I have owned and worked on a lot of cars but I have never seen this happen. My wife came home yesterday and said her oil pressure guage was jumping up and down and the engine was making noise (1990 300SL - 102K mi). I started it up and could hear a couple of noisy lifters but the oil pressure was fine. I took it for a spin and about a block up the road the oil pressure suddenly dropped to zero and the red light came on. Then within 2 seconds it came back out to full pressure. It repeated this 3 times in a short drive so I parked it. By then the lifters had stopped making noise. The oil level is up. This is a new one on me. Has anyone had this happen on the 104 engine? No speculation please, this could be a very expensive problem. Thanks. Craig

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90 300SL Pearl Gray
92 300CE Smoke Silver

Yikes!

No kidding that could be very expensive.

I've never had this happen -- can only be a couple of things: Bad oil pump, bad pressure relief valve, or a serious "leak" in the oil system.

First you need to get a mechanical oil pressure gauge and check the actual pressure in case the electrical sending unit is bad, but I'd guess you will see the same pressures.

Is the low oil light coming on when the pressure is low?

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

What type of oil do you have in it? How long since the last oil change?

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1989 420 SEL

Maybe she left out the part where she had just run over a curb, maybe squashed the oil pan?

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Chas

Had a 380SL, 450SL, 380SEL, 420SEL, 500SEL

Got a Euro 500SEC right now.

I had been running Chevron 20/50 and it had been about a year since change but its not driven much. I changed to 10/40 with a new filter over the weekend but the problem persists. When I first started it the oil pressure quickly came all the way up but after running it for about 2 or 3 minutes it would only come up to about 2 bar and did drop to 0 (even above 1500 RPM - red light came on) and then right back up to about 2 bar (even at 3000 RPM). Shortly there after the lifters started getting noisy so I shut it off. I need to put a mechanical guage on it (even though I suspect that these readings are correct) so if anyone has some info on the correct fitting connections, I would appreciate it. It may be an oil pump/relief valve but I have not heard of this as a problem in this engine. It looks like the pan will come off with the engine in the car but I am not sure. I am not looking forward to this project. At 60, everytime I get under a car not it wrecks my back big time. Craig

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90 300SL Pearl Gray
92 300CE Smoke Silver

As you indicated, the guage is probably working. My first step would be to drop the pan. I did that on my 89 420 SEL and found the tower, from the bottom of the oil pan to the pump, had broken. It is made of rubber, but was rock hard and brittle. There were a few other partsin the pan too, like part of broken rail, which blocked part of the inlet. My pan was dented, so it explains why the tower was broken.

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1989 420 SEL

Check the oil filter first. Have heard of some defective ones collapsing.

Which brand have you known to collapse?

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1989 420 SEL

Not Mann

Do the easy cheap stuff first. Replace the sending unit! My SDL was erratic as heck then ti quit. Then it started again. That is the first thing that I would do. Then you can trust all other checks.

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N. Hodges
1994 S350
1987 300 SDL (for sale)

Turned out to be the sending unit. I hooked up a mechanical gage using a banjo fitting from a 123 diesel. Never went below 1.2 bar at idle and over 3 bar at around 2500 Rpm. No noise from the lifters. All of this may have been brought on from not changing the oil for over a year - we don't drive it much. So, I have 1 more thing to be thankful for on Thanksgiving - I don't have to pull the filter housing or the pan! Craig

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90 300SL Pearl Gray
92 300CE Smoke Silver

Looks like it was premature to say that it was just the oil pressure sending unit. In the garage the oil pressure is fin with both the mechanical and electric guages. However, when I took it for a short drive the pressure would drop off to 0 under excelleration and then come back up when I let off on the gas or sitting still. This is indicated on both guages. I now suspect that its something in the pan when the oil moves around but I don't know what. I'll probably drop the pan this coming weekend unless someone out there has seen this before and knows the cause? It has me stumped. Craig

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90 300SL Pearl Gray
92 300CE Smoke Silver

Did you change the oil? You really should change it at least every 6 months regardless of mileage. It does sound like something got into the pan.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Oil pump pickup is damaged or loose, I'd bet, so that when the oil rolls back under acceleration, the pump sucks air instead of oil.

This may just be a loose bolt, could be a fractured pipe.

I would DEFINITELY drop the pan and check this out -- oil supply failures will cost you an engine eventually.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I have a definitive answer to the oil pressure problem. The pictures tell the story - the pump housing case is broken. The strange part is that there is a small hole in the pick up screen so something got into the gears and broke the housing. I will replace the pump and post after its running again. Craig
PS - getting the pan off was not too bad but you MUST hoist the engine about 4" to get the pan past the cross member. It's well discribed in the 124 Haynes book.
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90 300SL Pearl Gray
92 300CE Smoke Silver