Oil pressure issue - PeachParts Mercedes-Benz Forum

Willie White · #1 12-10-2005, 08:51 AM

I have had such a good experience getting my 300 SD back in shape here on the forum that I would like to throw out this problem with my Rabbit diesel pickup. It is an 83 with the 1.6 engine. Recently replaced the head gasket and since have had this problem. When starting up after sitting overnight the oil pressure sits at ZERO for about a minute. Then it will build up to sometimes over 100 PSI{cold temperature} then as it warms up will go back to 30-50 PSI. When the pressure is down I let it idle until it gains pressure but I am fearful that the bearings will suffer eventually. Anyone?? your input would be greatly appreciated Willie(Poor Soul}

thorsen · #2 12-10-2005, 09:12 AM

If the oil pressure sits at zero for a minute, you will be replacing main and rod bearings in short order.

You didn't mention what weight of oil and where you live (temperature). I managed to wipe the main bearings in my MGB this way. I forgot I had left the crankcase full of 20w-50. I leaned in to start it up in in the middle of winter, then slid back out to do something. 30 seconds later I looked at the oil pressue gauge and it was at zero. I turned it off until Spring came, and when hot, the engine only had 5 lbs of oil pressure at idle. Pulled the oil pan and the main bearing caps and I had scored the crankshaft. Time for a new engine.

So, depending on the weight of oil and the temperature where you are, I postulate that for the first minute, you are running your engine with no oil pressure as the oil pump strains to suck a thick gob of molasses and push it through a bunch of tiny passages. Once it finally makes it through, it spikes the oil pressure, then settles down to a 'normal' level, leaving bits of bearing in your oil pan.

zcc · #3 12-10-2005, 09:15 AM

Did u check the oil filter?

t walgamuth · #4 12-10-2005, 02:06 PM

filter rather than the heavy oil thing.

tom w

Willie White · #5 12-10-2005, 02:35 PM

Thanks! I will be replacing the filter with a change of oil before I start it again. I am in Northwestern Coinnecticut and its winter---tho the cars are inside the unheated garage. I have never had this problem before and everything I can think of as a cause doesnt make sense to me. {Bad oil pump;clogged sceen; plugged oil passage ,etc . will keep you posted.
Willie{poor Soul}

Willie White · #6 12-21-2005, 10:55 AM

New oil filter and 15W 40 oil............. Perhaps some slight improvement {maybe wishful thinking}. Delay seems to be like what you experience when you start up the first time after changing the oil and filter. Never happened before??????HELP!

dkveuro · #7 12-21-2005, 11:20 AM

Quote:

Originally Posted by Willie White

............Rabbit diesel pickup. It is an 83 with the 1.6 engine. Recently replaced the head gasket and since have had this problem. When starting up after sitting overnight the oil pressure sits at ZERO for about a minute. Then it will build up to sometimes over 100 PSI{cold temperature} then as it warms up will go back to 30-50 PSI. .........................................:

You problem could be many things...but let me list possibilities.

First you need to check with a master gauge at the oil pressure switch on top of the oil filter housing.....Cold, max = 125 psi.
Idle cold = 90 to 120+ psi.
Idle warm = 25 to 60 psi. (15W40 Rotella. )

Have you checked the head gasket for being on upside down....to check, look at the gasket tab next to the #3 cylinder injector with the gasket notches...okay ?

The oil pumps on these engines are prone to the relief valve sticking....usually closed but sometimes open.....the latter will cause vey low pressures and very long pressure rise from start up.
The only sure fire cure is replace the pump with the later 'hydrulic' head engine pump, which is slightly larger.

A windage try is also available and releases a little horse power too #037 115 220 B. I install these on every engine I maintain. They list at $87.15. I get them for $38.00. wholesale.

Next is the bearings for the intermediate shaft. These wear and there is a oil supply to the skew gear that drives the vac' pump. This acts a an internal leak....this problem shows up as a hot idle pressure problem, so it may be not yours.

Would like to know what you find.

.

Ralph69220d · #8 12-21-2005, 11:27 AM

If it turns out not to be the most likely filter/oil-weight issue, a bit of gasket sealant of certain types could do some odd things in the oil gallerie's depending on what it has gotten into. If you have zero oil-pressure on the guage and the rod's are not pounding, then you're getting oil to the crank. So, I'm guessing oil pressure is read after the crank. On the gasket sealant issue, which is a fantasy in my head, it's propertie's in an oil gallery changing with heat and flow could conceivably do some very odd things like you're seeing. But, you are getting oil pressure to the crank when it reads zero, or you would know immediately. When it reads 100psi you might be getting a complete blockage by my mythical gasket sealant right after the point where the oil pressure is sampled, which then "flaps away" with coolant temp increasing causing little restriction. In the same fantastic vein a sealant goop before the pressure read out, but after the crank, would give a zero read.
I'd be interested to hear what your oil filter looks like if you'd cut it open for us, assuming that's the problem. I do think the filter being a problem is much more likely than oil viscosity. I believe a modern mechanical pump will pump 90W gear grease at 40 degrees F; I mean I wouldn't rev the engine til it's eeked it's way into all the machine fits, but just making a point. Oil viscosity does not seem to acc't for all of the behaviors you're seeing and their temporal sequence; though I say this in the relative sense, as a combination of viscosity and filter problems might do so.
I probably should read this before I submit it, but, I like contributing ideas more than I dislike being embarassed. One of our Maste Tech member's (DieselGiant ?) makes the beautiful point of how, if we are astute, we learn much deeper from out mistakes in thinking and application.

Willie White · #9 12-22-2005, 04:09 PM

reply to follow

Willie White · #10 12-22-2005, 04:28 PM

Thanks for the responses...I have a pressure guage connected permanently to the top of the oil filter fitting...The head gasket is installed correctly{OBEN=UP}.{Dont ask me why I'm so sure}...The pressure relief valve sticking sounds like a possibility.How can I check that out??.... A "Windage Try" is beyond my experience level,but I am wondering if the "Fallopian Tube" might be the same part since the part numbers are so similar{37 115 240 3PH}???.....AS far as intermediate shaft bearings;;hot idle is about 29-30 PSI which I figure is pretty much normal for this age engine......The crank must be getting oil since I have no bearing issues so far.......A partial clog of an oil passage might be a possibility I guess. How do I determine that??......I will retreive the oil filter and perform surgery on it to see if theres anything to be learned there.......Am wondering if replacing the oil pump might be a good idea just on general principles. Would that eliminate the pressure relief valve possibility??? Thanks;; will keep posting.

Ali Al-Chalabi · #11 12-22-2005, 05:57 PM

Does it have a check vlave that keeps the oil filter full when the engine is shut off? If so, maybe there is a possibility that it is faulty and the oil is draining out of the oil filter on shutdown and there is a delay because the filter has to be first filled with oil before it can build pressure into the engine. Just a thought.

dkveuro · #12 12-23-2005, 12:18 AM

The oil pumps fail in the relief valve department often....a 'pattern failure'.
Do not attempt to repair the pump...replace it.

There is no check valve in the system although some filters are anti drain.
The warm idle pressure is okay.

What happens is, the oil pump opens to dump oil when the oil is cold and above 125 psi..... and stays open...as the oil warms up, the dump snaps closed and oil presure is normal.

The dump piston is a close fit in the pump and dirt wears it and it cocks in it's bore.

There is a faint possibility of another very rare oil pressure problem.
It is timing belt slip. The oil pump drive sprocket is smooth and is driven off the back side of the timing belt. When the weather is cold/wet/frosty...sometimes the thick oil stalls the oil pump drive and until the belt heats up, skidding on the sprocket, it only turns the oil pump sprocket very slowly.
I have actually witnessed this happening.

It was wetted by diesel fuel leaking from the IP front seal.

You need to check the tension on the belt COLD.
On the run between the cam and injection pump, it should be possible to twist the belt only about 45 degrees or less with your fingers....
If it is twisting past 45 degrees, rotate the tensioner pulley CLOCKWISE to tighten..( 15mm wrench.)..turning it the other way will allow it to rub on the belt cover. ( I have the SWT.....a handle with has two pins, that fit in the tensioner body...but you can use one side of a 90 degree circlip pliers tool or similar.. .)

If you over tighten the belt, it will whine slightly above idle speed.
The engine gets 'taller' as it warms, so the cold setting is to allow block expansion.

The later 1.9's use a spring loaded tensioner ....yours is a solid type.

Willie White · #13 12-23-2005, 08:11 AM

Seems like what is indicated is replace the oil pump... I will do so and will post results here.My thanks to all who responded Willie White {Poor Soul}

dkveuro · #14 12-23-2005, 11:04 AM

Quote:

Originally Posted by Willie White

Seems like what is indicated is replace the oil pump... I will do so and will post results here.My thanks to all who responded Willie White {Poor Soul}

Willi.......please check timing belt tension first !
If you need a pump, I can supply one and also a oil pan windage tray.
The tray is made by VW for all the 4 cylinder engines and it doubles as a very good pan/block seal.

The only problem with the job

is the two 6mm bolts between the oil pan and bell housing cover.....you might need a sharp chisel to tap them loose and then slot the head(s) to reinstal with a screwdriver.

.

Willie White · #15 12-23-2005, 02:30 PM

DK...I will remove the timing belt shield to make the int shaft pulley visible before going further...It would be just too much to ask if was just a matter of tightening the timing belt. In my world it takes maximum effort to get minimal results. I will go forward from that point and see what I need. Can you give me a ballpark price for whatever is needed to complete a pump replacement job? I have not the foggiest notion. Thank you very much and I wish you and yours A very very great holiday season.