Losing oil pressure when running hot

I've got an 85 280SE (w126 european model) with a injection 110 engine with oil cooler.
When the engine is hot it has low oil pressure on idle. That is - below 1 on the meter.
Yesterday it totally lost pressure (almost 0 on the meter) when idling after doing some kickdowns on a hot engine on my way home.
I usually drive very short trips. So it almost never runs hot. I checked the oil after the trip yesterday - but it seems it does not burn the oil.
I have 15w40 oil on it (less than 1000 miles "old")(I used to have 10w40 but changed to see if a thicker oil would do better - was that a bad idea?).
It idles around 600-700rpm in drive position, and a little more in park or neutral prosition. The engine has an unknown milage - probably around 300-400 kkm. It has a renewed head from two years ago.
What could be the culprit? Worn Crankshaft? Oil Cooler? General old age....
I'm not too nervous because it usually has enough oil pressure. Should I be worried?
Best Gunnar
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Gunnar A while back I was considering buying a 92 300E that would lose oil pressure as soon as it got warm. I had mechanic confirm that it was a faulty sending unit by removing it and installing a mechanical test guage. That cost me $50.00 but I didn't buy the car becasue the price was too high. You may have a bad sending unit.
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I have w140 with almost the same behavior. I haven't worried too much yet, but should I?
Jens
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You've done all the right things - but one.
engine has an unknown mileage - probably around 300-400 kkm (yet you're) doing some kick downs on a hot engine on my way home.
That's like asking your grandmother to play rugby or soccer, not age appropriate.
This is an old engine whose best days are long gone, its low oil pressure at idle isn't good but it's OK if you don't idle it for long periods. Yes, the bearings are worn, the oil pump is worn etc. and you could use even thicker oil (20 - 50) the next time. Drive it conservatively and the engine will be OK.
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You can easily check the oil cooler by driving the car for some time and feeling if the oil cooler is hot (OK) or not (not working).
I believe there's a thermostat for the oil cooler - about 200 degrees F. - that's probably located below the oil filter.
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Thanks for your excellent answers.
I don't kickdown much, but did it to see what would happen. I'll be nice to it. (Is kickdown worse on a hot engine or a cold engine?) Maybe I'll even get around to mount the calix engine heater I've acquired before the winter sets in... :-)
About the oil cooler - I'll check it the next time I have a longer trip.
Best Gunnar
T.G. Lambach wrote:

e oil pump is worn etc. and you

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Cold.
Being hard on a cold motor is never a good idea, do you not think?
DAS
For direct contact replace nospam with schmetterling
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Dori A Schmetterling wrote:

I do! I just got confused.
Gunnar
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Oh, good... after all, we wouldn't want to hammer a cold engine in a Frederikssund winter... :-)
DAS
For direct contact replace nospam with schmetterling
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I'm with T.G. You're asking a lot from a tired engine. I like the 15-40 oil since it is rated for diesel service limits. I use it in my tractor, pickup truck and two MB diesels. The 20-50 might be okay and you could add something like the old STP or something of the same caliber to increase viscosity. I would also do like a previous posted suggested and check the oil pressure with a separate gauge of known quality. I had low oil pressure on my Ford pickup with only 70k on a complete rebuild. Put in a new oil pump and things came right back to normal. Don't know how hard it is to replace the oil pump on your engine but if it can be done without too much trouble I'd try that before getting too far into the problem. That move never seems to hurt a tired engine.

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These are both the same viscosity when hot. Try running something thicker.
Like Mobil 1 15/50 or good old 20/50
Probably a main bearing is worn and losing some oil pressure.
Marty
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