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Old 12-30-2003, 06:08 PM
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Join Date: Dec 2003
Location: new zealand
Posts: 9
Question Problem: The oil pressure light stays on

Problem: The oil pressure light stays on (ran it for about 15 seconds). Just replaced 110 engine (Engine# 110994-20-000514 transmission # 720109-20-004743.

History: I was driving on the motorway when the oil pressure light came on. I had just picked the car up from the independent shop which is reputed to be the best German repair shop in Auckland where they were supposed to have fixed a delayed starter problem. Having spent over $1,000 for all sorts of new parts, it still did not work (it turned out that the problem was caused by the rear oil seal leaking, eventually filling the starter solenoid with oil and required the oil cook off before it would engage the starterů a simple $200, one hour repair once I removed the starter and noticed the mess), thus I was driving home, most frustrated.

I do not know how long the light stayed on, but long enough to starve the main bearings which eventually self-destructed. When the light came on, I had it taken back to the same shop. This time they decided the oil filter was blocked, thus charging me $120 for an oil change, pronouncing the problem solved. The oil pressure light did not come on again, but the thunk and then howl from the bearings when I got back on the motorway suggested I had a far more serious problem. I limped home, eventually down to below 20 mph to keep it from seizing, and like a faithful but wounded steed, it made it, although the last mile was a symphony of steel on steel turning the crank into an elliptical orbit which would make Haley's Comet proud.

Having lost faith in the repair shop, and because the engine had over 300,000 miles on it, I decided it would be cheaper to re-power than to rebuild the existing one. I located an identical engine, and replaced the dead one. I decided to do the replacement myself over the Christmas holidays.

Re-powering: I did not remove the oil filter housing (the aluminium unit attached to the block which holds the filter canister, and to which the oil pressure sending unit and the two oil cooler hoses are attached) from the replacement engine, which proved to be a mistake. When I started it in the vehicle, the housing gasket on the block leaked (but I should mention, the red oil pressure light did go off). So I took the housing off the dead engine, cleaned it up and took it to MB to make sure I would get the right gasket. Because it was cleaner, I installed this older housing unit, not the younger one that came with the replacement engine. I installed a new copper gasket in the oil pressure sending unit, and did clean up the sending unit before doing so (this could be a clue). I also installed an MB original oil filter.

When I put everything back together and started the replacement engine, the oil light stayed on. After about 15 seconds I shut the engine down, as I do not want a replay of the last self-destruct. I checked the oil level, added oil since it now had filled the filter and oil cooler. Repeated the process for 10 seconds, and the light stayed on, so I then quit and turned to the Internet for help. I'll spend the rest of the day cleaning the workshop and cutting out the rust holes so it can pass WOF (warrant of fitness), waiting for advice from one of you.

I see the following possibilities:

1. In cleaning the oil pressure sending unit (including inserting a pin in the unit sensor hole to make sure no dirt was clogging it), I either damaged it, or created an air pocket so it thinks there is no pressure when there really is.

2. Bad luck, the sending unit decided to pack it in and I really have oil pressure but no way to tell.

3. The housing from the old engine actually has something wrong with it that intermittently causes it to block the oil flow, and I have no oil pressure and could easily trash the engine.

4. Coincidentally, the oil pump died (which makes little sense under the circumstances).

Access to the housing is difficult, especially without a car hoist. Access to the sending unit requires I either unbolt the housing from below (hard because of the cooler hoses), or remove the fuel injection manifold (which is what I had to do to replace the gasketů a long job).

One option might be to cut into the rubber hose which runs from the housing to the radiator oil cooler and install a brass Tee off of which I could hook an oil pressure gauge to get an actual pressure reading. But I do not know how accurate this would be, given the location. Access is easy, and the return (bottom) rubber hose is new.

Any thoughts and any ideas? The engine is a standard 110 engine with an automatic transmission, but I hesitate to mention the vehicle MB installed it in, because few on this forum know much about Mercedes' army jeep, the G-wagon. I have posted an enquiry on the G-forum, but the replies to date are from owners rather than a technical person who might know how the oil pressure system actually works and what goes wrong.

Happy New Year to all.


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Old 12-30-2003, 06:59 PM
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Join Date: Oct 2002
Location: Near Raleigh, NC
Posts: 580
As far as I know:

The light on the cluster indicates LOW LEVEL of OIL, not oil pressure. The oil level sensor is located in the oil pan.

The pressure is indicated by a needle, and its readings are 1, 2 and 3 bars. They are on the instrument cluster (opposite to the temperature gauge). The pressure sensor is located by the oil filter.
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Old 12-30-2003, 08:31 PM
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Join Date: Dec 2003
Location: new zealand
Posts: 9
Originally posted by pesuazo
As far as I know:

The light on the cluster indicates LOW LEVEL of OIL, not oil pressure. The oil level sensor is located in the oil pan.

The pressure is indicated by a needle, and its readings are 1, 2 and 3 bars. They are on the instrument cluster (opposite to the temperature gauge). The pressure sensor is located by the oil filter.
The Model 460 does not have an oil pressure gauge, only an idiot light. When it went on last year, the oil level was fine, but the bearings failed, leading me to believe the oil light shows pressure, and when it goes red this means the bearings are not getting pressurised oil.

Any MB mechanics out there who can provide a technical perspective?

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Old 12-31-2003, 10:36 AM
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Join Date: Jan 2002
Posts: 18,350
Here's a link to a British G-Wagon forum that may be able to give more information:

I know nothing about your engine. But when the oil pressure sending switch failed in my 409d, it failed in the 'off' position. In other words, the light did not work at all. I do not know if this is the only way that pressure switches fail.

You can check the pressure a couple of other ways. Look in the valve cover thru the oil fill hole and see if oil is getting to the valve train. You could also loosen the cover on the oil filter housing and see if oil squirts out (this would be very messy if you have oil pressure). But if the filter housing filled with oil, reducing the oil level, you must have oil pressure of some kind.

T'ing into the oil cooler hoses will not help much, because if it is like the system on the 617 engines, the cooler is thermostatically controlled with no oil going thru it at low temperatures

Overall, I'm inclined to think that sticking the pin into the hole in the sender unit damaged it. If I were you, I'd bite the bullet and replace the sending unit with a new one.
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Old 11-22-2008, 04:44 PM
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Join Date: Nov 2008
Posts: 1
I have a 1999 C280 and been driving with my light on and off for 10 mos. It does not burn or leak. I plan on driving on a 700mile trip. Is it ok?

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