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  #1  
Old 02-25-2003, 04:13 PM
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High Oil Pressure

I posted this issue but in a different way and didnít get the help I needed so I am posting again with other facts I didnít list before hopefully this way I may have better luck on getting some ideas on what to look for that may have caused this.
I recently changed oil pan, gasket, oil level sender and oil pressure sender. I also changed oil (20W-50) and put a new filter (Mann). After all that, I started to have high oil pressure reading where my oil pressure gauge needle goes above 3 bar (see picture) and sets there until oil is warm and then drops to about 2.2bar at idle then back to above 3 bar when at high rpm (above 1500). I had to change the stuff above because I had a bent oil pan and just wanted to put new one. While I was at it, I decided to replace oil level sender. Also I had a problem with my oil gauge needle going to 0 while driving and was told to change the oil pressure sender (it wasnít the problem) the gauge itself was bad. So I got another gauge and start having the high pressure reading. Fixed the original gauge and put it back and still see high pressure reading.
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Old 02-25-2003, 04:42 PM
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Hi Taka,

yes I did remove the needle when i dad to remove the faceplate to investigate the gauge. I put it back. It's easy to remove and reinstall. the needle sweeps all the way up and down and should not be the cause for it to go this high ( also removed the fuel and temp needles and reinstalled them back without any problems). I can change the resistance value on a resister installed across the oil gauge coil and control how high the needle moves.. actually i did change the resister value from it's original 49.9ohms to 100 ohms to get the needle to go up to 3 bar, but i don't feel this is the correct thing to do since i don't know what caused the pressure to go that high the first place. I haven't done it myself yet, but my indep mechanic told me he measured 80 psi when he testing oil pressure mechanically. I measured about 285 ohms at the output connector of the oil pressure sending unit where it plugs into the gauge. this drops (as well as the psi reading) when engine is warmed up. but still high bar reading and as you know (1 bar = 14.5 psi) so i get about 5.5 bar reading when i first start the engine.
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Old 02-25-2003, 05:02 PM
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Quote:
Originally posted by tkamiya
Is the pin and the needle indexed or just press fit? Could you have put it back just few degrees off?
No the needle and pin are not indexed or marked to fit in any special way. Since the needle has female end and the gauge has male end just slip the needle over the pin. There is a stopper pin under the number "0" on this gauge to stop the needle from going down further and actually you can sweep the needle all the way up with your finger and watch it fall all the way down to 0 by itself when the gauge is out and no power applied.
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Old 02-25-2003, 09:16 PM
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unless you live in a hot climate state and do a lot of high speed freeway driving with a high milage engine,I would go to 15w 40 witch is recommend for summer driving in all the MB owners manuals that I have ,check your manual.20w 50 especialy in cool or cold weather will raise oil pressure and not provide proper lubrication especialy on start up......
William Rogers............
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Old 02-26-2003, 12:00 AM
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Well, I live in Houston where we get temps well above 90 in summer time. I drive mostly on highway and the mileage on this car is 38,000. You are second person to tell me this and I am considering changing to lighter weight oil. I will try 15w 40 next oil change and see how that goes. Thanks William!
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Old 02-26-2003, 06:21 AM
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Joseph_H,

The fact that MB don't put values on the gauge gives you an indication of how important they think they are..........


If you know the pressure from a mechanical gauge, and nothing terminal appears to be happening in the engine, why not set the needle to max at that point?

You have now calibrated your gauge. Good nights sleep should be available from now on...............
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Old 02-26-2003, 10:05 AM
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I would disconnect the wire to the oil pressure sensor, and see where the needle rests. With the disconnected wire, and infinite resistance, the needle should go the highest level possible, but that still should still be only at 3.2 Bar on the gauge....
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Old 02-26-2003, 10:06 AM
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forgot to mention, also if you ground that wire, the needle should go to zero. If you get a reading of 1 Bar or something like that, you will know that the needle is not positioned correctly...
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Old 02-26-2003, 05:55 PM
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Thumbs down 20W-50 !!!

This seems IMHO a little heavy for Texas in the Winter! If you were looking at a month of 100+ temps and a lot of idling (?) or sustained really high speeds in the Summer.... well, maybe?

The 15W-40 suggestion for year-round is probably a very good one. I know, I know! Those who are now dealing with -20 & wind chill can't believe it! Some of us do live in milder climates and don't have to deal with cars frozen solid, etc.

Pennzoil's LongLife is cheap, available almost anywhere, has a terrific base formulation, a top-shelf additive package including Moly, and will do a lot in keeping your engine clean internally. Delo's good, too.

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Old 02-27-2003, 01:13 PM
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Changed oil to 15W-40 and filter

Didn't make difference as far as oil pressure goes, but i am glad i changed to this weight. I meant to do it before but never did. I used oil filter made by Mann, is that good filter? or do i need to stick to ones made by MB? I also used Delo oil.
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Old 02-27-2003, 02:04 PM
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oil filters

I've been led to believe that MB doesn't actually make their own filters (like they don't make their "own" brake pads) but use Mann, Hengst & Bosch production.

I've been told they are pretty much interchangeable, but could certainly be wrong. I bet a search would find a discussion or two.

Delo's great stuff. It is my personal belief that any of the Fleet (S?/C?) type oils in 15W-40 provide tremendous protection & cleaning in gas engines. Not necessarily for those extra long "extended drain" intervals, though. That's where 100%Synthetics and oil analysis come in. I go 5K miles betwen changes. Oil's cheap: MB parts are NOT!

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Old 02-27-2003, 03:25 PM
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5K between changes?

I am from the old school of thinking; i tend to change after 3 or 3.5k... is that overkill?
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Old 02-27-2003, 04:07 PM
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hello joseph

here is my 2 cents

first off i don't feel that pressure is the right measure for judging your oiling system. what really counts is the volume. understanding the dynamics of pressure vs flow volume is key. you can have great pressure but there is not enough flow/volume to keep all the items lubed properly. pressure is just the indicator that you do have oil in the pan. even if you were at a stop, in gear, a/c on etc: and your gauge showed only 1 bar you'd have near 15psi so you know you have oil flowing. then when you step on the gas and the pressure goes up to 3 bar now you're at 45psi. where is the critical time in this situation? the engine needs oil when the engine is up in the rpms and when you first start in the morning.

as for changing oil weights the only increase or decrease will be in the first few moments of warming up the oil. once the oil is warm you're right back where you started. and talking about multi-viscosity oil the fact is the structure or the viscosity does not change. what that means is the oil is rated ok in this range meaning it will lubricate properly when the viscosity needed is 20w thru 50w.

so pick a number 20w50 for summer and say 5w40 for winter or whatever you think is right.

as for your gauge it's most likely to be a mechanical adjustment in the needle (you have mentioned you took it apart) or something somewhere is grounding out.

good luck with the problem
craig
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Old 02-27-2003, 04:49 PM
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Thumbs up Frequency

Hey, Joe!

"Old school" or not, there is certainly nothin' wrong about frequent oil & filter changes! Out with the old & in with the new sure can't hurt.

My frequency is based upon the MB recommendation of every 7,500 being the baseline: I find the nice, even, 5K intervals easier for my wife to remember, and my last 5 changes have shown very little darkening of the oil (most 15W-40's are a little dark to begin with), nothing particular (as in "particulate") coming out of the pan, very little debris in the filter itself, no need to add any additional oil between changes & what appears to still be a very clean valvetrain to begin with.

self-edit: "& 8 quarts of oil for a 4.2 liter motor is a fair amount"

Pretty much a personal preference, really. Some people believe you can't chage it often enough, special weights for different seasons, specific (and very limited) additives, by-pass filters, etc. And, yet, there surely are a ton of higher mileage cars running around with clean engines, low wear, and all due to taking it into the dealer every 7,500 miles or so...

Oil is generally SO much better now than it was even ten years ago that it is pretty tough to go wrong as long as you are still meeting the minimum MB spec and are in the general ballpark vis'-a-vis' viscosity. (I had to use that line once!) IMHO

This is all predicated, of course, on older vehicles out of the ol' warranty claim game. Newer models are designed to different spec. Be mindful of some newer BMW M3 owners whose choice(s?) may be effectively limited to one Euro oil, primarilly available ONLY at the dealership for whatever they choose to charge!

The "$100+ oil change" is, apparently, not a myth!

I think the advice on this site is "HOT! & often!", which ain't a bad way to go!

Regards!
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  #15  
Old 02-27-2003, 06:42 PM
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Quote:
Originally posted by afmcorp
. where is the critical time in this situation? the engine needs oil when the engine is up in the rpms and when you first start in the morning.

as for your gauge it's most likely to be a mechanical adjustment in the needle (you have mentioned you took it apart) or something somewhere is grounding out.
Craig,
Thanks for some useful info. I guess my concern is really more of it reading high oil pressure (~80PSI) after the things that I stated I did to the car in my original post and when you do the math you get about 5.5bar to equal 80PSi and I believe that is why my gauge is pegging up that high. The comfort zone to me would be is 80 PSI at initial start and during high rpm acceptable? It drops to about 1.75 - 2.00 bar once oil is warm and at idle.
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