87 300D oil pressure ... normal or not? - PeachParts Mercedes-Benz Forum

BodhiBenz1987 · #1 07-10-2011, 03:14 AM

I've noticed lately my oil pressure takes a little longer to register when starting not only cold, but even if the car's just been sitting an hour or two ... by a "little longer" I mean a full 4 seconds, if not a touch longer. I replaced the rubber seals on the filter housing stem and also cleaned out the holes with (filtered) compressed air. I thought that would help because the old rings were hard as rocks, but it did not make a difference. Once the pressure registers, it shoots right up to 3 bar, and slowly lowers down to 2 bar as it warms up. Once the engine is hot, it drops to 1.7-1.8 at idle, occasionally closer to 1.5 ... that seems OK to me in and of itself, but, it used to hang closer to 2. What concerns me more is that it doesn't peg as soon as I hit the throttle ... it isn't pegged until about 1,600 rpm (working it's way up along the way) ... if I recall right, it used to shoot up around 1,000-1,200 rpm.
I did put a brand new sensor in about a year ago because the old one leaked. I did notice the idle pressure read a hair lower with the new sensor than the old, but everything else seemed normal. Maybe it's still normal ... but it seems like it takes 1) too long to register on startup after sitting and 2) too long to peg when revving from idle when the engine is hot.
Thoughts? I'd really rather not find out the hard way that my oil pump is on the way out ... read enough horror stories along those lines ...

Stretch · #2 07-10-2011, 03:21 AM

I don't know enough about your engine to say for sure but it sounds like the sensor and gauge are working fine - they register "everything" - it is just slow.

May be just may be the oil pressure reading is slow because the oil is falling back into the sump. On an OM617 there are check valves in the oil filter housing that stop this. I guess it is similar in design on your engine but I can't say for sure.

You could remove the oil filter housing and check to see if you can see some check valves and see if that general area is gunked up with crud! But before you get your spanners out again - what viscosity oil are you using?

BodhiBenz1987 · #3 07-10-2011, 03:56 AM

Quote:

Originally Posted by Army

You could remove the oil filter housing and check to see if you can see some check valves and see if that general area is gunked up with crud! But before you get your spanners out again - what viscosity oil are you using?

Oops, I meant to mention the type of oil: I use Rotella 15w40, changing every 3,000 miles. I've been using that and a OE filter since I've had the car which is about 8 years.

compress ignite · #4 07-10-2011, 04:06 AM

All have to Remember that the Gauge Set Mercedes "Gifted" us with is A
"REPRESENTATION" of actual engine operations.(a La 1930s Technology)

The Real O.P. peaks FAR ABOVE 3 Bar.

If you were to remove the O.P. Sensor (A Screaming Bear to do,"For Fun".)
and replace it with an Actual Bourdon Tube Type O.P. Gauge fitting and line
to a Real O.P. gauge; you'd most likely be reassured.

That's the ONLY definitive way to tell...

Howeveah, with 300K ALMOST on the OM603 I'd be investigating...

Mos Likely , your Explanation of the Noted Differences with the New Sensor
is the Explanation.

I'd MAYBE try a Sump of Synthetic Rotella T 5W40 (just for grins and giggles)
and see if any diffenence.
(The synthetic Molecules are a little more Petite and Reaction might be Quicker.)

sixto · #5 07-10-2011, 04:38 AM

gsxr noted some goofiness in the oil pressure of his 2.5 when the head gasket failed allowing oil to leak here and there. 300K miles on a 603 head gasket seems like a long life to me.

Sixto
87 300D

aaa · #6 07-10-2011, 11:12 AM

+1 on headgasket.

scottmcphee · #7 07-10-2011, 11:14 AM

Your numbers and hunches are very close to my experiences with my 603. Sounds a *little* low at idle and a tad slow at rising with RPM. I guess the good news is that you're in a safe range and would not be harming the bearings at the numbers you are getting.

Describe how did you use compressed air to clean the stem. If you put 100psi into the side hole, maybe you blew the check valve out of it, or that valve is crudded open, and this contributes to leak down inside the filter housing while parked. If you were to blow into the end of the stem (mouth pressure), does air come out side hole?

Other thoughts, maybe an oil squirter on a piston, or by now maybe two, have liberated themselves from the block. Check the oil pan for debris with a magnet on a coiled flexible tube, through the oil plug.

Stretch · #8 07-10-2011, 01:23 PM

Going on the head gasket advice / warnings / comments I'd rule that out first before taking anything a part. Do a leak down test - and work out which part of the engine leaks the most.

Jeremy5848 · #9 07-10-2011, 02:52 PM

I must agree with the other poster children - 300,000 miles is a lot for an OM603, especially if it's got a #14 head and the original factory gasket. OTOH, you may simply be seeing the effects of wear on your bearings, which is another form of "leak" that can cause either a slow pressure rise upon starting or lower pressure at idle. An idle oil pressure of 1.5 bar is fine but as C.I. notes, the Mercedes gauge is more of a "serving suggestion" than a real, accurate oil pressure gauge. I added a VDO mechanical gauge to my 603 and found that the actual oil pressure at startup was well over 60 psi but at hot idle it drops to as low as 15 psi (~1 bar) even though the Mercedes gauge insists that it's at least 1.5 bar or more.

Since your oil pressure numbers currently meet Mercedes' specs, there's no immediate need for panic but you should make plans to panic in the next year or so, especially if you are seeing the early signs of head gasket failure. Otherwise, this may only be gradual wear on the crankshaft and camshaft bearings.

I don't have good information on oil pump failure but I suspect that if the oil has been kept clean all during the engine's life, the oil pump is less likely to wear out than simply stop pumping due to a broken chain or other mechanical failure. For that you need to keep a close eye on the oil pressure gauge and consider adding a low-pressure alarm like I did. Anything below 0.9 bar and I get a flashing red LED in my instrument cluster next to the oil pressure gauge.

You don't say how much oil the engine uses; that can be a guide to wear in the rings and valve guides/seals and an indication of overall engine wear. Also consider following Army's suggestion to have a compression/leakdown test. I assume you are not seeing evidence of coolant in the oil or oil in the coolant?

Finally, there's no way to really be sure that you do or do not have a developing head gasket problem other than to pull the head and inspect the gasket. That is a fairly good-sized job so start with the easy things first.

Jeremy

BodhiBenz1987 · #10 07-10-2011, 02:56 PM

Quote:

Originally Posted by scottmcphee

Your numbers and hunches are very close to my experiences with my 603. Sounds a *little* low at idle and a tad slow at rising with RPM. I guess the good news is that you're in a safe range and would not be harming the bearings at the numbers you are getting.

Describe how did you use compressed air to clean the stem. If you put 100psi into the side hole, maybe you blew the check valve out of it, or that valve is crudded open, and this contributes to leak down inside the filter housing while parked. If you were to blow into the end of the stem (mouth pressure), does air come out side hole?

Other thoughts, maybe an oil squirter on a piston, or by now maybe two, have liberated themselves from the block. Check the oil pan for debris with a magnet on a coiled flexible tube, through the oil plug.

I used about 40-50 psi right into the side hole, then also blew it into the bottom hole. When I blew compressed air into the bottom, it did come out the side hole ... but I did not try with mouth-pressure. Hope I didn't manage to mess that up ... though the oil pressure behavior did not get worse after I did that, it just stayed the same.
So to check the oil pan I stick the magnet into the drain plug? I'll have to shop for a very small magnet, I suppose they probably sell snaking magnets for similar uses. If it does turn out to be an oil squirter, what happens? I take it replacing them is fairly invasive ...

Looks like I'll be investigating the head gasket now. I figured it would need one someday. Though I have to admit the thought of doing that job myself terrifies me, not because of the skill needed (well, that too) but because if I mess up I could destroy the engine.

Big question: Would you continue to drive it? I certainly don't see any pattern of it worsening, but if the kind of thing that can go downhill in an instant, I'd rather not chance it. On the other hand I know the pressure readings are in "safe" range.

BodhiBenz1987 · #11 07-10-2011, 03:15 PM

Quote:

Originally Posted by Jeremy5848

I must agree with the other poster children - 300,000 miles is a lot for an OM603, especially if it's got a #14 head and the original factory gasket. OTOH, you may simply be seeing the effects of wear on your bearings, which is another form of "leak" that can cause either a slow pressure rise upon starting or lower pressure at idle. An idle oil pressure of 1.5 bar is fine but as C.I. notes, the Mercedes gauge is more of a "serving suggestion" than a real, accurate oil pressure gauge. I added a VDO mechanical gauge to my 603 and found that the actual oil pressure at startup was well over 60 psi but at hot idle it drops to as low as 15 psi (~1 bar) even though the Mercedes gauge insists that it's at least 1.5 bar or more.

Since your oil pressure numbers currently meet Mercedes' specs, there's no immediate need for panic but you should make plans to panic in the next year or so, especially if you are seeing the early signs of head gasket failure. Otherwise, this may only be gradual wear on the crankshaft and camshaft bearings.

I don't have good information on oil pump failure but I suspect that if the oil has been kept clean all during the engine's life, the oil pump is less likely to wear out than simply stop pumping due to a broken chain or other mechanical failure. For that you need to keep a close eye on the oil pressure gauge and consider adding a low-pressure alarm like I did. Anything below 0.9 bar and I get a flashing red LED in my instrument cluster next to the oil pressure gauge.

You don't say how much oil the engine uses; that can be a guide to wear in the rings and valve guides/seals and an indication of overall engine wear. Also consider following Army's suggestion to have a compression/leakdown test. I assume you are not seeing evidence of coolant in the oil or oil in the coolant?

Finally, there's no way to really be sure that you do or do not have a developing head gasket problem other than to pull the head and inspect the gasket. That is a fairly good-sized job so start with the easy things first.

Jeremy

Thanks, Jeremy. The thought of my engine wearing out depresses me, but I suppose that's how life works whether you're a car or a person. I read about your low-pressure alarm, I like that idea ... I do keep my eye on the gauge a lot, but obviously not 100 percent of the time. Of course, one of my fears is that it will drop while I'm in the middle of heavy traffic on the highway and even though I'll be aware of it, I'll be helpless (I am a chronic worrier, in case you guys can't tell).
As far as oil consumption goes, I don't think the car burns much at all. I don't have to add oil between 3,000-mile changes. The level on the dipstick usually goes down a little between one change and the next, but not much. It does leak a little at the front seal and oil level sender, and probably elsewhere ... it doesn't drip on the ground (well, once in a while), but there's always oil on the bottom of the pan, pretty far back. I suppose it's possible some is coming from the head gasket.
I sent an oil sample to Blackstone about 4,500 miles ago, and there was no coolant or signs of coolant in the oil. It also showed normal or below-normal levels of wear metals. I don't see any oil in the coolant, but I did not have that tested. No blow-by and I don't see any smoke. I'll follow Army's and your advice to try to a leak-down test as soon as I get the chance. I bought a compression tester a few months ago but I have to learn how to use it.

babyjames · #12 07-10-2011, 03:28 PM

When I bought my wagon last year the gauge stayed at 3 bar. I replaced the sender and am seeing pressures similar to yours, Bodhi. This is not the original engine for this car, and I don't know the mileage. Don't really care, for that matter. I used a Uro sender, and, quite frankly, don't really trust it. I do have occasional lifter noise in the winter (with syn 5/40) but not in the summer, yet. The car runs cool, no oil in the coolant, rad. hose is squishy in the morning. For what it's worth, I'm not sweating it on mine. The first thing I would try, though, is a VDO sender.

Jay

scottmcphee · #13 07-10-2011, 09:43 PM

For all you report, if the car was mine I'd continue to drive it. Not like it owes you anything, and to tear into the engine just to look at gasket is going to be $2000 later for all the parts you should replace while you're in there.

Still on the original vacuum pump?

compu_85 · #14 07-10-2011, 11:54 PM

So is the common wisdom to replace the head gasket every so often? How often?

-J

Jeremy5848 · #15 07-11-2011, 01:39 AM

Quote:

Originally Posted by compu_85

So is the common wisdom to replace the head gasket every so often? How often?

-J

I wouldn't replace the head gasket just because the engine has a certain number of miles on it. Some folks feel better knowing that the head gasket (timing chain, vacuum pump, etc.) have been changed. However, each individual must ask him/herself several questions before doing any of these "preventive" jobs, among which are:

1) What care (or lack of care) has the car enjoyed during the X miles and Y years it has existed? This almost always boils down to "what oil was used and how often was it and the filter changed?"

2) Is the proposed work (changing the head gasket or whatever) something I can do myself, for just the cost of the parts, or will I have to hire a mechanic?

3) If I do the work myself, do I know what I'm doing or am I likely to cause more harm than good?

4) While doing this job, as Scott says, are there other "while you're in there" jobs that should be done? How much will they cost?

That's just a sample. As a point of calibration, I just changed the head on my '87 300D (from a #14 to a #20). I bought a complete used head from a forum member and had a shop do a "light" valve job. I bought everything I possibly could from various on-line sources, going to the dealer only for those parts I couldn't get on line and for the valve stem seals, as I'm suspicious of after-market seals. Other than the valve job, I did all the work myself. Even so, counting all of the parts and cleaning supplies and special tools, the total for the project was just about $2,000.

The '87 was abused as a child; I expect to find things that need work (and I do) even at only 162,000 miles. OTOH, the '96 E300D that my wife drives has 278,000 miles of documented, regular care. Consequently, my recent inspection of the valve train and timing chain showed almost no wear. Unless something dies of old age (most likely me before the engine) I doubt that I'll ever have to do any serious work on this engine, because it has been so well cared for. BTW, I broke a couple of small things and also flooded the car with diesel by damaging one of the little return lines (should have replaced them). This demonstrates how easy it is to violate Rule 3 (above).

YMMV.

Jeremy