gdp_samson

pressure not exceeding (still) the 2.5 bar.

I searched the forum (thoroughly, I feel) so thought it was a bad sender... I bought a new original one,
installed it the 'smart' way by removing the block where the sender is screwed in,...and installed the new sender unit.

The clock itself is still working, meter jumps up to 5 bar when not connected to the pressure sender ...

Most alike threads seemed solved when new pressure sender was installed...but what's the next step when it is not solved by installing a new pressure sender ?

theiceman

have you put a mechanical pressure gauge on it and measured actual pressure ?

also do oy have the original gauge ? or one with numbers on it ? they require different senders.

But dont discount the possibility you have low oil pressure. I would be checking the bypass valve on that car by now, i think it may even have two !!

gdp_samson

Hi Iceman,

have never put a mechanical pressure gauge yet...is this something you can find practically everywhere (with the correct diameter of thread ?)

do you think it is OK to drive the car to the mechanic in this 'state', assuming I can't find the solution myself ?

theiceman

That is the very first ting the mechanic will do is put a gauge on and check the actual oil pressure .. you need to know what it is ...

most commercial oil pressure gauges are NPT thread but your mechanic should have an NPT/ Metric adapter. I have one for my Audi and it it NPT --> 10mm by 1.0 mm pitch so they are generally available.
as to whether it is okay to drive to the mechanic is really up to you, if its 5 mins away it might be . 2.5 bar is about 35 PSI so i would think so but you really have not told us enough

is it that pressure cold ? hot ? at idle ? at what rpm ? is your oil pressure light flickering ? what oil viscocity are you using ?

gdp_samson

Hot or cold, the pressure at 1,000 rpm is appr. 1 bar

The pressure rises to 2.5 bar when the rpm goes up to 2,500...but then you can press the pedal up to 5,000 rpm...the pressure does not climb anymore...it
stays at 2.5 bar.

If you drop the rpm back to 1,000 then the pressure drops to 1 bar.

Running Swepco 306 15W40 (oil change 3 months ago, new filter and new oil twice a year). I had a rather large oil leak via valve stems on cyl. 4 and 5...
a professional shop had this issue solved. Had the car back for 2 months after that without any oil consumption or other problems whatsoever...

The car revs fine, pulls fine,...temperature goes up 1/3rd, engine does not get any hotter except for stoplight traffic.
No electrical issues known (except for the oil switch light that never comes on).

theiceman

well if you can get a gauge or borrow one you will know instantly .
others might chime in but when i'm starting a cold engine my oil pressure instantly pegs for a few seconds as th eoil is cold.
your pressure at idle and at 2500 sound about right.

gdp_samson

definitely something wrong above 2,500 rpm

measuring resistance on the new oil sender unit (+ on sender output, - on chassis)

ignition on = 10 Ohm
stationairy = 1000 rpm = 78 Ohm
2000 rpm = 102 Ohm
3000 rpm = 110 Ohm
and everything above 3000 rpm stays with the same resistance of around 110 Ohm

new oil pressure sender also bad, or other problem (I would think the latter)

will order new pressure relief valve spring and install that first...

gdp_samson

OLD = 86 mm of spring setup

NEW = 90 mm of spring setup (4 mm extra thus raising pressure ???)

gdp_samson

will install the new (4mm longer) setup this week and report changes, but it is strange that the original is shorter than the new one (if I understood correctly then 86 mm is OK)
so no idea why the new oil relief valve spring setup is longer...

but this sounds promising, doesn't it ?

gdp_samson

It may have sounded promising, but it didn't do anything with the oil pressure readings...2.7 bar max, regardless of rpm...

have measured the resistance on the new oil pressure sender:
48 ohm at 1,000 rpm
100 ohm at 2,500 rpm and beyond...Not the wanted 186 Ohm at 4,500 rpm

any more options before opening the engine (this last thing does sound awfully expensive...could almost cry)

certainly because the car runs great, pulls strong, fires up instantly...really feels like nothing is wrong...

oldskewel

I'd definitely measure oil pressure with a completely independent sensor, like a mechanical gauge, prior to thinking about opening up the engine.

The behavior seems odd - works fine up to 2.5 bar / 2500 rpm, then no more. I can see how a pressure release valve at that value might give that result. Or a faulty gauge, even if new. Are you 100% sure your replacement gauge is exactly the right one? I replaced the one on my '85 many years ago, and do remember VDO made a bunch of options, some which were almost right, but not quite.

Can't think of any engine-related failure, other than the release valve that you already swapped, that would work like that (normal to 2500 then flat line).

gdp_samson

I have attached an oil pressure meter directly to the engine and at 4,000 rpm (with cold engine...oops)
never above the 3 bar, not even with a warmer engine some time later...



I have not swapped the horizontally mounted relief valve spring as this is 'hidden' above a header.
The vertical one was changed by new spring, see posts above...

Would this be your next step ?