Weird oil pressure issue

AdamR · Post by **AdamR** » Sun Jan 16, 2011 2:04 pm

Further to my previous thread (http://www.v8forum.co.uk/forum/viewtopic.php?t=8132), I've now got another strange oil issue with my 3.9 Rover V8.

The engine has the interim timing cover with crank driven oil pump. I'm measuring pressure with a capilery gauge plumbed into the main gallery.

When I run the engine up te temperature, the oil starts off at a rock solid 40psi. Revving the engine does not increase the pressure. As the temperate increases the oil pressure decreases down approx 20psi, as I'd expect to be normal. What is weird is that if I rev the warmed engine the measured oil pressure decreases - rather than increasing as I'd expect - and appears to stay low once the revs drop down to idle. From what I've read, it's normal to have idle pressure as low as 10psi, to not too worries about that. What's confusing me is that the pressure does not increase when revved.

I was initially running 10w40 oil, but have swapped to 20w50 to see what difference that would make. (Though my understanding was/is that 10w40 should be fine for engines with the crank-driven pump). The only difference this seems to have made is that when warm the pressure stays higher for longer. When running 10w40, the pressure would eventually drop to zero.

I also inspected the PRV several times over the last few weeks, and it seems to be in good condition and slide easily in it's bore. I've also replaced the PRV plunger and spring with brand new items and it made no difference. Today I experimented with replacing the PRV spring with something solid to remove this from the equation altogether. Just running the engine at idle for a few seconds the pressure built up to nearly 100psi and then started making a very strange noise! I know the PRV regulates pressure, but wouldn't expect it to operate at idle speeds?

Any thoughts or advice? Could be that the gauge is a dud - but it seems to have been validated by the oil warning light coming on at low pressures, and the weird engine noises at super-high pressures. Help!

ian.stewart · Post by **ian.stewart** » Sun Jan 16, 2011 2:49 pm

Pressure relief valve must be set at that pressure, real steel used to sell a adjuster so you could bump the pressure up, but rovers rely on volume rather than pressure

spend · Post by **spend** » Sun Jan 16, 2011 7:03 pm

The PRV popping reduces volume going to the engine as well since it just recirculates back to the pump inlet?

Darkspeed · Post by **Darkspeed** » Mon Jan 17, 2011 1:37 pm

Where in the engine are you reading the pressure? - I am just wondering if you are trying to read the pressure in a area of very high flow and therefore are having a bernoulli effect happening with the velocity of the oil passing the end of the sensing point.

Preferably you need to measure in a low velocity high capacity area such as near the oil filter.

Andrew

DEVONMAN · Post by **DEVONMAN** » Mon Jan 17, 2011 2:02 pm

Hi. Reduced oil pressure when the revs increase is normally due to a defect on the suction side of the pump. It could be a loose pickup pipe in the sump which allows a froth of bubbles in with the oil. Or, if you have a non standard sump the pickup may be too close to the floor of the sump and strangling the flow.
Also check the front cover bolts near the oil gallery.
It's possible that air is being sucked in at the oil pickup gallery gasket joint.

Regards Denis

AdamR · Post by **AdamR** » Mon Jan 17, 2011 3:49 pm

Devonman, give yourself a pat on the back you're 100% correct.

As a last resort yesterday afternoon I pulled off my low-profile trapdoor sump and pickup and replaced with standard items. Problem solved!

I'd already swapped the sump at least once when investigating my bogus oil flow issue, and had not noticed any difference at all - so wrongly assumed the trapdoor sump + pickup were fine. However looking at them once again on the bench, I reckon the pickup is too close to the sump.

Not 100% sure why I was seeing the oil pressure steadily decrease with heat and revs - perhaps expansion of the pickup pushing it harder against the sump. Whatever the reason, with the standard items I now see idle readings between 20psi and 50psi, depending on temp, and the needle moves in the correct direction when revved!

SuperV8 · Post by **SuperV8** » Mon Jan 17, 2011 11:58 pm

Result, did you measure the gap between pick up and modified sump? Just curious as i've modified/shortened my own sump & pickup. I measured the organal one (a lot!) Think it was 5mm gap, then measured (a lot) after modifiying it to make sure its also I think 5mm.

Tom

DEVONMAN · Post by **DEVONMAN** » Tue Jan 18, 2011 8:31 am

SuperV8 wrote:Result, did you measure the gap between pick up and modified sump? Just curious as i've modified/shortened my own sump & pickup. I measured the organal one (a lot!) Think it was 5mm gap, then measured (a lot) after modifiying it to make sure its also I think 5mm.

Tom

There are 2 types of pickup. The early type has a large flat open gauze about 100mm dia and the later type has an enclosed gauze and is smaller.
If you have sump clearence problems, you could modify the early type by grinding a load of v notches around the perimeter below the gauze level. On the later type you could drill holes in the can of the pickup below the gauze but be careful not to shoot the drill bit through the gauze.

Regards Denis

AdamR · Post by **AdamR** » Tue Jan 18, 2011 10:11 am

Result, did you measure the gap between pick up and modified sump? Just curious as i've modified/shortened my own sump & pickup. I measured the organal one (a lot!) Think it was 5mm gap, then measured (a lot) after modifiying it to make sure its also I think 5mm.

I thought I had measured it but this issue suggests otherwise. I certainly measured the standard pickup/sump clearance and from memory that was around 5mm as you say.

To be honest I've never been very happy with the pickup that came with my trapdoor sump (which appears to be identical to this one). The inside of the pipe is slightly obstructed by blobs of weld, and the end of the pipe pushes right up against the gauze meaning there is a much smaller area where oil can be drawn.

For these reasons, when I originally fitted this sump I decided to modify a standard pickup (small type) rather than using the one that came with it. Lots of measuring of clearance was done then too. But I later dumped this when trying to figure out my bogus oil flow issue, as I figured my cut n' shut pickup was more likely to be leaking air or causing another problem than the TIG welded & supposedly accurately made one that came with the sump . Ironically, after lots of careful thought around this, I ended up with the only sump/pickup combination that I hadn't measured properly!

Anyone know who manufactures these stainless trapdoor sumps, or if many other people run them? Would be interested to know how well the design works to control oil starvation etc in practice.

SuperV8 · Post by **SuperV8** » Tue Jan 18, 2011 1:12 pm

I'll be keeping a very close watch of my oil gauge on first start up, checking for dropping pressure with rising revs, very usefull thread.

Anyone know who manufactures these stainless trapdoor sumps, or if many other people run them? Would be interested to know how well the design works to control oil starvation etc in practice.

I looked into buying a trap door sump and I must admit I struggled to see the justification behind them. In my mind it would be much more benificial to have some one way valves/umbrella valves in the horizontal baffle plate letting oil into the sump bowl but not letting it climb out. I did some testing on my own sump, just filled my sump with oil after modifiying it (I made it shallower and winged) and sloshed it arround to see what happened. One thing I noted was the vertical trap doors I moched up needed to be a very good fit otherwise the oil will just flow past them. In the end I just used a horizontal baffle plate like the standard rover v8 but made it fit better around the edges so the oil couldn't climb out so easily. I also looked at using a scrapper finger plate but I measured it and could only fit one for less than 1/3 of the crank so I fitted a thin straight scrapper to the one edge which they do in the JE baffled sump.
In my mind it would be very usefull to be able to see the engine running with a clear sump so you could adjust the oil level so it's as deep/high as possible without touching the crank.

Probabbly all boils down to how good your tires are... If they are regular road tires I doubt you'd be able to pull enough g to dispalce the oil, and if you were using sticky tires then you'd need to find a long enough corner to pull a high g for an amount of time.

All just my humble.
Tom.

DEVONMAN · Post by **DEVONMAN** » Tue Jan 18, 2011 2:09 pm

Just coming back to the pickup/sump clearence problem, it's interesting to note that even the best engine builders get this wrong. A while ago on the American Hotrod programme they had a v8 built by a specialist at great expense and they ended up modifying the sump/pickup to give more clearance.
Regards Denis

TVRleigh · Post by **TVRleigh** » Thu Jan 20, 2011 4:00 pm

I've been running a 4.0 Rv8 in my TVR Tasmin Racer with SLICKS, and been using the standard 4.0 metal sump. I've got a Spa Digital pressure gauge (accurate to 0.1 psi) I also run a 10 Hz DL1 logger. the Car corners and brakes at 1.2-1.4G and I've done about 10 hours in the car, and I always check the logs, and I've never had any oil pressure problems on cornering, I get a slight drop on breaking but that's due to a drop in rev's

I have did buy a baffled sump but due to running the no dissy front End I needed a longer sump, so just used the standard one.

So unless you have a seriously fast car and running on slicks I'm not sure it's worth all the hassle.