Right now I've got a vac/boost gauge for watching the turbo boost. I'm going to switch that gauge to watch the vacuum/pressure on the fuel line to monitor when the filter is getting clogged (more for VO than for diesel). But I like having the boost gauge, so I am going to get another one. For simplicity, I was going to get one that only shows boost, but am I missing something? Is there a reason to have the vacuum portion of the gauge on a diesel?

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1985 300TD-euro 352,000 mi
1974 240D (1?)52,000 mi - has a new home now

Boost only should be OK on a diesel, the combo gauges are really intended for gassers.

As far as adapting the vac/boost gauge, I don't see how it can work for what you're trying to monitor. For a vacuum gauge to monitor a filter, you would have to mount it between the suction side of the pump and the filter. Or, it may be mounted between the pressure side of the pump and the filter but it will only register pressure never swinging between both.

Also, to use that gauge to monitor a liquid, you'll need an isolator.

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-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

I guess gas engines have more vacuum in the intake manifold...well I'll go with the boost only gauge.

The VO filter is on the suction side of the lift pump, so that's where the vac gauge tap will go...and I expect it to only read increasing amounts of vacuum as the filter clogs. I could put it between the lift pump and IP and get pressure, I haven't really decided yet, but since the gauge has both, I could put it wherever.

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1985 300TD-euro 352,000 mi
1974 240D (1?)52,000 mi - has a new home now

Diesel engines have no (or at best only a small amount of) vacuum in the intake manifold. This is because diesel engines do not have a throttle plate blocking the air flow into the manifold. In a diesel, the manifold is wide open with the only restriction being the air filter and the ducting. Vacuum in a diesel intake manifold means the air filter is badly stopped up with captured dirt. A turbocharged diesel has greater than atmospheric pressure which can be monitored with a "boost" gauge; a normally aspirated engine has no boost to monitor.

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 have a combination vac/boost gauge on my car. I do register a slight vacuum when free revving the engine until the turbo spools up. When in gear it doesn't register a vacuum however. I have not tested this with a dirty filter though.

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green 85 300SD 200K miles "Das Schlepper Frog" With a OM603 TBO360 turbo ( To be intercooled someday )( Kalifornistani emissons )
white 79 300SD 200K'ish miles "Farfegnugen" (RIP - cracked crank)
desert storm primer 63 T-bird "The Undead" (long term hibernation)

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