Oil Pressure Question

[Dan Stokes]

Does anyone know if there's an orifice somewhere in the lines/oil cooler on a 617? That would increase oil pressure and mine is low. I don't have the cooler as the engine won't be asked to run that long so I was wondering if that might account for the lower than expected OP (about 5 psi at idle and 30 when the engine is spun up). Everything from the oil filter assembly outward has been replaced with a simple loop of high pressure hose but there's no restriction anywhere in that line.

Thanks

Dan

[t walgamuth]

If your gauge is accurate, that is alarmingly low pressure. The gauge is calibrated in PSI? In the benz car the idle is from 1.5 to 2 bar when warm, and minimum Is IIRC 1.0 bar? Not sure what a bar is but suspect we are talking 60 psi at least on the top end. (I believe it is in bars).

[Shortsguy1]

A few points of clarification to Tom's post...
FSM allows the pressure of hot oil to drop to 0.5 bar at idle. A bar is roughly 1 atmosphere, which is 14.7 psi absolute pressure. So basically, the official lowest appropriate pressure to see on your gauge when you car is warm at idle is just above 7 psi. At any real load and non-idle conditions, you car should be pegged at max, which is probably 45 psi (aka approx 3 bar) on your gauge.

Sorry I cannot help with why you are seeing those low pressures. Does your car have an oil line that sends oil to the back of the gauge, or do you have an oil pressure sender which sends an electrical signal to the gauge cluster?

[leathermang]

I am pretty sure a ' bar' is one atmospheric pressure..... so about 15 lbs..
edit... well, shortsguy beat me to the post while I was typing...

[Maxbumpo]

Originally Posted by Dan Stokes

Does anyone know if there's an orifice somewhere in the lines/oil cooler on a 617?

There is an oil pressure relief valve, integrated into the oil pump assembly (lives in the oil pan/sump).

More than likely your engine is simply worn out. What weight oil are you using?

For the benefit of other readers: Your engine will not live very long at all without the oil cooler. We're talking minutes at highway speed on a hot day. The oil is not only for lubrication but also for cooling, and there is a thermostat to control when it gets routed via the cooler. I've heard too many sad tales of "my hoses/oil cooler is leaking, probably don't REALLY need that, I'll just bypass it..." and your engine is turned into a doorstop.

[mach4]

How are you measuring oil pressure? Are you confident you're getting a good reading?

[Shortsguy1]

Originally Posted by Maxbumpo

For the benefit of other readers: Your engine will not live very long at all without the oil cooler. We're talking minutes at highway speed on a hot day. The oil is not only for lubrication but also for cooling, and there is a thermostat to control when it gets routed via the cooler. I've heard too many sad tales of "my hoses/oil cooler is leaking, probably don't REALLY need that, I'll just bypass it..." and your engine is turned into a doorstop.

Maxbumpo, could you expand on this a little? My 1968 220d never had an oil cooler. At some point in the w115 run, MB decided to add these, and I respect their decision as my car does tend to run hot. But not having an oil cooler has not meant instant engine death in my case. Far from it.

Is your statement perhaps more true for the 5 cylinder, turbo engines? At some point I will need to replace my radiator and I need to figure out if I should do an identical swap or get one with an oil cooler and try to retrofit the lines to my engine. Given that others have lost engines due to bursting oil cooler lines, until I read your comment, I was actually happy to not have an oil cooler. Thanks.

[leathermang]

Originally Posted by Shortsguy1

.....Is your statement perhaps more true for the 5 cylinder, turbo engines? ......

YES.....

[charmalu]

Dan, there is a thermostat in the Oil Filter Housing, that opens to let oil into the Oil Cooler when the oil temp is at a certain level.

When the oil is cold, there is no oil going through the Cooler. That does depend on how efficiently the thermostat closes off the oil flow.

So if you have low oil pressure when the engine is cold, there is another problem.

Your loop shouldn`t cause a restriction.

Charlie

[VT220D]

Originally Posted by Shortsguy1

Maxbumpo, could you expand on this a little? My 1968 220d never had an oil cooler. At some point in the w115 run, MB decided to add these, and I respect their decision as my car does tend to run hot. But not having an oil cooler has not meant instant engine death in my case. Far from it.

Is your statement perhaps more true for the 5 cylinder, turbo engines? At some point I will need to replace my radiator and I need to figure out if I should do an identical swap or get one with an oil cooler and try to retrofit the lines to my engine. Given that others have lost engines due to bursting oil cooler lines, until I read your comment, I was actually happy to not have an oil cooler. Thanks.

I found a 68 cooler delete filter base for my 220D and it's going in this spring.

Mercedes added the oil cooler to the OM615 W115 in late 1968 and shortly thereafter changed to a deeper oil pan. The previous OM621 engine didn't have a cooler. When the W123 was introduced Mercedes deleted the oil cooler on OM615/616 powered cars sold without air conditioning. They also didn't use an oil cooler on OM615/616 powered vans like the 207/307. Even the (76PS) NA OM616 in the MB100 didn't have one. In fairness the MB100 has a huge oil sump. However, the other vans use the car sump.

From what I can gather the difference is AC. The W115 AC system was not installed by the factory. It was either dealer installed or installed by MBUSA on arrival (not sure which). Because of this all late 1968 and up W115 diesels came with a cooler. W123 AC was factory installed which allowed Mercedes to delete the cooler when it isn't needed. This is also true of non AC cars sent to warm climates.

The OM617 NA and turbo engines all have oil coolers. The oil filter housings used on all OM617 and W123 OM615/616 engines have a thermostatically regulated oil cooler. The OM615/616 W115 coolers are full flow at all times unless the cooler is restricted and the bypass valve opens. Full flow to the cooler is a disadvantage especially when operating in cold climates because the oil needs to get hot enough to flow well and evaporate out any condensation. Mercedes addressed this problem when the W115 OM617 was introduced by adding a thermostat.

IMHO Mercedes seems to think that all OM617 engines require oil coolers. They also seem to think that oil coolers should be thermostatically regulated to maintain proper oil temperature and the OM615/616 engines only require a cooler to deal with the additional thermal load of AC. OM615/616 engines do not need a cooler otherwise regardless of load, automatic transmission, power steering or geographic location.

So IMHO if you have an OM615/616 and you don't have AC you don't need the cooler. OM615/616 W115 coolers keep the oil too cool too long. W123 coolers work well but (per the factory) aren't necessary without AC. All coolers add the risk of catastrophic failure but that risk is minimal with maintenance. The change to a deep pan (and appropriate pickup) can't hurt though. Unless you have a low rider!

To the OP: Your oil pressure is very low as others have said. Any OM61x I've seen will peg the gauge at 3 bar when started cold. That translates into roughly 45psi. Remember that the gauge pegs at 3 bar. I have no idea what the actual cold pressure is. The difference between a worn and tight engine is usually only seen in the hot idle reading.

As has been said, the oil pressure regulator might be stuck or you might just have a worn out engine. Even if your cooler bypass hose were plugged there is a bypass valve in the oil filter body.

If this is an NA engine you may want to look at the oil pump drive bushing. This part wears heavily on the OM617 NA because of the higher capacity pump they use. On either the turbo or NA check the lower oil pan for damage. A cracked or damaged pump/pickup could cause this.

[Maxbumpo]

Originally Posted by Shortsguy1

Maxbumpo, could you expand on this a little? My 1968 220d never had an oil cooler. At some point in the w115 run, MB decided to add these, and I respect their decision as my car does tend to run hot. But not having an oil cooler has not meant instant engine death in my case. Far from it.

Is your statement perhaps more true for the 5 cylinder, turbo engines? At some point I will need to replace my radiator and I need to figure out if I should do an identical swap or get one with an oil cooler and try to retrofit the lines to my engine. Given that others have lost engines due to bursting oil cooler lines, until I read your comment, I was actually happy to not have an oil cooler. Thanks.

I know of two 123 cars which died on the first highway run when the oil cooler was deleted: a 240D and a 300D. I do not know if AC was installed or not. MB engineers put it there for a reason.

If your car did not have a cooler from the factory, then the MB engineers didn't think it was required, and given that your car has survived this long, it's quite obvious that you don't need one unless you make drastic changes to the car (like add air conditioning or a trailer hitch and start pulling big loads).

[vstech]

Originally Posted by Maxbumpo

I know of two 123 cars which died on the first highway run when the oil cooler was deleted: a 240D and a 300D. I do not know if AC was installed or not. MB engineers put it there for a reason.

If your car did not have a cooler from the factory, then the MB engineers didn't think it was required, and given that your car has survived this long, it's quite obvious that you don't need one unless you make drastic changes to the car (like add air conditioning or a trailer hitch and start pulling big loads).

was the run up a 9%grade 7 mile pass? I find it hard to believe an oil cooler bypassed, could cause an otherwise fine condition vehicle to fail on the first run.

we gotta have details of these two known cases.
what was done to the cars besides OCB? since it's unlikely in the extreme they were brand new MB cars with the oil coolers bypassed at the dealership... I'm thinking there is much more to the story.

[Maxbumpo]

Originally Posted by vstech

was the run up a 9%grade 7 mile pass? I find it hard to believe an oil cooler bypassed, could cause an otherwise fine condition vehicle to fail on the first run.

we gotta have details of these two known cases.
what was done to the cars besides OCB? since it's unlikely in the extreme they were brand new MB cars with the oil coolers bypassed at the dealership... I'm thinking there is much more to the story.

These were both shared on a listserv that I've subscribed to for about 14 years now, which has suffered at least two complete meltdowns with loss of archives. I think one of the fellows (the 240D) is still active on that list, I'll inquire and see if I can get more info. Will also put out the general request to see if the other fellow is still around or maybe someone can provide more info.

[Maxbumpo]

Originally Posted by vstech

was the run up a 9%grade 7 mile pass? I find it hard to believe an oil cooler bypassed, could cause an otherwise fine condition vehicle to fail on the first run.

we gotta have details of these two known cases.
what was done to the cars besides OCB? since it's unlikely in the extreme they were brand new MB cars with the oil coolers bypassed at the dealership... I'm thinking there is much more to the story.

OK, looks like I've got to eat some crow on the 240D story. I had SOME of it correct...

Here's the re-telling of the story from the owner:

"I did the oil cooler delete on my '83 240D after everybody including Herr Booth said it didn't need it.
They were all wrong. Well actually let me be clear if its always under 60F and you never want to go over 55mph you don't need an oil cooler. That said if its over 60F and you want to exceed 55mph you'll watch the coolant temp rise, sometimes at an alarming rate.
The engine in my car failed because the hose my Indy had used for the oil cooler delete failed, not because of the oil cooler delete itself. The hose failed after I messed with it so I can't blame him..."

[Dan Stokes]

As I posted in my build thread I found the problem. Moving the sender to the loop that replaces the oil cooler and grounding the sender for my electric OP gage yields 70 PSI at idle with a cold engine - I haven't fully heated it up yet. But my added oil port at the top of the oil filter is, for reasons still not fully understood, a bust. The mechanical gage installed there only shows 20ish PSI.

Tom - you mentioned the durability of the M-B bottom ends which was one of my reasons for selecting this engine in the first place. You may remember that I also replaced the mains while I was in there doing the rear seal (which so far looks OK). So I really wasn't EXPECTING any issues which is why I went ahead and ran the engine - I was pretty sure it was a gage issue and it was.

As far as removing the cooler. Remember that this is a very specialized vehicle and the considerations that Mercedes used during design largely don't apply. If I was building a S-10/617 for road use I'd definitely retain the oil cooler.

Thanks for everyone's input!

Dan