Oil Pressure Story - hopefully it will help someone else

66rover99

Active member
Apologies for writing a novel and shifting back and forth between Metric and Standard...

Last October I took our 1995 Defender 110 300tdi off the road to do some maintenance and upgrades. This included the following:

-- New front fenders (sides) to replace cracked plastic ones installed by previous owner. I can tell you that the plastic fenders do not last and crack on the folds.
-- New Allisport radiator
-- New Allisport intercooler
-- New Turner performance head
-- Plumbing for air cleaner to fender (thanks to Baldewin here for the parts)
-- Morgan Hill Boost Pin
-- Fourby Boost Ring
-- Viair Compressor
-- LED headlights
-- Madman gauge

So, the job took awhile as you can imagine. The reason for the gauge was primarily to keep an eye on oil pressure as I thought there was a problem. I replaced the original sender a few months back and still the issue I describe below persisted.

I first noticed there was an oil pressure issue on this truck about a year ago, when the oil light would come on under very specific conditions? 100 KPH, under slight load, usually up a long rise (not a hill) with the throttle held steady. I would hear the relay kick in, and the light would flicker. The slightest release of the throttle made the light go off. We were on a long trip at the time, and after all sorts of nervous humming and hawing we proceeded. As long as we kept it to 90 KPH it never turned on. But this process was fairly repeatable once the oil warmed up. Push it a little and the light would flicker under load. It also always seemed to be raining during the time, and so we were also looking at electrical connections, however never found any problems there.

The previous owner had installed the 300 tdi in the truck from a UK wrecker. This engine, like most we get here in Canada, had no known history. However it ran fairly well and didn't smoke. So he put a new rear main seal and a timing belt kit on it and I purchased the truck from him after he had run about 10,000 km.

Because it was only during a rare circumstance that the light flickered, the oil pressure wasn't the main concern I had with maintenance of the truck, and so I figured I'd deal with a new sender and a gauge when I had the engine torn down to deal with the head last fall.

At that time I installed a Madman gauge I had on hand with a new VDO 5 bar sender, also with oil light connection. The Madman readings confirmed to me that the pressure seems to be too low. I also put a mechanical shop gauge in to verify that it wasn't a sender issue, and it too came up with similar readings.

idle cold: 25 psi

idle warm: 15-20 psi

pressure at 2000 RPM warm: 15-20 psi

pressure at 2500 RPM warm: 11-15 psi

pressure at 3000 RPM warm: 8-12 psi

As it gets fully hot (water temp 86C) pressures get lower and at 2500 - 3000 seems to decrease to 8 psi, even flickered to 6-7 a couple of times. This was tested driving on city streets around 60 KPH in 3rd/4th. I did not take it on the highway in 5th but the RPM ranges would be similar.

Oil is Shell Rotella T4 15W40 in case anyone wonders. I tried Rotella T4 10W30 and the numbers were lower still with oil light coming on around 2500 RPM under load.

So, started doing some Interweb research?

Is it a worn pump?
Is it a worn timing case, which is aluminum and the pump may have worn out?
Is it a worn pump cover?
Might it be worn mains, rods or cam bearings?
Might it be worn out turbo?
Might it be a worn oil pressure relief spring?
Might it be a plugged up pickup tube?

All of these I considered and started going through the process of crossing from the list. The pump, pump cover and timing case went to the end of the list because that requires the most work just after completing a total top end overhaul and installation of new rad and intercooler. Definitely wasn't looking forward to tearing it all down again.

So I started with checking on the turbo. I went to a local turbo rebuilder and discussed. He felt that if the turbo bearings were worn to the point of dumping out all the oil thus causing low pressure the turbo wouldn't function. His opinion was that low oil pressure can damage a turbo, but a turbo is unlikely to cause low oil pressure. I agreed for now and tentatively crossed it off the list. (Note it got on the list because as I was replacing the boost pin, I removed the banjo bolt and top cover of the injection pump, and this cavity was full of oil. I assumed the worst however I've been told by the turbo/bosch pump rebuilder that its not abnormal over time to have oil in there).

Next I decide to drop the oil pan and see what it looked like inside. Everything looks well lubed and no signs of wear, very little in the way of solids (a little gasket fibre) in the bottom and the screen not blocked at all. Also no shiny stuff built up.

I removed the pressure relief spring and plunger and noticed the spring looked shorter than what the overhaul manual says. It is 45mm long and the overhaul manual says it should be 68mm. Hard to imagine the spring shrinking from 68mm to 45mm as even the 45mm spring doesn't look particularly worn. I sent an email to Richard at Turner Engineering to ask whether he knows how long a new spring is. He figures its typo in the manual because the new Land Rover spring is around 51mm length. However he doubts my theory that the spring is the problem. He's seen a lot of engines and he said he'd never seen this as a problem. Relatively few full stories of oil pressure issues on the Interweb, but there are a few about this spring fatiguing or breaking and the good pressure releasing prematurely due to weak spring. (A lot of the stories about low oil pressure either are unfinished, or they did several things at once so they couldn't say for sure it was the spring, or the engine was replaced so it was never fully pursued)

So, in order to cross this off the list, I ordered an new spring and plunger from Rovalution in Vancouver. While I was waiting for it, I had a few jobs to do:

-- inspect and plastigage some of the main and rod journals
-- clean the silicon sealant off the block and pan
-- hammer out a dent in the pan.

OK, here's where it takes a bit of a turn. The pan had a dent across the front of the sump about 15mm deep. It looks like in some previous configuration (remember it is from a wrecker so no known history) the front suspension had bottomed out and the track rod whacked the pan.

I built a wooden frame to sit the pan in and started hammering it out with a piece of 2x4. As I did so, I also started noticing the 2x4 had shined up the bottom of the pan and revealed a surprise -- there was a distinct circle about 2.5" round where the oil pickup had bean wearing agains the bottom of the oil pan, and a smaller 15mm circle where the pickup tube itself had impacted the pan, likely during the original impact of the track rod to the pan.

I talked to a couple of Rover friends and we concluded that its very likely that the pickup wasn't able to draw enough oil at higher RPM due to it touching the bottom of the pan. Would that cause the oil pressure problems? Well, if I put a new spring in as well as now hammering out the pan, I wouldn't really know. So I decided I would put the pan back on WITHOUT the new spring and plunger, using the old one instead.

Before the pan went on, I plastigaged the main and big end bearings and there were no signs of abnormal wear and the measurements with plastigauge were right in spec. So I was satisfied at this time to put the pan on.

Oil in, i crossed my fingers and started the truck. It took a few moments to develop oil pressure, but it then went up to 45 psi during the entire warmup.

I then took it for a drive, and now, instead of the pressure dropping under load, it increased, warm average of around 35 psi, and dropping to around 23 at idle.

I then drove it up the steepest longest hill in town, in 5th gear for about 5 KM, where it was pushing around 650c on the EGT steady, so really heavily loaded. It maintained no less than 30 psi as the oil got quite hot. Also the new rad did its job and I hit max water temperature of 88c.

I am happy to report that the oil pressure problem that had plagued this truck for some time was simply a dented oil pan. I overlooked this through the entire troubleshooting process, and was only repairing the pan because I had it off.

Should I have installed the new pressure relief spring? Well one day when all the other jobs on the truck are done, I likely will, but in the meantime its in my spares box.
 
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RBBailey

Well-known member
Callsign: KF7KFZ
Very interesting....

So are you saying this is something people should check for even without a dent?

My pressures are about the same as you describe, but it stays at about 18 psi idle, once fully warmed, really doesn't go below that much at all.
 

Red90

Well-known member
Pressure should always increase with engine speed up to the pressure relief point. If it does not, there is an oil supply issue.
 

66rover99

Active member
What I’m saying is that before you start thinking the worst, just check for a damned dent, and fix it ;-)
 

66rover99

Active member
BTW I’ve now been enjoying the benefits of the tuning, the torque is much better. The hill I climbed in 5th gear, I used to have to shift down to 3rd as it’s very steep. No notable increase in smoke. Time will tell how the mileage compares.
 

1of40

Well-known member
Enjoyed the story. It brought back memories of my tdi swap that finished up three years last week. I too had a dent in the oil pan that I had to take a 2x4 to. What was unexpected was that on inspection the inside of the pan had worn the a hole in the wire mesh. I replaced the pump bc I couldn’t find just a mesh basket to replace.
 
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