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  #16  
Old 02-02-2010, 08:34 AM
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Quote:
Originally Posted by bustedbenz View Post
I just don't understand (honestly, I swear I'm not trying to be a smartbutt) why people don't just learn a discipline of gauge-checking instead of relying on a buzzer.
If I have low oil pressure I want to know the INSTANT that it happens. Not 3 seconds later when I check the gauge, or 10 seconds later when I finally look down after merging onto the highway.

"I watch the gauge on the Benzes, but there's no way to do a good job of both driving and guarding the gauge."

My thoughts exactly. I can't be watching the gauge all the time, but I can be listening for an alarm all the time

-J

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  #17  
Old 02-02-2010, 08:41 AM
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Happened to me in a 1976 240D. One of those fast change oil places used the wrong gasket for the oil filter. Luckily I was real close to a store, bought 2 gallons of oil and went and complained to the shop.

engine was fine
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  #18  
Old 02-02-2010, 08:47 AM
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Anything helps to reduce risk. A buzzer is a smart thing.

As a pilot I do watch gauges, but you'll find many extra warning devices on a plane too. You don't just rely on your checklist either. You're supposed to watch your airspeed, but there's a nice stall horn just to remind you. Sometimes you get busy in the seat.
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  #19  
Old 02-02-2010, 08:57 AM
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If you lose oil pressure, would the low oil level light illuminate, or not necessarily?
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  #20  
Old 02-02-2010, 09:17 AM
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You can have the correct oil level but incorrect oil pressure... or vicea-versa. But, having that lamp triggered when the oil pressure is too low is a good idea.

-Jason
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  #21  
Old 02-02-2010, 09:51 AM
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Quote:
Originally Posted by Crazy_Nate View Post
Some of my non-gearhead friends don't understand an oil light on a newer car. Oh, it's time for an oil change? Oh...dear...what has the world come to?
Yep. That's why they call em idiot lights. If they ever come on, it means you're an idiot. You didn't check your oil for proper level and the damage is already done.

I love my oil pressure gauge. X3 on checking at least every 15 seconds.
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  #22  
Old 02-02-2010, 11:56 AM
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If it were not for the high average accumulated miles and those oil cooler hoses the normal gauge might be adaquate. The old oil pump or its drive can drop dead anytime as well. Few check even the drive chain and sprockets out.

I still see the loud buzzer as almost a mandatory addition. A tee off the turbo boost line that closes a pressure switch. Another sensor in series with it that is open above twenty pounds pressure again in series with a buzzer would do fine. The circuit is only active for high oil pressure monitoring if there is a certain amount of boost or more.

It is certain that a small percentage of owners will be really sorry they did not install this over time. It is far too late usually when you wish you had done it. You may catch the current oil gauge dropping but it is a fact most do not. Engines at higher speeds and loads do not have the tollerence for low oil pressure that an ideling engine has.

This is becoming like flogging a dead horse. After I figured the boost pressure could be used to enable the interlock it became fairly simple and practical to do this. No electronics or depending on a refference signal of any type other than the presence of boost pressure. Unfortunatly this will not apply to 240d owners. That is only natural as I have two of them.

I have been working on that issue a little between a hundred other things. My best possibility looks like using the base pressure in the crankcase if possible at the moment as the interlock. Truthfully this area has been on the backburner of my mind. I must have rejected at least another dozen approaches as well.

I should think it through and decide if this is about the only practical option for those 240ds and natural aspired 300ds. If the concept is not very simple and managable by all it will not fly well. With my electronics background it is easy to design systems that will never get installed by many.

Had I been smarter it would have taken me less time to come up with this. Parts requirements remember are just a sensor that determines when boost is present and closes. Plus a sensor that closes below twenty pounds oil pressure. And a buzzer that is loud enough. No rocket science at all.

The simple approaches like this are far better and cheaper. Well within the capability of all members. You could incorporate a red light as well if you wished. Maybe someone in the states could locate and price the two required sensors for the site members.

Also I do not want to finalise on the simplest possible practical setups for the natural aspired engines quite yet. There is a comprimise there I am not happy with.

Last edited by barry123400; 02-02-2010 at 12:10 PM.
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  #23  
Old 02-02-2010, 12:46 PM
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My concern is that, at highway speeds, by the time you notice that the oil pressure gauge has dropped to zero (due to some catastrophic failure) the damage has already been done. Granted that proper maintenance should prevent most catastrophic failures, it would still be nice to have an "unthinkable event" alarm.

There was a thread here about a month ago that mentioned a VW oil pressure alarm. It was sensitive to both oil pressure and (either) engine or road speed -- I forget which. At idle it would alarm at relatively low pressure, increasing as the speed increased. Something like that adapted to a Mercedes would alarm at 1 bar or so for engine speeds above 1500 RPM, roughly.

A universal alarm would be challenging since the 240D (and others?) doesn't have a tachometer. For cars that do, perhaps something involving an operational amplifier, with one input from an electric oil pressure sender and the other from the tachometer. The op-amp would be biased so that it would trigger an alarm (I like flashing LEDs) if the oil pressure signal was less than the tachometer signal.

Jeremy
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  #24  
Old 02-02-2010, 12:49 PM
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The bottom one will do for 20 psi:

http://www.allpartsexpress.com/ShopByVehicle.epc?q=1991-VOLKSWAGEN-Jetta--/--L4--1588cc--1.6l--Diesel--Fi--x--8--iv--x--9--97-Electrical&yearid=1991%40%401991&makeid=VOLKSWAGEN%40%40VOLKSWAGEN%40%40X&engineid=1283307%40%40JETTA++%2F+L4-1588cc+1.6L+DIESEL+FI++%28IV%29+97%40%40JETTA&catid=Electrical%40%40Electrical&subcatid=Oil+Pressure+Switch@@Oil+Pressure+Switch&mode=PA

...though I think that may be just a bit too high (hot idle on a warm engine may be lower)

what for boost?

www.vincewaldon.com has a good write up somewhere on the VW dynamic oil pressure system ( I can't paste the exact link because big brother has banned it at work, but it's on here). I don't know how you would get the electronics brought over to MB as there's some logic involved.
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  #25  
Old 02-02-2010, 01:27 PM
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It happened to me a month ago. No big deal for me. Expensive, but no engine damage beyond the broken oil pump itself.

The engine will not seize up in short amount of time w/o oil pressure as long as the cooling system is working properly. Your wife can drive a car 4 miles to the grocery store. Go do her shopping, and drive it home with no oil in the sump and the lifters clacking like a diesel. And over the next 100,000 miles, experience no noticeable ill effect from that event. Go ahead, ask how I know this.

If you ever have a car about to be scrapped, start a car up and drain the oil. If the cooling system is intact, you will be surprised how long it runs with no noticeable effect.

How many of the contributors to this tread have ever had this happen to them? I count 2. One had a timing chain failure that ruined the engine. The other had a failed filter gasket, lost oil and pressure, and had no ill effects.

I am not saying that this is not a big deal, I'm just saying that it is not as big a deal as some have made it out to be. For people who don't understand what the gauges mean and don't check them, well, they shouldn't be driving your car.
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  #26  
Old 02-02-2010, 01:33 PM
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Quote:
Originally Posted by Crazy_Nate View Post
I
Some of my non-gearhead friends don't understand an oil light on a newer car. Oh, it's time for an oil change? Oh...dear...what has the world come to?
A friend of mine with a Honda thought the red oil can light meant that oil was dripping. The car needed 2.5 quarts of oil to reach the top level on the dipstick, max capacity being about 4 quarts.
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  #27  
Old 02-02-2010, 01:46 PM
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Quote:
The engine will not seize up in short amount of time w/o oil pressure as long as the cooling system is working properly. Your wife can drive a car 4 miles to the grocery store. Go do her shopping, and drive it home with no oil in the sump and the lifters clacking like a diesel. And over the next 100,000 miles, experience no noticeable ill effect from that event. Go ahead, ask how I know this.
It's one thing to say that chances are, the car will still run if you don't catch it before it completely seizes. It's another to think you haven't measurably shortened the lifespan of the engine.

And that's why we are all here, right?
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  #28  
Old 02-02-2010, 01:53 PM
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Quote:
Originally Posted by GregMN View Post
The engine will not seize up in short amount of time w/o oil pressure as long as the cooling system is working properly. Your wife can drive a car 4 miles to the grocery store. Go do her shopping, and drive it home with no oil in the sump and the lifters clacking like a diesel. And over the next 100,000 miles, experience no noticeable ill effect from that event. Go ahead, ask how I know this.
.
Maybe if your engine has ball bearings on the crank instead of plain journal bearings. We had a engine on the dyno blow a turbo feed oil line once. The oil pressure alarm went off after it vented most of the crankcase oil, and it was shut down about 10 seconds later. All of the rod bearings were severely scuffed and damaged from running dry for even 10 seconds at 2500rpm and full load. Lead against steel sure does get hot and mate itself together fast. At very low loads you could get away with it for longer as most vehicles have a 2-3second lag of no oil pressure everytime they start, but they aren't under load either. I think a 5psi oil pressure switch that was hooked to a solenoid to supply vaccum to the pump would be a easy emergency shut down device to be installed on these cars.
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  #29  
Old 02-02-2010, 02:32 PM
Craig
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I understand why people want to add alarms and lights, but I'm not sure there is a cost justification. I had one loose of oil pressure in 350k miles of driving a 617, the vast majority of drivers will never lose pressure during the life of the car. I'm OK with the gauge.
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  #30  
Old 02-02-2010, 02:55 PM
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Craig,
Do you carry insurance on your vehicle ?
The vast majority of drivers will never have an accident during the life of the car.
Do you pay that insurance OVER and OVER again ?
This would pretty much be a one time expenditure... and if you check the cost of replacing the motive power in your MB I think the ' cost justification' is easy to see.

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