91 300E, 129K

I just noticed on my drive home today that my oil gauge peaks at 2.75 when pegged. I could have sworn that it used to go to a full 3.0, but I really don't remember. For all I know, maybe it always did this? Anyway, at idle in D, it is at about 1.0 or just slightly below and goes all the way to 2.75 pretty quickly when gas is applied, perhaps around 2500 RPM or thereabouts (I'll have to check again to be sure). Is this bad? Shouldn't it go all the way to 3.0? What damage could be caused by this lower pressure? It troubles me that there isn't a red zone either at the top or bottom of the gauge to indicate that the needle is sitting somewhere it shouldn't.

I just replaced my water pump last night, and got to thinking: could I have disturbed a wire or sensor in the process that might be contributing to this lower pressure reading? Could there be a higher resistance somewhere as a result of me jostling a connection or maybe spilling coolant on it? Where exactly is the oil pressure sending unit located?

I am hyper paranoid about damaging something by starving the engine - is this an overreaction? For the record, I am running 20W50 and don't burn a drop of oil. The engine is in perfect running condition. I just resealed the upper cam timing cover a few days ago to fix chronic seeping. I also just checked my oil level, and it is just under the high mark on the dipstick.

Any opinions please?

Thanks in advance!

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

I would suspect that its more likely that you have a problem with either the gauge, the sender, or the associated wires, rather than an engine problem.

A quick, and easy test you can do is to unplug the wire at the oil pressure sender unit and look at you oil pressure gauge. With the sender unit unplugged, the oil gauge should now peg at 3. If it does not, than your problem is in one of the items that I mentioned.

If it does peg at 3, than you either have a bad oil pressure sender unit, or you may indeed have a problem with the engine. I would bet on a defective sender unit however.

Phil

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'95 E300 Diesel, 264,000 Miles. [Sold it]

Thanks for the quick response! Now regarding my water pump replacement last night, is the oil pressure sender located somewhere in that vicinity (front driver's side of engine)? Could I have bumped it loose or spilled oil on the connections? Where exactly is the sender located? Thanks again in advance!

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

I watched the oil gauge the whole way to work today. Still pegged at about 2.75. Now here's the kicker - if I put the car in neutral and rev it really high, the pressure slowly moves up, hitting almost 3 right as the tach hits redline. Does this indicate a blockage somewhere?

I've been thinking about what I said before; I'm positive the gauge used to hit 3 before I did the water pump. I'm psycho about my gauges and always watch them as I drive around. I'm absolutely certain that I would have noticed the gauge at 2.75. So the question remains - could I have bumped something while doing the water pump that could have caused this to happen? Why would the gauge read a perfect 3 before the water pump replacement, and then only 2.75 afterwards? Could I have dripped antifreeze or oil onto an electrical connector somewhere, forming a resistance in a circuit? I don't really know how the gauge works - I'm just throwing a wild theory out there.

As a reminder, the gauge always reads steady at just below 1 when the car is hot and put in drive. Slightly higher when it's in neutral or park. Aside from the new maximum of 2.75, it seems to behave properly in every other way. I run dino 20W50 and change the oil every 3000 miles. It is always clean when it comes out.

It's going to be raining today when I get off work, and the big spring above our garage door broke last night, so the door is stuck in the down position (any suggestions on that problem are also welcome). As a result, I won't be able to troubleshoot this problem for at least the next day or so.

Help! Anyone??? I don't want to damage my engine!

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

It is possible you have a problem in the oiling system that won't let it build full pressure, but chances are good that it is an indicater problem. If you are really low on pressure, you have enough to not harm the engine. You didn't say how the oil gets changed. Do you do it yourself, take it to an Indie, take it to the dealer, or take it to Goofy Lube? Some of those cheap filters can cause low pressure. The problem of cheap filters and low pressure has come up in other threads. Good quality filters are still cheaper than engines.

Peter

__________________
Auto Zentral Ltd.

I change the oil myself and use good oil and a good filter. But again, the part that bugs me about this problem is that the gauge was reading 3.0 before I replaced the water pump, then only 2.75 afterwards. Is it just coincidental? Could I have broken something under there? On the other hand, if my pressure really is only 2.75, will that kill my engine? Doesn't the fact that the gauge pegs pretty quickly upon accelerating mean that the oil system is healthy overall?

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

Oh my god, did you say that you use Fram oil filters. I used to use them, and will never use them again. I only use OEM filters from the dealer or from Bosch. I once changed my oil, and then noticed that I also was only getting about 2.75 on the gauge. I looked at the wiring, and then the sensor as well. Finally decided that it may be the filter. Try a good filter (it is a cheap test to do of course), and then eliminate that as a problem source...