Oil pressure issue - PeachParts Mercedes-Benz Forum

Willie White · #1 12-10-2005, 09:51 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, 10:12 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, 10:15 AM

Did u check the oil filter?

t walgamuth · #4 12-10-2005, 03:06 PM

filter rather than the heavy oil thing.

tom w

Willie White · #5 12-10-2005, 03:35 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, 11:55 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!

Ralph69220d · #7 12-21-2005, 12:27 PM

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.

dkveuro · #8 12-21-2005, 12:20 PM

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.

.