350SDL oil pressure issue solved, what do you think? - PeachParts Mercedes-Benz Forum

MPH · #1 03-04-2011, 05:58 PM

A few months ago I posted about noticing lower oil pressure than before at idle. At that time I was seeing 1.3 bar on the gauge at idle. My wife drives the snot out of this vehicle daily. One week ago I got in the car and noticed virtually no oil pressure at idle. It would go to 3 bar as soon as you got the rpm above 1400 rpm.

I put a sending unit in and the results were the same. Pulled the pan down and found bolts that hold the windage tray had lost torque and had fallen out. The crankshaft picked them up and threw them towards 2 piston spray jets and nicked a 1/4 inch hunk from 2 piston skirts. The 2 jets were broken, which is where the oil pressure issue was coming from.

The car has 190K miles and will not use a quart of oil in 5K miles. My options are to put in 2 spray jets and an oil pump and run it, or repair the 2 pistons along with re-ringing the other 4. I really do not want to sink a small fortune in the engine, but the car is in excellent shape.

I would like opinions from those who are very familiar with this type of engine. Sorry for the long post, what do you guys thank as far as repair options?

babymog · #2 03-04-2011, 06:36 PM

Driving the snot out of it shouldn't hurt it, but at least it didn't grenade.

My '91 SDL had a similar situation where one of the oil spray jets' bolt had backed out, and the crank had crushed the spray unit, all parts were happily in the pan and no damage to the oil pump had occurred / screen intact (this included the ball and spring from the sprayer!).

The bolt and spray jet were destroyed.

You will probably need to replace the pistons, just seems like they're compromised and could fail, and that could be catastrophic. They are also no longer balanced, whether this could cause (or already has) damage from vibration is hard to predict.

The windage tray is something that I'm torn on. Looking up the tray in the EPC, it has been superceeded with a new number, and there is a note to NOT install the older version. I don't know when the change occurred (before or after the '91 production), and there is no part number on the windage-tray so no way to tell if it is the old or new design (this is the rear tray).

The tray is there because the 603.970 has a higher oil level and longer crank throws, so it seems important to replace it, but I'd get a new (later) rear pan. Is yours the rear or front pan/tray that came loose?

The down side to the windage tray is that it will keep debris above the tray, such as my and your sprayers, and throw them around instead of them quickly settling to the bottom of the sump. Are you sure that it was a windage-tray bolt that made it up there or could it possibly have been the oil sprayer that came loose first?

Also, do you have the side-sump on your engine? The FSM says that none of the .97x engines do, but mine did, I'm not sure whether it was replaced (I was not the original owner). The pan that the FSM says came on your car has no side-sump and the oil level sender is moved up 6mm for the additional oil capacity in the main sump.

Worse case, I have a good used 3.0L short-block I removed from my car this week, will be available as soon as the new engine is proven.

barry123400 · #3 03-04-2011, 06:37 PM

You need a really professional opinion on this one. That lets me out.

My first instinct is because the piston is much softer than the cylinder liner any rough edge if contacting the wall should polish up as needed. without damaging the bore. Actually I do not believe your engine has a cylinder liner unfortunatly so any bore damage would be very serious. There is not enough material to bore much larger for example.

The second question is what exact size are the missing small areas? I assume the bolt located between the piston skirt and the crank throw when the damage occured. Where you able to feel the cylinder walls in the vicinity of the skirt breaks?

Smooth with no evidence of damage I would hope and suspect not. Find the piston chunks? The car has been driven for quite awhile with this problem so if there was going to be additional damage it should have started.

If only a small piece missing out of each skirt you may get away with this. Still get a serious proffessional opinion as soon as possible.

MPH · #4 03-04-2011, 07:17 PM

It was the windage tray bolt that fell out and caused the damage. I do not have a side sump pan. The pieces of the piston are thumb nail 1/4 size and shape. They were in the pan.

Yes, the car has operated I am guessing 4-6 weeks in this type of condition, possibly longer.

There is no visible bore scuffing, the "nicks" are at the bottom of the skirt. I do realize a crack can propergate, but this isn't a high load area for the piston.

I will definately check for the updated tray. Thanks.

Any more thoughts or comments are welcome.

kerry · #5 03-04-2011, 07:20 PM

Given the general reputation of these engines, I'd probably just drive it instead of putting any money into the engine.

layback40 · #6 03-04-2011, 08:38 PM

A couple of pics of the damage would help you get better advice. As we speak, I have a tractor with a piece out of a piston skirt pulling a set of rippers, It has been doing this sort of work for about 1000 hrs with the bad piston, just havent had the time or motivation to fix it. When we can see the damage you will get more appropriate comments.

t walgamuth · #7 03-04-2011, 09:50 PM

Quote:

Originally Posted by kerry

Given the general reputation of these engines, I'd probably just drive it instead of putting any money into the engine.

I was thinking this myself. I would probably fix what I could without spending much on it and drive it.

Then replace it with a 3 liter short block if the car condition warrants keeping it in service.

MPH · #8 03-05-2011, 09:36 AM

Will the oil pan,bell housing,oil pump transfer over from the 3.5L to the 3.0L? I am pretty sure the cylinder head/camshaft does. Also will all of the other accessory items bolt up to the 3.0L block?

Can you transfer the fuel pump without having to perform claibrations for the 3.0L?

compu_85 · #9 03-05-2011, 09:42 AM

Can you post any pictures of this? I want to take my oil pan off and secure the fasteners in there. I'd love to get an idea of what I'm looking at beforehand.

-J

MPH · #10 03-05-2011, 09:50 AM

The car and myself are in a different location this weekend. I plan to get some pictures on Monday.

compu_85 · #11 03-05-2011, 09:50 AM

Sweet!

gsxr · #12 03-05-2011, 12:57 PM

babymog · #13 03-05-2011, 01:58 PM

As Dave said, everything transfers. The 3.0L is rated at a higher RPM and thus is a higher horsepower also than the 3.5L so turning up the RPM is a good idea (simple adjustment).

You're seeing the piston-spray casting in the center of the photo, Mercedes secures it with one bolt and a pin, the bolt is located where the crank counterweight will hit it if it backs out.

The windage-tray bolts on the rear (sorry no photo) are into the crank cap bolts (tapped head), the front piece (2-piece tray) is secured by the rear piece in the rear, and by the oil pump/pickup mounting bolts.

These are all good candidates to check if you have the oil pan off, as is the bolt holding the oil-pump chain to the oil pump (have been two fail that I've read here over the past few years, but it can be catastrophic).

MPH · #14 03-05-2011, 04:46 PM

Thanks Dave and Jeff. Good information sharing.

I hope this helps others that do not know they may have an unfortunate issue that could wreck the motor and cost big $$$'s.

My mechanic says mine is the 4th 350 that has had windage tray bolts back out and nick the pistons. Some were worse than mine.

t walgamuth · #15 03-05-2011, 05:35 PM

Larry perkins here has a similar personal experience. He has found a couple of them with the bolts which came apart and got against the screen on the oil pump and worked their way into the pump, locking it up and trashing the engine.