some change in gauge pin-outs in 88. There might have been similar changes in the W124 line.

Sixto
87 300D

I just finished this mod on my 380SL with an OM617.952 The SL has the economy gauge which I previously had hooked up to the vacuum system with the idea that if the vacuum started to fail the gauge would show a non-pegged condition. But it never did and so I decided to convert it to a boost gauge.

I pulled the cluster and hooked up a real boost gauge and the "economy" gauge in parallel and hooked that to my brake bleeder (a garden pressure sprayer) I know my turbo maxes out at 10psi so I put 10 psi of pressure on the sprayer as measured by the boost gauge and installed the needle on the economy gauge at the upper stop. Then I very slowly bled the pressure off and put a tick mark every pound of pressure. It hit the other peg at just under 2 psi.

I installed it in the car by teeing into the ALDA line and running the hose through the vacuum grommet to the gauge cluster. I wish the tick marks were a little better, but it's hardly noticeable, so I guess it's ok for now. Maybe some day I'll figure out how to do a vinyl overlay and re-label the gauge "boost" and add real numbers.

Unlike the comments above, I find the response to be the same as the boost gauge. I'm happy to be able to monitor boost without having to cut up the nice burl wood console to install an aftermarket gauge.

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

Gen 2 temp clusters will not work on a gen 1 W126. The pins are different. You can swap the face and vacuum gauge into the existing gen 1 cluster, though. That is what I did.

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1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
Monark Nozzle Install Video - http://tinyurl.com/ptd2tge

I put a gasser cluster in my diesel and connected the vacuum "Economy" gauge to the line between the VCV and the transmission. In that mode it acts as a (relative) system vacuum gauge, telling me if I have a vacuum problem; should the transmission ever start shifting harshly it will help with the diagnosis; since the gauge responds to throttle position it acts as an "economy" gauge just as labeled. By substituting the face from an older cluster, I got rid of the "premium unleaded" label. The other gauge movements in the cluster are identical (gas / diesel) in 124s so no modifications are required.

I looked into using the vacuum gauge for boost but as Sixto notes, the range is insufficient. In my (former) '87 300D Turbo I put gauges including 15psi Boost in the ashtray area; the current "fleet" is not turbocharged so no need.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

I was thinking about replacing a broken clock with a boost gauge needle. It would be nice to keep the RPM's and boost together on the same gauge. And the stereo already has a clock on it, so I won't be without one.

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1982 300CD Petrol/Black Leather

Ask Sixto -- I think he did something like that.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

I thought about doing the same thing and hooking it into the VCV line. I have not hooked mine up to anything yet.

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1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
Monark Nozzle Install Video - http://tinyurl.com/ptd2tge

I attempted to do something like that with a 1.5" Marshall 15 psi gauge (always available on eBay). I can make things work but I can't make things pretty. I couldn't center the gauge around the clock's axis so I drilled a new center hole then slapped the Marshall face plate over the clock gradients. The clock gradients are larger than the face plate, the limit posts extend to the hidden side of the face plate so it doesn't sit flush on the tach face plate, and clocking the boost gauge was a PITA so it looked like a kindergarten project... which is an affront to kindergarten'ers. The hidden side of the tach had scars where I drilled through the case for the pressure fitting. The project made me appreciate the converted economy gauge all the more

Sixto
87 300D