Quote:
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.
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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.