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Old 06-25-2021, 03:57 PM   #1
142 guy
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Default B20E No Oil Pressure Blues

I was out driving around a couple of evenings ago in my 1971 142E. I came up on a red light and had to do a firm stop and I noticed that the low oil pressure warning light on my electronic oil pressure gauge flickered on. Pulling away after the light changed I noticed that my pressure was lower than normal - about 30 - 35 psi @ 2500 RPM. The low pressure warning flickered again at the next stop light so I pulled over, got out and checked for oil leaks (I had checked levels a couple of days ago so I knew that was good), found none so I carefully drove home watching the pressure gauge to keep it up around 30 psi. The mechanical oil pressure switch never activated during this event so I never reached 0 pressure. Prior to the oil pressure warning light coming on that first time everything had been just fine. There were no strange mechanical noises before or after the warning light flickered.

This morning I double checked the sump oil level and it was at its normal level. On the off chance that the electronic gauge / sensor may have gone out of calibration, I disconnected the mechanical pressure switch and hooked up a mechanical oil pressure gauge so I could carry out a test to determine whether the electronic gauge was the problem. In order to hook up the temporary 'plumbing', I had to remove the oil filter to get at the fittings on the side of the block. Almost no oil drained out of the filter as I pulled it off which is not normal. After installing the fittings for the mechanical gauge I installed a new filter and then proceeded to carry out a cranking pressure test with the coil and injector fuses pulled so it would not start. I did 3 crank tests of about 5-6 seconds each and I am now getting absolutely no oil pressure on either the electronic gauge or the temporary mechanical gauge. The tube to the temporary mechanical gauge is translucent nylon and I could see that there was no oil flowing in the tube.

So, I have now gone to zero oil pressure which leads me to the following possibilities:
- one or both of the rubber rings that seal the oil delivery pipe have moved / fallen right out (I would have thought that I would still gets some oil flow to the galleries when cranking),
- the oil pump has had a drive end failure (I have that IPD re enforcing ring on the oil pump drive)
- the pump pressure relief mechanism has failed open (I have the IPD high pressure spring)
- the little tab on the end of the oil pump / distributor drive shaft that engages the oil pump has sheared right off (I would have expected this would have resulted in complete loss of oil pressure while driving).

Have I missed anything? I will add that the engine had a complete rebuild about 7 years ago and only has about 6000 km since the rebuild. Oil pressure prior to this event was just fine.

As I recall, I think the oil pump / distributor drive shaft can be removed and checked once the distributor is removed so I should be able to check that fairly easily (getting it back in to the pump with the IPD re enforcing ring will be a treat. However, if it did shear off I expect that the pump has to come off to get at the broken piece that will be stuck in the end of the pump drive. Everything else looks like removing the sump is a requirement. From the service manual, it appears that I can remove the sump with the engine in the car. This does require having the front of the car raised up, lifting the front of the engine and then dropping the front cross member a bit to get access. Once the oil pan is off I presume that access to R&R the pump is straightforward?

The sump gasket will have to be replaced. Any comments on Reintz / Felpro / Mahle / AJUSA / Elring? I am pretty sure the existing gasket is an Elring cork gasket which has weeped from day one so something that seals better would be nice. I have limited garage space so I want to get this repair turned around as fast as possible. In the event that the oil pump / pressure relief is buggered I want to have a replacement on hand so that the car is not taking up space for a couple of weeks while I wait for parts. It looks like the Melling M91 pump is the only replacement option?

If the problem was the seal rings on the oil delivery pipe, any words of wisdom on re installing those puppies so that they don't pop out again? Any other words of wisdom on possible causes or tricks in doing the repair?
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Old 06-25-2021, 04:44 PM   #2
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You could pull the distributor and drive gear just to see if you’re that lucky and maybe you’ll get off easy. Aside from that I’d assume the pan has to come off.

Edit - you suggested that
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Old 06-27-2021, 12:56 PM   #3
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I pulled the distributor drive gear off yesterday afternoon. The drive gear shaft is fine and the top of the oil pump where the drive gear shaft engages the pump looks to be fine (as much of it as you can see looking down through the distributor drive hole). So it looks like the pump must have failed or the connecting pipe gaskets failed or the pipe fractured.
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Old 07-27-2021, 11:05 AM   #4
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A bit of follow up.

After a 3+ week delay in getting the pan gasket from Rock Auto following Fed Ex losing the first one. I got around to dropping the sump to remove the oil pump. As to the cause of the low and then no oil pressure (during subsequent testing), that is a mystery. When I went to remove the oil pump and the feed line to the block, both rubber seals on the feed pipe were firmly in place. In fact, the B20 feed pipe has a ring on it on each end which backs the seals when the pipe is inserted in the pump and the block. You can't even see the seals when the pipe is inserted so I am thinking that there is pretty much zero possibility that the seals would ever pop out under pressure. When I unbolted the pump I had to give a very firm yank to get the feed pipe out of the block (same at the pump end). It definitely wasn't coming out on its own and the original seals were in good condition.

I installed the new Melling M91 pump and buttoned everything up with some new 5W50 oil. I modified a 12" flat blade screwdriver to allow it to be inserted down into the distributor drive hole and allow me to turn the pump by hand. I did a couple of CCW turns by hand and then the resistance increased as oil began to flow. I gave a few more turns and I could see oil flowing into the hole for the distributor drive gear (supply to the distributor drive bearing) and oil flowing in the nylon line to the test oil gauge. I installed the distributor drive gear and my cam sensor carefully following the alignment marks I had painted on the distributor hole so I would not have to go through a timing reset exercise. With the cam sensor in I reconnected the battery and did a test crank of the engine. A few seconds cranking gave about 30 -35 psi on both the dash and test gauge. The battery was a little low after sitting for 4+ weeks so cranking was a bit slow. I disconnected the test gauge, reinstalled the oil pressure switch, reinstalled all the fuses that I removed for the initial pressure check and then fired up the engine. Start up was quick and the oil pressure rose to around 55 psi very quickly. I let the engine run to check for leaks and allow the coolant temperature to come up to around 90 C for a few minutes. With the engine idling at around 850 RPM oil pressure was rock steady at 55 psi even after the temperature had been up around 90 C for about 10 minutes. That is a definite improvement over the old pump as pressure would sag to around 30 - 35 psi at idle when hot.

I pulled apart the old pump to see if I could spot the problems for my low / no oil pressure. I was expecting to find a broken oil pressure relief spring; but, the relief valve was intact. I looked to see if there were any objects holding the ball valve open; but, didn't spot anything. According to the service manual the tolerance on the tooth flank clearance is 0.006 - 0.014" and mine measured out at 0.013" on some of the teeth pairs; but, not all. Some of teeth pairs were tighter. The end float on the driven gear was between 0.002" (loose) and 0.003" (tight). The service limit is 0.004" so mine was within limits. The pump measurements were all within; but, close to the upper limit of the service tolerances. The pump wear probably lines up with the lowish oil pressures that I was getting at hot idle; but, I didn't see anything that would be responsible for the sudden drop in oil pressure that I experienced or the fact that during the test after getting the car home I was not able to generate any pressure of flow at all.

Out of curiosity I reassembled the old pump and then inserted the pump into a small pan that I filled with old oil. I rotated the pump drive gear and after a few rotations was able to generate flow through the pump. That is not a test of pressure; but, it is an indication that the pump could generate flow. Why I got the no flow results in my test remains a mystery. However, the new pump definitely does provide higher pressure at idle than the old pump.

As a side note for anybody considering using the shop manual procedure for dropping the oil pan with the engine in the car. The shop manual says:

Remove the rear bolts on the front axle member and screw on instead two auxiliary bolts (UNC 1/2-13x114). Remove the front bolts for the front axle member. Lower and remove the jack so that the front axle member is suspended in the two auxiliary bolts.

I assumed that 1/2-13x114 was a typo that meant UNC 1/2-13x1 1/4. Short answer is no. The bolts need to be about 4" to 4 1/2 " to drop the cross member sufficiently to get clearance. Perhaps the Volvo service writers decided to mix imperial measurements with metric because 114 would be about 4 1/2 " which is what is required. The other details that Volvo omitted were that I needed to remove 1 of the bolts on both the pitman arm mount and the steering box mount because the inside edge of both upper front A arm pivots was just catching on the bolt head. I also needed to disconnect the sway bar to allow the brake lines to move as the cross member was dropping. If you are doing this, watch the brake lines very carefully. Depending on how far the front of the car is jacked up and the inserted length of those bolts suspending the cross member, the crossmember and by extension the calipers may drop enough that they rip the brake lines right out of the bulk head mounts. Mine were definitely tight.
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Old 07-27-2021, 12:14 PM   #5
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must have been a sticking (open) pressure relief valve.
The way you described it can hardly be anything else.
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Old 07-27-2021, 02:00 PM   #6
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Quote:
Originally Posted by Janspeed View Post
must have been a sticking (open) pressure relief valve.
The way you described it can hardly be anything else.
I would normally be inclined to agree. My expectation was that when I pulled the pump apart I would find a broken spring in the pressure relief valve; but, it was intact. Given the design of the pressure relief valve it is pretty difficult for the check ball to stick open unless something gets jammed between the ball and its seat; but, I didn't spot anything like that when I pulled it apart. I suppose it is possible that the seat for the ball has some kind of nick in it allowing by-pass flow. However, it 'looked' OK. My little hand test in the pan of oil confirmed that the pump could pump some oil. But, because there was no back pressure it didn't test the operation of the relief valve.

The exact problem remains a mystery. I would have been happier if I had found something like a broken relief valve spring or serious wear on the pump end plate. Then I would know that pump replacement definitely fixed the problem. Right now, the only thing I know is that pump replacement seems to have made the problem go away and provided nice solid oil pressure at hot idle.

I will say that the Melling pump does appear to be a nice solid piece of hardware. It is definitely heavy. Drop this sucker on your toes when you are wearing sandals and you are likely taking a trip to the emergency ward.
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Old 07-27-2021, 05:22 PM   #7
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Curious why you're using 5W-50.
Maybe that's why it was cranking slow.
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Old 07-27-2021, 11:12 PM   #8
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I have used 5W50 synthetic for the last 5 years. Cranks like it has 5W at start up. I expect the slow cranking was due to the battery sitting for around since June 23 gradually being dragged down by the parasitic loads in the car. Its a relatively small type 51 battery.
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