I have a 1983 240D and I have noticed my oil pressure dropping occassionally from 3-2 bar during breaking and/or pushing in the clutch. It does not drop consistently. Would anyone be able to offer an explanation?

If you are reducing the engine revolutions the oil pressure will drop. Usually before or during a clutch disengagement and engagement you let up on the fuel pedal.

When you re engage the clutch the revs come back up. Less than when you changed up from the lower gear but still upward from the engine trying to find idle. You are once again adding fuel.

Now when youy transfer your foot from the fuel pedal to the brake pedal revs are certainly going to start to drop. Effectivly if you push in the clutch then the engine is going to idle speed. Two bar is quite normal and indicates the engine is still in good shape oil pressure wise.

Just some random thoughts:
The easiest way to raise the hot idle oil pressure is to use oil with a higher viscosity (the member did not say what oil he was using).
Installing a new oil pump may or may not help. If your oil pressure is low due to worn bearings a new oil pump might not make much differance (higher viscosity oil would help here).
At idle I do not think the oil pressure relief valve in the oil pump is doing much as the pressure is too low to move it.
I also do not think that the dash board oil pressure guage is very accurate. If I had 0.5 bar or less at idle I would be hooking up a test guage to be sure what the oil pressure really was. If nothing else for peace of mind.

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84 300D, 82 Volvo 244Gl Diesel

Here are my thoughts:
On my car with cold (thick) oil pressure guage pegs at the top 3 bar mark. When the oil is hot (thin) at idle it goes down to 1 to1.5 bar at idle. So the oil pressure issue is related to the viscosity of the oil.

The rest as the other member said is related to engine rpm and the oil volume pumped by the oil pump at different engine speeds.
At a higher engine rpm you are pumping a larger volume of oil per second than you are when at idle. The oil is being pumped through oil passages whoes size not change so at a higer rpm and more volume of oil trys to pump through the oil passages but meets a lot of resistance and the pressure rises. (At high engine rpm even with the thin hot oil the oil volume pumped by the oil pump on my car is enough that the gauge pegs at 3 bar.)
At low engine rpm (idle) the volume of oil going through the oil passages is smaller and creates less resistance going through the oil passages and creates less pressure.
So changes in engine speed cause changes in oil pressure up to the point where the oil pump relief valve opens and relieves the pressure.

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84 300D, 82 Volvo 244Gl Diesel

I'm using Rotella-T 15w40 nonsynthetic oil... and don't suspect I have any oiling problems at all. There's no increased noise (tapping, whining... nothing out of the ordinary) and it's always back up to 1 bar or .9 bar within 30 seconds after slowing back down.

I think it's perfectly reasonable for the oil to get thin enough to drop the pressure under extreme conditions... as long as it doesn't go to zero, and it comes right back after a very brief (as in my case, 15-30 seconds) period - I can't see being too worried about it. Certainly not enough to start throwing parts at what doesn't seem to be a problem.

The last 4 or 5 days here have been hovering right around 100 degrees outside... 98 or 99 air temp, road surfaces higher... and it's behaving consistently. OP stays above 1 bar at all RPMS except when I get off the freeway during my trip home from work right in the heat of the day. At that point, at the off-ramp, if I have to stop to get into traffic, it'll drop to .3 or .4 bar. By my stop light (less than half a mile) it's idling at 1 bar again.

Don't suspect any problems as of yet.

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

Barry, were you ever able to assemble a kit?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

A few things can cause this, oil thermostat stuck closed, causing the oil to not be cooled and lowering the viscosity. or you have an internal leak lowering the pressure.

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Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac?

As long as they would add one additional commandment for you to keep thy religion to thyself.
George Carlin (Wonder where he is now..)

1981 240d (engine donor 1983 240d) recently rebuilt engine hurray! - No more.. fought a tree and the tree won.

pearl black 1983 240d 4speed (Converted!@$$%) atleast the tranny was rebuilt.

On backburner at present because of so many variables. Use of the transmission neutral switch and relay required to eliminate annoying shreik. Or if someone has a better ideal I am all ears. Kits should have adjustable pressure sensor to optimize each installation. Although a five pound or less pressure switch is far far better than nothing.

If you are not protecting your engine with some system at least change out oil cooler hoses of unknown age with quality replacements and check oil pump chain,tensioner and drive sprocket condition. I personally do not consider a working oil pressure gauge adaquate protection at all.

I expect the failure rate percentagewise to increase as these cars continue to age unfortunatly. You do not want it to be your car but statistically it has to be someones. After the fact seems to be expensive and with a little effort mostly preventable.

I know a comprehensive cost efective well though out kit is needed. Especially as it saves all the running around for misc fittings and parts. You also would be spared the fatigue design issues introduced on diesel level vibrations and fittings. This factor alone almost drove me to feed sensor from the flexable oil pressure line. Then the thought occured. Where all people competent to get the compression connections installed right? Compounded by the plastic is so old. So back to a pressure splitter to accomidate the two senders. Unfortunatly probably a custom fitting.

Add to it a variable threshhold oil pressure fitting to increase costs and optimise the system on most 616/617 engines. Or perhaps more a plain jane type of kit is what is required?

I really do not know if I can get the time to finalise all this. I can only hope I will. If not someone should. Perhaps one of our younger members. If nothing else it should be a great learning experience.

For engines with an electrical oil pressure gauge it should be possible to use a simple transistor switch that looks at the gauge circuit and turns on an alarm. It could be adjustable so that it wouldn't go off with the drop in oil pressure of a hot idling engine. It would be nice if the alarm didn't go off when the engine was not running. Perhaps a cut-out circuit using the alternator light could be added. A fail-safe design would really be nice but that is hard to do. let me think about it.

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 like the idea of keeping it fairly simple. simple to put in. simple to use.
I am not very concerned about it going off at 5lbs or 10 lbs, as someone just said anything is better than nothing. I KNOW my wife would never notice the gauge, and honestly how often do any of us look? We maybe watch it pop up and feel good about that. Maybe notice how low does it drop when hot. But cruising on the freeway, I'm looking down the road!(-hope you are too!)

I manage to work on my own cars but my forte is woodwork, and while I install electronic pick-ups in acoustic guitars; I don't understand them, (much less design them), so I am hoping one of our talented members will cook us up a good simple kit and market it to us. Count me in!

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Thanx,
Alberta Luthier
1983 300CD ('Stinky')155k miles, 2.47 diff, EGR removed, AAZ injectors with 265 nozzles from Sean,and vogtland lowering springs.
1984 300SD ('Old Blue')150k Klicks from Japan originally, came with rear head rests, no sunroof and never had an EGR

The Cole Hersee Marine engine kit is the most simple I've seen yet.
(In Aftermarket offerings) (Even with it's super low OP threshold)
[Cole-Hersee (COLE # M-40177-BP) ]
It Encompasses BOTH High Temperature and Low Oil Pressure with an Audible
Alarm.

Yanmar uses the same Dual Alarm type on some of it's smaller Marine Diesels...
I'll call the distributor's service people maybe this coming Monday.

Hell, some mornings a Buzzer screaming during the "Glow" would serve to Keep
You Awake long enough to start the engine.

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'84 300SD sold
124.128

'stumbled across this one..ADJUSTABLE for Low + High pressure alarm.
('Need place to "Put" it and Sensor,unless it'll work off the MB one on the
oil filter housing)

EDIT:
'just found the price, OUCH, $115.00 USD

http://homepages.ihug.co.nz/~bvdb/op30.html

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__________________
'84 300SD sold
124.128

It looks like that might work on the 125 with an electric sender switch but would need to be adapted to the mechanical guage on the 123's and 116's.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Since our cars already have a gauge, the new one doesn't even need to be displayed, right? We're using it for its alarm so it can be buried under the dash somewhere. BTW, I see the web site is in New Zealand; perhaps someone can do a little hunting and find sources in Europe and USA for all our members.

The CruzPro OP60 gauge comes with "Built-in calibration curves for all popular senders from Teleflex, VDO, GM, Stewart-Warner, Faria, etc." so it should work with our electric senders as-is. For 123s and others with mechanical gauges, the oil pressure line could be tee'd somewhere convenient and an electric sensor inserted, one of the ones that the gauge already understands, of course.

My only personal preference would be for an alarm that doesn't scream during pre-glow. Perhaps a relay could be added, an option to the afterglow mod, maybe? (Granted that screaming during pre-glow functions as a self-test.)

Jeremy

__________________

"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

Distributor and a few US dealers:

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__________________
'84 300SD sold
124.128