Good, I share the same thought regarding the HG. Definitely is leaking from the back of the head, and definitely also have an exhaust leak, but I think both unrelated to low oil pressure on startup. I suspect that these check valves all eventually die when they get old enough.

No kinks or cracks or leaks in the oil pressure gauge line. Not leaking in the cabin either.

I’ve been using the Costco Delo 15-40w for the past 10 yrs or so. Haven’t had this issue before. Pretty sure it’s the right viscosity...

Viscosity is not the issue and 15w40 is fine anyway. Delo is a good choice.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

I have no pics of the OM601 to look at so I don't know. If someone would post one of those free online manual sites you could look that up.

I think if you have a similar tube attached to the Oil Filter Cap there is likely a valve inside of that tube.

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84 300D, 82 Volvo 244Gl Diesel

Maybe there is a member near you that would come over and allow you to remove his oil filter cap and install in yours for trouble shooting purposes.

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84 300D, 82 Volvo 244Gl Diesel

Worn main bearing, cam bearing, or oil pump. Live with it until you can't.

Maybe, but hopefully not!

Knowing the HG is seeping externally and that a salvage oil filter housing is $100. I found a mostly complete engine pullout on CL for $150. Figured if I drop the housing in and it doesn’t work, I’ll just RR the salvage motor and swap it.

Supposedly the donor car was crashed, smashed the oil cooler, sprayed the motor with oil, yet run for a minute or two afterward. It’s not seized and doesn’t feel shot out. Thoughts?

Try an oil filter housing cap first.

For $150 it's worth a try; but, I'd inspect the crank bearings before installing it in a car. Can you pull the valve cover to look at the cam and followers? Is there oil on the dipstick that looks used vs a clean refill of the oil lost. If the oil looks really clean...run!

Drop the lower oil pan and check a bearing. If it's good pull the upper pan and check the rear bearing/farthest from the oil pump first.

If the bearing checked first from the lower pan looks bad that is a bad sign.

If the bearings look good do a compression test.

How many miles on the donor motor?

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Supposedly around 170k mi on it. I’m hesitant to diagnose my current motor as being worn out. Twas a factory replacement long block with the previous owner.

What does swapping oil filter caps accomplish? I’ve already replace the oil filter rod O rings...

I'm not convinced there is anything wrong with your motor, just the gauge or its supply line.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I have a spare gauge cluster, however, how would I plumb up the cluster under the hood without a spare oil line to it? For what it costs to fish one out of the JY or cob one together from the hardware store, it’s cheaper to just swap to the spare filter housing with new gaskets.

That said, is there an off the shelf tool I can buy that threads in place of the oil pressure gauge line?

In addition to the o-rings which were replaced being a potential problem, there is a passage way in the oil filter cap that sometimes gets a foreign object lodged in it and there is a check valve inside the tube that the o-rings go on.

170k on a donor motor sounds promising if no oil starvation occurred.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

If the exit tube was obstructed, you would expect HIGHER oil pressure readings.

The fixation on the bypass tube in the oil filter housing lid is fascinating. It is a TINY orifice, seriously small. Even *IF* it were stuck open and bleeding down, the level will only drop to the orifice, which is 3/4 of the way up the shaft, and the size of it would mean it would take quite some time to bleed down that far.

Since the problem seems to have occurred after an oil change, has the OP tried changing the oil filter? Perhaps the wrong one is installed. I seem to recall that there is one that's slightly shorter than the other, they'll both fit the housing, but only one is correct for each application.

If wanting a definitive test of how far down the oil bleeds overnight, pull the filter housing cover and immediately pull out the filter cartridge. See where the oil line is on the cartridge body. If the filter housing is empty or nearly empty, the only real big-ticket items are the bypass valve or the O-rings on the filter stem.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Diseasel300, I'm in not fixated on the tube and/or check valve in the oil filter cap, rather was thinking it was a possibility to test it by r&r'ing two nuts in under five minutes vs changing the oil filter housing or engine. I agree trying another oil filter would be a good idea.

MxFrank, Agree, a restriction would usually cause higher pressure. I don't think it would in this case, it would just be bypassed. I think that tube, check valve and o-rings in the cap are a way to hold the oil in the housing to prevent drain back. A drain back would empty the housing causing the exact symptom the OP describes.

I may be wrong and look forward to learning the solution.

OP please close the thread once it's solved.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

I don't want to hijack this thread, but I decided to give my oil filter cap a quick check as I've been having the same issues with oil pressure on cold starts. Here is what I've found.



To put this in context, on the last oil change I did I had to use a cheapo oil filter because I couldn't find a good one (Mann or Hengst). It was only meant as a stop gap before I could find decent filter. Well I ended up forgetting about it and now is time for an oil change once again.
Lesson learned: don't use cheap oil filters on old Mercs!
To go back on topic, I don't see how this check valve thing could be the cause of the delay on oil pressure on startup, as the entrance hole is almost a the top of the cap.
Maybe it could be the check valve located on the filter housing?

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